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Exercise Tolerance in Calves Supported by Continuous Flow Total Artificial Heart
*Andrew C.W. Baldwin1,2, *William E. Cohn2, *Steven M. Parnis2, *O.H. Frazier2
1Yale School of Medicine, New Haven, CT;2Texas Heart Institute, Houston, TX
Objective: The widespread clinical adoption of continuous-flow (CF) ventricular assist devices (VADs) suggests the potential utility of this technology in the development of a total artificial heart (TAH). However, little is known regarding the physiologic consequences of completely non-pulsatile blood flow. In order to better understand the effects of CF cardiopulmonary support, we sought to examine the hemodynamic and metabolic response to exercise in calves supported with biventricular CF-VADs.
Design: Case series.
Setting: Academic tertiary-care center.
Patients: Eight Corriente-crossbread calves underwent bilateral ventriculectomy and dual CF-VAD implantation for total heart replacement. Four types of rotary VADs were paired: the HeartMate II (Thoratec Corp.; Pleasanton, CA), HeartMate III (Thoratec Corp.), HeartAssist 5 (ReliantHeart, Inc.; Houston, TX), and HeartWare HVAD (HeartWare, Inc.; Framingham, MA).
Interventions: n/a
Main Outcome Measured: Pump flows were recorded, along with continuous hemodynamic monitoring that included systemic, pulmonary artery, right atrial, and left atrial pressure measurements. Arterial and venous blood gases were measured both at rest and during exercise, and serum lactate levels were trended throughout the activity period.
Results: All 8 calves completed 30 minutes of exercise at variable treadmill speeds within 2-6 weeks after implant. Pump flows increased by an average of 8% in response to augmented venous return and filling pressures with exercise, and balanced flows were maintained autonomously without necessitating the adjustment of pump speeds. A rise in blood lactate levels was noted, and VO2 was comparable with physiologic total-body VO2 during exercise.
Conclusion: Physical activity is well tolerated in calves supported with a CF-TAH. Balanced and physiologically responsive pump flows suggest a degree of hemodynamic automaticity inherent in CF technology that may prove advantageous for total heart replacement.
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