Simultaneous left ventricular echocardiography and aortic blood velocity during rapid right ventricular pacing in man

Left ventricular echocardiograms and phasic instantaneous Doppler aortic blood velocities were simultaneously recorded during short paroxysms of rapid right ventricular pacing in 20 conscious subjects. Right ventricular pacing at rates of 100, 120, 140, 160 and 180/min produced stepwise reductions of mean estimates for diastolic (D) and systolic (S) left ventricular internal dimensions (LVID) along with a diminution of aortic blood velocity. Mean (X +/- 1 standard deviation) per cent decline of LVID-D, LVID-S and peak aortic blood velocities for the study group ranged from 8.9 +/- 6.1, 8.5 +/- 5.7 and 13.7 +/- 7.7 at 100 beats/min to 29.3 +/- 10.6, 25.2 +/- 10.5 and 55.2 +/- 13.1 at 180 beats/min, respectively. When LVID-D, LVID-S, and aortic blood velocity X % reductions were plotted for all heart rates there was a high degree of positive correlation (r = 0.99). Two types of abnormal septal motion were observed during rapid pacing: Type I--paradoxical septal motion at all pacing rates (n = 7, 6/7 with left coronary artery disease); Type II--hypokinetic septal motion at lower pacing rates with flat or paradoxical motion at rates greater than 140/min (n = 13, 10/13 with normal coronary arteries). It is concluded that short episodes of rapid right ventricular pacing result in reduced LVID and abnormal septal motion with the latter possibly related to septal ischemia. Such study provides insight into the untoward influence of rapid ventricular rhythms on cardiac performance.