Atrial fibrillation

In 2000, some 2.3 million Americans were affected by atrial fibrillation, and that number is expected to rise as our population ages. Atrial fibrillation is both a reflection of active physiologic stressors on the body and a marker of future cardiac disease progression. The disorganized atrial activity that characterizes atrial fibrillation affects cardiac function, metabolic demand, and quality of life. However, our understanding of the etiology and treatment of this condition continues to advance with the result of recent large-scale clinical trials. Diabetes, hypertension, congestive heart failure, valvular disease, and myocardial infarction are all risk factors in the development of atrial fibrillation. And the diagnosis confers a five-fold increase in the incidence of stroke. (Patients at increased risk for stroke include those with congestive heart failure, hypertension, age greater than 75, diabetes, and previous stroke.) Anticoagulation is a critical action in most cases of atrial fibrillation, as data show a 68% relative risk reduction of stroke when patients are treated with warfarin. Prior to recent trials, achieving sinus rhythm was thought to invariably improve symptoms, cardiac function, and mortality. The adverse effects of antiarrhythmic medications are now being recognized, and treatment strategies emphasizing ventricular rate control have been recommended in recent clinical practice guidelines. This shift in thinking is influencing both outpatient and emergency department management. Controlling the ventricular rate in atrial fibrillation increases cardiac output, decreases the metabolic demand of the heart, and avoids the potentially dangerous side effects of rhythm-control drugs. Rate-control agents should be selected based on the clinical profile of individual patients. A well-chosen subset of patients may benefit from either chemical or electrical cardioversion; this appears to be a reasonably safe procedure and can be accomplished on an outpatient basis. Understanding causal etiologies, managing risk for stroke (and need for anticoagulation), addressing rate, and assessing the risks of cardioversion are key elements in a comprehensive approach to atrial fibrillation.     

Atrial fibrillation: the nonpharmacologic strategy

Pharmacologic treatment has been used for decades for conversion and prevention of recurrent atrial fibrillation (AF). But the use of antiarrhythmic drugs is associated with substantial side effects and mortality in some patients. Accordingly, it is not surprising that nonpharmacologic techniques have been developed for the management of AF, including the use of atrial defibrillators, atrial pacing methods, and several surgical and radiofrequency catheter ablation procedures. The atrial defibrillator has been found to detect and treat atrial and ventricular arrhythmias appropriately, with successful termination of spontaneous AF through low energy shocks. Although these devices are promising, the factor which limits their widespread use is not safety or efficacy, but patient comfort. Several studies suggest that atrial-based cardiac pacing may have a beneficial effect in decreasing and preventing AF episodes in patients with sick sinus syndrome. Palliative ablative procedures also available for the treatment of atrial fibrillation include AV junctional modification and AV nodal ablation with permanent pacing, the latter technique being associated with improvements in ejection fraction. Two potentially curative procedures are the surgical MAZE and endocardial catheter ablation. These techniques are based on placing strategically located lesions in the atrium to disrupt the conduction pathway(s). Recent studies have focused on ablative therapies aimed at the area of the pulmonic veins. The main therapy for maintaining sinus rhythm after conversion is predominantly pharmacologic. Similarly, in the absence of heart block, if conversion to sinus rhythm is not successful, pharmacologic modalities may be required to control ventricular rate. In any case, planning a treatment regimen for the management of AF should include evaluation of the risks inherent in the use of various drugs as well as more invasive strategies.     

Atrial fibrillation post-cardiac surgery: changing perspectives

ABSTRACT

Perioperative atrial fibrillation (AF) is one of the most frequent complications of cardiac surgery. Its development is associated with an increased morbidity and mortality, for example from perioperative stroke, as well as ventricular arrhythmias, postoperative myocardial infarction, congestive cardiac failure, renal failure, increased use of inotropic medications and the need for intra-aortic balloon pump. Furthermore, AF after cardiac surgery results in prolonged hospitalization after the procedure, as well as an excess utilization of hospital resources and increased hospital costs. Given the importance of AF for patient outcome, a wide variety of prophylactic pharmacologic strategies have been evaluated.

The risk of post-operative AF should be reduced by the administration of amiodarone, a beta- blocker, sotalol or rate-limiting calcium antagonists. In addition, in patients undergoing cardiac surgery on pre-existing beta-blocker therapy, this treatment should be continued unless contraindications develop (such as post-operative bradycardia or hypotension). Unless contraindicated, a rhythm control strategy is recommended as the initial option for the treatment of post-operative AF following cardiothoracic surgery. More recently, some data regarding magnesium, statins and n-3 olyunsaturated fatty acids in reducing post-op AF are available. Clearly, perspectives are changing in our management of this common arrhythmia.     

Atrial fibrillation post-cardiac surgery: changing perspectives

Perioperative atrial fibrillation (AF) is one of the most frequent complications of cardiac surgery. Its development is associated with an increased morbidity and mortality, for example from perioperative stroke, as well as ventricular arrhythmias, postoperative myocardial infarction, congestive cardiac failure, renal failure, increased use of inotropic medications and the need for intra-aortic balloon pump. Furthermore, AF after cardiac surgery results in prolonged hospitalization after the procedure, as well as an excess utilization of hospital resources and increased hospital costs. Given the importance of AF for patient outcome, a wide variety of prophylactic pharmacologic strategies have been evaluated. The risk of post-operative AF should be reduced by the administration of amiodarone, a beta-blocker, sotalol or rate-limiting calcium antagonists. In addition, in patients undergoing cardiac surgery on pre-existing beta-blocker therapy, this treatment should be continued unless contraindications develop (such as post-operative bradycardia or hypotension). Unless contraindicated, a rhythm control strategy is recommended as the initial option for the treatment of post-operative AF following cardiothoracic surgery. More recently, some data regarding magnesium, statins and n-3 polyunsaturated fatty acids in reducing post-op AF are available. Clearly, perspectives are changing in our management of this common arrhythmia.     

