Continuous-flow left ventricular assist devices (cfLVADs) have been proven safe and effective for bridge-to-transplant and destination therapy (DT) in patients with advanced heart failure. However, the fixed pump speed of these devices may lack response to activity and oxygen demand, thereby limiting exercise tolerance. The objective of this observational study was to describe exercise capacity as measured by peak oxygen consumption (peak VO2) that may be expected during support with a cfLVAD. Peak VO2 was measured in patients (mean age: 58.3 ± 11.7 years; 66.7% ischemic and 33.3% DT) before cfLVAD support (11.2 ± 3.0 ml/kg/min, n = 25), between 3 and 6 months (12.7 ± 3.5 ml/kg/min, n = 31), at 1 year (10.7 ± 2.6 ml/kg/min, n = 16), and longer than 1 year (11.2 ± 1.7 ml/kg/min, n = 10). There was no statistical improvement in peak VO2 at any time point after implantation. In addition, ventilatory efficiency remained poor after LVAD implantation at all time points. Although studies have shown an increase in survival and patient's quality of life, exercise capacity as measured by cardiopulmonary exercise testing remains low during cfLVAD support.

An implantable rotary blood pump was developed to provide long-term mechanical right heart support for patients who have failing Fontan circulation. The objective of this study was to evaluate the pump in vivo in a 30 day sheep study. Pump speed was set at 3,900 rpm for the duration of the study, and pump power was between 4.3 and 4.6 W. The pump inlet pressures for the superior vena cava (SVC) and inferior vena cava (IVC) were 14 ± 15 and 11 ± 15 mm Hg, respectively, over the duration of the study. Hematocrit remained stable at 30% ± 4%. Partial thromboplastin time (PTT) steadily increased from 30 s preoperatively to a high of 59 s on postoperative day 20, while prothrombin time (PT) remained at 20 ± 2 s for the duration of the study. The implantation and postoperative recovery were successful, and the animal demonstrated normal physiologic pulmonary and venous pressures and cardiac output. On pump inspection, the IVC and SVC inlets were completely clear of any deposits, but there were small thrombi (approximately 0.5 mm diameter) between each of the three rotor blades and along 20% of the parting line of the two volute halves. A complete right heart bypass was performed, postoperative recovery was successful, and the pump demonstrated adequate circulatory support and normal physiologic pulmonary and venous pressures. This study was the first successful test of a right heart replacement device in a chronic animal study.

Reentrant spiral waves can become pinned to small anatomical obstacles in the heart and lead to monomorphic ventricular tachycardia that can degenerate into polymorphic tachycardia and ventricular fibrillation. Electric field-induced secondary source stimulation can excite directly at the obstacle, and may provide a means to terminate the pinned wave or inhibit the transition to more complex arrhythmia. We used confluent monolayers of neonatal rat ventricular myocytes to investigate the use of low intensity electric field stimulation to perturb the spiral wave. A hole 2-4 mm in diameter was created in the center to pin the spiral wave. Monolayers were stained with voltage-sensitive dye di-4-ANEPPS and mapped at 253 sites. Spiral waves were initiated that attached to the hole (n = 10 monolayers). Electric field pulses 1-s in duration were delivered with increasing strength (0.5-5 V/cm) until the wave terminated after detaching from the hole. At subdetachment intensities, cycle length increased with field strength, was sustained for the duration of the pulse, and returned to its original value after termination of the pulse. Mechanistically, conduction velocity near the wave tip decreased with field strength in the region of depolarization at the obstacle. In summary, electric fields cause strength-dependent slowing or detachment of pinned spiral waves. Our results suggest a means to decelerate tachycardia that may help to prevent wave degeneration.

Continuous flow left ventricular assist devices (LVADs) are commonly used as bridge-to-transplantation or destination therapy for heart failure patients. However, non-optimal pumping speeds can reduce the efficacy of circulatory support or cause dangerous ventricular arrhythmias. Optimal flow control for continuous flow LVADs has not been defined and calls for an implantable pressure sensor integrated with the LVAD for real-time feedback control of pump speed based on ventricular pressure. A MEMS pressure sensor prototype is designed, fabricated and seamlessly integrated with LVAD to enable real-time control, optimize its performance and reduce its risks. The pressure sensing mechanism is based on Fabry-Pérot interferometer principle. A biocompatible parylene diaphragm with a silicon mirror at the center is fabricated directly on the inlet shell of the LVAD to sense pressure changes. The sensitivity, range and response time of the pressure sensor are measured and validated to meet the requirements of LVAD pressure sensing.