Malpositioned Left Ventricular Assist Device Cannula: Diagnosis and Management with Transesophageal Echocardiography Guidance

Abstract

A 72-yr-old man was transferred from an outside hospital with a diagnosis of ventricular assist device (VAD) malfunction. The patient had initially experienced cardiogenic shock after an acute myocardial infarction a year ago, for which a temporary VAD had been placed (Abiomed BVS 5000, Abiomed, Danvers, MA), and the patient was transferred to our institution. He was considered to be a poor transplant candidate and the Abiomed device was replaced with an implantable, pulsatile, Heartmate XVE Left Ventricular Assist System (Thoratec, Pleasanton, CA) as destination therapy. At the present admission, the patient described “grinding noises” and temporary pump stoppages and it was determined that his device would need to be replaced. His medical history was also significant for chronic renal insufficiency, degenerative joint disease, gout, hypertension, and a cerebrovascular accident in 1990. The patient was taken to the operating room for the VAD exchange, which was complicated by an innominate vein injury requiring emergent institution of cardiopulmonary bypass (CPB). A new VAD inflow cannula was placed in the apex of the left ventricle (LV) through the preexisting sewing ring and the malfunctioning device was replaced with an identical one. The outflow graft was not replaced. CPB was discontinued uneventfully. During the immediate post-CPB period, VAD flows decreased unexpectedly. Transesophageal echocardiography (TEE) showed anteroseptal angulation and turbulent flow due to the inflow VAD cannula positioned against the interventricular septum (Fig. 1, please see video clips available at www.anesthesia-analgesia.org). Under TEE guidance, the cannula was repositioned and normal flows reestablished. Subsequent TEE images showed proper VAD inflow cannula position with appropriate color flow pattern (Fig. 2, please see video clip available at www.anesthesia-analgesia.org).Figure 1.: Midesophageal four-chamber long axis transesophageal echocardiography view showing a ventricular assist device inflow cannula angulated towards the anteroseptal wall. Turbulent flow through the cannula tip can be seen in the color flow Doppler window.Figure 2.: Same view as in Figure 1 after inflow cannula repositioning. The cannula can be seen with nonturbulent, laminar flow by color flow Doppler and appropriate decompression of the left ventricular chamber.DISCUSSION Throughout the years, as the use of VADs has become more prevalent, TEE has been demonstrated to be an invaluable tool in this setting for preoperative assessment and patient selection, intraoperative VAD function assessment, and cannula position, as well as for the postoperative differential diagnosis of device malfunction (Table 1) (2,3). Although systemic circulation is most commonly supported with a LV assisted device (LVAD), biventricular failure mandates the placement of a right ventricular assist device along with a LVAD.Table 1: Important Considerations During Perioperative TEE Examination in Patients Undergoing VAD ImplantationBefore implantation, TEE is essential in diagnosing 1) intracardiac shunts, such as patent foramen ovale, atrial, or ventricular septal defects, which can lead to a right-left shunt with systemic hypoxemia or paradoxical emboli, 2) atrial septal aneurysm, which can obstruct the VAD inflow cannula in case of atrial placement of the VAD inflow cannula for preservation of the ventricle, 3) mitral stenosis, which impedes VAD filling by restricting LV inflow, 4) intracavitary thrombi, especially in the LV apex and in the left atrial appendage, 5) aortic valve (pulmonic valve in the case of a right ventricular assist device) insufficiency, which results in an inefficient cycle of blood flow from the aortic cannula being shunted back through the incompetent aortic valve into the VAD inflow cannula, 6) evaluation of ascending aorta for aneurismal dilatations or atheroma, and 7) evaluation of right ventricle (RV) function as an adequate LVAD flow depends on adequate flow generated by the RV (3,4). After placement, it is important to ensure proper positioning of the VAD cannula at the LV apex. TEE is also valuable during deairing of the heart before VAD activation. Appropriate unidirectional low-velocity flow can be detected through the inflow and outflow cannula using color Doppler and pulsed wave Doppler with peak velocities ranging usually from 1.0 to 2.0 m/s (4). RV geometry can be considerably altered by the presence of a decompressed LV, leading to RV failure. This situation may especially arise during hypovolemia with nonpulsatile, axial flow pumps when the VAD inflow cannula may get obstructed by a suction effect on the interventricular septum. Previous case reports suggest that VAD cannula malpositioning is not uncommon and can have dramatic consequences (2,5,6). In our case, TEE helped to differentiate among different causes of decreased VAD flows such as RV failure, pericardial effusion or hematoma compressing the right atrium or the RV, hypovolemia, obstruction of the outflow cannula or of the inflow cannula or malpositioning of the cannulas. These images demonstrate the appearance and Doppler color flow pattern of an obstructed and an appropriately positioned VAD cannula. Intraoperative TEE can be a valuable tool for assessment of complications and management of malpositioned VAD cannulae.