Heart rate, pacing, and outcome in the Dual Chamber and VVI Implantable Defibrillator (DAVID) trials.
BACKGROUND
Slower heart rates are believed to confer a better prognosis in heart disease. The Dual Chamber and VVI Implantable Defibrillator (DAVID) Trial found that patients with ventricular dysfunction and isolated sinus bradycardia (rate <60 with normal PR interval) had an unusually low incidence of heart failure (HF) hospitalization and mortality when paced infrequently.


OBJECTIVES
The purpose of this study was to prospectively test our hypotheses that a similar benefit from bradycardia would be conferred in DAVID II as in DAVID but that this would be nullified by the faster heart rate achieved during atrial pacing in DAVID II.


METHODS
Effects of atrial versus minimal ventricular pacing on outcome in defibrillator recipients with isolated bradycardia in DAVID II were prospectively evaluated.


RESULTS
Ninety-eight DAVID II patients with isolated bradycardia were similar to 502 patients without it but had less baseline HF. HF medications were used comparably in both groups at baseline and throughout the study. Overall, patients with isolated bradycardia were less likely to die or be hospitalized for HF than others (12.2% vs. 26%; P = .01). There was no evidence that atrial pacing diminished this association. Adjusted for covariates, particularly baseline HF and its treatment, isolated bradycardia patients had substantially reduced risk for HF/death (P = .018) with or without atrial pacing (relative risk 0.47 and 0.71, respectively).


CONCLUSIONS
Isolated bradycardia identifies patients at lower risk for HF and mortality, an association that is not necessarily negated by accelerating heart rate with atrial pacing. This apparent conundrum challenges the use of heart rate as a therapeutic target in patients with ventricular dysfunction.


TRIAL REGISTRATION
http://www.clinicaltrials.gov NCT00187187.