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 alpha 1-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 alpha 1-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 alpha 1-adrenergic stimulation.