Intrinsic conduction maximizes cardiopulmonary performance in patients with dual chamber pacemakers.

Dual chamber pacemaker programmability allows the possibility of atrially-tracked ventricular pacing in patients who would otherwise have intrinsic atrioventricular (AV) conduction. Thirteen patients with permanent AV sequential pacemakers (ages 50-79) were evaluated with paired exercise tests to determine the cardiopulmonary effects of pacemaker induced right ventricular activation compared with normal AV and intraventricular conduction. Peak oxygen uptake (VO2), oxygen pulse (O2P), respiratory rate (RR), and respiratory exchange ratio (RER) were determined using breath-by-breath analysis of expired gases. Patients exercised to fatigue and exercise tests were performed in random sequence. For patients with intrinsic AV conduction (group I, n = 8) the AV delay was programmed to preserve intrinsic conduction during one study; the alternate test used AV delay programming to produce ventricular pacing. Five patients with chronic AV block (group II) acted as a control for the effects of a rate adaptive AV delay compared to a fixed AV delay. Paired t-testing showed a significantly lower peak VO2 (P less than 0.015) and O2P (P less than 0.01) in patients with atrially-tracked ventricular pacing compared to intrinsic conduction. In contrast, group II showed a significant improvement in peak VO2 with rate adaptive AV delay compared to fixed AV delay programming (P less than 0.05). In conclusion, intrinsic conduction should be preserved in patients with dual chamber pacemakers whenever possible.