Maintenance of exercise stroke volume during ventricular versus atrial synchronous pacing: role of contractility.

Abstract

Although atrial synchronous and rate-responsive ventricular pacing have been compared, the importance of maintaining synchronized atrial systole in addition to rate responsiveness has been incompletely defined. That is, the effects of these two pacing modes on cardiac volumes and contractility have not been studied. Accordingly, 16 patients with normal ventricular function were studied while in the upright position and at rest with gated radionuclide ventriculography during both atrial synchronous and ventricular pacing. Twelve of these patients were also studied during low-level upright exercise (300 kilopond-meters). Rest and exercise ventricular pacing heart rates were matched to those recorded with synchronous pacing. Ventricular volumes were determined with a counts-based method. The ejection fraction and peak systolic pressure/end-systolic volume ratio were used as measures of contracility. At rest there were no significant differences in either volumes or contractility between the two pacing modes. However, during exercise to identical heart rates, blood pressures, and workloads, although stroke volume was the same during exercise with atrial synchronous and ventricular pacing (78 + 13 vs 75 12 ml), end-diastolic and end-systolic volumes were lower with ventricular pacing than with atrial synchronous pacing (end-diastolic volume 101 13 vs 113 + 16 ml, p < .001; end-systolic volume 26 ± 4 vs 35 ± 7 ml, p < .001). Stroke volume during ventricular paced exercise was maintained at atrial synchronous pacing levels by means of increased contractility (ejection fraction of 74 4% during ventricular pacing vs 69 5% during atrial synchronous pacing, p = .002; peak systolic pressure/end-systolic volume ratio of 6.51 + 1 during ventricular pacing vs 4.85 + 1 during atrial synchronous pacing, p < .001). Thus, during upright bicycle exercise to workloads corresponding to those of usual daily activities, rate-responsive atrial synchronous pacing results in enhanced ventricular filling and spares contractile reserve when compared with rate-responsive ventricular pacing. Circulation 72, No. 5, 1037No. 5, -1043No. 5, , 1985

Asymptomatic versus symptomatic persistent atrial fibrillation: clinical and noninvasive characteristics

“…Many, although, not all patients are symptomatic with palpitations, dyspnoea and decreased exercise capacity as the most important complaints. Symptoms associated with atrial fibrillation may relate to a loss of normal atrioventricular synchronization and loss of effective atrial contractions reducing cardiac output by 15–25% [4, 5]. Moreover, irregular R‐R intervals cause decreased cardiac output, increased pulmonary wedge pressure and increased right atrial pressure [6–9].…”

Single-chamber cardiac pacing with activity-initiated chronotropic response: evaluation by cardiopulmonary exercise testing.

“…More recently, Fananapazir et al 34 reported that the approximate 40% increase in exercise capacity associated with heart rate responsiveness in their patients (compared with fixedrate ventricular pacing) was independent of whether rate responsiveness was provided in conjunction with AV synchrony. The latter observations have been confirmed by Ausubel et al 35 although these investigators noted that at comparable rates the increased cardiac output achieved with single-chamber rate-responsive ventricular pacing was associated with a need to invoke compensatory contractile reserve as evidenced by Exercise Duration (minutes) with pacemakers, provision of both AV synchrony and an appropriate response in heart rate is desirable when feasible. On the other hand, for patients in whom primary atrial arrhythmias (e.g., atrial fibrillation, inexcitable atria) preclude maintenance of AV synchrony or in whom abnormal sinoatrial function results in symptoms caused by inadequate chronotropic responsiveness, a cardiac pacing system that provides an activity-initiated heart rate response permits quantitative (oxygen consumption, exercise duration) and qualitative (perceived exertion) improvements in exercise tolerance.…”

The contribution of atrial systole to mitral diastolic blood flow increases during exercise in humans.

“…Our study would suggest that the importance of atrial systole to overall cardiac output in impaired ventricles without high filling pressure would increase further on exercise. This has indeed been shown in patients with heart block who have been paced either by ventricular stimulation alone and thus have atrioventricular asynchrony or with atrioventricular synchronous pacing (Pehrsson & Astrom, 1983;Ausubel, Steingart, Shimshi, Klementowicz & Furman, 1985).…”