A Novel Means of Mechanical Circulatory Support Speed Variation: Utilizing the Sino-Atrial Node

Abstract

Mechanical circulatory support (MCS) including left ventricular assist devices (LVADs) are increasingly important in managing patients with end-stage heart failure. Current generation LVADs, such as the HeartWare HVAD operate on a continuous flow basis. Many authors have identified the lack of physiological pulsatility as a limitation in these devices. We sought to test the feasibility of implementing physiological pulsatility using sino-atrial node (SAN) electrograms. Three different rabbits had SAN tissue extracted, placed in a tissue bath and superfused with Krebs-Ringer solution. An extracellular fine metal electrode was placed into the tissue preparation for activity capture. The rate of spontaneous SAN activity was modulated by changing the temperature of the superfusing solution. Electrical activity was captured and identified using a data acquisition system and custom-made software. This was used to trigger a stepwise speed change in an HVAD running in a mock circulation loop. Signal capture was tested in three heart rate ranges (>120, 60-80 and ∼60 beats per minute). Unipolar electrogram signals were successfully recorded for all tissue extracts. To simulate physiological settings, we implemented a 100 ms delay between capture and effect, as well as a speed change duration of 30% per cycle (obtained from the beat-to-beat variation). HVAD motor speed was successfully increased from 2500 RPM to 2800 RPM in synchronicity with the firing of the SAN. Similarly, we were also able to achieve a reduction of speed from 2500 RPM to 2000 RPM in synchronicity with the firing of the SAN. We were able to successfully capture electrical activity from the SAN for the purpose of introducing physiological pulsatility in all three of our rabbit experiments. This has the potential to change fundamental MCS flow hemodynamics.