Simple and non-invasive techniques to evaluate the function of CircuLite Synergy

The Synergy CircuLite micropump is a novel partial-support miniature left ventricular assist device that propels 2-3 l/min blood from the left atrium into the right subclavian artery. The ability of currently available investigative modalities to confirm Synergy pump malfunction is limited. The Synergy speed fluctuates periodically (at 10-s intervals) from the baseline to a transient decrease followed by a transient increase (alternating speed algorithm, ASA) with the purpose of changing the blood flow behaviour, thereby reducing thrombogenicity. The aim of this study was to develop a simple non-invasive monitoring technique to assess pump function based on the detection of the ASA in the peripheral microcirculation.

Between February 2012 and July 2013, 10 patients with advanced chronic heart failure underwent Synergy implantation at our institution. The pump function was assessed by echocardiography and invasive monitoring according to standard protocols; additionally, the pump speed and power consumption were monitored. During the pump function assessment, the pulse oximeter waveform was recorded from the index fingers of the left and right hand with simultaneous pump auscultation using a stethoscope positioned on the pump (right infra-clavicular pocket).

The pulse oximeter waveform was readily detectable from the right and left hand of all study patients. If the Synergy function was normal, there was a significant difference in the morphology of the pulse oximeter waveform from each hand: the ASA algorithm produced a more pronounced variation (giant wave) in the trace from the right hand than from the left. The giant waves invariably coincided with the sound variation associated with the ASA algorithms, which were detected regularly at 10-s intervals.

We describe a simple, readily applicable, inexpensive, non-invasive technique that allows evaluation of Synergy pump function and may have diagnostic utility under conditions of suspected pump thrombus/malfunction. This technique is readily applicable from the early post-implant period throughout support and allows clinical personnel to verify blood flow variation through the Synergy, thereby providing a novel method of assessing device function.