Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia, occurring predominantly in structural heart disease (the underlying cause of heart failure), and causing persistent tachycardia, substantial morbidity, and decreased survival. The loss of atrial forward output, estimated at 30% of total cardiac output, coupled with already compromised left ventricular function, compounds hemodynamic and clinical status. AF is also a cause of thromboembolism. Various studies define AF as chronic if it has lasted for at least 2 weeks; unfortunately, most of the many studies on its management in heart failure have been uncontrolled. Nevertheless, it is clear that not every patient benefits from cardioversion, nor is it feasible in many cases.
Cardioversion is the restoration of sinus rhythm using antiarrhythmic drugs or the more effective alternative, external or internal shock therapy, which has an initial 70% success rate. The indications for electrical cardioversion include minimal or absent electrophysio-logic or structural remodeling of the atria, and youngish patients in early heart failure with limited sympathetic activation and atrial distension, hence lower general anesthetic risk.
Pharmacologic cardioversion is much less effective. The data for individual drugs are unconvincing. The various studies with amiodarone, for example, differ too much in choice of dose, duration of AF, and the effects of concomitant therapy, such as digoxin, for any consistent conclusion to be drawn.
With newer alternatives, such as ibutilide, the data remain preliminary. Heart failure contraindicates the use of class I antiarrhythmics due to their proarrhythmic effects and the risk of worsening left ventricular contractility. As for digoxin, the data are inconsistent. There is no evidence to date that diltiazem or (3-blockers possess cardioverting properties.
Following cardioversion, whether electrical or pharmacologic, the concern is to maintain sinus rhythm. Amiodarone has proved the most effective prophylactic in this regard, with 1-year success rates ranging from 42% to 85%. However, its long-term use can cause toxicity and intolerance.
Dofetilide, a novel class III antiarrhythmic, is also effective, with no adverse effect on survival in heart failure. Class I antiarrhythmics are effective, but must be used with caution, for the reasons already given.
Heart rate control
Because the 5-year success rate is relatively low, around 30%, it is important to identify those patients in whom cardioversion is likely to be cost-ineffective using current therapeutic strategies. Predictors of poor outcome include longstanding AF, rheumatic valvular disease, and severe heart failure. The arrhythmia-free interval is likely to be very short in such patients in whom attempts at cardioversion should be limited in favor of rate control regimens.
Drugs are the first approach to rate control. The various drugs available include digoxin, diltiazem, 13-blockers, and amiodarone. Digoxin is slow and ineffective in lowering the heart rate, although its inotropic and neurohormonal actions may improve symptoms. Diltiazem is not indicated in heart failure. Landmark trials have shown that (3-blockers have survival and symptomatic benefits in heart failure, but whether they are an appropriate rate-control therapy
Nonpharmacologic treatments for chronic AF remains undetermined. They are best used in a stable clinical and hemodynamic setting, with gradual uptitration. Little is known about therapeutic synergy between P-blockers, digoxin, and/or amiodarone. Although amiodarone is effective in achieving rapid rate control, its long-term use can cause problems related to side effects and intolerance. Combination with digoxin remains an open issue, but the combination of (3-blockers and digoxin is not contraindicated (see also Question 91). A marked synergic antiarrhythmic activity of P-blockers and amiodarone has been noted in post-hoc analyses of pooled (Canadian) Amiodarone MI (Myocardial Infarction) Arrhythmia Trials (AMIAT and CAMIAT) data.
The main nonpharmacologic interventions are radiofrequency ablation of the atrioventricular node and permanent pacemaker implantation. These are most suitable for patients whose ventricular rate is threatening and pharmacologically uncontrollable. In such cases, ablation is followed by permanent pacemaker implantation, with the advantage that the optimized ventricular rate can provide clinical improvement. However, this is an invasive and costly option, which is indicated only after exhausting the alternatives.
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The management of chronic AF in heart failure is complex, being patient-specific and involving numerous therapeutic options. Familiarity with the patient’s history and clinical condition coupled with informed appreciation of all the issues surrounding chronic AF will determine whether cardioversion or rate control is the more appropriate option. Recently, 3 trials on rhythm versus rate control were reported: the pilot study Strategies of Treatment of Atrial Fibrillation (STAF); RAte Control versus Electrical cardioversion (RACE), and Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM). In patients randomized to rate control, P-blockers, digitalis, nondihydropiridine calcium antagonists, or atrioventricular mode ablation/modification with or without pacemaker implantation were used. Overall, the results consistendy failed to show any substantial differences in outcome between the rate and rhythm control groups. As the patients enrolled in these trials did not have heart failure, extrapolation of the findings to heart failure patients is not appropriate. Nevertheless, the impact of these new findings on clinical practice appears to have slowed down the trend toward the use of device therapy in atrial fibrillation, including repeated cardioversions.
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Van GeJder 1C, Hagens Vi, Bosker HA et al. A comparison of rate control and rhythm control in patients with recurrent persistent atrial fibrillation. N Engl J Med. 2002;347:1834-1840.
Wyse DG, Waldo AL, DiMarco JP, et al, for the AFFIRM Investigators. A comparison of rate-control and rhythm control in patients with atrial fibrillation. N Engl J Med. 2002;347:1825-1833.
management; atrial fibrillation; arrhythmia; heart rate control; antiarrhythmic; cardioversion; nonpharma-cological treatment