Principal Findings:

A total of 203 patients were randomized to dual-chamber pacing; the remaining 204 patients were assigned to ventricular pacing. The indications for the implantation of a permanent pacemaker included atrioventricular block in 201 patients (49 percent, of whom 119 patients, or 59 percent, had third-degree block), sinus-node dysfunction in 175 patients (43 percent), and other diagnoses in 31 (8 percent). Ventriculoatrial (retrograde) conduction at the time of implantation was present in 29 percent.

Follow-up visits and health-status assessments took place 3, 9, and 18 months after enrollment and at the end of the study. Assessment of health status before randomization was performed at the local clinical site, before the pacemaker mode was assigned. Subsequent assessments were made by telephone from the coordinating center.

During the course of the trial, pacemaker syndrome severe enough to warrant reprogramming from ventricular to dual-chamber pacing was diagnosed in 53 patients assigned to ventricular pacing (26 percent), in 45 percent of whom sinus-node dysfunction was the reason for implantation. Crossover from ventricular to dual-chamber pacing occurred early: 44 percent of the 53 crossovers occurred within one month after implantation, and 77 percent within six months. After crossover, the patients had improvement in SF-36 scores, including scores for physical function (+22, P = 0.03) and emotional role (+27, P = 0.01).

In the overall group, there was significant improvement in health-related quality of life between base line (before implantation) and three months after implantation, as measured by several SF-36 subscales (social function, P<0.001; physical role, P<0.001; emotional role, P<0.001; mental health, P<0.001; energy, P<0.001).

There were no significant differences in scores between the ventricular-pacing group and the dual-chamber-pacing group in any of the SF-36 subscales at 3 months or 18 months. After nine months of follow-up, there was a significant difference favoring dual-chamber pacing only in scores for the mental health subscale (P = 0.03)

Longitudinal analyses, detected a borderline improvement in scores on the emotional-role subscale in patients assigned to dual-chamber pacing (P= 0.04).

There were no significant differences in cardiovascular functional status between groups, as assessed by the Specific Activity Scale, at either the three-month or the nine-month assessment. However, there was a significant difference favoring dual- chamber pacing at the 18-month visit ( Table 4), and longitudinal analysis demonstrated a significant difference favoring dual-chamber pacing (P = 0.045).

There were no significant differences between the ventricular-pacing group and the dual-chamber-pacing group in the rates of death from all causes, stroke or death, stroke or death or hospitalization for heart failure, and the development of atrial fibrillation.

Among the patients who received pacemakers because of sinus-node dysfunction, there were significant differences favoring dual-chamber pacing at three months in scores on the physical-role subscale (P = 0.02), social-function subscale (P = 0.03), and emotional-role subscale (P = 0.002) of SF-36.

Among the patients with atrioventricular block at implantation, there were no significant differences between groups in any of the SF-36 subscales, in longitudinal analyses of the Specific Activity Scale, or in any of the prespecified clinical endpoints.