Background
Cardiac cirrhosis (congestive hepatopathy) includes a spectrum of hepatic derangements that occur in the setting of right-sided heart failure. Clinically, the signs and symptoms of congestive heart failure (CHF) dominate the disorder. Unlike cirrhosis caused by chronic alcohol use or viral hepatitis, the effect of cardiac cirrhosis on overall prognosis is unknown. Because of this, treatment is aimed at managing the patient's underlying heart failure.
Distinguish cardiac cirrhosis from ischemic hepatitis. The latter condition may involve massive hepatocellular necrosis caused by sudden cardiogenic shock or other hemodynamic collapse. Typically, sudden and dramatic serum hepatic transaminase elevations lead to its discovery. Although cardiac cirrhosis and ischemic hepatitis arise from distinct underlying cardiac lesions (right-sided heart failure in the former and left-sided failure in the latter), in clinical practice they may present together.
Despite its name, cardiac cirrhosis rarely satisfies strict pathologic criteria for cirrhosis. The terms congestive hepatopathy and chronic passive liver congestion are more accurate, but the name cardiac cirrhosis has become convention.
Pathophysiology
Decompensated right ventricular or biventricular heart failure causes transmission of elevated central venous pressures directly to the liver via the inferior vena cava and hepatic veins. At a cellular level, venous congestion impedes efficient drainage of sinusoidal blood flow into terminal hepatic venules. Sinusoidal stasis results in accumulation of deoxygenated blood, parenchymal atrophy, necrosis, collagen deposition, and, ultimately, fibrosis.
A separate theory proposes that cardiac cirrhosis is not simply a response to chronically increased pressure and sinusoidal stasis. That intrahepatic vascular lesions are confined to areas of the liver with higher fibrotic burden suggests that cardiac cirrhosis requires a higher grade of vascular obstruction, such as intrahepatic thrombosis, for its development. The theory proposes that thrombosis of sinusoids and terminal hepatic venules propagates to medium-sized hepatic veins and to portal vein branches, resulting in parenchymal extinction and fibrosis.
Frequency
United States
Cardiac cirrhosis rarely occurs in the United States. Its true prevalence is difficult to estimate, since the disease typically remains subclinical and undiagnosed. The incidence of cardiac cirrhosis at autopsy has decreased significantly over the past several decades. This may be due to lower rates of uncorrected rheumatic heart disease and constrictive pericardial disease.
Mortality/Morbidity
The effect of cardiac cirrhosis on mortality and morbidity rates is unknown. The severity of the patient's underlying cardiac disease, which is typically advanced and chronic, is the major determinant of overall outcome.
Sex
Comparative sex data for cardiac cirrhosis do not exist. However, because CHF is more common in men than women in the United States, the same is likely for cardiac cirrhosis.
Age
No published data exist. However, the prevalence of cardiac cirrhosis in the United States, like that of CHF, almost certainly increases with age.
Read more HERE
Showing posts with label Cardiology. Show all posts
Showing posts with label Cardiology. Show all posts
Wednesday, 16 July 2008
Friday, 27 June 2008
Treadmill and Pharmacologic Stress Testing
Cardiovascular exercise stress testing in conjunction with an ECG has been established as one of the focal points in the diagnosis and prognosis of cardiovascular disease, specifically coronary artery disease (CAD).
Feil and Seigel first noticed the significance of cardiovascular exercise stress testing in 1928; they reported ST and T changes following exercise in 3 patients with chronic stable angina.1 The following year, Master and Oppenheimer introduced a standardized exercise protocol to assess functional capacity and hemodynamic response.
Continued research into causal mechanisms of ST displacement, refinement of exercise protocols, and determination of diagnostic and prognostic exercise variables in clinical patient subsets have continued to evolve since 1929.
After the establishment of coronary angiography as a diagnostic tool, the limitation of exercise-induced ST-segment depression as a diagnostic marker for obstructive CAD in patient populations with a low disease prevalence became apparent.
Introduction
Exercise testing is a cardiovascular stress test using treadmill bicycle exercise with ECG and blood pressure monitoring. Pharmacologic stress testing, established after exercise testing, is a diagnostic procedure in which cardiovascular stress induced by pharmacologic agents is demonstrated in patients with decreased functional capacity or in patients who cannot exercise. Pharmacologic stress testing is used in combination with imaging modalities such as radionuclide imaging and echocardiography.
Exercise stress testing, which is now widely available at a relatively low cost, is currently used most frequently to estimate prognosis and determine functional capacity, to assess the probability and extent of coronary disease, and to assess the effects of therapy. Ancillary techniques, such as metabolic gas analysis, radionuclide imaging, and echocardiography, can provide further information that may be needed in selected patients, such as those with moderate or prior risk.
Exercise physiology
The initiation of dynamic exercise results in increases in the ventricular heart rate, stroke volume, and cardiac output due to vagal withdrawal and sympathetic stimulation. Also, alveolar ventilation and venous return increase as a result of sympathetic vasoconstriction. The overall hemodynamic response depends on the amount of muscle mass involved, exercise efficiency, conditioning, and exercise intensity.
In the initial phases of exercise in the upright position, cardiac output is increased by an augmentation in stroke volume mediated through the use of the Frank-Starling mechanism and heart rate. The increase in cardiac output in the later phases of exercise is due primarily to an increase in ventricular rate.
During strenuous exertion, sympathetic discharge is maximal and parasympathetic stimulation is withdrawn, resulting in autoregulation with generalized vasoconstriction, except in the vital organs (cerebral and coronary circulations).
Venous and arterial norepinephrine release from sympathetic postganglionic nerve endings is increased, and epinephrine levels are increased at peak exertion, resulting in an increase in ventricular contractility. As exercise progresses, skeletal muscle blood flow increases; oxygen extraction increases as much as 3-fold; peripheral resistance decreases; and systolic blood pressure (SBP), mean arterial pressure, and pulse pressure usually increase. Diastolic blood pressure (DBP) remains unchanged or may increase or decrease by approximately 10 mm Hg. The pulmonary vascular bed can accommodate as much as a 6-fold increase in cardiac output, with only modest increases in pulmonary arterial pressure, pulmonary capillary wedge pressure, and right atrial pressure; this is not a limiting determinant of peak exercise capacity in healthy subjects.
The maximum heart rate and cardiac output are decreased in older individuals, related in part to decreased beta-adrenergic responsiveness. Maximum heart rate can be calculated by subtracting the patient's age (y) from 220 (has a standard deviation of 10-12 beats per minute [bpm]). The age-predicted maximum heart rate is a useful measurement for safety reasons and as an estimate of the adequacy of the stress to evoke inducible ischemia. A patient who reaches 80% of the age-predicted maximum is considered to have a good test result, and an age-predicted maximum of 90% or better is considered excellent.
In the postexercise phase, hemodynamics return to baseline within minutes of discontinuing exercise. The return of vagal stimulation is an important cardiac deceleration mechanism after exercise and is more pronounced in well-trained athletes but blunted in patients with chronic congestive heart failure. Intense physical work or important cardiorespiratory impairment may interfere with achievement of a steady state, and an oxygen deficit occurs during exercise. The oxygen debt is the total oxygen uptake in excess of the resting oxygen uptake during the recovery period.
Feil and Seigel first noticed the significance of cardiovascular exercise stress testing in 1928; they reported ST and T changes following exercise in 3 patients with chronic stable angina.1 The following year, Master and Oppenheimer introduced a standardized exercise protocol to assess functional capacity and hemodynamic response.
Continued research into causal mechanisms of ST displacement, refinement of exercise protocols, and determination of diagnostic and prognostic exercise variables in clinical patient subsets have continued to evolve since 1929.
After the establishment of coronary angiography as a diagnostic tool, the limitation of exercise-induced ST-segment depression as a diagnostic marker for obstructive CAD in patient populations with a low disease prevalence became apparent.
Introduction
Exercise testing is a cardiovascular stress test using treadmill bicycle exercise with ECG and blood pressure monitoring. Pharmacologic stress testing, established after exercise testing, is a diagnostic procedure in which cardiovascular stress induced by pharmacologic agents is demonstrated in patients with decreased functional capacity or in patients who cannot exercise. Pharmacologic stress testing is used in combination with imaging modalities such as radionuclide imaging and echocardiography.
Exercise stress testing, which is now widely available at a relatively low cost, is currently used most frequently to estimate prognosis and determine functional capacity, to assess the probability and extent of coronary disease, and to assess the effects of therapy. Ancillary techniques, such as metabolic gas analysis, radionuclide imaging, and echocardiography, can provide further information that may be needed in selected patients, such as those with moderate or prior risk.
Exercise physiology
The initiation of dynamic exercise results in increases in the ventricular heart rate, stroke volume, and cardiac output due to vagal withdrawal and sympathetic stimulation. Also, alveolar ventilation and venous return increase as a result of sympathetic vasoconstriction. The overall hemodynamic response depends on the amount of muscle mass involved, exercise efficiency, conditioning, and exercise intensity.
