Wave Intensity Analysis of Right Ventricular Function during Pulsed Operation of Rotary Left Ventricular Assist Devices

Abstract

Changing the speed of left ventricular assist devices (LVADs) cyclically may be useful to restore aortic pulsatility; however, the effects of this pulsation on right ventricular (RV) function are unknown. This study investigates the effects of direct ventricular interaction by quantifying the amount of wave energy created by RV contraction when axial and centrifugal LVADs are used to assist the left ventricle. In 4 anesthetized pigs, pressure and flow were measured in the main pulmonary artery and wave intensity analysis was used to identify and quantify the energy of waves created by the RV. The axial pump depressed the intensity of waves created by RV contraction compared with the centrifugal pump. In both pump designs, there were only minor and variable differences between the continuous and pulsed operation on RV function. The axial pump causes the RV to contract with less energy compared with a centrifugal design. Diminishing the ability of the RV to produce less energy translates to less pressure and flow produced, which may lead to LVAD-induced RV failure. The effects of pulsed LVAD operation on the RV appear to be minimal during acute observation of healthy hearts. Further study is necessary to uncover the effects of other modes of speed modulation with healthy and unhealthy hearts to determine if pulsed operation will benefit patients by reducing LVAD complications.

Figure 1. Schematic representation of LVAD pump speeds

When the centrifugal pump was used: constant speed = 2700 rpm, systolic speed = 3400 rpm, and diastolic speed = 2300 rpm. When the axial pump was used: constant speed = 7000 rpm, systolic speed = 7800 rpm, and diastolic speed = 6600 rpm.

Figure 2. Example of wave intensity analysis when a centrifugal LVAD was implanted

Panel A: Main pulmonary artery pressure and flow waveforms are shown for one cardiac cycle. Panel B: Calculated net wave intensity is labeled with the 2 major waves created by the right ventricle. Wave energy is represented by the grey shaded area. Panel C: Net wave intensity is separated into the contributions of forward- (red line) and backward-going (blue line) waves. The forward compression wave (FCW) and decompression wave (FDW) created by the right ventricle are labeled.

Figure 3. LVAD outflow patterns during control and asynchronous pulsatile operation

The different LVAD outflow patterns for the centrifugal pump (Panel A) and the axial pump (Panel B) are shown during the initial transition between control and pulsatile modes of operation. The difference between the intrinsic heart rate and pulsatile LVAD rate result in the amplitude changes of pump flow. Co-pulse is identified by the individual cardiac cycles with high amplitude and counter-pulse is identified by the individual cardiac cycles with low amplitude.

Figure 4. Main pulmonary artery wave intensity patterns with centrifugal and axial pumps

(A) The net wave intensity is shown during baseline physiologic conditions and control mode (i.e. constant pump speed). The peak intensity of the forward compression wave (FCW) and forward decompression wave (FDW) are labeled. The time domain is normalized to compare cardiac cycles (0 = start; 1 = end) with different heart rates. (B) Effects of pulsatile pump operation on wave intensity patterns are shown during baseline physiologic conditions. Control (i.e. constant speed), co-pulse, and counter-pulse (i.e. speed modulation) modes are indicated by the colored lines. The time domain is normalized to compare cardiac cycles (0 = start; 1 = end) with different heart rates. (C) Effects of physiological interventions on wave intensity patterns are shown during control mode (i.e. constant speed). Each physiologic condition is indicated by the colored lines. The time domain is normalized to compare cardiac cycles (0 = start; 1 = end) with different heart rates.