Influence of acute changes in preload, afterload, contractile state and heart rate on ejection and isovolumic indices of myocardial contractility in man

Abstract

To determine the sensitivity of several isovolumic and ejection phase indices of myocardial contractility to loading, inotropic stimulation and heart rate in man, 14 patients (pts) were studied during cardiac catheterization with simultaneous recordings of left ventricular (LV) pressures and ultrasound dimensions. Measurements were made of instantaneous and mean circumferential fiber shortening velocity (V(CF)) maximal (max) rate of LV pressure rise (dP/dt), dP/dt divided by end diastolic circumference [(dP/dt)C], (dP/dt)/C divided by aortic valve opening pressure [(dP/dt)/CP], peak contractile element velocity (V(CE)) using total LV pressure, V(CE) extrapolated to zero total pressure (V(max)), V(CE) at a developed pressure of 10 mm Hg (V(CE)DP10) and dP/dt at a common isovolumic developed pressure of 40 mm Hg [(dP/dt)/DP40]. Results are expressed in per cent change of the mean for the group. Acute preload increase (8.6% increase in end diastolic circumference) with volume expansion at constant heart rate in 7 pts produced insignificant changes in V(CF), an 8.3% increase in max dP/dt, no change in (dP/dt)/C, a variable response in (dP/dt)/CP, 18% reduction in peak V(CE), 16% reduction in V(max), 14% increase in V(ce)DP10 and a 10% increase in (dP/dt)/DP40. An acute increase in afterload produced by angiotensin in 8 pts (44% increase in peak stress) led to a 38% decrease in V(CF), a 2.5% increase in max dP/dt, no significant change in (dP/dt)/C, a 26% reduction in (dP/dt)/CP, variable responses in peak V(CE) and V(max), an 11% increase in V(CE)DP10 and minor changes in (dP/dt)/DP40. All of the contractility indices were augmented significantly by isoproterenol and atrial pacing. In a given patient, max dP/dt appears to be useful in the assessment of acute changes in inotropic state since the magnitude of its response to abrupt changes in preload is small and to afterload insignificant. Normalizing max dP/dt for end diastolic circumference assures better stability during loading with good sensitivity to inotropic stimulation. V(CF) may be used whenever changes in afterload are minimal. The isovolumic measurements of V(CE) (regardless of whether total or developed pressure is used) lack sufficient stability during acute changes in loading conditions to warrant their use in the quantitative assessment of acute changes in inotropic state.