Muscle-powered cardiac assist device (MCAD) for right ventricular support: Current status and future directions

Summary

To develop an implantable muscle-powered cardiac assist device (MCAD), ex vivo and in vivo pump performance studies of a skeletal muscle ventricle (SMV) for right ventricular (RV) support were performed. Latissimus dorsi muscle for SMV construction was transformed into predominantly type I fibers after stimulation for one year; this transformation was associated with a 63.4% increase in blood flow. The device itself consisted of a latex pouch with inflow and outflow valves, assembled with a supporting spring to augment diastolic filling. An ex vivo study in 6 dogs showed that the isovolumetric SMV pressure increased more than 50 mmHg with 15 mmHg preload, and a maximum pump flow of 0.631/min was obtained with 15 mmHg preload and 30 mmHg afterload. SMV stroke work was 0.27 × 10⁶ erg, and power output was 0.04 watts; these were dependent on SMV diastolic filling in the range of 40 mmHg afterload. In vivo SMV performance for total RV support in 14 dogs showed and off-to-on increase in pulmonary artery blood flow (PABF) of 70% and in pressure (PAP) of 112%, while PABF increased by only 10% and PAP by 7% with partial RV support. Power output dissipated into the pulmonary artery was 0.04 W with total support and 0.02 W with partial support. These studies predict that the SMV MCAD requires optimization of stroke volume according to the recipient’s heart size, and active diastolic filling assisted by a spring, magnet, alternative muscle contraction, or total bypass from the right atrium. In conclusion, SMV potentially provides sufficient power output to substitute for the RV. The future MCAD will have to overcome existing problems related to thrombogenesis, muscle vascular delay, fatigue, and power transmission efficiency for blood pumping.