RPM and flow modulation for a continuous flow left ventricular assist device to increase vascular pulsatility : a computer simulation, mock circulation, and in-vivo animal study.

Purpose: Continuous flow (CF) left ventricular assist devices (LVAD) support diminishes vascular pressure pulsatility. Despite its recent clinical success and reliability, CF LVAD support has been associated with adverse events including gastrointestinal bleeding, aortic valve insufficiency, and hemorrhagic strokes. To overcome these limitations, we have developed flow/RPM modulation algorithms to provide vascular pulsatility using a CF LVAD. Methods: The effects of timing and synchronizing the CF LVAD flow/RPM modulation to the native ventricle, modulation amplitude, and modulation widths were studied on the native ventricle and vasculature using computer simulation, mock loop, and animal model studies. A total of over 100 combinations of flow modulation algorithms to modulate CF LVAD flow/RPM were tested for partial and full LVAD support modes. Results: Modulation of CF LVAD flow/RPM resulted in an increased arterial pressure pulsatility of up to 50 mmHg during asynchronous modulation and 20 mmHg during synchronous modulation. Synchronous CF LVAD RPM modulation allowed for a range of reduced left ventricular external work (LVEW) as compared to un-modulated CF LVAD support conditions. Full support co-pulsation (high RPM during systole, low RPM during diastole) created greater pulse pressures as compared to counter pulsation (high RPM during diastole, low RPM during systole). However, all full support modulation timings yielded higher pulse pressure than normal full support CF LVAD flow at low ventricular contractilities. Importantly, reduction in LVEW and increase in pulsatility may be adjusted to user-defined values while maintaining the same average CF LVAD flow rate. Conclusions: These LVAD flow/RPM modulations may reduce the incidence of adverse events associated with the CF LVAD therapy by increasing vascular pulsatility and reducing vascular impedance. Further, these methods of CF LVAD flow/RPM 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

Cavopulmonary assist for the failing Fontan circulation: impact of ventricular function on mechanical support strategy

Mechanical circulatory support--either ventricular assist device (VAD, left-sided systemic support) or cavopulmonary assist device (CPAD, right-sided support)--has been suggested as treatment for Fontan failure. The selection of left- versus right-sided support for failing Fontan has not been previously defined. Computer simulation and mock circulation models of pediatric Fontan patients (15-25 kg) with diastolic, systolic, and combined systolic and diastolic dysfunction were developed. The global circulatory response to assisted Fontan flow using VAD (HeartWare HVAD, Miami Lakes, FL) support, CPAD (Viscous Impeller Pump, Indianapolis, IN) support, and combined VAD and CPAD support was evaluated. Cavopulmonary assist improves failing Fontan circulation during diastolic dysfunction but preserved systolic function. In the presence of systolic dysfunction and elevated ventricular end-diastolic pressure (VEDP), VAD support augments cardiac output and diminishes VEDP, while increased preload with cavopulmonary assist may worsen circulatory status. Fontan circulation can be stabilized to biventricular values with modest cavopulmonary assist during diastolic dysfunction. Systemic VAD support may be preferable to maintain systemic output during systolic dysfunction. Both systemic and cavopulmonary support may provide best outcome during combined systolic and diastolic dysfunction. These findings may be useful to guide clinical cavopulmonary assist strategies in failing Fontan circulations