Continuous flow (CF) left ventricular assist devices (LVAD) support diminishes vascular pressure pulsatility. Despite its recent clinical success CF LVAD support has been associated with a higher incidence of gastrointestinal bleeding, aortic valve dysfunction and hemorrhagic strokes. To overcome this limitation, we are developing algorithms to provide vascular pulsatility using a CF LVAD. The effects of timing and synchronizing the CF LVAD flow modulation to the native myocardium, modulation amplitude, and modulation widths were studied on the native ventricle and vasculature using a computer simulation model of the circulatory system simulating heart failure. A total of over 150 combinations of varying pulse widths, beat frequencies, time shifts, and amplitudes to modulate CF LVAD flow were tested. All control algorithms maintained a mean CF LVAD flow of 5.0 ± 0.1 L/min (full support) or 2.5 ± 0.1 L/min (partial support). These algorithms resulted in an increased arterial pressure pulsatility of up to 59 mmHg, reduced left ventricular external work (LVEW) by 10-75%, and increased myocardial perfusion by up to 44% from baseline heart failure condition. Importantly, reduction in LVEW and increase in pulsatility may be adjusted to userdefined values while maintaining the same average CF LVAD flow rate. These methods of CF LVAD flow modulation may enable tailored unloading of the native ventricle to provide rest and rehabilitation (maximal unloading to rest followed by gradual reloading to wean), which may promote sustainable myocardial recovery. Further, these LVAD flow modulation patterns may reduce the incidence of adverse events associated with the CF LVAD therapy by increasing vascular pulsatility.

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A counterpulsation device (Symphony) that works synchronously with the native heart to provide partial circulatory support was developed to treat patients with advanced heart failure. Symphony is implanted in a 'pacemaker pocket' without entry into the chest, and requires timing with ECG for device filling and ejection. Surface leads are limited to short-term use due to signal distortion and lead management. Transvenous leads are a clinical standard for pacemakers and internal defibrillators, but increase the complexity of the implant procedure. In this study, the feasibility of using subcutaneous leads for synchronized timing of Symphony was investigated. ECG waveforms were simultaneously measured and recorded using epicardial (control) and subcutaneous (test) leads in a bovine model for 7-days (n = 6) and 14-days (n = 2) during daily activity and treadmill exercise. Landmark features and R-wave triggering detection rates for each lead configuration were calculated and compared. Lead placement, migration, durability, and infection were quantified using fluoroscopy and histopathological examination. There were 2,849 data epochs (30-s each) recorded at rest (133,627 analyzed beats) and 35 data epochs (20 min each) recorded during treadmill exercise (37,154 analyzed beats). The subcutaneous leads provided an accurate and reliable triggering signal during routine daily activity and treadmill exercise (99.1 ± 0.4% positive predictive value, 96.8 ± 1.5% sensitivity). The subcutaneous leads were also easily placed with minimal lead migration (0.5 ± 0.1 cm), damage (no fractures or failures), or infection. These findings demonstrate the feasibility of using subcutaneous leads for synchronized timing of mechanical circulatory support while offering the advantage of less invasive surgery and associated risk factors.