11 Intraoperative Echocardiography for Heart and Lung Transplantation
Background
• Heart, lung, and heart-lung transplantation have become well-established therapies for suitable patients with end-stage cardiac and pulmonary disease. There are currently over 200 centers performing heart transplants and over 120 centers performing lung transplants worldwide who report their results to the International Society for Heart and Lung Transplantation.
• This chapter provides an overview of intraoperative echocardiography for donor heart retrieval procedures, heart transplants, and lung transplants. Fewer than 100 heart-lung transplants are currently performed worldwide each year. The principles of echocardiography described in this chapter can be applied to heart-lung transplantation, but the technique is not specifically discussed further.
• In most transplant centers, echocardiography is used routinely throughout the perioperative period for patients undergoing heart or lung transplantation.
• Transesophageal echocardiography (TEE) is used intraoperatively for both diagnosis and monitoring.
• In particular, echocardiographic assessment of the right ventricle (RV) is of fundamental importance during both heart and lung transplant procedures because both procedures impose risks of acute right ventricular (RV) failure.
• TEE is used both to detect changes in RV function and to monitor therapy instituted to reverse RV dysfunction.
• In the intraoperative setting, most RV assessment is qualitative. Owing to the complex geometry of the RV, and with rapid changes in RV volumes and function occurring during transplant procedures, quantitative assessment of RV function is difficult.
Heart Transplant: Donor Echocardiography
Overview of Echocardiographic Approach
• A baseline transesophageal echocardiography (TTE) study is usually undertaken as part of donor assessment.
Anatomic Imaging and Physiologic Data: Acquisition, Analysis, and Pitfalls
• Baseline echocardiogram as part of donor assessment
• Typically, a TTE study is undertaken with emphasis on the assessment of global and segmental left ventricular (LV) function, LV wall thickness, RV function, and valvular function.
• Because the donor is intubated and ventilated, TTE image quality may be suboptimal and some views may be unobtainable.
• LV size and function: Current consensus guidelines suggest that a heart is not suitable for transplantation if there are echocardiographic findings of discrete wall motion abnormalities, a left ventricular ejection fraction (LVEF) less than 40% despite optimization of hemodynamics with inotropes, or severe LV hypertrophy.
• Valvular function. Ideally, no significant valve lesions should be present. Bench repair before implantation of diseased mitral valves and repair or replacement of donor aortic valves have been reported. A normally functioning bicuspid aortic valve is not a contraindication to transplantation. As discussed later, some centers routinely perform bench tricuspid valve (TV) annuloplasty during heart transplant procedures.
• TEE use during the organ retrieval procedure
• Use of TEE can aid decision making if there is doubt about the suitability of the heart for retrieval (e.g., in the setting of borderline LV function or an increase in vasopressor/inotrope therapy during the interval between acceptance as a suitable heart for retrieval and before commencement of the retrieval operation).
• Compared with TTE, TEE may provide better images and more clearly define anatomy (e.g., if there is doubt about the severity or mechanism of a valvular lesion).
• Monitoring with TEE is useful to assist with optimizing hemodynamic management during the retrieval procedure by assisting with fluid management (e.g., assessing changes in LV end-diastolic area in response to fluid administration) and assessing the response of LV and RV function to changes in inotrope doses.
• If TEE is used, it is also important to assess the donor heart for the presence of a patent foramen ovale (PFO) (see later) and common congenital problems such as atrial septal defect (ASD) or persistent left superior vena cava (SVC).
• At the author’s institution, a cardiac anesthesiologist is part of the retrieval team. When there is any doubt about the suitability of the donor heart for transplantation, a portable echocardiography machine and TEE probe are taken on the retrieval and a TEE study is performed before commencing the retrieval procedure. TEE findings are taken into consideration when the final assessment of suitability of the heart for retrieval is made.
• Results of echocardiograms undertaken on the donor heart should be communicated to the implanting team, with particular emphasis on global and segmental LV function, RV function, significant valvular lesions, and the presence of a PFO.
Heart Transplant: Recipient Echocardiography
Background
• During the surgical procedure, recipient cardiectomy is followed by implantation of the allograft.
• Typically, bicaval venous cannulation and distal ascending aortic cannulation, just proximal to the origin of the innominate artery, are established, following which cardiopulmonary bypass (CPB) is initiated.
• The most common surgical technique used for implantation is the bicaval anastomotic technique. The right atrium (RA) is completely excised. A cuff of left atrium (LA) and lengths of SVC and inferior vena cava (IVC) from the native heart and great vessels are left in situ. The native aorta and pulmonary artery (PA) are divided, and cardiectomy is then completed.
