ALTERATION OF LEFT-VENTRICULAR ENDOCARDIAL FUNCTION BY INTRACAVITARY HIGH-POWER ULTRASOUND INTERACTS WITH VOLUME, INOTROPIC STATE, AND ALPHA-1-ADRENERGIC STIMULATION

Background. High-power intracavitary ultrasound abbreviates left ventricular (LV) ejection duration, thereby decreasing mechanical LV performance, presumably by selective impairment of endocardial endothelial function. Methods and Results. Effects of ultrasound were evaluated in the ejecting LV of anesthetized, open-chest dogs under different conditions of LV volume and contractile state and after mild selective alpha1-adrenergic stimulation. LV pressures, left atrial pressures, and regional segment lengths were measured in anterior and posterior midwall. A cylindrical ultrasound probe (0.9 MHz, 25 W) mounted on a catheter was inserted into the LV cavity through the apex and was activated for 4 minutes in each condition. In protocol A (n=7), LV volume was altered with caval vein occlusion and intravenous dextran infusion. The ultrasound probe was activated at low (4.1+/-0.9 mm Hg), mid (10.6+/-1.5 mm Hg), and high (17.9+-1.8 mm Hg) LV end-diastolic pressure (EDP). Effects of ultrasound were less pronounced at higher EDP. For example, the time interval from end-diastole to peak (-)dP/dt decreased by 7.5+/-2.3% at low, 4.4+/-2.2% at mid, and 1.9+/-1.6% at high LVEDP (p<0.001). In protocol B (n=7), LV inotropic state was altered by slow intravenous infusion of low-dose calcium. The ultrasound probe was activated before and after calcium. Effects of ultrasound were less pronounced after calcium. Time from end-diastole to peak (-)dP/dt decreased by 8.4+/-3.1% at baseline and by 3.5+/-2.1% after calcium (p<0.001). In protocol C (n=7), activation of the ultrasound probe was performed at baseline and after mild selective alpha1-adrenergic stimulation (propranolol plus phenylephrine). Effects of ultrasound were similar at baseline and after propranolol but increased after phenylephrine. Time from end-diastole to peak (-)dP/dt decreased by 5.2+/-2.4% at baseline, by 5.3+/-1.9% after propranolol, and by 8.9+/-3.2% after phenylephrine (p<0.05). Conclusions. Effects of intracavitary ultrasound, which are presumably mediated through modulation of endocardial endothelial function, were more important at low volume, lower calcium, and under mild selective alpha1-adrenergic stimulation.