Biomechanical Hearts

Abstract

Background — As shown previously in goats, clenbuterol increased the power of electrically conditioned skeletal muscle ventricles (SMVs) of clinically relevant size (150 mL), which were constructed around a mock system. They pumped against a pressure of 60 to 70 mm Hg immediately during surgery and up to several months after, finally at >1 L/min. SMVs without clenbuterol administration failed. Thus, we expected that clenbuterol-supported SMVs might become integrated into the circulation by a 1-step operation instead of the 2-step procedure required up to now. Methods and Results — In adult Boer goats (n=5), latissimus dorsi muscle was wrapped around a polyurethane chamber of 150 mL that was connected to the descending aorta. This muscular flow-through pumping chamber containing a stabilizing inner layer (called a biomechanical heart [BMH]) was formed and immediately made to work against a systemic load with the support of clenbuterol (5×150 μg/wk). During surgery, the mean stroke volume of BMHs was 53.8±22.4 mL. One month after surgery, in peripheral arterial pressure, the mean diastolic (P MD ) and minimal diastolic (P min ) pressures of BMH-supported heart cycles differed significantly from unsupported ones (P MD =+2.9±1.1 mm Hg [ P <0.04], P min =−2.4±0.9 mm Hg [ P <0.04]). After BMH-supported heart contractions, the subsequent maximal rate of pressure generation, dP/dt max , increased by 20.5±8.1% ( P <0.02). One BMH, catheterized 132 days after surgery, shifted a volume of 34.8 mL per beat and 1.4 L/min with a latissimus dorsi muscle of 330 g. Depending on duration of training, the percentage of myosin heavy chain type 1 ranged between 31% and 100%. Conclusions — Under support of clenbuterol, BMHs of a clinically relevant size can be trained effectively in the systemic circulation after a 1-step operation and offer the prospect of a sufficient volume shift and probably unloading of the left ventricle.