Skeletal Muscle Ventricles: Improved Left Ventricular Performance Associated with a Prolongation of Ventricular Relaxation

Skeletal muscle ventricles (SMV) have been shown to pump blood effectively in both acute and chronic models. In this study SMVs were placed in circulation in series with the descending thoracic aorta to function as diastolic counterpulsators. The SMVs were stimulated to contract at a 1:2 ratio with the heart. The R-wave delay and the burst duration were varied, both as a percentage of the total R-R′ interval to determine the effect of the SMV on left ventricular (LV) relaxation in relation to other parameters of LV function. Optimal hemodynamic benefit was obtained using a 40% R-wave delay and a 30% burst duration. At these settings, the time constant of LV relaxation (τ) increased from a control value of 29.1 ± 1.6 to 39.8 ± 2.1 msec (P < 0.001). The tension time index decreased from a control value of 15.24 ± .31 to 13.88 ± .7 mm Hg-sec-1 (P < 0.001). The endocardial viability ratio, an indicator of myocardial blood flow, improved from 1.12 ± .11 to 1.55 ± .16 (P < 0.001) and LV dP/dt increased from 1555 ± 180 to 2320 ± 210 mm Hg-sec-1 (P < 0.05). In conclusion, this study demonstrates SMV diastolic counterpulsation results in improved LV performance which is associated with a prolongation of LV relaxation. A 40% R-wave delay interval and a 30% burst duration were the stimulation parameters which benefitted myocardial function optimally in this study.