Contrast-enhanced ultrasound evaluation of skeletal muscle perfusion in response to left ventricular assist device (LVAD) therapy

Chronic and advanced heart failure patients experience reduced capacity for exercise, likely due to reduced cardiac output and exercise-induced capillary vasodilation. To address these symptoms, clinicians implant a left ventricular assist device (LVAD) to improve physical function for this patient population. However, most LVADs, including the HeartMateII investigated in this study, are designed to provide continuous flow, and cannot respond to exercise-mediated demand for increased blood flow in skeletal muscles. This study investigates whether skeletal muscle perfusion and exercise capacity improved following LVAD implantation using contrast-enhanced ultrasound (CEUS) imaging of the quadriceps muscle. To date, eight patients have enrolled in and completed the CEUS study, and were evaluated prior to LVAD implantation (baseline), 2 weeks after LVAD implantation, and again at 3 months after LVAD implantation. Patients underwent two CEUS exams at each time point, one at a resting muscle state and the other at a muscle fatigue state after completing knee extensor exercises. We observed that patients experienced a reduction in quadriceps muscle area and diameter following LVAD implantation, but were regaining muscle area by approximately 4% by the 3-month postoperative evaluation compared to the 2-week post-operative evaluation (p<;0.0001). Additionally, patients experienced approximately 35% increase in muscle strength at the 3-month post-operative evaluation, compared to their baseline assessment (p=0.0033). While there were no significant differences in skeletal muscle perfusion across the three study time points (p=0.0765), we did observe that the time to initial contrast visualization (p <; 0.04) and time to peak contrast intensity (p <; 0.03) decreased after exercise across all time points, compared to pre-exercise evaluations. LVAD therapy appears to improve physical function in patients with heart failure and reduced cardiac output, and does not appear to diminish exercise-induced blood flow to skeletal muscle. CEUS-estimated muscle perfusion seems to indicate appropriate physical function in patients with LVAD therapy, although more data is required to bolster these preliminary results.