Hemodynamic evaluation of a chronically implanted, electrically powered left ventricular assist system: responses to acute circulatory stress

Charles A. Dana Institute, Boston, Massachusetts.

Hemodynamic stress testing was performed in four calves with a chronically implanted left ventricular assist device consisting of a double-valved pump interposed between the left ventricular apex and the descending thoracic aorta. The device was powered either pneumatically (n = 1) or with a transcutaneous energy transmission system (n = 3). Hemodynamic evaluation (cardiac output and right and left ventricular and pulmonary and carotid artery pressures) was carried out at baseline and during all hemodynamically stressed states. Atrial pacing and ventricular pacing to a heart rate of 140 beats/min resulted in no significant change in right or left heart filling pressures or cardiac output. Preload reduction with nitroprusside or transient inferior vena cava balloon occlusion resulted in a marked decrease in left ventricular pressure with preservation of mean arterial pressure. Phenylephrine administration resulted in a marked rise in mean arterial pressure with no change in cardiac output or filling pressure. Induction of ventricular fibrillation resulted in a decrease of mean left ventricular pressure to 11 +/- 8 mm Hg, but mean arterial pressure was maintained at greater than or equal to 50 mm Hg. It is concluded that a multicomponent, implantable, electrically powered assist system is capable of maintaining a normal cardiac output under a wide range of loading conditions and chronotropic states. Although this device is clearly preload dependent, it is capable of maintaining normal systemic pressures during conditions of severe left ventricular dysfunction and circulatory collapse.