Abstract 16514: Screening for Outflow Cannula Malfunction of Left Ventricular Assist Devices Using Doppler Echocardiography: Establishing New Reference Values

Abstract

Background: Echocardiographic assessment of left ventricular assist devices (LVAD) is used as a screening tool to evaluate the integrity and mechanics of the pump and circuit. We aimed to 1) establish the normal range and upper reference limit of peak velocity of the outflow cannula for the modern era of LVADs and 2) assess the performance of the current reference limit and our new reference limit in patients with continuous flow LVADs as a screening tool for cannula malfunction. Methods: LVAD outflow peak velocities were measured with Doppler echocardiography (TTE) in 57 patients with LVADs (HeartMate II (HMII) = 44, HeartWare (HW) = 13). The average velocity and the upper and lower normal reference limits (defined as +/- two standard deviations from the mean) for each LVAD type was then calculated. The upper reference limit was then used as a screening threshold for cannula malfunction. Results: The average outflow cannula peak velocity for the HMII cohort was 1.94 m/sec +/- 0.42 with an upper and lower reference limit of 2.78 m/sec and 1.10 m/sec, respectively. The average outflow cannula peak velocity for the HW cohort was 2.36 +/- 0.53 with an upper and lower reference limit of 3.42 m/sec and 1.3 m/sec, respectively, which was significantly higher than the HMII cohort (p=0.004). Velocities from both cohorts were dramatically higher than the commonly citied upper reference limit velocities of 2 m/sec. Use of the previously cited reference limit poorly discriminated between normal and malfunctioning LVAD cannulas whereas our new reference limit identified all four patients with outlet cannula malfunction (Figure1). Conclusions: In both HeartMate II and HeartWare LVADs, the average peak outflow velocity and reference limit for the normal population as measured by Doppler-TTE was markedly higher than currently cited LVAD reference limits. Patients with peak outflow velocities above our upper reference limit should be evaluated for LVAD outflow cannula malfunction.