EVALUATION OF LEFT-VENTRICULAR MECHANICAL EFFICIENCY IN THE HUMAN HEART BY ECHOCARDIOGRAPHY

It has been proved that ventricular systolic wall stress and myocardia l mass are two major determinants of myocardial oxygen consumption (MV O2) in the intact human heart. The product of stress and mass, which w e named the stress-mass-index (SMI), has the correct unit for work (cm X dyns/cm = dyns X cm), and is very similar to the pressure-volume wo rk of the heart. To examine whether SMI might be used as a predictor o f MVO2, left ventricular mean systolic wall stress (Msigma(c), Msigma( m)), left ventricular wall mass (Mm), and stroke work (SW) were measur ed by echocardiography in normal and diseased human hearts. The area b ounded by the end-diastolic and end-systolic pressure-volume lines, an d the systolic segment of the pressure-volume loop (PVA) were also mea sured in each subject. It has been proved repeatedly in the past that PVA correlates significantly with MVO2. Our results showed that there was a close correlation between PVA and SMI in every group (r = 0.76-0 .91, P < 0.001 all), which proved indirectly that SMI may reflect MVO2 . On this basis, left ventricular efficiency (Eff) was estimated as SW /SMI X 100%. Eff in 30 patients with essential hypertension (17.1% +/- 1.6%) was normal compared to the control subjects (19.9% +/- 2.4%). H owever, Eff of 22 hypertensive patients with mild left ventricular dys function (13.3% +/- 2.1%), 33 coronary artery heart disease patients ( 10.8% +/- 1.8%), and 11 chronic congestive heart failure patients (6.6 % +/- 2.1%) was significantly decreased compared to the control. These changes in Eff were in agreement with clinical findings and left vent ricular ejection fractions (EF). For the first time, we have measured Eff noninvasively; the results are very close to those evaluated invas ively in human hearts by others. This reflects the fact that it is pos sible to calculate Eff noninvasively. We conclude that the product of left ventricular systolic wall stress could reflect the change in MVO2 at rest. SW/SMI may be a useful method in evaluating Eff and ventricu lar function.