Introduction of fixed-flow mode in the DexAide right ventricular assist device

Abstract

Background While some continuous-flow left ventricular assist device algorithms have been created to respond to varying patient physiology, very little research has been conducted on control of right ventricular support in univentricular and biventricular applications. The purpose of this study was to develop and evaluate a simple and reliable fixed-flow algorithm for the DexAide right ventricular assist device (RVAD). This algorithm automatically adjusts speed to maintain a target flow while preventing ventricular suction when a requested target flow exceeds available tricuspid flow. Methods Fixed-flow control mode was evaluated in 17 DexAide RVAD chronic bovine studies whose duration ranged from 14 - 90 days (33 ± 24 days). Targeted fixed-flow levels ranged from 4.0 to 6.5 L/min. Data were monitored on an hourly basis. Pump flow data were also recorded on a weekly basis to document the speed increment required to increase pump flow from 5 to 8 L/min at 0.5 L/min increments. Results The fixed-flow control mode was evaluated for a total duration of 5,283 hours without complications related to pump flow or left/right circulation imbalance. The pump speed varied between 2,000 – 3,220 rpm to maintain the flow constant at each target level. The average absolute mismatch between the target flow and measured flow was 0.6 ± 0.5 L/min. Conclusions Fixed-flow control mode with a predetermined maximum automatic pump speed can be safely and effectively used in the DexAide RVAD. It provided target flows by adjusting the pump speed while monitoring pump flow response to automatic speed increment requests.

Biventricular Assist Devices: A Technical Review

“…This is particularly pertinent for rotary BiVADs to prevent pulmonary edema or ventricular suction. 57 Sensor-less systems using pulsatility as a surrogate for preload will benefit individually actuated pumps such as dual rotary devices, although their safety in biventricular support scenarios must to be assessed. 7,21 Combined pumps such as the AnyHeart and BiVACOR may not be able to easily infer preload from pulsatility as the left and right ventricular pulsatility will be transmitted to a common actuator/hub, however, suitable force/pressure signals may be extracted from the magnetic bearing to achieve this in a sensor-less fashion.…”

“…Although the inherent Frank-Starling-like flow balancing fullto-empty mode of these devices allows for simple physiological control, limitations in patient mobility, comfort and quality of life exist until a donor heart is found. 57,66 The lack of focus on RVAD development has probably hindered the clinical progression and the availability of a third generation, implantable BiVAD. This is not surprising considering the requirement for left ventricular assistance compared with right ventricular assistance.…”

“…18 Meanwhile, the RVAD uses fixed flow control with an added observer suction detection system which compares changes in flow with speed variation. 57 However, if low LVAD flow pulsatility is recorded, the dual pump controller responds by increasing the RVAD pump speed until either the LVAD flow pulsatility is restored, or the RVAD controller senses excessive RV unloading. 57 …”

“…57 However, if low LVAD flow pulsatility is recorded, the dual pump controller responds by increasing the RVAD pump speed until either the LVAD flow pulsatility is restored, or the RVAD controller senses excessive RV unloading. 57 …”

Implantable Continuous-Flow Right Ventricular Assist Device: Lessons Learned in the Development of a Cleveland Clinic Device

“…The algorithm includes the above discussed method to detect ventricular unloading and prevent ventricular suction based on a d flow /d speed limit, below which pump speed is decreased. The CFRVAD Fixed Flow control mode was successfully evaluated in 16 DexAide CFRVAD chronic calf studies whose mechanical support ranged from 14 to 90 days (33 ± 24 days, 1.44 implant years total) with no pulmonary complications related to pump flow or atrial pressure imbalance and no incidence of ventricular suction (34). The pump speed was varied automatically between 2,000 and 3,220 rpm to maintain targeted fixed pump flow levels over a 4.0–6.5 L/min range in calves with resting total cardiac outputs of approximately 8.0–10.0 L/min.…”