Functional assessment of skeletal muscle ventricles after pumping for up to four years in circulation

Background. The successful treatment of cardiac failure by heart transplant ation is severely limited by the shortage of donor organs, and alternative surgical approaches are needed. An experimental approach that holds conside rable promise is the skeletal muscle ventricle (SMV), an auxiliary blood pu mp formed from a pedicled graft of latissimus dorsi muscle and connected to the circulation in a cardiac assist configuration. Adaptive transformation , or conditioning, by electrical stimulation enables the skeletal muscle to perform a significant proportion of cardiac work indefinitely without fati gue. Methods. In 10 dogs, SMVs were constructed from the latissimus dorsi muscle , lined internally with pericardium, and conditioned by electrical stimulat ion to induce fatigue resistant properties. The SMVs were connected to the descending thoracic aorta via two 12-mm Gore-Tex conduits and the aorta was ligated between the two grafts. The SMV was stimulated to contract during the diastolic phase of alternate cardiac cycles. The animals were monitored at regular intervals. Results. At initial hemodynamic assessment, SMV contraction augmented mean diastolic blood pressure by 24.6% (from 61 +/- 7 to 76 +/- 9 mm Hg). Presys tolic pressure was reduced by 15% (from 60 +/- 8 to 51 a 7 mm Hg) after an assisted beat. Four animals died early, 1 from a presumed arrhythmia, and 3 during propranolol-induced hypotension. The other 6 animals survived for 2 73, 596, 672, 779, 969, 1,081, and 1,510 days. Diastolic augmentation was 2 7.4% at 1 year (93 +/- 9 vs 73 +/- 6 mm Hg; n = 5), 34.7% at 2 years (85 +/ - 6 vs 63 +/- 7 mm Hg; n = 3), 21.2% (89 +/- 10 vs 73 +/- 8 mm Hg; n = 2) a t 3 years, and 34.5% (78 vs 58 mm Hg; n = 1) after 4 years in circulation. After 4 years, the isolated SMV was able to maintain a pressure of over 80 mm Hg while ejecting fluid at 20 mL/s. No animal showed evidence of SMV rup ture or thromboembolism. Conclusions. The SMVs in this study provided effective and stable hemodynam ic assistance over an extended period of time. There was no evidence that t he working pattern imposed on the muscular wall of the SMV compromized its viability. Areas of fibrofatty degeneration were suggestive of early damage that future protocols should seek to minimize. (C) 2000 by The Society of Thoracic Surgeons.