Phentolamine in low cardiac output states: an assessment with ECG-gated cardiac scintigraphy.

Abstract

We examined the effect of parenteral phentolamine in 11 critically ill patients with a low cardiac output state and a high systemic resistance. Because vasodilators often affect left ventricular end-diastolic pressure-volume relationships (compliance) in acute cardiac disease, changes in the pulmonary capillary wedge pressure (WP) may conceivably not reflect the true effect of vasodilators on left ventricular preload. Hence, we measured left ventricular ejection fraction (LVEF) with ECG-gated cardiac scintigraphy and stroke volume by thermodilution before and during phentolamine infusion. We then calculated left ventricular end-diastolic volume index (LVEDVI). Phentolamine infusion was associated with an increase in the mean cardiac index (CI) (1.96 +/- .53 [mean +/- SD] to 2.45 +/- .69 L/min X m2; p less than .0025) whereas the mean WP fell (19.5 +/- 7.5 to 13.5 +/- 7.3 mm Hg; p less than .05). There was no simultaneous change in the mean LVEDVI (100 +/- 48 to 110 +/- 40 ml/m2; p = NS), implying that one of the effects of phentolamine infusion was to improve left ventricular diastolic compliance. Multiple regression analysis suggested that the major effect of phentolamine on stroke volume was mediated by concomitant changes in the LVEDVI (r2 = .64). Therefore, benefit from phentolamine in low cardiac output states is multifactorial and phentolamine likely improves left ventricular compliance in some patients.