Significance and Prevention of Atrial Fibrillation Occurring After Cardiac Surgery: A Time for Fundamental Change in Strategy?

Pharmacological management of atrial fibrillation following cardiac surgery

Atrial fibrillation (AF) is the most common complication following coronary artery bypass graft surgery (CABG). Post-CABG AF occurs most commonly on the second postoperative day and declines in incidence thereafter. A number of risk factors have been found to be associated with a higher frequency of post-CABG AF. These risk factors include advanced age, a prior history of AF, hypertension, and heart failure. Postoperative complications--including low cardiac output, use of an intra-aortic balloon pump, pneumonia, and prolonged mechanical ventilation--are also associated with higher rates of post-CABG AF. Post-CABG AF increases the risk of stroke, and the length and cost of hospitalization. Prophylactic administration of conventional beta-adrenoceptor antagonists (beta-blockers) or sotalol produces a consistent and significant reduction in the incidence of post-CABG AF; however, results with prophylactic amiodarone or magnesium are less consistent. Termination of post-CABG AF, once it occurs, can be accomplished with a number of antiarrhythmic agents. Ibutilide has been the most widely studied agent for this indication. Sotalol is not indicated for cardioversion of AF and has not been studied in the post-CABG setting. Electrical cardioversion and biatrial pacing have also been used to terminate post-CABG AF. Ventricular rate is best controlled with beta-blockers and calcium channel antagonists. Esmolol has a rapid onset of action and is easily titrated to effect. Digoxin can control the ventricular rate, but has a slow onset of action. There are limited data available to guide decisions regarding the optimal management of post-CABG AF.

Esmolol versus diltiazem in atrial fibrillation following coronary artery bypass graft surgery

PURPOSE

Atrial fibrillation (AF) is the most common arrhythmic complication following coronary artery bypass graft surgery (CABG). The efficacy and safety of esmolol and diltiazem were compared in patients with post-CABG AF.

METHODS

This study was a retrospective medical record review of consecutive patients with post-CABG AF > or =15 min in duration with a ventricular rate > or =110 b.p.m. who received either i.v. esmolol (n = 59) or i.v. diltiazem (n = 48) with or without concomitant digoxin therapy at a single university-affiliated teaching hospital. Treatment success was defined as either cardioversion to sinus rhythm or a reduction in the ventricular rate to < or =90 b.p.m. at 24 h after the start of therapy. Time to treatment success and the occurrence of adverse effects were considered secondary outcomes.

RESULTS

A total of 107 patients with post-CABG AF were treated with i.v. esmolol (n = 59) or i.v. diltiazem (n = 48). The mean maximum dose of esmolol and diltiazem were 115 +/- 38 microg/kg/min and 11.2 +/- 3.5 mg/h, respectively. The average duration of the esmolol and diltiazem infusions were 19.3 +/- 8.5 h and 20.1 +/- 11.3 h, respectively. Based on the combined efficacy endpoint of cardioversion or ventricular rate control, esmolol was significantly more effective than diltiazem (90% vs 77%; p = 0.038). Time to treatment success was significantly better for esmolol than diltiazem at all time points (1, 2, 4, 6, 12, and 24 h post-treatment). The overall incidence of adverse effects was 44% with esmolol and 60% with diltiazem (p = 0.04). Rates of drug discontinuance for adverse effects were significantly less for esmolol (20%) compared with diltiazem (38%) (p = 0.04).

CONCLUSIONS

Esmolol is significantly more effective than diltiazem in the management of post-CABG AF. More patients converted to sinus rhythm with esmolol as compared to diltiazem. Esmolol was associated with fewer adverse effects than diltiazem, including adverse effects leading to drug discontinuance. Due to study design limitations (retrospective data collection), an adequately powered randomised, controlled trial is needed to confirm these preliminary findings.

Intravenous antiarrhythmic regimens with focus on amiodarone for prophylaxis of atrial fibrillation after open heart surgery

Atrial fibrillation commonly occurs after coronary bypass surgery. Most studies suggest that atrial fibrillation develops in approximately 20% to as many as 50% of patients undergoing coronary artery bypass surgery. Over the years, a number of prophylactic regimens have been utilized to prevent atrial fibrillation after coronary bypass surgery. The majority of these studies have used oral agents in various combinations. Few studies have used intravenous agents, and most of these studies have used either beta blockers, calcium antagonists, or class I antiarrhythmic drugs. Recent evidence suggests that intravenous amiodarone may provide safe and effective prophylaxis against atrial fibrillation in many patients undergoing coronary bypass surgery. The evolving data that support such an approach are discussed in this article.

Antiarrhythmic agents for atrial fibrillation: focus on prolonging atrial repolarization