In the initial phases of exercise in the upright position, cardiac output is increased by an augmentation in stroke volume mediated through the use of the Frank-Starling mechanism and heart rate. The increase in cardiac output in the later phases of exercise is due primarily to an increase in ventricular rate.
During strenuous exertion, sympathetic discharge is maximal and parasympathetic stimulation is withdrawn, resulting in autoregulation with generalized vasoconstriction, except in the vital organs (cerebral and coronary circulations).
Venous and arterial norepinephrine release from sympathetic postganglionic nerve endings is increased, and epinephrine levels are increased at peak exertion, resulting in an increase in ventricular contractility. As exercise progresses, skeletal muscle blood flow increases; oxygen extraction increases as much as 3-fold; peripheral resistance decreases; and systolic blood pressure (SBP), mean arterial pressure, and pulse pressure usually increase. Diastolic blood pressure (DBP) remains unchanged or may increase or decrease by approximately 10 mm Hg. The pulmonary vascular bed can accommodate as much as a 6-fold increase in cardiac output, with only modest increases in pulmonary arterial pressure, pulmonary capillary wedge pressure, and right atrial pressure; this is not a limiting determinant of peak exercise capacity in healthy subjects.
The maximum heart rate and cardiac output are decreased in older individuals, related in part to decreased beta-adrenergic responsiveness. Maximum heart rate can be calculated by subtracting the patient's age (y) from 220 (has a standard deviation of 10-12 beats per minute [bpm]). The age-predicted maximum heart rate is a useful measurement for safety reasons and as an estimate of the adequacy of the stress to evoke inducible ischemia. A patient who reaches 80% of the age-predicted maximum is considered to have a good test result, and an age-predicted maximum of 90% or better is considered excellent.
In the postexercise phase, hemodynamics return to baseline within minutes of discontinuing exercise. The return of vagal stimulation is an important cardiac deceleration mechanism after exercise and is more pronounced in well-trained athletes but blunted in patients with chronic congestive heart failure. Intense physical work or important cardiorespiratory impairment may interfere with achievement of a steady state, and an oxygen deficit occurs during exercise. The oxygen debt is the total oxygen uptake in excess of the resting oxygen uptake during the recovery period.
Thursday, 26 June 2008
Cor pulmonale
Cor pulmonale is defined as an alteration in the structure and function of the right ventricle caused by a primary disorder of the respiratory system. Pulmonary hypertension is the common link between lung dysfunction and the heart in cor pulmonale. Right-sided ventricular disease caused by a primary abnormality of the left side of the heart or congenital heart disease is not considered cor pulmonale, but cor pulmonale can develop secondary to a wide variety of cardiopulmonary disease processes. Although cor pulmonale commonly has a chronic and slowly progressive course, acute onset or worsening cor pulmonale with life-threatening complications can occur.
Pathophysiology: Several different pathophysiologic mechanisms can lead to pulmonary hypertension and, subsequently, to cor pulmonale. These pathogenetic mechanisms include (1) pulmonary vasoconstriction due to alveolar hypoxia or blood acidemia; (2) anatomic compromise of the pulmonary vascular bed secondary to lung disorders, eg, emphysema, pulmonary thromboembolism, interstitial lung disease; (3) increased blood viscosity secondary to blood disorders, eg, polycythemia vera, sickle cell disease, macroglobulinemia; and (4) idiopathic primary pulmonary hypertension. The result is increased pulmonary arterial pressure.
The right ventricle (RV) is a thin-walled chamber that is more a volume pump than a pressure pump. It adapts better to changing preloads than afterloads. With an increase in afterload, the RV increases systolic pressure to keep the gradient. At a point, further increase in the degree of pulmonary arterial pressure brings significant RV dilation, an increase in RV end-diastolic pressure, and circulatory collapse. A decrease in RV output with a decrease in diastolic left ventricle (LV) volume results in decreased LV output. Since the right coronary artery, which supplies the RV free wall, originates from the aorta, decreased LV output diminishes blood pressure in the aorta and decreases right coronary blood flow. This is a vicious cycle between decreases in LV and RV output.
Right ventricular overload is associated with septal displacement toward the left ventricle. Septal displacement, which is seen in echocardiography, can be another factor that decreases LV volume and output in the setting of cor pulmonale and right ventricular enlargement. Several pulmonary diseases cause cor pulmonale, which may involve interstitial and alveolar tissues with a secondary effect on pulmonary vasculature or may primarily involve pulmonary vasculature. Chronic obstructive pulmonary disease (COPD) is the most common cause of cor pulmonale in the United States.
Cor pulmonale usually presents chronically, but 2 main conditions can cause acute cor pulmonale: massive pulmonary embolism (more common) and acute respiratory distress syndrome (ARDS). The underlying pathophysiology in massive pulmonary embolism causing cor pulmonale is the sudden increase in pulmonary resistance. In ARDS, 2 factors cause RV overload: the pathologic features of the syndrome itself and mechanical ventilation. Mechanical ventilation, especially higher tidal volume, requires a higher transpulmonary pressure. In chronic cor pulmonale, right ventricular hypertrophy (RVH) generally predominates. In acute cor pulmonale, right ventricular dilatation mainly occurs.
Frequency:
In the US: Cor pulmonale is estimated to account for 6-7% of all types of adult heart disease in the United States, with chronic obstructive pulmonary disease (COPD) due to chronic bronchitis or emphysema the causative factor in more than 50% of cases. Although the prevalence of COPD in the United States is about 15 million, the exact prevalence of cor pulmonale is difficult to determine because it does not occur in all cases of COPD and the physical examination and routine tests are relatively insensitive for the detection of pulmonary hypertension. In contrast, acute cor pulmonale usually is secondary to massive pulmonary embolism. Acute massive pulmonary thromboembolism is the most common cause of acute life-threatening cor pulmonale in adults. In the United States, 50,000 deaths are estimated to occur per year from pulmonary emboli and about half occur within the first hour due to acute right heart failure.
Internationally: Incidence of cor pulmonale varies among different countries depending on the prevalence of cigarette smoking, air pollution, and other risk factors for various lung diseases.
Mortality/Morbidity: Development of cor pulmonale as a result of a primary pulmonary disease usually heralds a poorer prognosis. For example, patients with COPD who develop cor pulmonale have a 30% chance of surviving 5 years. However, whether cor pulmonale carries an independent prognostic value or it is simply reflecting the severity of underlying COPD or other pulmonary disease is not clear. Prognosis in the acute setting due to massive pulmonary embolism or ARDS has not been shown to be dependent on presence or absence of cor pulmonale.
Pathophysiology: Several different pathophysiologic mechanisms can lead to pulmonary hypertension and, subsequently, to cor pulmonale. These pathogenetic mechanisms include (1) pulmonary vasoconstriction due to alveolar hypoxia or blood acidemia; (2) anatomic compromise of the pulmonary vascular bed secondary to lung disorders, eg, emphysema, pulmonary thromboembolism, interstitial lung disease; (3) increased blood viscosity secondary to blood disorders, eg, polycythemia vera, sickle cell disease, macroglobulinemia; and (4) idiopathic primary pulmonary hypertension. The result is increased pulmonary arterial pressure.
The right ventricle (RV) is a thin-walled chamber that is more a volume pump than a pressure pump. It adapts better to changing preloads than afterloads. With an increase in afterload, the RV increases systolic pressure to keep the gradient. At a point, further increase in the degree of pulmonary arterial pressure brings significant RV dilation, an increase in RV end-diastolic pressure, and circulatory collapse. A decrease in RV output with a decrease in diastolic left ventricle (LV) volume results in decreased LV output. Since the right coronary artery, which supplies the RV free wall, originates from the aorta, decreased LV output diminishes blood pressure in the aorta and decreases right coronary blood flow. This is a vicious cycle between decreases in LV and RV output.
Right ventricular overload is associated with septal displacement toward the left ventricle. Septal displacement, which is seen in echocardiography, can be another factor that decreases LV volume and output in the setting of cor pulmonale and right ventricular enlargement. Several pulmonary diseases cause cor pulmonale, which may involve interstitial and alveolar tissues with a secondary effect on pulmonary vasculature or may primarily involve pulmonary vasculature. Chronic obstructive pulmonary disease (COPD) is the most common cause of cor pulmonale in the United States.
Cor pulmonale usually presents chronically, but 2 main conditions can cause acute cor pulmonale: massive pulmonary embolism (more common) and acute respiratory distress syndrome (ARDS). The underlying pathophysiology in massive pulmonary embolism causing cor pulmonale is the sudden increase in pulmonary resistance. In ARDS, 2 factors cause RV overload: the pathologic features of the syndrome itself and mechanical ventilation. Mechanical ventilation, especially higher tidal volume, requires a higher transpulmonary pressure. In chronic cor pulmonale, right ventricular hypertrophy (RVH) generally predominates. In acute cor pulmonale, right ventricular dilatation mainly occurs.
