The Value of Pump Audiosignals in Patients with Left Ventricular Assist Devices

Abstract

Purpose The HeartWare Ventricular Assist Device (HVAD) is an implantable, continuous-flow centrifugal pump with a magnetically and hydro-dynamically suspended impeller capable of delivering flows of up to 10L/min. Although clinicians routinely listen over the HVAD with a stethoscope, there is no literature on a systematic analysis of audiosignals generated by the implanted pump.This study explores the HVAD audiosignals produced across a variety of pump and haemodynamic scenarios. Methods and Materials A wireless stethoscope was used to record pump audiosignals in 7 Left and 2 Bi-Ventricular HVAD recipients. Welch Power Density Spectral Analysis was used to determine the frequency content of recorded pump audiosignals and also to correlate these signals with both clinical events as well as with the stored pump parameter data. The nature of the audiosignals under a range of pressure, speed and fluid viscosity scenarios were assessed in a HVAD Mock Loop circulation model. Results Spectral analysis revealed the presence of a signature audiosignal for the HVAD in the form of 2 frequency peaks that are independent of pump and haemodynamic conditions. Pump speed determined the frequency peak position in VAD recipients and in the Mock Loop studies, while Mean Arterial Pressure (MAP) appeared to influence the 2 peak’s power density (R²=0.697, P=0.019 & R²=0.857, P=0.003). Audiosignal production in 2 BiVAD patients with outflow graft thrombus was described pre and post thrombolytic therapy. Changes in fluid viscosity altered peak height of this signature in Mock Loop recordings. Conclusions Audiosignals from HVAD pump impellers can be recorded using wireless technology. Spectral analysis of these audiosignals reveals pump-specific frequency peaks in VAD recipients and Mock Loop scenarios which show a relationship with pump settings and patient haemodynamic status. We believe that audiosignal profiling of implantable VADs may offer a novel approach to assess pump function and may even provide an early diagnostic tool for pump related complications.