Atrial fibrillation (AF) has been the subject of considerable attention and intensive clinical research in recent years. Current opinion among physicians on the management of AF favors the restoration and maintenance of normal sinus rhythm. This has several potential benefits, including the alleviation of arrhythmia-associated symptoms, hemodynamic improvements, and possibly a reduced risk of thromboembolic events. After normal sinus rhythm has been restored, antiarrhythmic therapy is necessary to reduce the frequency of AF recurrence. In the selection of an antiarrhythmic agent, both efficacy and safety should be taken into consideration. Many antiarrhythmic agents have the capacity to provoke proarrhythmia, which may result in an increase in mortality. This is of particular concern with sodium-channel blockers in the context of patients with structural heart disease. Flecainide and propafenone are well tolerated and effective in maintaining sinus rhythm in patients without significant cardiac disease but with AF. Recent interest has focused on the use of class III antiarrhythmic agents, such as amiodarone, sotalol, dofetilide (recently approved), ibutilide (approved for chemical conversion of AF and atrial flutter), and azimilide (still to be approved) in patients with AF and structural heart disease. To date, amiodarone and sotalol still hold the greatest interest, and although controlled clinical trials with these agents have been few, a number are in progress and some have been recently completed. These agents are effective in maintaining normal sinus rhythm in patients with paroxysmal and persistent AF and are associated with a low incidence of proarrhythmia when used appropriately. Because of the relative paucity of placebo-controlled trials of antiarrhythmic agents in patients with AF, experience until recently has tended to dictate treatment decisions. Increasingly, selection of drug therapy is being based on a careful and individualized benefit-risk evaluation by means of controlled clinical trials, an approach that is likely to dominate the overall approach to the control of atrial fibrillation in the largest numbers of cases of the arrhythmia. Pharmacologic therapy is likely to be dominated by compounds that exert their predominant effect by prolonging atrial repolarization.

Current antiarrhythmic drugs: an overview of mechanisms of action and potential clinical utility

Reorientation in drug therapy to control cardiac arrhythmias continues to evolve in the wake of ongoing refinements in techniques and indications for radiofrequency ablation and the use of implantable devices for atrial and ventricular arrhythmias. The role of sodium channel blockers continues to be questioned, and data from clinical trials indicate that the use of this class of drugs should be limited to control symptoms in patients who have arrhythmias and either no or minimal heart disease. The decline in the use of sodium channel blockers has led to greater use of beta blockers and complex Class III agents, such as sotalol and amiodarone, as both primary therapy and adjunctive therapy with implantable defibrillators in patients with cardiac disease of varying degrees of ventricular dysfunction. Success with these Class III agents in the context of their side effects has led to the synthesis and characterization of compounds with simpler ion channel-blocking properties. The need for such compounds stemmed from the observation that atrial fibrillation (AF) as an arrhythmia is, for the most part, still not amenable to curative therapy by interventional procedures. The isolated block of the rapid component of the delayed rectifier current (IKr) has been found to have either a neutral (e.g., dofetilide) or deleterious (e.g., d-sotalol) effect on mortality in survivors of myocardial infarction. Thus, the objective of drug development should be the appropriate match between the substrate and an antiarrhythmic drug. The so-called pure Class III agents have been shown to have beneficial antifibrillatory effects in patients with AF. They are effective in inducing acute chemical conversion, preventing paroxysmal AF, and maintaining sinus rhythm in patients with persistent AF restored to sinus rhythm with DC cardioversion. AF is a complex arrhythmia, undoubtedly a result of multifaceted derangement of atrial ionic currents. Attention has therefore focused on newer compounds that have the propensity to block more than one ion channel. Examples of such agents are tedisamil and azimilide, the latter having been studied extensively in humans. It is the first of the Class III agents that block both components (IKr and IKs) of the delayed rectifier current, which results in a spectrum of electrophysiologic properties that includes lack of rate or use dependency in terms of effect on repolarization and refractoriness of atrial and ventricular myocardium. Available but unpublished clinical data indicate that azimilide may be effective over a wide range of tachycardia cycle lengths with a low incidence of torsades de pointes. In these respects, its properties, at least in terms of its use in AF, resemble those of amiodarone. However, the drug has little or no effect on AV conduction, which precludes the modulation of ventricular response in patients relapsing to AF.

Sotalol: Current Status and Expanding Indications

BACKGROUND: The role of antiarrhythmic drug therapy continues to undergo major changes. The change is necessitated by the advent of invasive interventional procedures, such as catheter ablation of arrhythmias and the use of implantable devices for sensing and terminating life-threatening ventricular arrhythmias and symptomatically traublesome supraventricular arrhythmias. Many conventional and time-honored drugs, such as sodium channel blockers, have been found either to be ineffective or to have the potential to produce serious proarrhythmic reactions. Attention is therefore focused on compounds that prolong repolarization and reduce sympathetic stimulation. Two compounds, amiodarone and sotalol, have emerged as prototypes of drugs of the future. METHODS AND RESULTS: This review focuses on sotalol for controlling supraventricular and ventricular tachyarrhythmias. Sotalol is a major antiarrhythmic agent that combines potent class III action with nonselective beta-blocking properties. The drug's pharmacokinetics is simple. Its elimination half-life is 10-15 hours, the drug being excreted almost exclusively by the kidneys. Sotalol's pharmacokinetics allows development of optimal dosing for initiation of therapy relative to changes in creatinine clearance with further dose adjustment by monitoring the QT interval on the surface electrocardiogram. The compound exerts broad-spectrum antiarrhythmic actions in supraventricular and ventricular arrhythmias. It prevents inducible ventricular tachycardia (VT) and ventricular fibrillation (VF) in approximately 30% of patients with a higher figure for the suppression of spontaneously occurring arrhythmias documented on Holter recordings. CONCLUSIONS: The major role of sotalol is in the management of VT/VF often in conjunction with an implantable cardioverter/defibrillator, in which context it lowere the defibrillation threshold. Sotalol is superior to class I agents, especially in VT/VF and in survivors of cardiac arrest. Sotalol has emerged as a major antifibrillatory compound for the control of life-threatening ventricular arrhythmias as the main indication. Data have indicated its potential for the maintenance of stability of sinus rhythm in patients with atrial fibrillation and flutter after electrical conversion and in preventing their occurrence in a variety of clinical settings.