Echocardiography in Assessment of Ventricular Assist Devices

Short-Term Ventricular Assist Devices

For acute or short-term mechanical circulatory support, several devices are currently available. The intraaortic balloon pump (IABP) is the “original” short-term VAD and is frequently used for very short-term support in shock, often during revascularization procedures. It augments left ventricle (LV) output via balloon deflation in systole (decreasing afterload), and improved coronary perfusion by inflation during diastole. On transthoracic echocardiography, it can be viewed on parasternal long-axis and subcostal windows within the thoracic and abdominal aorta ( Video 26.1 ). Percutaneously placed VADs (PVADs) that are Food and Drug Administration (FDA) approved include the TandemHeart (CardiacAssist, Inc., Pittsburgh, Pennsylvania) and Impella system (Abiomed Inc., Danvers, Massachusetts). The TandemHeart is an extracorporeal centrifugal pump that draws blood out of the body through an inflow cannula positioned in the left atrium ( Video 26.2 ) (access via femoral vein and transseptal puncture) and delivers blood through an outflow cannula positioned in a femoral artery. The Impella is a catheter-based system that contains a microaxial continuous flow pump at its distal end and outflow cannula more proximally. The Impella catheter is placed via a femoral or axillary artery retrograde across the aortic valve such that the distal cannula lies in the LV and proximal outflow port lies in the ascending aorta ( Video 26.3 ). Echocardiographic imaging is useful prior to PVAD placement to identify contraindications to their use; for example, left atrial or left ventricular thrombus, severe aortic or mitral stenosis (Impella), or severe aortic regurgitation. Echocardiography may help guide placement of these devices, and assess proper catheter position and stability: the TandemHeart catheter should cross the interatrial septum, with the perforated end residing in the left atrium only. Prolapse of the perforated segment into the right atrium would result in desaturated venous blood being drawn in to the LVAD. The Impella catheter should be seen traversing the left ventricular outflow tract (LVOT) into the aortic root and ascending aorta. Serial echocardiography may also be used to assess the ventricular response to mechanical unloading.

Surgically implanted short-term extracorporeal VADs include the Thoratec Paracorporeal Ventricular Assist Device and CentriMag (Thoratec Corp., Pleasanton, California), which are pneumatically driven pulsatile and centrifugal continuous flow pumps, respectively. Similar to the TandemHeart, these devices have inflow cannulas placed in the chamber proximal to the failing ventricle (i.e., the left atrium), which draw blood out of the body via an extracorporeal pump and then into an outflow cannula that is surgically implanted into the vessel distal to the failing ventricle (i.e., the aorta). Echocardiography is used for preimplant evaluation and postimplant surveys for complications and/or myocardial recovery.

Long-Term Surgically Implanted Ventricular Assist Devices

The two currently FDA-approved continuous-flow left VADs are the HeartMate II (Thoratec Corp., Pleasanton, California) and heartware ventricular assist device Ventricular Assist System (Heartware International Inc., Framingham, Massachusetts). The HeartMate II is approved for both bridge to transplantation and destination therapy, while the Heartware device is approved for bridge to transplantation. Both devices have an inflow cannula implanted near the LV apex, a mechanical impeller, and outflow graft to the ascending aorta. The axillary flow impeller for the HeartMate II is implanted subdiaphragmatically, whereas the centrifugal flow Heartware impeller is intrapericardial ( Fig. 26.1A, B ). The impeller location influences echocardiographic imaging because of the shadowing and artifact produced, as described later. The remainder of this chapter will focus on long-term surgically implanted LVADs, with regard to echocardiographic imaging needed when planning for LVAD, during LVAD implantation, and post-LVAD placement.