Tight vs Loose Rate Control in Permanent Atrial Fibrillation
Abstract & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco does research for Medtronic, is a consultant for Medtronic, Novartis, and St. Jude, and is a speaker for Boston Scientific.
Source: Groenveld HF, et al. Rate control efficacy in permanent atrial fibrillation: Successful and failed strict rate control against a background of lenient rate control. Data from RACE II (Rate Control Efficacy in Permanent Atrial Fibrillation). J Am Coll Cardiol 2013;61:741-778.
The Rate Control Efficacy in Permanent Atrial Fibrillation (RACE II) trial compared strict rate control vs lenient rate control in patients with permanent atrial fibrillation. In this substudy, the RACE II investigators report results based on three groups of patients: those with successful strict rate control, those with unsuccessful rate control, and those with lenient rate control. In RACE II, lenient rate control was defined as a resting heart rate < 110 beats per minute (bpm). Strict rate control required a resting heart rate < 80 bpm and a heart rate < than 110 bpm during moderate exercise. The primary outcome was a composite of cardiovascular morbidity and mortality. Patients in the strict rate control group were classified as failures if one of the heart rate criteria was not met. Heart rate control was assessed at the end of a dose-adjustment phase. Quality of life was assessed with a several instruments, including the Medical Outcome Study SF-36, the University of Toronto AF Severity Scale, and the Multidimensional Fatigue Inventory 20.
There were 608 patients included in this analysis. In the strict rate control group, 203 patients achieved strict rate control and 98 patients did not meet target heart rate. The reasons for failure of strict rate control included manifest drug-related adverse affects, no or acceptable symptoms despite faster heart rates, and an inability to achieve rate control with drug therapy. Among the patients in the lenient rate control group, 69% were controlled with a single AV nodal blocking agent or did not require any drug therapy for rate control. Only 31% required two or more AV nodal blocking agents. In contrast, in the strict rate control group, 72% of patients required two or more agents. There was no difference in the primary outcome after the dose-adjustment phase with 27 of 203 (13.3%) in the successful strict control group, 14 of 98 (14.3%) in the failed strict control group, and 35 of 307 (11.4%) in the lenient group reaching a primary endpoint. There also were no differences between the three groups in all-cause mortality or when patients with an ejection below 40% were analyzed separately. During follow-up, additional visits were more frequently required in the strict rate control group. There were no significant changes in mean ejection fractions in any of the three groups over time. There was also no change in any of the reported symptom scales or in quality of life between the three groups. The authors conclude that lenient rate control is as effective as strict rate control even if patients who fail to achieve strict rate control are excluded.
RACE II data have now shown that very intense heart rate control in patients with atrial fibrillation is not required for reasonable short-term outcomes. However, physicians should still be cautious in accepting heart rates in the upper portion of the acceptable range. Most of the patients in the RACE II lenient control group had resting rates below 100 bpm, so we would expect them to do reasonably well. We must also remember that tachycardia-associated cardiomyopathies at slower heart rates (110-130 bpm) may take years to develop and RACE II was a relatively short-term study. I continue to try to keep the resting heart rate in a range I know to be safe (70-90 bpm) and will reevaluate patients outside this range or with symptoms at more frequent intervals.