Effects of Left Ventricular Assist Device Support and Outflow Graft Location Upon Aortic Blood Flow

Abstract

Although continuous flow (CFVAD) and pulsatile (PVAD) ventricular assist devices (VADs) are being clinically used, their effects upon aortic blood flow as a measure of overall blood distribution remain unclear. The objective of this study was to compare the effects of CFVAD and PVAD support for ascending (AscA) and descending (DA) aorta outflow cannulation upon mean aortic blood flow and waveform morphology. Six experiments were conducted in a normal, acute calf model, in which an inflow cannula was implanted in the left ventricle apex and outflow cannulae were anastomosed to both the AscA and DA. Flow probes were placed around the pulmonary artery, pump outflow, brachiocephalic trunk, and aorta proximal and distal to the DA outflow. For each acute experiment, calves received randomly selected levels of VAD support (0-100% of cardiac output) and pump failure (VAD off and outflow cannula unclamped) for each of four randomly selected test conditions: (1) PVAD and AscA, (2) PVAD and DA, (3) CFVAD and AscA, and (4) CFVAD and DA. Regardless of pump type or support level, proximal and distal aorta mean flows were lower (p < 0.05) for DA compared with the AscA. No differences in mean aortic flows between pump types at either outflow graft location were discerned. Differences in morphologic features of blood flow waveforms between PVAD and CFVAD were observed. During simulated pump failure, retrograde aortic blood flow in both the aortic arch and DA was observed. Partial ventricular suction was also observed during the greatest levels of CFVAD support and suggested pronounced effects upon both the right and left ventricle. Collectively, these findings imply that VAD outflow location may have an important role in patient response and recovery. Investigation of the long-term pathophysiologic responses to pump type and outflow location is ongoing.

Numerical simulation of cardiovascular dynamics with different types of VAD assistance

“…In the counterpulsation mode for the displacement pump (case 4) and in the reciprocating-valve pump (case 6), the left ventricle is more adequately unloaded. These coincide with corresponding results in similar research in Drakos et al's (2005) in vivo study on 18 domestic pigs, and Koenig et al's (2004) in vitro study in an adult mock circulation loop. According to previous researches, pulsatile flow has an important effect on the circulation physiology: it promotes perfusion in the kidney and liver, and promotes microcirculation at the cell level which is quite important in early treatment of acute heart failure (Sezai et al, 1999;Ü ndar, 2004).…”

“…It was concluded that the pulsatility associated with the intra-aortic balloon provides additional circulatory benefit with respect to the centrifugal pump alone. Litwak et al (2004) examined the effect of constant flow and pulsatile flow VAD support and outflow graft location on aortic flow in an acute calf model. Litwak et al (2005) and Koenig et al (2004) conducted similar research in an adult mock circulation test rig.…”

Ventricular Assist Device Outflow-Graft Site: Effect on Myocardial Blood Flow

“…The descending aortic anastomosis also preserves the sternum for subsequent cardiac transplantation or other cardiac procedures that require a median sternotomy. So far, however, controversial results from some animal and in vitro studies have precluded wide use of this method, even for primary LVAD implantations [3,14,15]. Kar and colleagues [14] reported that LVADs implanted with an outflow-graft anastomosis to the descending aorta have potential drawbacks such as aortic valve fusion and aortic-root flow stagnation that may alter myocardial perfusion.…”

Screening for Outflow Cannula Malfunction of Left Ventricular Assist Devices (LVADs) With the Use of Doppler Echocardiography: New LVAD-Specific Reference Values for Contemporary Devices

“…All of these variables combine to result in a unique LVAD type–dependent normal flow-velocity pattern across the outflow cannula. 17,18 Outflow cannula malfunction adds yet another layer of complexity to the flow patterns of LVAD outflow cannulas. Accurate knowledge of the normal flow properties of a particular LVAD is therefore of particular importance because variations may indicate LVAD malfunction.…”