Frequency:
In the US: Cor pulmonale is estimated to account for 6-7% of all types of adult heart disease in the United States, with chronic obstructive pulmonary disease (COPD) due to chronic bronchitis or emphysema the causative factor in more than 50% of cases. Although the prevalence of COPD in the United States is about 15 million, the exact prevalence of cor pulmonale is difficult to determine because it does not occur in all cases of COPD and the physical examination and routine tests are relatively insensitive for the detection of pulmonary hypertension. In contrast, acute cor pulmonale usually is secondary to massive pulmonary embolism. Acute massive pulmonary thromboembolism is the most common cause of acute life-threatening cor pulmonale in adults. In the United States, 50,000 deaths are estimated to occur per year from pulmonary emboli and about half occur within the first hour due to acute right heart failure.
Internationally: Incidence of cor pulmonale varies among different countries depending on the prevalence of cigarette smoking, air pollution, and other risk factors for various lung diseases.
Mortality/Morbidity: Development of cor pulmonale as a result of a primary pulmonary disease usually heralds a poorer prognosis. For example, patients with COPD who develop cor pulmonale have a 30% chance of surviving 5 years. However, whether cor pulmonale carries an independent prognostic value or it is simply reflecting the severity of underlying COPD or other pulmonary disease is not clear. Prognosis in the acute setting due to massive pulmonary embolism or ARDS has not been shown to be dependent on presence or absence of cor pulmonale.
Wednesday, 25 June 2008
Brugada Syndrome
Background
Brugada syndrome is a disorder characterized by coved or saddle-shaped ST-segment elevation in leads V1 through V3 on ECG. It is associated with complete or incomplete right bundle-branch block and T-wave inversion. In its initial description, the heart was reported to be structurally normal, but this has recently been challenged (Frustaci, 2005). Moreover, subtle structural abnormalities in the right ventricular outflow tract can also be observed. The ECG abnormality may not be evident until it is unmasked by infusion of flecainide or procainamide, or is augmented by a beta-blocker.
Patients with Brugada syndrome are prone to develop ventricular tachyarrhythmias, which may lead to syncope, cardiac arrest, or sudden cardiac death (Martini, 1989; Brugada, 1992; Brugada, 2001). Brugada syndrome is genetically determined and has an autosomal dominant pattern of transmission in about 50% of familial cases. About 5% of survivors of cardiac arrest have no clinically identified cardiac abnormality; about half of these cases are thought to be due to Brugada syndrome (Alings, 1999).
Pathophysiology
Dysfunction in cardiac ion channels underlies the clinical manifestations of Brugada syndrome (cardiac channelopathy). In 10-30% of patients and families, mutations in the gene SCN5A, encoding the cardiac voltage-gated sodium channel Nav1.5, have been reported. Another locus has also been reported on chromosome 3. Most SCN5A mutations lead to loss of function of the Nav1.5 channel by reducing the sodium current (INa) available during the phases 0 (upstroke) and 1 (early repolarization) of the cardiac action potential. Gain-of-function SCN5A mutations may also cause long QT syndrome type 3.
Repolarization disorder hypothesis
ECG alterations in Brugada syndrome have been proposed to be due to an imbalance between the depolarizing and repolarizing currents during phase 1 of the action potential, most particularly in cells expressing a large, transient outward Ito current, such as the epicardial cells of the right ventricle free wall. In patients with loss-of-function SCN5A mutations that result in less INa during phase 1, the large Ito current may prematurely repolarize the membrane and produce a loss of the dome (phase 2) of the action potential (see Image 1).
When such premature shortening of the action potential heterogeneously occurs in the myocardium, it may generate phase 2 reentries that can cause ventricular tachycardia and ventricular fibrillation. The large transmural voltage gradients generated by the short action potentials in the right ventricular outflow epicardium are thought to be the basis of the ECG patterns of Brugada syndrome. These specific alterations in cardiac electrical activity, which mainly affect the right ventricle, manifest at ST-segment elevation in precordial leads V1 through V3, with a QRS morphology resembling that of a right bundle-branch block (RBBB). Such a pattern may also be due to a J point elevation. This pattern is called coved-type when ST elevation is the most prominent feature, and it is called saddleback-type when J point elevation occurs without ST elevation (see Image 2).
Depolarization disorder model
An alternative hypothesis for the ECG alterations is based on conduction delay in the right ventricular outflow tract compared with the right ventricle free wall. The mechanisms underlying the Brugada syndrome ECG pattern are reviewed by Meregalli (Meregalli, 2005).
The ECG pattern in Brugada syndrome may only be intermittent. The ECG alterations may fluctuate with changes in autonomic balance or body temperature. The abnormality may only be apparent during administration of drugs that block the sodium channel (eg, flecainide, procainamide, ajmaline). The ECG abnormality may disappear with infusion of isoprenaline or with exercise, and it may increase with beta-blockers. These effects are explained by a reduced sodium current in the etiology of Brugada syndrome.
Frequency
United States
Because of its recent identification, the incidence of the Brugada syndrome is not well established. It may cause 4-10 sudden deaths per 10,000 population per year.
International
In Asia (eg, the Philippines, Thailand, Japan), Brugada syndrome seems to be the most common cause of natural death in men younger than 50 years. It is known as Lai Tai (Thailand), Bangungut (Philippines), and Pokkuri (Japan). In Northeast Thailand, the mortality rate from Lai Tai is approximately 30 per 100,000 population per year (Nademanee, 1997).
Mortality/Morbidity
Brugada syndrome may lead to polymorphic ventricular tachycardia that can degenerate into ventricular fibrillation and cause sudden cardiac death.
Prolonged syncope and aborted cardiac arrest may cause nightmares, seizures, other neurologic deficits, or brain damage.
Race
Brugada syndrome is most common in people from Asia. The reason for this observation is not yet fully understood but may be due to an Asian-specific sequence in the promoter region of SCN5A (Bezzina, 2005).
Sex
Brugada syndrome is 8-10 times more prevalent in men than in women, although the probability of having a mutated gene does not differ by sex. The penetrance of the mutation appears to be much higher in men than in women.
Age
Brugada syndrome most commonly affects otherwise healthy men aged 30-50 years, but affected patients aged 0-84 years have been reported. The mean age of patients who die suddenly is 41 years (Antzelevitch, 2005).
Read more HERE
Brugada syndrome is a disorder characterized by coved or saddle-shaped ST-segment elevation in leads V1 through V3 on ECG. It is associated with complete or incomplete right bundle-branch block and T-wave inversion. In its initial description, the heart was reported to be structurally normal, but this has recently been challenged (Frustaci, 2005). Moreover, subtle structural abnormalities in the right ventricular outflow tract can also be observed. The ECG abnormality may not be evident until it is unmasked by infusion of flecainide or procainamide, or is augmented by a beta-blocker.
Patients with Brugada syndrome are prone to develop ventricular tachyarrhythmias, which may lead to syncope, cardiac arrest, or sudden cardiac death (Martini, 1989; Brugada, 1992; Brugada, 2001). Brugada syndrome is genetically determined and has an autosomal dominant pattern of transmission in about 50% of familial cases. About 5% of survivors of cardiac arrest have no clinically identified cardiac abnormality; about half of these cases are thought to be due to Brugada syndrome (Alings, 1999).
Pathophysiology
Dysfunction in cardiac ion channels underlies the clinical manifestations of Brugada syndrome (cardiac channelopathy). In 10-30% of patients and families, mutations in the gene SCN5A, encoding the cardiac voltage-gated sodium channel Nav1.5, have been reported. Another locus has also been reported on chromosome 3. Most SCN5A mutations lead to loss of function of the Nav1.5 channel by reducing the sodium current (INa) available during the phases 0 (upstroke) and 1 (early repolarization) of the cardiac action potential. Gain-of-function SCN5A mutations may also cause long QT syndrome type 3.
Repolarization disorder hypothesis
ECG alterations in Brugada syndrome have been proposed to be due to an imbalance between the depolarizing and repolarizing currents during phase 1 of the action potential, most particularly in cells expressing a large, transient outward Ito current, such as the epicardial cells of the right ventricle free wall. In patients with loss-of-function SCN5A mutations that result in less INa during phase 1, the large Ito current may prematurely repolarize the membrane and produce a loss of the dome (phase 2) of the action potential (see Image 1).
