Ventricular vs. Dual Chamber Pacing
ABSTRACT & COMMENTARY
Synopsis: Among patients with sinus node dysfunction, significant differences in some portions of the general health survey and trends in mortality and atrial fibrillation development favored dual-chambered pacing.
Source: Lamas GA, et al. N Engl J Med 1998;338: 1097-1104.
Lamas and colleagues studied the results of ventricular pacing (VVIR) compared to dual chamber pacing (DDDR) in elderly patients with sinus node dysfunction and atrioventricular block. Four hundred seven patients scheduled to receive a pacemaker for clinically documented bradyarrhythmias received a dual chamber pacing device as their initial implant. Patients were randomly assigned in a single, blind design at the time of implant to have either single chamber or dual chamber programming. Patients were followed at periodic intervals during a follow-up period of 30 months. Before randomization and at three-month intervals after implant, patients completed a 36-item quality-of-life and clinical outcome survey. The follow-up surveys after discharge were conducted via telephone by two interviewers who did not know the patients' programming.
Four hundred seven elderly (65-96 years of age) patients were entered into the study. The indications for pacing were atrioventricular block in 49% (of whom 59% had third degree AV block) sinus node dysfunction in 43%, and other unspecified diagnoses in 8%. Results were analyzed using an intention-to-treat approach, but 53 patients (26%) assigned to VVIR crossed-over to DDDR because of symptoms compatible with pacemaker syndrome (fatigue, dyspnea, orthopnea, exercise). Among these, there was a significant improvement in quality-of-life scores after cross-over. Most of the crossovers occurred early after implant. Four patients originally assigned to DDDR were later reprogrammed to VVIR due to atrial arrhythmias.
Both single and dual chamber pacing groups demonstrated an improvement in health-related quality-of-life after pacemaker implantation. The magnitude of improvement was similar between the two groups. There was a relative improvement in the cardiovascular specific activity scale that was apparent by 18 months of follow-up in the dual chamber group, compared to the ventricular pacing group. There was no difference in total mortality, stroke or heart failure hospitalization rates, or atrial fibrillation occurrence when these events were looked at for the two groups. Among patients with sinus node dysfunction, significant differences in some portions of the general health survey and trends in mortality and atrial fibrillation development favored DDDR.
COMMENT BY JOHN DiMARCO, MD, PhD
The study by Lamas et al may cause most U.S. cardiologists who implant pacemakers some initial distress. Over the last 15 years, DDDR has become the standard in the United States as devices and leads have become smaller and more reliable and have included advanced diagnostic and pacing functions. However, this report, the first relatively large scale, long-term randomized study to examine the value of DDDR, describes only modest improvement with the more complex pacing strategy. Should cardiologists go back to implanting single chamber pacemakers in most patients?
The design of this study minimized the chance of showing any early difference with DDDR. Lamas et al no doubt believed that DDDR was likely to be superior. Therefore, in order to permit late conversion to DDDR, every patient had a dual chamber system implanted. Therefore, patients incurred the risk of increased complications with a two-lead system but received no benefit if left in a single chamber pacing mode. More than 26% of the patients initially assigned to single chamber pacing crossed over to dual chamber pacing because of symptoms. However, since the cross-overs took place soon after implant, their symptoms are not included in the data for their original group at the prespecified time points in the intention-to-treat analysis.
In clinical practice, upgrading someone from single chamber pacing to dual chamber pacing, if the former were poorly tolerated, would require re-operation to insert a new lead, a revision, or an enlargement of the pocket. Also, the original pulse generator would have to be discarded. These problems were eliminated by the study design.
Furthermore, as shown recently by Andersen and colleagues (Lancet 1997;950:1210-1216), the benefits of an atrial based pacing system on mortality and serious morbidity are cumulative over time. Important benefits are likely to be found only after several years of follow-up, not within 18 months as in this study.
At present, I believe an atrial based pacing system should be considered for most patients in whom this is technically possible. Patients with rare, spontaneous episodes of bradycardia who will require only brief intermittent pacing with chronic atrial arrhythmias may receive single chamber ventricular pacemakers. Patients with sinus node dysfunction who have intact AV conduction can often be managed with single chamber atrial pacing. Other patients should continue to receive dual chamber systems.
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