Background: Noninvasive cardiac-specific analysis of contractile function in patients with dilated heart failure remains problematic. This study tests whether maximal power divided by the square of end-diastolic volume (PWR(mx)/EDV2, or preload-adjusted PWR(mx)) can provide such assessment. Methods and Results: To validate the load insensitivity of the PWR(mx) index and determine its response to contractile change, 24 subjects with chronic dilated cardiomyopathy underwent invasive pressure-volume catheterization study using the conductance catheter technique. Preload was transiently reduced by 30% using balloon occlusion of the inferior vena cava, and afterload impedance was lowered by 50%, induced by a bolus injection of nitroglycerin. Contractile state was varied by intravenous dobutamine, verapamil, or esmolol. PWR(mx) was calculated from the simultaneous product of ventricular pressure and rate of volume change (dV/dt), the latter derived from the volume catheter signal. PWR(mx) varied directly with preload but was minimally influenced by afterload. However, PWR(mx)/EDV2 was not significantly altered by either loading change. PWR(mx)/EDV2 did vary with contractility, correlating closely with changes in the end-systolic pressure- volume relation (r=.91, P<.001). To test the noninvasive application of this index, 12 additional patients were studied, with PWR(mx)/EDV2 derived from nuclear ventriculography combined with a novel method to measure central arterial pressures. Subjects received intravenous nitroprusside or dobutamine in random order. Ejection fraction increased similarly with both agents (+42.9±8.9% for dobutamine and +29.4±5.3% for nitroprusside, both P<.01). In contrast, PWR(mx)/EDV2 did not significantly change with nitroprusside but increased by 126±16.1% with dobutamine (P<.01). Conclusions: Preload- adjusted PWR(mx) is a steady-state index of ventricular systolic function that is sensitive to inotropic state and minimally influenced by physiological changes in afterload impedance or volume load. It appears useful for noninvasive cardiac-specific analysis of acute drug effects.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine
- Physiology (medical)