Measurement of Left Ventricular Chamber Function in the Setting of Ventricular Assist Device Support

Abstract

Purpose Due to inadequacy of current LV chamber contractility measures, in the continuous-flow left ventricular assist device (cfLVAD) unloaded ventricle, new indices have been developed. These include RI Q (modified I Q ), a ratio between maximum flow acceleration and flow pulsatility; K, a logarithmic relationship between volumes moved in systole and diastole; and PPI, which defines the power of flow pulsatility. We investigated these indices under clinical scenarios in cfLVAD patients, along with a traditional measure – 2D LV fractional shortening (FS). Methods and Materials A total of 30 HeartWare HVAD patients (mean age 51.5±13.6yrs) were studied. We used a series of studies of pump speed adjustment (n=11), heart rate variation by ventricular pacing (n=8), preload variation using tilt-table (n=5) and the inotropic effect of exercise at constant pump speed (n=11) to assess the validity of these measures. A further longitudinal analysis in the acute ICU setting (days 0, 1, 7; n=15) and recovery/outpatient setting (days 7, 30, 90; n=16) was conducted to determine if our cohort demonstrated myocardial recovery based on these indices. Results Of the indices tested, only RI Q and K were sensitive to inotropic status, increasing from 7.61±0.89 to 8.05±1.12s -1 (P=0.003) and 1.08±0.43 to 1.43±0.42ml -1 (P=0.01) respectively. They also had the lowest coefficients of variation, respectively 13% and 25%. RI Q , K and FS were not significantly affected by pump speed, heart rate or preload. While PPI was also unaffected by heart rate and preload, it was closely related to pump speed (P Conclusions RI Q and K may be valid markers of intrinsic myocardial function with cfLVAD support, as they are significantly independent of pump speed, heart rate and preload variation, whilst being sensitive to contractility changes. Further studies assessing impact of remodelling and recovery are required.