When such premature shortening of the action potential heterogeneously occurs in the myocardium, it may generate phase 2 reentries that can cause ventricular tachycardia and ventricular fibrillation. The large transmural voltage gradients generated by the short action potentials in the right ventricular outflow epicardium are thought to be the basis of the ECG patterns of Brugada syndrome. These specific alterations in cardiac electrical activity, which mainly affect the right ventricle, manifest at ST-segment elevation in precordial leads V1 through V3, with a QRS morphology resembling that of a right bundle-branch block (RBBB). Such a pattern may also be due to a J point elevation. This pattern is called coved-type when ST elevation is the most prominent feature, and it is called saddleback-type when J point elevation occurs without ST elevation (see Image 2).
Depolarization disorder model
An alternative hypothesis for the ECG alterations is based on conduction delay in the right ventricular outflow tract compared with the right ventricle free wall. The mechanisms underlying the Brugada syndrome ECG pattern are reviewed by Meregalli (Meregalli, 2005).
The ECG pattern in Brugada syndrome may only be intermittent. The ECG alterations may fluctuate with changes in autonomic balance or body temperature. The abnormality may only be apparent during administration of drugs that block the sodium channel (eg, flecainide, procainamide, ajmaline). The ECG abnormality may disappear with infusion of isoprenaline or with exercise, and it may increase with beta-blockers. These effects are explained by a reduced sodium current in the etiology of Brugada syndrome.
Frequency
United States
Because of its recent identification, the incidence of the Brugada syndrome is not well established. It may cause 4-10 sudden deaths per 10,000 population per year.
International
In Asia (eg, the Philippines, Thailand, Japan), Brugada syndrome seems to be the most common cause of natural death in men younger than 50 years. It is known as Lai Tai (Thailand), Bangungut (Philippines), and Pokkuri (Japan). In Northeast Thailand, the mortality rate from Lai Tai is approximately 30 per 100,000 population per year (Nademanee, 1997).
Mortality/Morbidity
Brugada syndrome may lead to polymorphic ventricular tachycardia that can degenerate into ventricular fibrillation and cause sudden cardiac death.
Prolonged syncope and aborted cardiac arrest may cause nightmares, seizures, other neurologic deficits, or brain damage.
Race
Brugada syndrome is most common in people from Asia. The reason for this observation is not yet fully understood but may be due to an Asian-specific sequence in the promoter region of SCN5A (Bezzina, 2005).
Sex
Brugada syndrome is 8-10 times more prevalent in men than in women, although the probability of having a mutated gene does not differ by sex. The penetrance of the mutation appears to be much higher in men than in women.
Age
Brugada syndrome most commonly affects otherwise healthy men aged 30-50 years, but affected patients aged 0-84 years have been reported. The mean age of patients who die suddenly is 41 years (Antzelevitch, 2005).
Read more HERE
Tuesday, 27 May 2008
Atrial Fibrillation
Background:
Atrial fibrillation (AF) is a common arrhythmia (see Image 1) and is a significant public health problem in the United States, affecting 2.2 million Americans and almost 5% of the population older than 69 years and 8% of the population older than 80 years. Thus, the prevalence of AF increases with advancing age. Data from the Framingham heart study show that AF is associated with a 1.5- to 1.9-fold higher risk of death, which may be due to thromboembolic stroke. While patients can be asymptomatic, many experience a wide variety of symptoms, including palpitations, dyspnea, fatigue, dizziness, angina, and congestive heart failure (CHF). In addition, the arrhythmia can be associated with hemodynamic dysfunction, tachycardia-induced cardiomyopathy, and systemic embolism.
Overall, approximately 15-25% of all strokes in the United States (75,000/y) can be attributed to AF. Known risk factors include male sex, valvular heart disease (rheumatic valvular disease), CHF, hypertension, and diabetes. Additional risk factors, such as advanced age and prior history of stroke, diabetes, and hypertension, place patients with preexisting AF at even higher risk for further comorbidities such as stroke. Patients with nonvalvular AF and risk factors have a 5-fold increased risk for stroke. Patients with rheumatic heart disease and AF have an even higher risk for stroke (17-fold). At least 4 large clinical trials have clearly demonstrated that anticoagulation with warfarin decreases the risk of stroke by 50-80%.
Given the frequency of these comorbidities, management can result in significant medical costs. Therapeutic goals include rate control, maintenance of sinus rhythm, and prevention of thromboembolism. Additionally, current practice and economic pressures force many physicians to reconsider outpatient treatment options.
Pathophysiology: Several classification schemas have been proposed for the study of AF, but none fully accounts for all aspects of AF. A number of different labels and nomenclature have been used to describe patterns of AF, including acute, chronic, paroxysmal, intermittent, and permanent. The vagaries of each of these definitions make comparing the results of studies assessing the magnitude and treatment of AF difficult.
Recently published guidelines from expert committees of the American College of Cardiology/American Heart Association and European Society of Cardiology on the treatment of patients with AF suggest that AF be classified into 3 patterns. These include a first detectable episode, irrespective of whether it is symptomatic or self-limited. Recurrent AF is considered to be present when a patient has 2 or more episodes of AF. If AF terminates spontaneously, then recurrent AF is designated as paroxysmal; if this arrhythmia becomes sustained, then AF is considered persistent (irrespective of whether AF is terminated with pharmacologic therapy or electrical cardioversion).
Persistent AF may be either the first presentation of AF or the result of recurrent episodes of paroxysmal AF. Patients with persistent AF also include patients with long-standing AF in whom cardioversion has not been indicated or attempted, often leading to permanent AF. Permanent AF is recognized as the accepted rhythm, and the only treatment goals are rate control and anticoagulation.
This classification schema pertains to cases that are not related to a reversible cause of AF (eg, thyrotoxicosis, electrolyte abnormalities, acute ethanol intoxication). The occurrence of AF secondary to acute myocardial infarction, cardiac surgery, pericarditis, pulmonary embolism, or acute pulmonary disease is considered separately because in these situations, AF is less likely to recur once the precipitating condition has been resolved and adequately treated.
Some patients with paroxysmal AF, typically younger patients, have been found to have distinct electrically active foci within their pulmonary veins. These patients generally have many atrial premature beats noted on Holter monitoring. Isolation or elimination of these foci can lead to elimination of the trigger for paroxysms of AF.
Patients can also have AF as a secondary arrhythmia associated with cardiac disease that affects the atria (eg, CHF, hypertensive heart disease, rheumatic heart disease, coronary artery disease [CAD]). These patients tend to be older, and AF is more likely to be chronic. Paroxysmal AF may progress to chronic AF, and aggressive attempts to restore and maintain sinus rhythm may prevent comorbidities associated with AF.
Persistent AF with an uncontrolled, rapid ventricular heart rate response can cause a dilated cardiomyopathy and can lead to electrical remodeling in the atria (atrial cardiomyopathy). Therapy, such as drugs or atrioventricular (AV) nodal ablation and permanent pacemaker implantation, to control the ventricular rate can improve left ventricular (LV) function and improve quality-of-life scores.
New developments aimed at curing AF are being actively explored. By reducing the critical mass required to sustain AF with either surgical or catheter-based compartmentalization of the atria (ie, MAZE procedure), fibrillatory wavelets collide with fixed anatomic obstacles, such as suture lines or complete lines of ablation, thus eliminating or reducing the chance of chronic AF. Some patients with focal origins of their AF also may be candidates for catheter ablation. Still, much remains to be accomplished before either of these procedures is appropriate for primary treatment.
Frequency:
In the US: AF affects 2.2 million Americans. It can occur in the absence of comorbidities, as it does in 10-15% of individuals (lone AF); however, AF is associated more frequently with hypertension; organic heart disease; CHF; ischemic heart disease; and valvular, dilated, hypertrophic, restrictive, and congenital cardiomyopathies. Paroxysmal AF is commonly associated with cardiac surgery, pulmonary disease, thyrotoxicosis, acute ethanol intoxication, and electrolyte imbalance. Given the almost epidemic proportions of patients with AF, clinicians must be aware of the multiple mechanisms and presentations and then correct the underlying etiology, if possible. For example, a logical decision may be to correct an overactive thyroid gland before attempting cardioversion.
Mortality/Morbidity: AF is associated with increased morbidity. The static nature of blood flow during AF can lead to the development of thrombus, most commonly in the left atrial appendage. Dislodgement of clot can lead to embolic phenomena, including stroke. Thus, anticoagulation remains the primary focus in appropriate patient populations. A target international normalized ratio of 2-3 limits the risks of hemorrhage while providing protection against the formation of thrombus.
Age:
AF is strongly age-dependent, affecting 4% of individuals older than 60 years and 8% of persons older than 80 years. The rate of ischemic stroke among elderly patients not treated with warfarin averages approximately 5% per year.
Read more HERE
Atrial fibrillation (AF) is a common arrhythmia (see Image 1) and is a significant public health problem in the United States, affecting 2.2 million Americans and almost 5% of the population older than 69 years and 8% of the population older than 80 years. Thus, the prevalence of AF increases with advancing age. Data from the Framingham heart study show that AF is associated with a 1.5- to 1.9-fold higher risk of death, which may be due to thromboembolic stroke. While patients can be asymptomatic, many experience a wide variety of symptoms, including palpitations, dyspnea, fatigue, dizziness, angina, and congestive heart failure (CHF). In addition, the arrhythmia can be associated with hemodynamic dysfunction, tachycardia-induced cardiomyopathy, and systemic embolism.
