Estimation of left ventricular pressure with the pump as “sensor” in patients with a continuous flow LVAD

Introduction: In long-term ventricular support of patients with LVADs, left ventricular pressure (p_lv) is relevant for indicating the unloading level of the heart. Monitoring of p_lv over time might give more insight into the increase or decrease in native ventricular function. In this study, we aim to assess dynamic p_lv noninvasively, using the LVAD as a pressure sensor. Methods: Pressure head (dp_lvad) was estimated from pump flow with a dynamic pump model (1). Estimated dp_lvad and measured aortic pressure were used to calculate left ventricular pressure. Moreover, parameters dp/dt_max and mean, minimum, and maximum p_lv were derived. The method was validated with a porcine ex vivo beating heart model by measurements conducted in 4 hearts supported with a Micromed DeBakey VAD and 3 hearts with a Heartmate II VAD. During each measurement, aortic and left ventricular pressure, pump flow, and pressure head were recorded for 30 s with a sampling frequency of 1 kHz. Results: The estimation of left ventricular pressure appeared to be accurate for both pumps. The parameters mean and minimum pressure were estimated with high accuracy. The degree of accuracy of the estimated p_lv was proportional to the degree of accuracy of the dynamic pump model. Conclusions: We proved that the LVAD model described in this paper can be used as a pressure indicator to determine LV pressure at any time based on noninvasive measurements of pump flow, aortic pressure, and the properties of the outlet graft.