Rate control versus rhythm control for the management of atrial fibrillation: the verdict of the AFFIRM trial

Atrial fibrillation is the most common sustained cardiac arrhythmia encountered in clinical practice that affects cardiovascular morbidity and mortality and generates significant healthcare costs. There are two approaches for the management of atrial fibrillation: rate control and rhythm control. Rate-control strategy involves using rate-controlling agents such as beta-blockers, calcium channel blockers or digoxin, or a combination thereof to control symptoms while allowing atrial fibrillation to persist. Rhythm-control strategy involves cardioversion and treatment with antiarrhythmic drugs to maintain sinus rhythm. Although each strategy has its own advantages as well as limitations, it has long been debated which of the strategies offers better long-term outcomes and thus should be the preferred and recommended approach for the management of patients with atrial fibrillation. The Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study was the first large-scale randomised study to address this important issue. In this article, the long awaited verdict of the AFFIRM study with its implications for the clinical management of patients with atrial fibrillation is discussed.     

Dronedarone or amiodarone for rhythm control for atrial fibrillation: implications from the DIONYSOS study

Management of persistent AF involves rhythm or rate control strategies and thromboprophylaxis for cardioembolic events. Although amiodarone appears to be more effective than other current antiarrhythmics for a rhythm control approach in AF patients, many side effects limit its long-term use. Dronedarone is a new antiarrhythmic drug that may offer advantages for rhythm control, given its relative safety (although not in patients with decompensated heart failure), efficacy and tolerability. With regard to the latter, dronedarone has fewer adverse effects and is better tolerated than amiodarone. Nonetheless, in one head-to-head comparison of dronedarone and amiodarone, the latter drug was superior to dronedarone for maintenance of sinus rhythm post cardioversion, but dronedarone was safer and better tolerated, with useful benefit to decrease hospitalizations and thus healthcare costs. This provides clinicians (and patients) with a new option when choosing antiarrhythmic therapy.     

Dronedarone or amiodarone for rhythm control for atrial fibrillation: implications from the DIONYSOS study

Management of persistent AF involves rhythm or rate control strategies and thromboprophylaxis for cardioembolic events. Although amiodarone appears to be more effective than other current antiarrhythmics for a rhythm control approach in AF patients, many side effects limit its long-term use. Dronedarone is a new antiarrhythmic drug that may offer advantages for rhythm control, given its relative safety (although not in patients with decompensated heart failure), efficacy and tolerability. With regard to the latter, dronedarone has fewer adverse effects and is better tolerated than amiodarone. Nonetheless, in one head-to-head comparison of dronedarone and amiodarone, the latter drug was superior to dronedarone for maintenance of sinus rhythm post cardioversion, but dronedarone was safer and better tolerated, with useful benefit to decrease hospitalizations and thus healthcare costs. This provides clinicians (and patients) with a new option when choosing antiarrhythmic therapy.     

Rate versus rhythm control in patients with atrial fibrillation: what the trials really say

Despite new insights into the pathophysiological triggers of atrial fibrillation (AF) and the development of novel ablative techniques and antiarrhythmic drugs, the management of this chronic rhythm disturbance remains problematic. At present, there are two fundamental interventional choices: restoration and maintenance of normal sinus rhythm (NSR) or control of the ventricular rate. While there are compelling theoretical benefits in restoring and maintaining NSR, until recently there has been little evidence supporting the comparative advantages of either strategy. During the past few years, five randomised trials investigating the two treatment strategies have been completed: PIAF (Pharmacological Intervention in Atrial Fibrillation), STAF (Strategies of Treatment of Atrial Fibrillation), RACE (RAte Control versus Electrical conversion), AFFIRM (Atrial Fibrillation Follow-up of Rhythm Management) and HOT-CAFE (How to Treat Chronic Atrial Fibrillation). Results from these studies indicate that a strategy of rate control in AF patients can be at least as effective as efforts to control rhythm with respect to several specific outcomes. These trials have also revealed the necessity of continuing antithrombotic treatment even when long-term sinus rhythm is obtained. However, these trials had different patient selection criteria, endpoints and therapeutic interventions, limiting the applicability of their findings to all AF populations. This article looks beyond the primary results from these important studies, using recent substudy analyses to draw new conclusions and to generate hypotheses that will require prospective evaluation in adequately powered trials. One substudy suggested, for instance, that failure of rhythm control to show superiority may be a result of the toxicity of current antiarrhythmic drugs. New class III compounds with novel mechanisms are now in varying stages of clinical development. These drugs appear to block multiple membrane ion channels, with predominant effects on the atria and low proarrhythmic potential. It is anticipated that these agents will be safer than, and at least as effective as, currently available drugs, thereby reducing AF-related morbidity and mortality. Until more effective treatments are available, physicians should use the evidence generated from the major studies to guide decision making based upon the characteristics and symptomatic presentation of individual patients.