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