CHAPTER 5

In the absence of intrinsic atrioventricular (AV) conduction disease or AV nodal blocking agents, atrial fibrillation (AF) will result in a rapid ventricular rate that can be hemodynamically unfavorable, can result in debilitating symptoms or in some cases a tachycardia-induced cardiomyopathy.1 Rate control can be achieved pharmacologically with a number of agents or with ablation of the AV junction in conjunction with implantation of a permanent pacemaker. Recent clinical investigation has better defined the goal of pharmacologic rate control. Regardless of the long-term strategy of rate versus rhythm control, caring for patients with AF requires knowledge of rate-control options, whether in the acute setting or chronically.

PHARMACOLOGIC RATE CONTROL

Numerous clinical trials have shown that in older patients in whom AF is well tolerated with minimal symptoms, a strategy of rate control combined with the appropriate anticoagulation strategy is not inferior to pharmacologic rhythm control.^2–7 The outcome measures varied in these trials, but included overall mortality, stroke, and heart failure. In the largest such trial, the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM), there was a trend toward improved survival in the rate-control group versus the rhythm-control group (P = 0.08). It is important to note that no large-scale randomized trial has readdressed this question in the era of AF ablation. A strategy of rate control tends to be simpler than rhythm control, by avoiding both procedures such as cardioversions and ablations and the long-term use of potentially toxic antiarrhythmic drugs. Although one may choose a rhythm-control strategy in a particular patient, they, too, will likely encounter periods of rapid ventricular rates requiring rate control.

If rate control is desired either acutely or chronically, there are a limited number of medications that achieve that goal, all of them acting by prolonging AV nodal refractoriness. The choice of medication should be guided by the patient’s comorbidities, with both specific reasons to include or exclude a particular drug. Medication classes that can be used include β-adrenergic blockers, nondihydropiridine calcium channel blockers, and digitalis glycosides. As first-line agents, β-blockers or calcium channel blockers are recommended in paroxysmal, persistent, or permanent AF.8 These agents can be used as monotherapy or in combination. A retrospective analysis of the data from the AFFIRM trial revealed that β-blockers were more effective in achieving adequate rate control compared with calcium channel blockers when used as monotherapy or in combination with digoxin.⁹ Digoxin as monotherapy is generally not recommended, owing to the inability of the drug to control the ventricular rate during exercise.¹⁰ Calcium channel blockers, specifically verapamil and diltiazem, are effective agents for rate control in AF either chronically or acutely. In the acute setting, both medications should be administered intravenously, and because of their short half-lives, continued as an infusion after a bolus.¹⁰ Intravenous β-blockers, esmolol, metoprolol, and propranolol are all effective in the acute setting. Particular care should be taken when using verapamil in combination with other AV nodal blocking agents, as the interaction may affect drug metabolism. For example, coadministration of verapamil and digoxin may dangerously increase serum digoxin levels.

The choice of agent for rate control should be guided by the patient’s other medical conditions. Patients with coronary artery disease, systolic dysfunction, or heart failure should be treated with β-blockers as a first choice. In patients with systolic dysfunction and heart failure, the combination of β-blocker and digoxin may be ideal. AF associated with high sympathetic tone, such as hyperthyroidism-related, exercise-induced, or postoperative AF, should all be treated preferentially with β-blockers. Calcium channel blockers, with negative ionotropic properties should be avoided in patients with systolic dysfunction. β-blockers can be problematic in patients with bronchospasm and depression, and may exacerbate either condition. Combination regimens of rate-controlling medications may be needed to achieve adequate rate control. In such situations, careful follow up may be necessary given the higher risk of bradycardia and hypotension.

Some antiarrhythmic drugs can, in specific situations, be used to control the heart rate in AF. In patients intolerant to β-blockers or calcium channel blockers, amiodarone can be used to provide rate control but should be considered as the last resort given its potential toxicity. Sotalol and propafenone both provide some β-blockade, which can improve ventricular rate control in AF. In general, antiarrhythmic drugs should not be used as first-line agents for rate control, but rather as a coincidental benefit during a rhythm control strategy or as a last resort. In critically ill patients, intravenous amiodarone has been shown to be useful as a rate-controlling agent with minimal effects on blood pressure.11

RATE-CONTROL GOALS

The need for rate control in AF as a means to prevent congestive heart failure and the possibility of a tachycardia induced cardiomyopathy is very well established. However, until recent data emerged from clinical trials, prior heart-rate targets for rate control were not evidence-based. The 2006 AHA/ACC/ESC guidelines stipulated the goal of rate control as a resting heart rate between 60 to 80 beats per minute (bpm) and 90 to 115 bpm during moderate exercise.¹⁰ In the AFFIRM trial, the goal of heart rate control was less than 80 bpm at rest and less than 110 bpm during a 6-minute walk test. In addition, the trial guided practitioners to achieve an average heart rate of less than 100 bpm over 18 hours of Holter monitoring, with no heart rates over 100% of the maximum predicted heart rate for age.² Analysis of the data from AFFIRM showed no difference in survival or quality-of-life outcomes in patients when divided by quartiles of resting and exercise heart rates.¹² Retrospective analysis of the data from the Rate Control Versus Electrical Cardioversion for Persistent Atrial Fibrillation Study (RACE) showed no difference in similar outcomes when patients were stratified to resting heart rate of less than or greater than 80 bpm.¹³

Stay updated, free articles. Join our Telegram channel

Join