Systematic Echocardiographic Approach to Left Ventricular Assist Device Therapy

As the population ages, the prevalence of heart failure continues to escalate. Heart failure with reduced ejection fraction (HFrEF) comprises approximately 50% of the admission diagnoses for heart failure. The American College of Cardiology/American Heart Association categorizes heart failure into four stages labeled A to D. Patients with stage D heart failure have the worst outcomes. Clinically, they have persistent symptoms despite optimal doses of guideline-directed medical therapy and cardiac resynchronization devices when appropriate. These patients, classified as “advanced” or “end stage,” may be eligible for advanced therapies such as mechanical assist devices and cardiac transplantation. Unfortunately, the number of patients with stage D HFrEF far surpasses donor heart availability, such that cardiac transplantation is not an option for many patients, and alternative options must be considered. The ventricular assist device (VAD) is one such alternative.

The left ventricular (LV) assist device or LVAD is a battery-operated pump that conducts blood from the left ventricle via an inflow cannula implanted at the LV apex to the aorta by way of an outflow graft with direct anastomosis to the ascending aorta. In so doing, it augments cardiac output in the failing heart by reducing the afterload on the left ventricle and decreasing filling pressures, pulmonary artery pressures, and mitral regurgitation (MR; Fig. 175.1 ). Patients eligible for LVADs generally have stage D HFrEF (explained earlier) with New York Heart Association class III to IV symptoms and LV ejection fraction (EF) less than 25%, with or without cardiac resynchronization therapy with most often a dilated left ventricle.

Open full size image

End-stage heart failure with reduced ejection fraction is associated with a low-output state with high pulmonary venous pressures, left ventricular end-diastolic pressures, central venous pressures, right atrial pressures (green arrows), and a deviated interventricular septum (IVS) to the right. With left ventricular assist device (LVAD) implantation, the IVS should move leftward as blood is drawn from the left ventricle to the ascending aorta. Cardiac output increases, and left atrial and ventricular pressures decrease (yellow arrows) . At the same time, the venous return to the right ventricle (RV) increases, and right atrial pressure also increases (yellow arrows) . The extent to which these pressures (the central venous and right atrial pressures) remain high varies depending on a variety of factors, including the extent of right ventricular dysfunction before LVAD insertion. CVP, Central venous pressure; IVC, inferior vena cava; LA, left atrium; LV, left ventricle; PA, pulmonary artery; PCWP, pulmonary capillary wedge pressure; RA, right atrium.

According to the INTERMACS registry, more than 20,000 LVADs have been implanted in the United States with more than 2500 new implants occurring every year. VADs can be commissioned for short- (hours to days) or long- (months to years) term support. VADs are differentiated based on a number of factors: (1) location of implant (intracorporeal versus extracorporeal), (2) implantation approach (percutaneous versus surgical), (3) flow characteristics (pulsatile versus continuous), (4) pump mechanism (volume displacement, axial, centrifugal), and (5) ventricle supported (left, right, both).

Transthoracic echocardiography (TTE) is the noninvasive imaging modality of choice for the assessment of patients with continuous-flow (CF) LVADs. The purpose of this chapter is to focus on the echocardiographic imaging recommendations for CF LVADs. Most of the data supporting the use of echocardiography in these patients come from the experience with axial-flow pumps (HeartMate II), which are described in more detail later.

The Left Ventricular Assist Device

Three types of CF LVADs are currently approved for implantation in the United States: the Heartmate II (Abbott Laboratories), which houses an axial-based pump, and the HeartWare (Medtronic) and HeartMate III, both of which house a centrifugal-based pump. CF LVADs have been shown to have improved device performance and patient survival profiles compared with the earlier pulsatile-flow devices. The axial pump generates flow parallel to the axis of rotor or impeller rotation using a propeller in pipe mechanism while the centrifugal pump generates flow perpendicular to the axis of rotation with a spinning bladed disk. Studies based on two-dimensional (2D) and three-dimensional (3D) echocardiographic measurements have shown that the HeartWare Ventricular Assist System (HVAD) results in less of a reduction in LV chamber diameter and 3D volumes with increasing pump speed compared with the Heart Mate II pump. Both pumps, however, have been shown to provide similar overall flows in the normal working range of speed so that the differential shape changes seen in these studies during unloading may be attributable to the location of the pumps in the thorax. The HeartMate II pump is located subdiaphragmatically, likely resulting in inferior displacement of the LV apex because of the pull of the inflow cannula. In contrast, the HVAD and HeartMate III pumps are inserted intrathoracically at the LV apex, resulting in less distortion of the LV apex ( Fig. 175.2 ). LVADs can be used as (1) a bridge to cardiac transplantation, (2) a bridge to cardiac transplant candidacy, 3) a bridge to recovery, and (4) destination therapy.