Overall, approximately 15-25% of all strokes in the United States (75,000/y) can be attributed to AF. Known risk factors include male sex, valvular heart disease (rheumatic valvular disease), CHF, hypertension, and diabetes. Additional risk factors, such as advanced age and prior history of stroke, diabetes, and hypertension, place patients with preexisting AF at even higher risk for further comorbidities such as stroke. Patients with nonvalvular AF and risk factors have a 5-fold increased risk for stroke. Patients with rheumatic heart disease and AF have an even higher risk for stroke (17-fold). At least 4 large clinical trials have clearly demonstrated that anticoagulation with warfarin decreases the risk of stroke by 50-80%.
Given the frequency of these comorbidities, management can result in significant medical costs. Therapeutic goals include rate control, maintenance of sinus rhythm, and prevention of thromboembolism. Additionally, current practice and economic pressures force many physicians to reconsider outpatient treatment options.
Pathophysiology: Several classification schemas have been proposed for the study of AF, but none fully accounts for all aspects of AF. A number of different labels and nomenclature have been used to describe patterns of AF, including acute, chronic, paroxysmal, intermittent, and permanent. The vagaries of each of these definitions make comparing the results of studies assessing the magnitude and treatment of AF difficult.
Recently published guidelines from expert committees of the American College of Cardiology/American Heart Association and European Society of Cardiology on the treatment of patients with AF suggest that AF be classified into 3 patterns. These include a first detectable episode, irrespective of whether it is symptomatic or self-limited. Recurrent AF is considered to be present when a patient has 2 or more episodes of AF. If AF terminates spontaneously, then recurrent AF is designated as paroxysmal; if this arrhythmia becomes sustained, then AF is considered persistent (irrespective of whether AF is terminated with pharmacologic therapy or electrical cardioversion).
Persistent AF may be either the first presentation of AF or the result of recurrent episodes of paroxysmal AF. Patients with persistent AF also include patients with long-standing AF in whom cardioversion has not been indicated or attempted, often leading to permanent AF. Permanent AF is recognized as the accepted rhythm, and the only treatment goals are rate control and anticoagulation.
This classification schema pertains to cases that are not related to a reversible cause of AF (eg, thyrotoxicosis, electrolyte abnormalities, acute ethanol intoxication). The occurrence of AF secondary to acute myocardial infarction, cardiac surgery, pericarditis, pulmonary embolism, or acute pulmonary disease is considered separately because in these situations, AF is less likely to recur once the precipitating condition has been resolved and adequately treated.
Some patients with paroxysmal AF, typically younger patients, have been found to have distinct electrically active foci within their pulmonary veins. These patients generally have many atrial premature beats noted on Holter monitoring. Isolation or elimination of these foci can lead to elimination of the trigger for paroxysms of AF.
Patients can also have AF as a secondary arrhythmia associated with cardiac disease that affects the atria (eg, CHF, hypertensive heart disease, rheumatic heart disease, coronary artery disease [CAD]). These patients tend to be older, and AF is more likely to be chronic. Paroxysmal AF may progress to chronic AF, and aggressive attempts to restore and maintain sinus rhythm may prevent comorbidities associated with AF.
Persistent AF with an uncontrolled, rapid ventricular heart rate response can cause a dilated cardiomyopathy and can lead to electrical remodeling in the atria (atrial cardiomyopathy). Therapy, such as drugs or atrioventricular (AV) nodal ablation and permanent pacemaker implantation, to control the ventricular rate can improve left ventricular (LV) function and improve quality-of-life scores.
New developments aimed at curing AF are being actively explored. By reducing the critical mass required to sustain AF with either surgical or catheter-based compartmentalization of the atria (ie, MAZE procedure), fibrillatory wavelets collide with fixed anatomic obstacles, such as suture lines or complete lines of ablation, thus eliminating or reducing the chance of chronic AF. Some patients with focal origins of their AF also may be candidates for catheter ablation. Still, much remains to be accomplished before either of these procedures is appropriate for primary treatment.
Frequency:
In the US: AF affects 2.2 million Americans. It can occur in the absence of comorbidities, as it does in 10-15% of individuals (lone AF); however, AF is associated more frequently with hypertension; organic heart disease; CHF; ischemic heart disease; and valvular, dilated, hypertrophic, restrictive, and congenital cardiomyopathies. Paroxysmal AF is commonly associated with cardiac surgery, pulmonary disease, thyrotoxicosis, acute ethanol intoxication, and electrolyte imbalance. Given the almost epidemic proportions of patients with AF, clinicians must be aware of the multiple mechanisms and presentations and then correct the underlying etiology, if possible. For example, a logical decision may be to correct an overactive thyroid gland before attempting cardioversion.
Mortality/Morbidity: AF is associated with increased morbidity. The static nature of blood flow during AF can lead to the development of thrombus, most commonly in the left atrial appendage. Dislodgement of clot can lead to embolic phenomena, including stroke. Thus, anticoagulation remains the primary focus in appropriate patient populations. A target international normalized ratio of 2-3 limits the risks of hemorrhage while providing protection against the formation of thrombus.
Age:
AF is strongly age-dependent, affecting 4% of individuals older than 60 years and 8% of persons older than 80 years. The rate of ischemic stroke among elderly patients not treated with warfarin averages approximately 5% per year.
Read more HERE
Monday, 26 May 2008
What is Ashman Phenomenon?
Ashman phenomenon is an aberrant ventricular conduction due to a change in QRS cycle length. In 1947, Gouaux and Ashman reported that in atrial fibrillation, when a relatively long cycle was followed by a relatively short cycle, the beat with a short cycle often has right bundle-branch block (RBBB) morphology. This causes diagnostic confusion with premature ventricular complexes (PVCs). If a sudden lengthening of the QRS cycle occurs, the subsequent impulse with a normal or shorter cycle length may be conducted with aberrancy.
Pathophysiology
Ashman phenomenon is an intraventricular conduction abnormality caused by a change in the heart rate. This is dependent on the effects of rate on the electrophysiological properties of the heart and can be modulated by metabolic and electrolyte abnormalities and the effects of drugs.
The aberrant conduction depends on the relative refractory period of the conduction tissues. The refractory period depends on the heart rate. Action potential duration (ie, refractory period) changes with the R-R interval of the preceding cycle; shorter duration of action potential is associated with a short R-R interval and prolonged duration of action potential is associated with a long R-R interval. A longer cycle lengthens the ensuing refractory period, and, if a shorter cycle follows, the beat ending it is likely to be conducted with aberrancy.
Aberrant conduction results when a supraventricular impulse reaches the His-Purkinje system while one of its branches is still in the relative or absolute refractory period. This results in slow or blocked conduction through this bundle branch and delayed depolarization through the ventricular muscles, causing a bundle-branch block configuration (ie, wide QRS complex) on the surface ECG, in the absence of bundle-branch pathology. A RBBB pattern is more common than a left bundle-branch block (LBBB) pattern because of the longer refractory period of the right bundle branch.
Several studies have questioned the sensitivity and specificity of the long-short cycle sequence. Aberrant conduction with a short-long cycle sequence has also been documented.
Frequency
United States
No geographic variations occur. Ashman phenomenon is related to the underlying pathology and is a common ECG finding in clinical practice.
History
The diagnosis of Ashman phenomenon is made using ECG evaluation findings. Patients may be asymptomatic or may have symptoms of the underlying cardiac condition.
Ashman phenomenon, per se, causes no symptoms. Symptoms, if present, are related to the premature complexes and are not related to whether the complexes are conducted aberrantly.
Physical
No specific physical examination findings are described for Ashman phenomenon.
Pulse findings may include an irregular pulse, tachycardia, and/or pulse deficit in atrial fibrillation.
Causes
Conditions causing an altered duration of the refractory period of the bundle branch or the ventricular tissue cause Ashman phenomenon. These conditions are commonly observed in (1) atrial fibrillation, (2) atrial tachycardia, and (3) atrial ectopy.
Read more about it HERE
Pathophysiology
Ashman phenomenon is an intraventricular conduction abnormality caused by a change in the heart rate. This is dependent on the effects of rate on the electrophysiological properties of the heart and can be modulated by metabolic and electrolyte abnormalities and the effects of drugs.
The aberrant conduction depends on the relative refractory period of the conduction tissues. The refractory period depends on the heart rate. Action potential duration (ie, refractory period) changes with the R-R interval of the preceding cycle; shorter duration of action potential is associated with a short R-R interval and prolonged duration of action potential is associated with a long R-R interval. A longer cycle lengthens the ensuing refractory period, and, if a shorter cycle follows, the beat ending it is likely to be conducted with aberrancy.
