Non-Invasive Flow Measurement of a Rotary Pump Ventricular Assist Device Using Quantitative Contrast Echocardiography

Background

Many implantable ventricular assist devices (VADs) have no direct measurement of pump output. The aim of this study was to test the hypothesis that quantitative contrast echocardiography can be used to measure VAD output.

Methods

Contrast-enhanced Doppler velocity-time integral (VTI) was measured in the VAD inlet and outlet cannulae. Doppler flow (Doppler Q = Doppler VTI × cannula area) was compared with measured flow (Q). A total of 130 flow measurements were made (at 6400 and 12,000 rpm).

Results

Doppler Q in the outflow and inflow cannulae showed an excellent correlation with measured Q (outlet Doppler Q = 1.0052 × Q + 0.048, R² = 0.9865; inlet Doppler Q = 1.5043 × Q + 0.003, R² = 0.9904), but inlet Doppler Q was 50% higher. Correcting for the flow profile of the conical inlet tube yielded excellent correlation (inlet Doppler Q = 1.0029 × Q + 0.002, R² = 0.9904).

Conclusion

Noninvasive Doppler flow techniques can be used to accurately measure VAD flow, but the flow profile in the cannula needs to be taken into account.

Keywords: Ventricular assist device, VAD, Contrast echocardiography