Improved cardiovascular hemodynamics with atrioventricular sequential pacing compared with ventricular demand pacing

To determine the advantages of atrioventricular (AV) sequential pacing over ventricular demand pacing, paired cardiovascular hemodynamic studies were performed in each pacing mode at a constant heart rate. The paired studies included determination of ejection fraction (EF) by echocardiography and gated blood pool radionuclide scanning, and of cardiac output (CO) by the indicator-dilution method. There was no significant difference in EF with either pacing mode. Determined by echocardiography, EF with AV sequential pacing was 57% compared with 56% with ventricular demand pacing; by the gated blood pool method, EF with AV sequential pacing was 58% compared with 57% in the ventricular mode. Significant improvement with AV sequential pacing was seen in CO (4.75 L/min from 3.75 L/min; p less than 0.01); stroke volume (58 ml from 48 ml; p less than 0.02); arteriovenous oxygen content difference (4.9 vol% from 5.6 vol%; p less than 0.01); total peripheral resistance (1,724 dynes sec cm-5 from 2,025 dynes sec cm-5; p less than 0.01); and cardiac contractility, as reflected by mixing time (6.9 seconds from 8.0 seconds; p less than 0.02). No significant changes were noted in mean arterial or atrial pressure or in systemic oxygen consumption. In a second group of 6 patients, similar paired studies were done in AV sequential pacing modes before and after therapeutic reduction of total peripheral resistance. A significant increase in CO (43%) was observed following reduction in total peripheral resistance. We conclude that AV sequential pacing improves CO more effectively than ventricular demand pacing. Cardiac output can be further enhanced in patients with congestive heart failure by pretreatment with agents to reduce total peripheral resistance.