Reliable suction detection for patients with rotary blood pumps

Abstract

All rotary blood pumps (RBPs) are prone to the harmful effects of ventricular collapse or "suction events" because of over-pumping, because they are inherently preload insensitive devices, yet RBP controllers do not comprise a clinically reliable suction detector. We therefore investigated the clinical performance of seven expertly selected time domain indices of suction based on the observed positive spike induced in the RBP impeller speed waveform. Using expert panel classifications, a balanced set of 404 five-second speed snapshots of normal and suction events was created from the impeller speed 25 Hz data in 12 VentrAssist implant patients. Initially, suction index threshold levels were set differently for each patient, giving best sensitivity 95% and specificity 99%. However, analysis of paired combinations of suction indices with fixed thresholds identified one pair giving an acceptable sensitivity of 99.5% and specificity 97.5%; the low number of high speed data samples relative to the speed snapshot mean and maximum OR the largest increase in successive speed maxima. The additional precondition of RBP speed amplitude exceeding a low threshold level allows its more general application to patients with low cardiac contractility. This gives a suction detector with high clinical utility; requiring three index threshold settings only. © 2008 Amercian Society of Artificial Internal Organs.