The "double whammy" of a continuous-flow left ventricular assist device on von Willebrand factor

A sensorless, physiologic feedback control strategy to increase vascular pulsatility for rotary blood pumps

Continuous flow rotary blood pumps (RBP) operating clinically at constant rotational speeds cannot match cardiac demand during varying physical activities, are susceptible to suction, diminish vascular pulsatility, and have an increased risk of adverse events. A sensorless, physiologic feedback control strategy for RBP was developed to mitigate these limitations. The proposed algorithm used intrinsic pump speed to obtain differential pump speed (ΔRPM). The proposed gain-scheduled proportional-integral controller, switching of setpoints between a higher pump speed differential setpoint (ΔRPM Hr ) and a lower pump speed differential setpoint (ΔRPM Lr ), generated pulsatility and physiologic perfusion, while avoiding suction. The switching between ΔRPM Hr and ΔRPM Lr setpoints occurred when the measured ΔRPM reached the pump differential reference setpoint. In-silico tests were implemented to assess the proposed algorithm during rest, exercise, a rapid 3-fold pulmonary vascular resistance increase, rapid change from exercise to rest, and compared with maintaining a constant pump speed setpoint. The proposed control algorithm augmented aortic pressure pulsatility to over 35 mmHg during rest and around 30 mmHg during exercise. Significantly, ventricular suction was avoided, and adequate cardiac output was maintained under all simulated conditions. The performance of the sensorless algorithm using estimation was similar to the performance of sensor-based method. This study demonstrated that augmentation of vascular pulsatility was feasible while avoiding ventricular suction and providing physiological pump outflows. Augmentation of vascular pulsatility can minimize adverse events that have been associated with diminished pulsatility. Mock circulation and animal studies would be conducted to validate these results.

Vascular Function in Continuous Flow LVADs: Implications for Clinical Practice

Left ventricular assist devices (LVADs) have been increasingly used in patients with advanced heart failure, either as a destination therapy or as a bridge to heart transplant. Continuous flow (CF) LVADs have revolutionized advanced heart failure treatment. However, significant vascular pathology and complications have been linked to their use. While the newer CF-LVAD generations have led to a reduction in some vascular complications such as stroke, no major improvement was noticed in the rate of other vascular complications such as gastrointestinal bleeding. This review attempts to provide a comprehensive summary of the effects of CF-LVAD on vasculature, including pathophysiology, clinical implications, and future directions.

Vascular function in continuous-flow left ventricular assist device recipients: effect of a single pulsatility treatment session

Vascular function is further attenuated in patients with chronic heart failure implanted with a continuous-flow left ventricular assist device (LVAD), likely due to decreased arterial pulsatility, and this may contribute to LVAD-associated cardiovascular complications. However, the impact of increasing pulsatility on vascular function in this population is unknown. Therefore, 15 LVAD recipients and 15 well-matched controls underwent a 45-min, unilateral, arm pulsatility treatment, evoked by intermittent cuff inflation/deflation (2-s duty cycle), distal to the elbow. Vascular function was assessed by percent brachial artery flow-mediated dilation (%FMD) and reactive hyperemia (RH) (Doppler ultrasound). Pretreatment, %FMD (LVAD: 4.0 ± 1.7; controls: 4.2 ± 1.4%) and RH (LVAD: 340 ± 101; controls: 308 ± 94 mL) were not different between LVAD recipients and controls; however, %FMD/shear rate was attenuated (LVAD: 0.10 ± 0.04; controls: 0.17 ± 0.06%/s^-1, P < 0.05). The LVAD recipients exhibited a significantly attenuated pulsatility index (PI) compared with controls prior to treatment (LVAD: 2 ± 2; controls: 15 ± 7 AU, P < 0.05); however, during the treatment, PI was no longer different (LVAD: 37 ± 38; controls: 36 ± 14 AU). Although time to peak dilation and RH were not altered by the pulsatility treatment, %FMD (LVAD: 7.0 ± 1.8; controls: 7.4 ± 2.6%) and %FMD/shear rate (LVAD: 0.19 ± 0.07; controls: 0.33 ± 0.15%/s^-1) increased significantly in both groups, with, importantly, %FMD/shear rate in the LVAD recipients being restored to that of the controls pretreatment. This study documents that a localized pulsatility treatment in LVAD recipients and controls can recover local vascular function, an important precursor to the development of approaches to increase systemic pulsatility and reduce systemic vascular complications in LVAD recipients.