Effect of Clenbuterol on Cardiac and Skeletal Muscle Function During Left Ventricular Assist Device Support

Background: High-dose clenbuterol (a selective β₂-adrenergic agonist) has been proposed to promote myocardial recovery during left ventricular assist device (LVAD) support, but its effects on cardiac and skeletal muscle are largely unknown. Methods: Seven subjects with heart failure (5 ischemic, 2 non-ischemic) were started on oral clenbuterol 5 to 46 weeks post-LVAD implantation and up-titrated to daily doses of 720 μg. The following procedures were performed at baseline and after 3 months of therapy: echocardiography at reduced support (4 liters/min); cardiopulmonary exercise testing; body composition analysis; and quadriceps maximal voluntary contraction (MVC). Myocardial histologic analysis was measured at device implantation and explantation. Results: There were no serious adverse events or arrhythmias. Creatine phosphokinase (CPK) was elevated in 4 subjects, with no clinical sequelae. No change in ejection fraction was seen. End-diastolic dimension increased significantly (4.73 ± 0.67 vs 5.24 ± 0.66; p < 0.01), despite a trend toward increased LV mass. Body weight and lean mass increased significantly (75.5 ± 17.9 vs 79.2 ± 25.1 kg, 21.1 ± 8.9 vs 23.6 ± 9.7 kg, respectively; both p < 0.05). Exercise capacity did not change, but MVC improved significantly from 37.0 ± 15.7 to 45.8 ± 20.6 kg (p < 0.05). No significant change in myocyte size or collagen deposition was seen. Conclusions: Cardiac function did not improve in this cohort of LVAD patients treated with high-dose clenbuterol. However, clenbuterol therapy increased skeletal muscle mass and strength and prevented the expected decrease in myocyte size during LVAD support. Further study will clarify its potential for cardiac and skeletal muscle recovery.