Dual-chamber vs. Single-chamber Ventricular Pacemakers

A new study by Toff et al. intended to confirm or refute the considerations according to which dual-chamber ventricular pacing is much more beneficial than single-chamber pacing. The results of the multi-center trial were published in the July 14 issue of the "New England Journal of Medicine".

Cardiac pacing is the established treatment for atrio-ventricular block, and dual-chamber cardiac pacing has been considered to offer more clinical benefit than single-chamber pacing. The authors, however, bear in mind that the supporting evidence for this was obtained mainly from retrospective studies and also observe that data may be confounded by a selection bias, as dual-chamber pacing was preponderantly used in younger patients,

who have few coexisting illnesses. Single-chamber pacing prevents bradycardia (slow heart rate, usually defined as less than 60 beats per minute) and death from ventricular standstill, but dual-chamber ventricular pacing was found to restore atrio-ventricular synchrony and match the ventricular pacing rate to the sinus rate (the normal regular rhythm of the heart set by the the sinoatrial or sinus, node). Thus, dual-chamber pacing better emulates normal cardiac physiology.

The authors found an uncertainty persisting "particularly in the elderly, in whom it is used less often than in younger patients." This United Kingdom Pacing and Cardiovascular Events (UKPACE) trial compares the clinical benefits of the two pacing modes in elderly patients with atrio-ventricular block.

2021 patients 70 years of age or older who were undergoing their first pacemaker implant were under study; 1009 patients received a single-chamber pacemaker (approximately one half of the group, fixed-rate pacing and the other half, rate-adaptive pacing) and 1012, a dual-chamber pacemaker. The mean annual mortality rate was 7.2 percent in the single-chamber group and 7.4 percent in the dual-chamber group, observed during a follow-up period of 4.6 years. As for secondary outcomes - atrial fibrillation, heart failure, and a composite of stroke, transient ischemic attack, or other thromboembolism, no significant differences were noted between the two groups.

Thus, the authors conclude that the pacing mode does not influence the rate of death from all causes during the first five years or of cardiovascular events during the first three years after implantation of a pacemaker, in elderly patients with high-grade atrio-ventricular block.

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