FUNCTIONAL MYOCARDIAL PERFUSION ABNORMALITY INDUCED BY LEFT-VENTRICULAR ASYNCHRONOUS CONTRACTION - EXPERIMENTAL-STUDY USING MYOCARDIAL CONTRAST ECHOCARDIOGRAPHY

Objectives. The aim of this study,vas to clarify how myocardial perfus ion is impaired by asynchronous contraction. Background. False septal hypoperfusion is noted in some patients with left bundle branch block. Methods. Eight dogs were examined with epicardial pacing at the left ventricular posterior wall, the right ventricular anterior wall and, a s a control, the right atrial appendage. The pacing rate was 80, 110 a nd 150 beats/min (bpm), Myocardial perfusion was assessed by contrast echocardiography. Results. Left ventricular pacing at 80 and 110 bpm d id not change systolic wall thickening or contrast intensity at the pa cing site, although an early excitation notch was noted at the pacing site. However, at 150 bpm, systolic thickening was impaired (23.3 +/- 4.2% vs. 37.0 +/- 2.6% during atrial pacing, p < 0.05), and the peak i ntensity ratio of the pacing site to the ventricular septum was signif icantly decreased (24.1 +/- 5.7% vs. 37.0 +/- 2.8% at a pacing rate of 80 bpm, p < 0.01). The peak intensity ratio correlated,vith systolic wall thickening at the pacing site (y = 0.413 x -0.028, r = 0.81, p < 0.0001). However, right ventricular pacing did not change either systo lic thickening or the peak intensity ratio at any pacing rate, althoug h an early excitation notch was noted on the ventricular septum. Concl usions. Wall motion abnormalities after early excitation vary dependin g on the pacing mode. When tachycardia induces regional wall motion ab normalities, the ventricular wall of the pacing site is functionally h ypoperfused. (C) 1997 by the American College of Cardiology.