Mechanical performance and efficiency of the left ventricle during ventricular stimulation.

BOERTH, ROBERT C., AND JAMES MT. COVELL. Mechanical performance and ejkiency of the leji ventricle during ventricular stimuluhn. Am. J. Physiol. 221(6): 16864691. 1971.-The effects of electrical stimulation of the right atrium and right ventricular outflow tract on left ventricular performance and efficiency were compared in dogs in the isovolumic left ventricle in which end-diastolic volume was constant. During right ventricular outflow-tract pacing there were significant decreases in peak left ventricular pressure, peak left ventricular wall stress, and peak left ventricular dP/dt. Despite these decreases, myocardial contractility did not appear to be changed by right ventricular stimulation since there was no downward shift of the stress-velocity relationship at low stresses. During right ventricular outflow-tract stimulation myocardial oxygen consumption (MVo2) was unchanged, and the efficiency of the isovolumically contracting left ventricle was decreased. It is concluded that electrical stimulation of the right ventricular outflow tract produces an abnormal pattern of contraction which depresses the function and efficiency of the left ventricle. The mechanism of this may be through altered synchronism of fiber contraction without an alteration of myocardial inotropic state.