Principal Findings:

Among the 1474 patients randomized to VVI pacing, 25.2% received VVI devices, 73.3% received VVIR, 0.7% crossed over to a DDD, DDDR, or AAI device, and 0.2% did not receive a pacer. For the 1094 randomized to physiologic pacing, 52.8% received a DDD device, 35.2% received DDDR, 1.9% received AAI, 3.5% received AAIR, 5.7% crossed over to a VVI device, and 0.9% did not receive a pacer. The complication rate in the physiologic pacing group was 9.0% compared to 3.8% for the VVI arm, and was attributed to the additional lead needed for dual-chamber pacing. The two groups were equal with respect to pacer dependency, indication for implantation, and concomitant anti-ischemic, anti-platelet, and anti-arrhythmic therapy. The total study duration was 5 years, with a mean follow-up of 36 months. The event rate for the primary endpoint was 5.43 events per year for the VVI group and 4.78 events per year for the physiologic pacing group (p=.205). For all cause mortality, the event rate was 6.54 for the VVI group, and 6.25 events per year for the physiologic group. There were 1.09 strokes per year in the VVI group compared to 1.02 strokes per year in the physiologic pacing group. The incidence of CHF was 3.62 events per year in the VVI group compared to 3.02 per year in the physiologic group. None of these differences were statistically significant. Physiologic pacing was associated with a significant 18% relative reduction in the occurrence of atrial fibrillation (6.59 to 5.34 events per year, p = 0.0357), although this benefit did not become apparent until after 2 years. Seventy-five percent of patients were tested with a six-minute walk to assess their functional capacity. There was no significant difference in pre- or post- walk heart rates or in the total distance walked (VVI: 350+127 m, Phys: 356+127 m).