Optimum AV interval in dual chamber pacemakers.

Approximately 50-70% of permanent implanted pacemakers are dual chamber pacemakers. However, little is known concerning adjustment of the atrioventricular (AV) interval to maximize cardiac output. Ten consecutive patients with complete heart block and dual chamber pacemakers were paced at heart rates of 80, 100, and 118 beats/minute and at five AV intervals with simultaneous measurements of cardiac output using pulsed Doppler. Maximum cardiac output occurred at AV intervals of 150 and 200 ms at rates of 80 and 100 beats/minute, and at 150 ms at a rate of 118 beats/minute (p less than .05). An increase in the AV interval to 250 ms resulted in a decrease in cardiac output at all heart rates (p less than .01). We recommend the noninvasive measurement of cardiac output, if available, for determining the optimum AV interval in an individual patient; otherwise, an AV interval of 150 or 200 ms will provide the highest cardiac output in most patients.