VENTRICULAR SYSTOLIC ASSESSMENT IN PATIENTS WITH DILATED CARDIOMYOPATHY BY PRELOAD-ADJUSTED MAXIMAL POWER - VALIDATION AND NONINVASIVE APPLICATION

Background Noninvasive cardiac-specific analysis of contractile functi on in patients with dilated heart failure remains problematic. This st udy tests whether maximal power divided by the square of end-diastolic volume (PWR(mx)/EDV(2), 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, 2 4 subjects with chronic dilated cardiomyopathy underwent invasive pres sure-volume catheterization study using the conductance catheter techn ique. Preload was transiently reduced by 30% using balloon occlusion o f the inferior vena cava, and afterload impedance was lowered by 50%, induced by a bolus injection of nitroglycerin. Contractile state was v aried by intravenous dobutamine, verapamil, or esmolol. PWR(mx) was ca lculated from the simultaneous product of ventricular pressure and rat e of volume change (dV/dt), the latter derived from the volume cathete r signal. PWR(mx) varied directly with preload but was minimally influ enced by afterload. However, PWR(mx)/EDV(2) was not significantly alte red by either loading change. PWR(mx)/EDV(2) did vary with contractili ty, correlating closely with changes in the end-systolic pressure-volu me relation (r=.91, P<.001). To test the noninvasive application of th is index, 12 additional patients were studied, with PWR(mx)/EDV(2) der ived from nuclear ventriculography combined with a novel method to mea sure central arterial pressures. Subjects received intravenous nitropr usside or dobutamine in random order. Ejection fraction increased simi larly with both agents (+42.9+/-8.9% for dobutamine and +29.4+/-5.3% f or nitroprusside, both P<.01). In contrast, PWR(mx)/EDV(2) did not sig nificantly 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 inot ropic state and minimally influenced by physiological changes in after load impedance or volume load. It appears useful for noninvasive cardi ac-specific analysis of acute drug effects.