Atrioventricular sequential pacing: comparison with ventricular pacing using systolic time intervals

Nine patients with programmable atrioventricular sequential pacers were studied using systolic time intervals (QS2--the total electrical and mechanical systole, left ventricular ejection time, and pre-ejection period). These measurements were obtained by simultaneous recording of the electrocardiogram, phonocardiogram, and carotid pulse tracing. There was a dramatic fall of left ventricular ejection time (LVET) and an increase of the pre-ejection time (PEP) in all patients when the pacers were programmed from the atrioventricular to the ventricular mode at constant heart rate. This resulted in an increase of the ratio PEP/LVET from .428 to .574 suggesting loss of ventricular function. These measurements all reversed to baseline values when the pacers were re-programmed back to the atrioventricular mode. This study suggests systolic time intervals might be useful to select non-invasively pacer parameters such as mode, rate, and effective PR interval in order to provide the best hemodynamics in a given patient.