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 RIQ (modified IQ), ratio between maximum flow acceleration and flow pulsatility; K, logarithmic relationship between volumesmoved in systole anddiastole; andPPI, powerofflow pulsatility. We investigated these under clinical scenarios in cfLVAD patients, along with a traditional measure–2D LV fractional shortening (FS). Methods:A total of 30HeartWareHVADpatients (mean age 51.5± 13.6 yrs) were studied using 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). A further longitudinal analysis in the acute ICU(days0, 1, 7;n= 15) andrecovery settings (days7, 30, 90; n= 16) were conducted to determine myocardial recovery. Results: Of indices tested, only RIQ and K were sensitive to inotropic status, increasing from 7.61± 0.89 to 8.05± 1.12 s−1 (P= 0.003) and 1.08± 0.43 to 1.43± 0.42ml−1 (P= 0.01) respectively. They alsohad the lowest coefficients of variation, respectively 13% and 25%. RIQ,K and FSwere 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< 0.001). There was no significant change across the cohort in the longitudinal studies. Conclusions: RIQ and Kmay be valid markers of intrinsic myocardial function with cfLVAD support. Further studies assessing impact of remodelling and recovery are required.
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