• The allograft LA is anastomosed to the remaining recipient left atrial (LA) cuff. End-to-end anastomoses of the IVC and SVC are performed followed by an end-to-end PA anastomosis. Finally, the aortic anastomosis is performed.
Overview of the Echocardiographic Approach
Anatomic Imaging and Physiologic Data: Acquisition, Analysis, and Pitfalls
Before Cardiopulmonary Bypass
• A limited amount of useful information is obtained with the pre-CPB TEE.
Step 1: Image the left atrial appendage (LAA) and the LV apex and examine for thrombus
• Findings that increase the likelihood of thrombus include the presence of an enlarged LA, atrial fibrillation, the presence of spontaneous echo contrast in the LA and LAA, and low pulsed wave (PW) Doppler velocities in the LAA (e.g., <20 cm/s sampled 1 cm from the orifice of the LAA).
• The presence of significant mitral regurgitation (MR) tends to lessen the likelihood of thrombus in the LAA. Pectinate muscles may be confused with LAA thrombus.
• Because the heart is often dilated in patients undergoing heart transplantation, imaging of the LV apex may be suboptimal. The probe frequency should be reduced to optimize ultrasound beam penetration.
• In patients with a left ventricular assist device (LVAD) in situ, the area around the inflow cannula in the LV apex should be assessed for thrombus, and inflow cannula velocities should be measured. Elevated velocities on spectral Doppler imaging may indicate partial inflow obstruction by thrombus. Epicardial echocardiography may be used to image the inflow cannula if TEE views are suboptimal.
Step 2: Image the aorta for the presence of atheroma, especially in older patients
• TEE and surgical digital palpation are of limited value for assessing the ascending aorta. Epiaortic ultrasound can be used to locate aortic cannulation and cross-clamp sites that are free of atheroma.
Weaning from Cardiopulmonary Bypass and after Cardiopulmonary Bypass
• Once the heart is filled and ejection is established, an assessment of the adequacy of deairing, LV and RV systolic function, and valvular function should be made before separation from CPB.
• After separation from CPB, a complete TEE examination should be performed with focus on the assessment of systolic LV and RV function, valvular function, and an assessment of the atrial septum and the surgical anastomoses.
• Primary graft dysfunction may be a result of LV, RV, or biventricular dysfunction. RV dysfunction is the most common cause.
• In the presence of significant primary graft dysfunction, TEE is helpful to assess changes in ventricular function in response to medical therapy (e.g., inotropes or pulmonary vasodilators), and to assist with positioning of mechanical support devices (e.g., IABP, right ventricular assist device [RVAD] or LVAD, or venoarterial extracorporeal membrane oxygenation [ECMO]), should they prove necessary.
• It may be necessary to use nonstandard transducer rotation to obtain standard two-dimensional (2D) echocardiography views.
Step 1: Assess for Deairing
• Before weaning from CPB, there is often a significant amount of air present on the left side of the heart.
• Typical sites of accumulation include the pulmonary veins, atrial septum, the LAA, the midapical ventricular septum, and the LV apex.
• Although TEE is very sensitive for detecting air, it is difficult to adequately detect air until the heart is full and LV ejection is established.
Step 2: Assess Left Ventricular Function
• An assessment of global and segmental LV function should be made utilizing the ME and transgastric (TG) LV views. Diastolic function should be assessed using PW Doppler of mitral inflow velocities, pulmonary vein velocities, and mitral annular tissue Doppler imaging. In addition, LV wall thickness should be assessed.
• LV systolic function and assessment of LV preload.
• Although LV systolic function is often assessed subjectively, it is helpful to measure fractional area change or formal LVEF to allow comparisons over time (see Chapter 6).
• LV systolic function may be impaired in the immediate post-CPB period owing to the effects of brain death on the allograft as well as the effects of imperfect myocardial preservation. This should improve over the hours after implant.
• Serial visual assessments and measurements such as LV end-diastolic area, measured in the TG mid short axis (SAX) view, can be used to assess LV preload to help guide fluid administration and titrate vasoactive medications.
• Segmental wall motion abnormalities.
• As is common in post-CPB assessments, particularly in the presence of ventricular pacing, a “flat” ventricular septum or paradoxical ventricular septal motion is often seen. If abnormal septal motion is present, careful assessment of RV function should be undertaken to exclude RV dysfunction as the cause of the abnormal septal motion.
Step 3: Assess Right Ventricular Function
• A thorough initial assessment of RV systolic function should be made and then ongoing serial assessments should be made as necessary in response to changes in the clinical state of the patient.
• Typically, qualitative assessment is made via visual assessments of ME RV views. Quantitative imaging may be useful if time allows.
