Cardiac Pacing for Bradycardia Support: Evidence-based Approach to Pacemaker Selection and Programming.

The vast majority of pacemakers implanted in the United States for the treatment of symptomatic bradycardia are dual-chamber systems with a complex array of functions, such as rate responsiveness, dynamic atrioventricular delay, and automatic mode switching. Basic hemodynamic studies have convincingly demonstrated the superiority of maintaining atrioventricular synchrony. However, clinical trials have failed to demonstrate the impressive results expected based on physiologic data. The most recent randomized clinical trials have demonstrated that dual-chamber devices, when compared with single-chamber ventricular pacing, do not prevent mortality or stroke, and lead to an unexpectedly small reduction in heart failure hospitalizations. Although improvements in quality of life have not been consistently found when comparing ventricular-based versus atrial-based pacing, a reduction in the incidence of newly diagnosed atrial fibrillation in dual chamber-paced patients has been reported by most trials. Dual-chamber pacing has been reported to reduce pacemaker syndrome in US trials. The addition of rate modulation, in spite of attempting to replicate the normal response to exercise, has not shown a consistently positive impact on quality of life or treadmill time. The use of pacemakers for the treatment of vasovagal syncope is controversial. Adding dual-chamber sensing ability to current implanted defibrillators considerably reduces the number of inappropriate shocks but may increase mortality if not programmed to minimize ventricular stimulation.