Intrathoracic and extrathoracic skeletal muscle ventricles in circulation: left ventricular apex-to-aorta configuration

Power output of pericardium-lined skeletal muscle ventricles, left ventricular apex to aorta configuration: up to eight months in circulation

OBJECTIVE

The purpose of this experiment was to evaluate the potential for a skeletal muscle ventricle connected to the circulation between the left ventricle and the aorta to provide effective, long-term cardiac assist.

METHODS

Skeletal muscle ventricles were constructed from the latissimus muscle in 10 dogs. After conditioning, the skeletal muscle ventricles were connected to the left ventricle and the aorta with 2 valved conduits. The skeletal muscle ventricle was programmed to contract during diastole.

RESULTS

At time of implantation, skeletal muscle ventricles stimulated at 33 Hz and in a 1:2 ratio with the heart significantly decreased left ventricular work by 56% (P <.01) and at 50 Hz by 65% (P <.01). At a 1:2 ratio, the power output of the skeletal muscle ventricles was 59% of left ventricular power output at 33 Hz (P <. 01) and 93% at 50 Hz (P <.01). Animals survived 7, 11, 16, 17, 72, 99, 115, 214, and 249 days. Three deaths were directly related to the skeletal muscle ventricle. One animal is alive at 228 days. In the animal that survived 249 days, skeletal muscle ventricle power output at 8 months with a 33 Hz stimulation frequency and a 1:2 contraction ratio was 57% of left ventricular power output and 82% at 50 Hz. At a 1:1 ratio, skeletal muscle ventricle power output was 97% and 173% of the left ventricle at 33 and 50 Hz, respectively.

CONCLUSIONS

Left ventricular assist with a skeletal muscle ventricle connected between the left ventricle and the aorta is the most hemodynamically effective configuration we have tested and can maintain significant power output up to 8 months.

Skeletal muscle ventricles, left ventricular apex-to-aorta configuration. 1 to 11 weeks in circulation

BACKGROUND

Skeletal muscle ventricles (SMVs) have been used in animals in a variety of configurations to provide circulatory assistance. Long-term survival and function have been demonstrated. Our laboratory recently obtained promising short-term hemodynamic data in a left ventricular apex-to-aorta model.

METHODS AND RESULTS

SMVs were constructed from the left latissimus dorsi muscle in five adult mongrel dogs. After a 3-week period of vascular delay and 5 to 7 weeks of electrical conditioning, valved conduits were used to connect the left ventricular apex to the SMV and the SMV to the descending aorta. The SMV was then stimulated to contract during cardiac diastole. Initial measurements showed a significant increase in the mean femoral diastolic pressure (62 +/- 6 versus 51 +/- 5 mm Hg, P < .05). There was also a decrease in the left ventricular tension-time index (11.5 +/- 2.5 versus 14.6 +/- 2.1 mm Hg.s, P < .05), indicating a decrease in the work requirement of the left ventricle. During SMV stimulation, the majority of flow (65%) was through the SMV circuit and was associated with reversal of flow in the proximal descending thoracic aorta. The longest-surviving animal survived 76 days, at which time pressure augmentation was still seen (mean femoral diastolic pressure, 63 +/- 0.9 versus 50 +/- 1.2 mm Hg, P < .05).

CONCLUSIONS

Survival beyond the acute setting is possible with this model. Diastolic pressure augmentation can be effectively maintained over time.

Skeletal muscle ventricles in continuity with the bloodstream

BACKGROUND AND AIM OF STUDY

The prevalence of end-stage congestive heart failure and limitation of clinical alternative treatments present the need for creative new solutions. Formation of a ventricle from skeletal muscle (SMV) has shown promise in the animal laboratory. Two modes of the SMV for cardiac assistance, the counterpulsation (CP-SMV) and the ventricular assist (VA-SMV), using the latissimus dorsi muscle were applied in a canine model. Ability to augment arterial pressure was assessed. The effect of stimulation delay on the degree of augmentation was also evaluated.

METHODS AND RESULTS

Thirty-five SMVs were connected in continuity with the bloodstream in the two modes: (1) CP-SMV (aorta-to-aorta) (n = 12); and (2) VA-SMV (left ventricular [LV] apex-to-aorta) (n = 23). In the CP-SMV mode, designed to simulate the intra-aortic balloon pump, the SMV was simply interposed into the path of the descending aorta (DAo) without prosthetic valves in either the inflow or the outflow conduit. In order to obligate blood flow through the SMV, the DAo was ligated between the two grafts. In the VA-SMV mode, the connection was made with valved conduits from the LV apex (inflow) to the ascending aorta (outflow) (n = 11) or to the DAo (n = 12). The ascending aorta (AAo) was also ligated proximal to the outflow conduit for the same reason of obligating blood flow through the SMV. The SMV was timed to contract in diastole in both the CP-SMV mode and the VA-SMV mode. In the VA-SMV mode, the average systolic pressure without stimulation was 101.6 +/- 2.2 mmHg and with stimulation 118.21 +/- 4.78 mmHg (mean augmentation, 14.5 +/- 2.6 mmHg) (p < 0.01). In the CP-SMV mode, the average systolic pressure without stimulation was 97 +/- 32 mmHg and with stimulation, 122 +/- 26 mmHg (mean augmentation, 25 +/- 8.6 mmHg) (p < 0.001). We also extended earlier work on timing of stimulation of isolated SMV by evaluating the effect of stimulation delay on the degree of augmentation in continuity with the bloodstream with the SMV in the VA-SMV configuration. Delays of 50 msec to 225 msec were evaluated. SMV stimulation was via the thoracodorsal nerve at an amplitude of 1.5 V and a frequency of 25 Hz. The greatest augmentation occurred at a stimulation delay of 150 msec (p < 0.001).

CONCLUSION

Both counterpulsation and assist configurations produced effective diastolic augmentation. Although diastolic augmentation occurred with all timing delays, the optimal delay was 150 msec. Complications in the survival animals include AAo problems, SMV rupture, respiratory insufficiency, intraoperative instability, and thrombosis (which occurred in 51% [18/35] of the animals). This high frequency of thrombosis in the canine model suggests the use of a less thrombogenic SMV lining, more aggressive or prolonged anticoagulation, or an alternative animal model.

Skeletal muscle ventricles: frontiers in 1995

Skeletal muscle ventricles (SMVs) constructed from electrically conditioned latissimus dorsi muscle (LDM) may become an alternative for assisting the failing heart. Left and right heart circulatory assist using SMVs has been performed successfully in both acute and chronic animal models. The configurations used to connect SMVs to the circulation have included a left atrium to aorta bypass, a left ventricle apex to aorta bypass, aortic counterpulsators, a cavopulmonary bypass, and a right ventricle to pulmonary artery bypass. One SMV used as an aortic counterpulsator functioned effectively in the circulation for more than 27 months. Recent application of the pericardium to the SMV as an inner layer and design changes in the connection of the SMV to the circulation have reduced the risk of thrombus formation and SMV rupture. Although several problems have yet to be solved, the goal of the SMV as a permanent circulatory assist device without the limitation of an external power source seems within reach.