Aberrant conduction results when a supraventricular impulse reaches the His-Purkinje system while one of its branches is still in the relative or absolute refractory period. This results in slow or blocked conduction through this bundle branch and delayed depolarization through the ventricular muscles, causing a bundle-branch block configuration (ie, wide QRS complex) on the surface ECG, in the absence of bundle-branch pathology. A RBBB pattern is more common than a left bundle-branch block (LBBB) pattern because of the longer refractory period of the right bundle branch.
Several studies have questioned the sensitivity and specificity of the long-short cycle sequence. Aberrant conduction with a short-long cycle sequence has also been documented.
Frequency
United States
No geographic variations occur. Ashman phenomenon is related to the underlying pathology and is a common ECG finding in clinical practice.
History
The diagnosis of Ashman phenomenon is made using ECG evaluation findings. Patients may be asymptomatic or may have symptoms of the underlying cardiac condition.
Ashman phenomenon, per se, causes no symptoms. Symptoms, if present, are related to the premature complexes and are not related to whether the complexes are conducted aberrantly.
Physical
No specific physical examination findings are described for Ashman phenomenon.
Pulse findings may include an irregular pulse, tachycardia, and/or pulse deficit in atrial fibrillation.
Causes
Conditions causing an altered duration of the refractory period of the bundle branch or the ventricular tissue cause Ashman phenomenon. These conditions are commonly observed in (1) atrial fibrillation, (2) atrial tachycardia, and (3) atrial ectopy.
Read more about it HERE
Paroxysmal Supraventricular Tachycardia
Supraventricular tachycardia (SVT), a common clinical condition, is any tachyarrhythmia that requires only atrial and/or atrioventricular (AV) nodal tissue for its initiation and maintenance. It is usually a narrow-complex tachycardia that has a regular, rapid rhythm; exceptions include atrial fibrillation (AF) and multifocal atrial tachycardia (MAT). Aberrant conduction during SVT results in a wide-complex tachycardia. SVT occurs in persons of all age groups, and treatment can be challenging.
Paroxysmal supraventricular tachycardia (PSVT) is episodic, with an abrupt onset and termination. Manifestations of SVT are quite variable; patients may be asymptomatic or they may present with minor palpitations or more severe symptoms. Results from electrophysiology studies have helped determine that the pathophysiology of SVT involves abnormalities in impulse formation and conduction pathways. The most common mechanism identified is reentry (Denes, 1973; Rosen, 1974; Akhtar, 1984; Waldo, 1993). This article focuses on SVT, including the pathophysiology, clinical presentation, diagnosis, management, and treatment options of this condition.
Pathophysiology
The development of intracardiac electrophysiology studies has dramatically changed the classification of SVT. Intracardiac recordings have identified the various mechanisms of SVT. Depending on the site of origin of the dysrhythmia, SVTs may be classified as an atrial or AV tachyarrhythmia (Klein, 1987; Basta, 1997).
Atrial tachyarrhythmias include (1) sinus tachycardia, (2) inappropriate sinus tachycardia (IST), (3) sinus nodal reentrant tachycardia (SNRT), (4) atrial tachycardia, (5) MAT, (6) atrial flutter, and (7) AF.
AV tachyarrhythmias include (1) AV nodal reentrant tachycardia (AVNRT), (2) AV reentrant tachycardia (AVRT), (3), junctional ectopic tachycardia (JET), and (4) nonparoxysmal junctional tachycardia (NPJT).
Atrial tachyarrhythmias
Sinus tachycardia
Sinus tachycardia is an accelerated sinus rate that is a physiologic response to a stressor. It is characterized by a heart rate faster than 100 beats per minute (bpm) and generally involves a regular rhythm (see Image 1). Underlying physiological stresses such as hypoxia, hypovolemia, fever, anxiety, pain, hyperthyroidism, and exercise usually induce sinus tachycardia (Tintinalli, 2000; Ganz, 2002). Treatment involves addressing the basic underlying stressor. Certain drugs, such as stimulants (eg, nicotine, caffeine), medications (eg, atropine, salbutamol), recreational drugs (eg, cocaine, amphetamines, ecstasy), and hydralazine, can also induce sinus tachycardia.
Inappropriate sinus tachycardia
IST is an accelerated baseline sinus rate in the absence of a physiological stressor. In this situation, healthy adults may have an elevated resting heart rate and an exaggerated heart rate response to even minimal exercise. This tachyarrhythmia is observed most commonly in young women without structural heart disease (Bellet, 1963; Krahn, 1995; Xie, 1998). The underlying mechanism of IST may be hypersensitivity of the sinus node to autonomic input or an abnormality within the sinus node, its autonomic input, or both (Bellet, 1963; Krahn, 1995; Xie, 1998).
Sinus nodal reentrant tachycardia
SNRT is frequently confused with IST. SNRT is due to a reentry circuit, either in or near the sinus node. Therefore, it has an abrupt onset and offset. The heart rate is usually 100-150 bpm, and ECG tracings usually demonstrate normal sinus P-wave morphology (Bellet, 1963; Krahn, 1995; Xie, 1998).
Atrial tachycardia
Atrial tachycardia is an arrhythmia originating in the atrial myocardium. Enhanced automaticity, triggered activity, or reentry may result in this rare tachycardia (Wellens, 1978; Farre, 1981; Brugada, 1984; Lesh, 1994; Xie, 1998). The heart rate is regular and is usually 120-250 bpm. The P-wave morphology is different from the sinus P waves and is dependent on the site of origin of the tachycardia (see Image 2). Because the arrhythmia does not involve the AV node, nodal blocking agents such as adenosine and verapamil are usually unsuccessful in terminating this arrhythmia. Atrial tachycardia has also been associated with digoxin toxicity via the triggered mechanism (Wellens, 1978; Farre, 1981; Brugada, 1984; Lesh, 1994; Xie, 1998).
Multifocal atrial tachycardia
MAT is a tachyarrhythmia that arises within the atrial tissue; it is composed of 3 or more P-wave morphologies and heart rates. This arrhythmia is fairly uncommon and is typically observed in elderly patients with pulmonary disease. The heart rate is greater than 100 bpm, and ECG findings typically include an irregular rhythm, which may be misinterpreted as AF (see Image 3). Treatment involves correcting the underlying disease process (Phillips, 1969; Habibzadeh, 1980; Scher, 1989). Magnesium and verapamil may sometimes be effective.
Atrial flutter
Atrial flutter is a tachyarrhythmia arising above the AV node with an atrial rate of 250-350 bpm. The mechanism behind atrial flutter is generally reentrant in nature. Typically, counterclockwise atrial flutter is due to a macroreentrant right atrial circuit. It is commonly observed in patients with ischemic heart disease, myocardial infarction, cardiomyopathy, myocarditis, pulmonary embolus, toxic ingestion (eg, alcohol), or chest trauma. It may be a transitional rhythm and can progress to AF. ECG findings of typical atrial flutter include negative sawtooth flutter waves in leads II, III, and aVF. AV conduction is most commonly 2:1, which yields a ventricular rate of approximately 150 bpm (see Image 4) (Akhtar, 1984; Tintinalli, 2000; Josephson, 2001).
Atrial fibrillation
AF is an extremely common arrhythmia arising from chaotic atrial depolarization. The atrial rate is usually 300-600 bpm, while the ventricular rate may be 170 bpm or more. ECG findings characteristically include an irregular rhythm with fibrillatory atrial activity (see Image 5). This arrhythmia is associated with rheumatic heart disease, hypertension, ischemic heart disease, pericarditis, thyrotoxicosis, alcohol intoxication, mitral valve prolapse and other disorders of the mitral valve, and digitalis toxicity (Akhtar, 1984; Tintinalli, 2000; Josephson, 2001). When AF occurs in young or middle-aged patients in the absence of structural heart disease or any apparent cause, it is called lone or idiopathic AF.
AV tachyarrhythmias
AV nodal reentrant tachycardia
The most common cause of PSVT is AVNRT. AVNRT is diagnosed in 50-60% of patients who present with regular narrow QRS tachyarrhythmia (Josephson, 1977; Akhtar, 1984; Jazayeri, 1992; Akhtar, 1993). The heart rate is 120-250 bpm and is typically quite regular (see Images 6-7). AVNRT may occur in healthy, young individuals, and it occurs most commonly in women (Jazayeri, 1992). Most patients do not have structural heart disease. However, occasionally these individuals may have an underlying heart condition such as rheumatic heart disease, pericarditis, myocardial infarction, mitral valve prolapse, or preexcitation syndrome (Josephson, 1977; Akhtar, 1984; Jazayeri, 1992; Akhtar, 1993).
