Physiology of the native heart and Thermo Cardiosystems left ventricular assist device complex at rest and during...

Studies of patients supported with a left ventricular assist device have considered determinants of acute survival emphasizing the role of right heart function. In patients with refractory heart failure awaiting heart transplantation, chronic left ventricular assist device implantation may provide an opportunity for rehabilitation before surgery if hemodynamics are adequate at rest and during activities of daily life. For the assessment of the efficacy of the left ventricular assist device in this setting, four patients in whom the HeartMate pneumatic left ventricular assist device had been implanted were tested during graded supine bicycle exercise with Doppler echocardiography interrogation and central hemodynamic measurements. Patients with left ventricular assist device increased total left ventricular-left ventricular assist device complex output with exercise as Fick cardiac output increased from 5.7 +/- 1.5 to 8.6 +/- 3.1 L/min (mean +/- standard deviation). In two patients, peak left ventricular assist device rate and output were either present at the start of exercise or reached at mid-exercise and were associated with abrupt increases in left ventricular filling pressures (pulmonary capillary wedge pressure = 9 to 27 mm Hg and 12 to 24 mm Hg, respectively). During exercise, left ventricular end-diastolic size and pressure increased as right ventricular dimensions decreased or remained the same (patients 1, 3, and 4: 1.7 to 1.8 cm, 4.7 to 3.9 cm, and 2.6 to 1.8 cm, respectively) despite increased right atrial filling pressures, implying a decrease in functional right ventricular diastolic compliance. Although the left ventricular assist device functioned as a series pump at rest, Fick cardiac output exceeded left ventricular assist device output during exercise consistent with parallel ejection of the left ventricle through the native aortic valve. During exercise, residual left ventricular function may contribute to the hemodynamic response by (1) active filling of the left ventricular assist device to reduce filling time and to overcome left ventricular assist device inflow cannula impedance, (2) augmentation of total cardiac output with parallel ejection out of the native aortic valve, or (3) reduction of ventricular interaction-related changes in functional right ventricular diastolic compliance. When residual left ventricular function is sufficient, hemodynamics with exercise may be limited by peak left ventricular assist device rate. Although right ventricular function may affect acute postoperative survival, residual left ventricular function and peak left ventricular assist device rate may be important determinants of exercise performance during chronic implantation. A preliminary model of factors affecting the "left ventricular-left ventricular assist device complex" performance at rest and during exercise is presented.