AV Delay Optimization vs. Intrinsic Conduction in Pacemaker Patients With Long PR Intervals

Cardiac pacing is the only effective treatment for symptomatic sinus node dysfunction. Most patients with preserved left ventricular function receive dual chamber pacemakers; however, right ventricular pacing can have detrimental effects on left ventricular function due to the abnormal electrical and mechanical activation pattern of the ventricles. Many patients receiving dual chamber pacemakers for symptomatic bradycardia have prolonged intrinsic AV conduction (first degree AV block), and as a result, will receive a significant amount of ventricular pacing if programmed at physiologic AV intervals. As an alternative, many pacemakers can be programmed to minimize ventricular pacing at the expense of allowing longer AV delays. However, these long AV delays may not be physiologic and may also lead to reduced cardiac output. At present the standard of care is either to program the pacemaker at an physiologic "natural" AV delay of about 160 msec or to program the pacemaker with a long AV delay to minimize ventricular pacing. The main scientific questions being addressed in this study are to evaluate the acute and chronic effects on cardiac output, functional status, sense of well-being, and cardiac remodeling of a long AV delay allowing for intrinsic conduction as compared to an echocardiographically optimized AV delay during dual chamber pacing. Patients enrolled in the trial will complete a run-in period of two weeks prior to randomization in which pacemakers will be programmed with a long-fixed AV delay to allow intrinsic conduction and minimize ventricular pacing (standard). At two weeks, patients will receive a baseline echocardiogram. To determine optimal AV delay, all patients will undergo echocardiographic analysis at varying AV delays. Optimal AV delay will be defined as the AV delay associated with the largest average aortic Doppler velocity time integral (VTI). Then, patients will be randomized to either the short, optimized (experimental) or long, fixed (standard) AV delay groups. To assess functional status and sense of well-being, patients will complete a six minute walk test and Short Form-36 Medical Outcomes Study Questionnaire. Patients return to clinic for another study visit at 6 months and repeat research procedures, including baseline echocardiogram, questionnaire, and 6 minute walk test.