Regional Contraction patterns of the Left Ventricle during Ventricular Pacing

Abstract

Mongrel dogs (10) were used to assess regional myocardial function in response to electrical pacing from the inflow (RVI), outflow tracts (RVO), apex (RVA) of the right ventricle and apex (LVA) and lateral wall (LVL) of the left ventricle. Strain gauge arches were sutured to the epicardial segments of the apical and lateral walls of the left ventricle and their mechanical shortening was measured during right atrial (RA) and during ventricular pacing. Shortening 2 segments did not differ significantly in RA and RVI pacing, while the stimulation of RVA and LVA caused the initial contraction of the apical segment, and RVO and LVL pacing caused contraction of the lateral segment, i.e. Asynchrony of contraction was not accompanied by a uniform change in peak tension of regional myocardial segments, but preejection tension rose and ejection tension fell at the pacing site. The reduction in mean aortic pressure inversely correlated with the prolongation of the time interval between the onset of shortening of 2 segments during left ventricular pacing. The decrease in cardiac performance observed during ventricular pacing was related to the severity of asynchrony rather than the direction of the ventricular depolarization or change in regional myocardial tension.