Date on Master's Thesis/Doctoral Dissertation

8-2018

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Bioengineering

Degree Program

JB Speed School of Engineering

Committee Chair

Koenig, Steven

Committee Member

Soucy, Kevin

Committee Member

Gentry, Elizabeth

Committee Member

Monreal, Gretel

Author's Keywords

heart failure; lvad; pulsatile; asynchronous modulation; hvad

Abstract

Background: Continuous-flow (CF) left ventricular assist devices (LVADs) have gained widespread clinical acceptance as a treatment option for advanced heart failure (HF); however, they have also been associated with an increased risk of adverse events, including gastrointestinal bleeding, aortic insufficiency, and hemorrhagic stroke. It has been hypothesized that the increase in adverse event incidence may be due in part to diminished vascular pulsatility and high shear stress when CF-LVADs are operated at fixed speeds. Previous studies have shown that pump speed modulation generates greater levels of pulsatility in rotary pumps than when operated at fixed speeds. The objective of this study was to characterize the hemodynamic and pump performance of LVADs operated with a low-frequency asynchronous pump speed modulation algorithm in a chronic healthy bovine model with partial VAD support.

Materials and Methods: Clinical-grade LVAD with aortic (HeartWare HVAD, n=3) or transaortic (proprietary VADx, n=4) outflow were implanted into chronic (30-day) healthy male Jersey calves (60-110 kg). An asynchronous pump speed modulation algorithm (frequency = 20 bpm, amplitude = 2500-4000 RPM for HVAD or 11000-19000 RPM for VADx) was implemented by controlling pump current. Hemodynamic measurements (pressures, flows) were recorded throughout the study duration (30s epochs collected hourly at 400Hz), echocardiographic data was recorded during the implant, weekly, and at terminal, and blood laboratory measurements were regularly collected throughout the study. All data were analyzed to characterize aortic pulsatility, LV unloading, blood damage, and device power usage. Statistical analysis was performed to determine significance between fixed and pump speed modulation operating conditions.

Results and Discussion: Two HVAD and four VADx animals achieved the 30-day study endpoint. Due to surgical complications, one animal died intraoperatively. Both HVAD devices maintained asynchronous modulation for the full study duration with mean high and low speeds of 4000 RPM and 2500 RPM, respectively. Two of the four VADx devices maintained asynchronous modulation at average high and low speeds of 17238 RPM and 11333 RPM over the 30-day study; however, the other two VADx devices operated at fixed pump speed for 1 and 2 days, respectively, due to unforeseen controller malfunctions, which were corrected to restore asynchronous modulation. Near-physiologic aortic pulse pressure for HVAD (45±4 mmHg) and VADx (46±9 mmHg) was demonstrated. HVAD and VADx with asynchronous modulation reduced stroke volume by 27% and 23%, respectively. HVAD (n=2) and VADx (n=3) maintained plasma free hemoglobin (pfHb) less than 40 mg/dL for the entire study duration while one VADx had pfHb > 40 mg/dL for a period of 3 days, which resolved. Asynchronous modulation increased power consumption with HVAD (25%) and VADx (6%) compared to fixed speed operation.

Conclusion: This study demonstrated asynchronous modulation of HVAD and VADx maintained near-physiologic pulsatility and LV unloading at the expense of minimal hemolysis and increased power consumption in the partial VAD support model. Future studies in clinically-relevant heart failure models warrant further investigation.

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