An understanding of the electrophysiology of AV nodal tissue is very important in order to comprehend the mechanism of AVNRT. In most people, the AV node has a single conducting pathway that conducts impulses in an anterograde manner to depolarize the bundle of His. In certain cases, AV nodal tissue may have 2 conducting pathways with different electrophysiological properties (see Image 8). One pathway (alpha) is a relatively slow conducting pathway with a short refractory period, while the second pathway (beta) is a rapid conducting pathway with a long refractory period. The coexistence of these functionally different pathways serves as the substrate for reentrant tachycardia (Josephson, 1977; Akhtar, 1984; Akhtar, 1993; Ganz, 1995). Electrophysiologic studies have demonstrated dual AV nodal pathways in 40% of patients.
Onset of AVNRT is triggered by a premature atrial impulse. A premature atrial impulse may reach the AV node when the fast pathway (beta) is still refractory from the previous impulse but the slow pathway (alpha) may be able to conduct. The premature impulse then conducts through the slow pathway (alpha) in an anterograde manner; the (beta) pathway continues to recover because of its longer refractory period. After the impulse conducts in an anterograde manner through the slow (alpha) pathway, it may find the fast (beta) pathway recovered; the impulse then conducts in a retrograde manner via the fast (beta) pathway. If the slow pathway (alpha) has repolarized by the time the impulse completes the retrograde conduction, the impulse can then reenter the slow (alpha) pathway and initiate AVNRT (see Image 8).
Importantly, note that AVNRT does not involve the ventricles as part of the reentry circuit; the necessity of perinodal atrial tissue to the circuit is controversial. Because the impulse typically conducts in an anterograde manner through the slow pathway and in a retrograde manner through the fast pathway, the PR interval is longer than the RP interval. Thus, in patients with typical AVNRT, the P wave is usually located at the terminal portion of the QRS complex (Josephson, 1977; Akhtar, 1984; Akhtar, 1993; Ganz, 1995; Josephson, 2001). In patients with atypical AVNRT, anterograde conduction is via the fast pathway, while retrograde conduction is via the slow pathway. For these atypical patients, the RP interval is longer than the PR interval (Josephson, 1977; Wu, 1977; Akhtar, 1984; Jazayeri, 1992; Akhtar, 1993; Ganz, 1995; Josephson, 1997; Josephson, 2001).
AV reentrant tachycardia
AVRT is the second most common form of PSVT. The incidence rate of AVRT in the general population is 0.1-0.3%. AVRT is more common in males than in females (male-to-female ratio of 2:1), and patients with AVRT commonly present at a younger age than patients with AVNRT. AVRT is associated with the Ebstein anomaly, although most patients with AVRT do not have evidence of structural heart disease. AVRT occurs in the presence of accessory pathways, or bypass tracts. Accessory pathways are errant strands of myocardium that bridge the mitral or tricuspid valves (Josephson, 1977; Murdock, 1991; Ganz, 1995; Xie, 1998).
AVRT is the result of 2 or more conducting pathways: the AV node and 1 or more bypass tracts. In a normal heart, only a single route of conduction is present. Conduction begins at the sinus node, progresses to the AV node, and then to the bundle of His and the bundle branches. However, in AVRT, 1 or more accessory pathways connect the atria and the ventricles. The accessory pathways may conduct impulses in an anterograde manner, a retrograde manner, or both (Wolff, 1930; Coumel, 1967; Josephson, 1977; Gallagher, 1978; Murdock, 1991; Oren, 1993; Ganz, 1995; Xie, 1998). When impulses travel down the accessory pathway in an anterograde manner, ventricular preexcitation results. This produces a short PR interval and a delta wave as is observed in persons with Wolff-Parkinson-White (WPW) syndrome (see Image 9) (Wolff, 1930).
Importantly, note that not all accessory pathways conduct in an anterograde manner. Concealed accessory pathways are not evident during sinus rhythm, and they are only capable of retrograde conduction. A reentry circuit is most commonly established by impulses traveling in an anterograde manner through the AV node and in a retrograde manner through the accessory pathway; this is called orthodromic AVRT. A reentry circuit may also be established by a premature impulse traveling in an anterograde manner through a manifest accessory pathway and in a retrograde manner through the AV node; this is called antidromic AVRT (see Image 10) (Bardy, 1984; Obel, 1997). While the orthodromic AVRT is typically a narrow-complex tachycardia (see Image 11), antidromic AVRT inscribes a bizarre, wide-complex tachycardia (see Image 12) (Bardy, 1984; Atie, 1990; Obel, 1997).
Patients with WPW syndrome can develop AF and atrial flutter (see Image 13). The rapid nondecremental conduction via the accessory pathways can result in extremely rapid rates, which can degenerate to ventricular fibrillation and cause sudden death. Patients with preexcitation syndromes with AF must not be administered an AV nodal blocking agent; these agents can further increase conduction via the accessory pathway, which increases the risk of ventricular fibrillation and death (Campbell, 1977; Sung, 1977; Klein, 1979; Bardy, 1984; Vidaillet, 1987; Montoya, 1991; Obel, 1998).
Junctional ectopic tachycardia and nonparoxysmal junctional tachycardia
JET and NPJT are rare and presumably arise because of increased automaticity, triggered activity, or both. They are usually observed following valvular surgery, after myocardial infarction, during active rheumatic carditis, or with digoxin toxicity. These tachycardias are also observed in children following congenital heart surgery. ECG findings include a regular narrow QRS complex, although P waves may not be visible. Patients with AV dissociation have also been described (Ganz, 1995; Pieper, 1995; Trohman, 2000).
Paroxysmal supraventricular tachycardia (PSVT) is episodic, with an abrupt onset and termination. Manifestations of SVT are quite variable; patients may be asymptomatic or they may present with minor palpitations or more severe symptoms. Results from electrophysiology studies have helped determine that the pathophysiology of SVT involves abnormalities in impulse formation and conduction pathways. The most common mechanism identified is reentry (Denes, 1973; Rosen, 1974; Akhtar, 1984; Waldo, 1993). This article focuses on SVT, including the pathophysiology, clinical presentation, diagnosis, management, and treatment options of this condition.
Pathophysiology
The development of intracardiac electrophysiology studies has dramatically changed the classification of SVT. Intracardiac recordings have identified the various mechanisms of SVT. Depending on the site of origin of the dysrhythmia, SVTs may be classified as an atrial or AV tachyarrhythmia (Klein, 1987; Basta, 1997).
Atrial tachyarrhythmias include (1) sinus tachycardia, (2) inappropriate sinus tachycardia (IST), (3) sinus nodal reentrant tachycardia (SNRT), (4) atrial tachycardia, (5) MAT, (6) atrial flutter, and (7) AF.
AV tachyarrhythmias include (1) AV nodal reentrant tachycardia (AVNRT), (2) AV reentrant tachycardia (AVRT), (3), junctional ectopic tachycardia (JET), and (4) nonparoxysmal junctional tachycardia (NPJT).
Atrial tachyarrhythmias
Sinus tachycardia
Sinus tachycardia is an accelerated sinus rate that is a physiologic response to a stressor. It is characterized by a heart rate faster than 100 beats per minute (bpm) and generally involves a regular rhythm (see Image 1). Underlying physiological stresses such as hypoxia, hypovolemia, fever, anxiety, pain, hyperthyroidism, and exercise usually induce sinus tachycardia (Tintinalli, 2000; Ganz, 2002). Treatment involves addressing the basic underlying stressor. Certain drugs, such as stimulants (eg, nicotine, caffeine), medications (eg, atropine, salbutamol), recreational drugs (eg, cocaine, amphetamines, ecstasy), and hydralazine, can also induce sinus tachycardia.
Inappropriate sinus tachycardia
IST is an accelerated baseline sinus rate in the absence of a physiological stressor. In this situation, healthy adults may have an elevated resting heart rate and an exaggerated heart rate response to even minimal exercise. This tachyarrhythmia is observed most commonly in young women without structural heart disease (Bellet, 1963; Krahn, 1995; Xie, 1998). The underlying mechanism of IST may be hypersensitivity of the sinus node to autonomic input or an abnormality within the sinus node, its autonomic input, or both (Bellet, 1963; Krahn, 1995; Xie, 1998).
Sinus nodal reentrant tachycardia
SNRT is frequently confused with IST. SNRT is due to a reentry circuit, either in or near the sinus node. Therefore, it has an abrupt onset and offset. The heart rate is usually 100-150 bpm, and ECG tracings usually demonstrate normal sinus P-wave morphology (Bellet, 1963; Krahn, 1995; Xie, 1998).
