Ventricular Rate Control During AF: A Call for Leniency

Dear Readers, A 65-year-old truck driver with hypertension is referred for further management of newly diagnosed atrial fibrillation (AF). He had visited his internist six months ago for lower back pain and was found to have an elevated heart rate (HR). An electrocardiogram (EKG) showed AF with a rapid ventricular response at 130 beats per minute (bpm). Stress echocardiogram revealed normal ventricular function, moderate left atrial enlargement, and no inducible ischemia. Thyroid function was found to be normal. He was started on metoprolol 25 mg daily and warfarin. An attempt at electrical cardioversion a few months ago was unsuccessful with an immediate recurrence of his AF. He is presently unaware of his heart rhythm, is entirely asymptomatic, and has no functional limitations. His electrocardiogram is shown (Figure). What is your next step? The EKG confirms the diagnosis of AF with a ventricular response that is 110 bpm. Based on the results of the AFFIRM and RACE trials, one could make a strong case for a rate control strategy in this patient, given that he is asymptomatic and has failed one cardioversion. But what should this patient’s HR be? Most physicians would look at that EKG with a rate of 110 bpm and immediately make a diagnosis of “inadequate rate control.” Although adequate rate control is poorly defined for patients with AF, and there is no standard measure of rate control, based on evidence that inadequate rate control can lead to a tachycardia-mediated cardiomyopathy, and common teaching, most physicians strive to achieve a HR well below 110 bpm. Criteria for rate control vary with patient age, but usually involve achieving ventricular rates between 60 and 80 bpm at rest and between 90 and 115 bpm during moderate exercise. In the AFFIRM trial, adequate control was defined as an average HR below 80 bpm at rest, and either an average rate below 100 bpm during Holter monitoring with no rate above 100% of the maximum age-adjusted predicted exercise HR, or a maximum HR of 110 bpm during a 6-minute walk test. At the recent ACC meeting in March, the RACE II trial was presented during the Late Breaking Clinical Trials Session. It was also published in the New England Journal of Medicine.¹ In this Dutch study, 614 patients with long-standing persistent AF that had been present for less than 12 months, were randomized to a lenient rate control strategy (resting HR goal 80 bpm and on oral anticoagulant therapy. The patient above would have met the inclusion criteria for RACE II. Surprisingly, there was no difference between the two groups with regard to the primary outcome — a composite endpoint of death, heart failure, stroke, bleeding, pacemaker, and others. Nearly all patients in the lenient group reached their assigned HR target, compared with only two-thirds of the strict group. Furthermore, the patients in the strict group had to see their physicians about 10 times more often for drug titration compared to the lenient group. Although the RACE II trial has limitations, it offers reassuring data that aggressive rate control may not be necessary in all patients and might lead to more harm than good. It suggests that a more lenient approach is acceptable in asymptomatic patients like the one presented above, especially if more aggressive rate control with medications causes side effects or leads to symptomatic bradycardia. It should be noted, however, that about half of patients in the RACE II trial continued to have symptoms including dyspnea, fatigue, and palpitations, regardless of the degree of rate control. This continues to beg the question of whether or not some of these patients would be better off if they were treated more aggressively to restore and maintain sinus rhythm.