Cardiodynamic effects of experimental right bundle branch block in canine hearts with normal and hypertrophied right ventricles

Abstract

Cardiodynamic effects of acute experimental right bundle branch block (RBBB) were studied in canine hearts: group A included 15 normal hearts; group B-1 had seven hearts with mild right ventricular hypertrophy (RVH), and group B-2 had 11 hearts with marked RVH. The main sequential changes following RBBB were marked prolongation of the Q upstroke interval of the right ventricle and striking shortening of right ventricular systolic time that affected right and left ventricular interaction, particularly in the hearts with RVH. Hemodynamic changes were: the right ventricular end-diastolic pressure was elevated markedly (4.4 ± 2.2 → 9.8 ± 2.6 mm Hg, p < 0.001) in group B-2, moderately ( p < 0.01) in group B-1, and not at all in group A. The right ventricular positive peak dp dt decreased remarkably (1036 ± 151 → 827 ± 152 mm Hg/sec, p < 0.001) in group B-2 and negligibly in the other groups. A significant correlation existed between the percentage of decrease in right ventricular peak dp dt and the QRS duration of RBBB in each group ( p < 0.01). The left ventricular peak negative dp dt decreased distinctly (2570 ± 326 → ± 2055 ± 362 mm Hg/sec, p < 0.01) in group B-2 and not at all in the other groups. The atroke volume showed 12% decrease in group B-2 ( p < 0.001), 8% decrease in group B-1 (NS), and no decrease in group A. In the presence of RVH, acute RBBB causes significant impairment of right and left ventricular function. The magnitude of the impairment invariably depends upon both the prior degree of RVH and the width of the QRS complex.