Atrial tachycardia
Atrial tachycardia is an arrhythmia originating in the atrial myocardium. Enhanced automaticity, triggered activity, or reentry may result in this rare tachycardia (Wellens, 1978; Farre, 1981; Brugada, 1984; Lesh, 1994; Xie, 1998). The heart rate is regular and is usually 120-250 bpm. The P-wave morphology is different from the sinus P waves and is dependent on the site of origin of the tachycardia (see Image 2). Because the arrhythmia does not involve the AV node, nodal blocking agents such as adenosine and verapamil are usually unsuccessful in terminating this arrhythmia. Atrial tachycardia has also been associated with digoxin toxicity via the triggered mechanism (Wellens, 1978; Farre, 1981; Brugada, 1984; Lesh, 1994; Xie, 1998).
Multifocal atrial tachycardia
MAT is a tachyarrhythmia that arises within the atrial tissue; it is composed of 3 or more P-wave morphologies and heart rates. This arrhythmia is fairly uncommon and is typically observed in elderly patients with pulmonary disease. The heart rate is greater than 100 bpm, and ECG findings typically include an irregular rhythm, which may be misinterpreted as AF (see Image 3). Treatment involves correcting the underlying disease process (Phillips, 1969; Habibzadeh, 1980; Scher, 1989). Magnesium and verapamil may sometimes be effective.
Atrial flutter
Atrial flutter is a tachyarrhythmia arising above the AV node with an atrial rate of 250-350 bpm. The mechanism behind atrial flutter is generally reentrant in nature. Typically, counterclockwise atrial flutter is due to a macroreentrant right atrial circuit. It is commonly observed in patients with ischemic heart disease, myocardial infarction, cardiomyopathy, myocarditis, pulmonary embolus, toxic ingestion (eg, alcohol), or chest trauma. It may be a transitional rhythm and can progress to AF. ECG findings of typical atrial flutter include negative sawtooth flutter waves in leads II, III, and aVF. AV conduction is most commonly 2:1, which yields a ventricular rate of approximately 150 bpm (see Image 4) (Akhtar, 1984; Tintinalli, 2000; Josephson, 2001).
Atrial fibrillation
AF is an extremely common arrhythmia arising from chaotic atrial depolarization. The atrial rate is usually 300-600 bpm, while the ventricular rate may be 170 bpm or more. ECG findings characteristically include an irregular rhythm with fibrillatory atrial activity (see Image 5). This arrhythmia is associated with rheumatic heart disease, hypertension, ischemic heart disease, pericarditis, thyrotoxicosis, alcohol intoxication, mitral valve prolapse and other disorders of the mitral valve, and digitalis toxicity (Akhtar, 1984; Tintinalli, 2000; Josephson, 2001). When AF occurs in young or middle-aged patients in the absence of structural heart disease or any apparent cause, it is called lone or idiopathic AF.
AV tachyarrhythmias
AV nodal reentrant tachycardia
The most common cause of PSVT is AVNRT. AVNRT is diagnosed in 50-60% of patients who present with regular narrow QRS tachyarrhythmia (Josephson, 1977; Akhtar, 1984; Jazayeri, 1992; Akhtar, 1993). The heart rate is 120-250 bpm and is typically quite regular (see Images 6-7). AVNRT may occur in healthy, young individuals, and it occurs most commonly in women (Jazayeri, 1992). Most patients do not have structural heart disease. However, occasionally these individuals may have an underlying heart condition such as rheumatic heart disease, pericarditis, myocardial infarction, mitral valve prolapse, or preexcitation syndrome (Josephson, 1977; Akhtar, 1984; Jazayeri, 1992; Akhtar, 1993).
An understanding of the electrophysiology of AV nodal tissue is very important in order to comprehend the mechanism of AVNRT. In most people, the AV node has a single conducting pathway that conducts impulses in an anterograde manner to depolarize the bundle of His. In certain cases, AV nodal tissue may have 2 conducting pathways with different electrophysiological properties (see Image 8). One pathway (alpha) is a relatively slow conducting pathway with a short refractory period, while the second pathway (beta) is a rapid conducting pathway with a long refractory period. The coexistence of these functionally different pathways serves as the substrate for reentrant tachycardia (Josephson, 1977; Akhtar, 1984; Akhtar, 1993; Ganz, 1995). Electrophysiologic studies have demonstrated dual AV nodal pathways in 40% of patients.
Onset of AVNRT is triggered by a premature atrial impulse. A premature atrial impulse may reach the AV node when the fast pathway (beta) is still refractory from the previous impulse but the slow pathway (alpha) may be able to conduct. The premature impulse then conducts through the slow pathway (alpha) in an anterograde manner; the (beta) pathway continues to recover because of its longer refractory period. After the impulse conducts in an anterograde manner through the slow (alpha) pathway, it may find the fast (beta) pathway recovered; the impulse then conducts in a retrograde manner via the fast (beta) pathway. If the slow pathway (alpha) has repolarized by the time the impulse completes the retrograde conduction, the impulse can then reenter the slow (alpha) pathway and initiate AVNRT (see Image 8).
Importantly, note that AVNRT does not involve the ventricles as part of the reentry circuit; the necessity of perinodal atrial tissue to the circuit is controversial. Because the impulse typically conducts in an anterograde manner through the slow pathway and in a retrograde manner through the fast pathway, the PR interval is longer than the RP interval. Thus, in patients with typical AVNRT, the P wave is usually located at the terminal portion of the QRS complex (Josephson, 1977; Akhtar, 1984; Akhtar, 1993; Ganz, 1995; Josephson, 2001). In patients with atypical AVNRT, anterograde conduction is via the fast pathway, while retrograde conduction is via the slow pathway. For these atypical patients, the RP interval is longer than the PR interval (Josephson, 1977; Wu, 1977; Akhtar, 1984; Jazayeri, 1992; Akhtar, 1993; Ganz, 1995; Josephson, 1997; Josephson, 2001).
AV reentrant tachycardia
AVRT is the second most common form of PSVT. The incidence rate of AVRT in the general population is 0.1-0.3%. AVRT is more common in males than in females (male-to-female ratio of 2:1), and patients with AVRT commonly present at a younger age than patients with AVNRT. AVRT is associated with the Ebstein anomaly, although most patients with AVRT do not have evidence of structural heart disease. AVRT occurs in the presence of accessory pathways, or bypass tracts. Accessory pathways are errant strands of myocardium that bridge the mitral or tricuspid valves (Josephson, 1977; Murdock, 1991; Ganz, 1995; Xie, 1998).
AVRT is the result of 2 or more conducting pathways: the AV node and 1 or more bypass tracts. In a normal heart, only a single route of conduction is present. Conduction begins at the sinus node, progresses to the AV node, and then to the bundle of His and the bundle branches. However, in AVRT, 1 or more accessory pathways connect the atria and the ventricles. The accessory pathways may conduct impulses in an anterograde manner, a retrograde manner, or both (Wolff, 1930; Coumel, 1967; Josephson, 1977; Gallagher, 1978; Murdock, 1991; Oren, 1993; Ganz, 1995; Xie, 1998). When impulses travel down the accessory pathway in an anterograde manner, ventricular preexcitation results. This produces a short PR interval and a delta wave as is observed in persons with Wolff-Parkinson-White (WPW) syndrome (see Image 9) (Wolff, 1930).
Importantly, note that not all accessory pathways conduct in an anterograde manner. Concealed accessory pathways are not evident during sinus rhythm, and they are only capable of retrograde conduction. A reentry circuit is most commonly established by impulses traveling in an anterograde manner through the AV node and in a retrograde manner through the accessory pathway; this is called orthodromic AVRT. A reentry circuit may also be established by a premature impulse traveling in an anterograde manner through a manifest accessory pathway and in a retrograde manner through the AV node; this is called antidromic AVRT (see Image 10) (Bardy, 1984; Obel, 1997). While the orthodromic AVRT is typically a narrow-complex tachycardia (see Image 11), antidromic AVRT inscribes a bizarre, wide-complex tachycardia (see Image 12) (Bardy, 1984; Atie, 1990; Obel, 1997).
Patients with WPW syndrome can develop AF and atrial flutter (see Image 13). The rapid nondecremental conduction via the accessory pathways can result in extremely rapid rates, which can degenerate to ventricular fibrillation and cause sudden death. Patients with preexcitation syndromes with AF must not be administered an AV nodal blocking agent; these agents can further increase conduction via the accessory pathway, which increases the risk of ventricular fibrillation and death (Campbell, 1977; Sung, 1977; Klein, 1979; Bardy, 1984; Vidaillet, 1987; Montoya, 1991; Obel, 1998).
Junctional ectopic tachycardia and nonparoxysmal junctional tachycardia
JET and NPJT are rare and presumably arise because of increased automaticity, triggered activity, or both. They are usually observed following valvular surgery, after myocardial infarction, during active rheumatic carditis, or with digoxin toxicity. These tachycardias are also observed in children following congenital heart surgery. ECG findings include a regular narrow QRS complex, although P waves may not be visible. Patients with AV dissociation have also been described (Ganz, 1995; Pieper, 1995; Trohman, 2000).
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