Hemodynamic alterations in left ventricular function consequent to ventricular pacing

Mongrel dogs were used to quantify left ventricular function (LVF) in response to subendocardial electrical pacing from three left ventricular sites and one right ventricular site (RVO). Ventricular pacing sites were compared with atrial pacing at constant heart rates. LVF was significantly diminished with ventricular pacing when left ventricular pressure, maximal rate of left ventricular pressure rise, cardiac output, stroke work, and stroke power were considered. Left ventricular pacing values were significantly greater than RVO pacing values. Developed tension (DT) and maximal rate of tension development (max. dT/dt) were recorded from a strain-gauge arch; max. dT/dt decreased disproportionately greater than the decrease in DT with ventricular pacing. The reduced LVF was shown to be independent of myocardial contractility, heart rate, end-diastolic fiber length, previous tension, and resistance to shortening. Temporal dyssynergy of left ventricular contraction was shown to be an important determinant of LVF in addition to the above variables. Left ventricular synergism must be taken into account when assessing myocardial contractility in the intact left ventricle.