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.
Heart Transplant: Donor Echocardiography
Overview of Echocardiographic Approach
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.
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.
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.
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.
• 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.
• Echocardiographic manifestations of acute RV impairment are outlined in Box 11-2. In the setting of acute RV impairment, TEE should be used to assess changes in RV function in response to therapeutic maneuvers.
• In the presence of significant tricuspid regurgitation (TR), RV function may appear less impaired than it actually is (i.e., significant TR “flatters” the RV).
• RV compression resulting in significant worsening of RV function can result from chest closure, particularly in the setting of myocardial edema or lung dysfunction requiring high levels of positive end-expiratory pressure. It is the author’s practice to leave the TEE probe in situ after the chest is closed to reassess RV function.
Box 11-1 Potential Etiologies of Right Ventricular Impairment during Separation from Cardiopulmonary Bypass and the Early Post-Cardiopulmonary Bypass Period in Heart Transplant Patients
Step 4: Assess Valvular Function
• Standard 2D and color flow Doppler imaging of the valves should be undertaken. In the presence of abnormalities, the mechanism should be ascertained.
• TR
• MR
• Trivial or mild MR is often seen and may be related to being present in the donor heart, to changes in LA geometry at implantation, or to transient segmental wall motion abnormalities affecting the inferior LV wall.
• In the presence of significant MR, ascertaining the mechanism is important because surgical intervention may be appropriate.
Step 5: Assess the Atria
• The LA often appears enlarged, with an “hourglass” shape and an echo-dense, suture line ridge across the mid part of the atrium (Figure 11-2). If the ridge is mobile or pedunculated, LA thrombus should be considered.
• Excessive donor atrial tissue, if present, can prolapse and cause an acquired cor triatriatum which can, rarely, lead to obstruction to mitral valve inflow.
Step 6: Assess the Caval Anastomoses
Step 7: Assess the Pulmonary Veins
Step 8: Assess the Pulmonary Artery and Aorta
• The PA anastomosis is best assessed using 2D, color flow, and spectral Doppler imaging in the ME ascending aortic SAX view or the upper esophageal aortic arch SAX view. Epicardial echocardiography can be used if these views are suboptimal.
• Redundancy in the PA at the anastomosis can lead to kinking of the vessel, causing obstruction to RV outflow and RV failure. With TEE, distortion can be visualized on 2D imaging. In addition, there is turbulence on color flow Doppler imaging and elevated velocities with spectral Doppler imaging (Figure 11-3).
Step 9: Check for Patent Foramen Ovale
• The atrial septum should be assessed for the presence of a PFO, even if no PFO was found during the donor retrieval procedure.
• Elevated right-sided pressures after implantation, which is common, can result in right-to-left shunting across a previously undetected PFO and contribute to hypoxia.
• In addition, should ventricular function deteriorate and LVAD implantation be required, it is important to know if a PFO is present.
Key Points Post-Cardiopulmonary Bypass Transesophageal Echocardiography Assessment during Heart Transplant
• If primary graft dysfunction occurs, the most common manifestation is acute RV failure. LV failure and biventricular failure both occur but are less common.
• The most common valvular abnormality is functional TR, which can range from mild (common) to severe (uncommon). Prophylactic TV annuloplasty is performed at some transplant centers.
Lung Transplant: Recipient Echocardiography
Background
• Lung transplant procedures may be single or bilateral.
• Single lung transplants (SLTs) are undertaken via a lateral thoracotomy with a pneumonectomy then implantation of the lung allograft with anastomoses at the proximal main bronchus, pulmonary veins, and proximal PA.
• Use of CPB varies depending on the transplant center. Some use CPB routinely, others rarely.
• Patients undergoing lung transplantation usually have minimal cardiopulmonary reserve.
• Depending on their underlying disease, they usually have at least some degree of pulmonary hypertension and RV impairment.
Overview of Echocardiographic Approach
• In the absence of contraindications, TEE is commonly used during BLT procedures, and sometimes in SLT procedures to monitor cardiac function and to evaluate surgical anastomoses. At the author’s institution, TEE is used routinely for all lung transplant procedures.
Anatomic Imaging and Physiologic Data
Acquisition, Analysis, and Pitfalls: Initial Assessment after Anesthetic Induction
• Time and clinical condition of the patient permitting, a complete baseline TEE study with 2D, color, and spectral Doppler imaging is performed.
• It is particularly important to image and assess the following:
• RV
• Valvular function
• A baseline assessment of valvular function, particularly of the tricuspid valve, should be performed.
• Atrial septum
• Normally, the septum bows toward the RA, expect for a brief reversal during midsystole when it transiently bows toward the LA.
• In those patients with elevated RA pressure or significant TR, the septum typically bows toward the LA throughout the cardiac cycle.
• The presence of a PFO should be sought with color flow Doppler imaging and (sometimes) a contrast study using agitated saline.
• Color flow Doppler images should be assessed with the Nyquist limit at 50 to 60 cm/s, and also at 20 to 30 cm/s if no flow across the septum is seen at 50 to 60 cm/s. It is the practice of the authors to complete a contrast study using agitated saline if no PFO is present with color flow Doppler imaging.
Acquisition, Analysis and Pitfalls: Native Lung Explant and Allograft Implant (No Cardiopulmonary Bypass)
• To assess RV function, the ME four-chamber view, with the probe turned to the right to optimize images of the RV, is generally the most useful view.
• One-lung ventilation and especially clamping of the PA tends to increase RV afterload, which may lead to acute RV failure (see Box 11-2).
• TEE should be used to assess deairing when PA anastomoses are unclamped.
• After allograft implantation, the pulmonary venous and PA anastomoses should be examined.
• Figure 11-5 shows the relationship between the LA cuff and the pulmonary veins, both from the donor organ.
• It is important to undertake a detailed assessment of the pulmonary veins because stenotic pulmonary vein anastomoses can result in venous hypertension in the lung draining toward the stenosed vein causing pulmonary edema, primary graft dysfunction, and potentially, pulmonary infarction.
• The pulmonary veins should be examined with 2D and color Doppler imaging, and velocities should be recorded using PW and, if necessary, continuous wave (CW) Doppler (Figure 11-6).
• It is not possible to state 2D diameters that are acceptable, but a value greater than 5 mm appears to be acceptable, and measurements of less than 2.5 mm have a high frequency of clinical sequelae.
• It is not uncommon in lung transplant patients to have flows of up to 120 cm/s or even higher without any clinical sequelae. However with narrowed veins, turbulent flow, and high velocities in the setting of clinical problems, surgical revision may be necessary.
• Pulmonary vein thrombosis has also been reported to occur. Thrombi ranged from nonocclusive, mobile thrombi to occlusive thrombi. Although typically seen on 2D imaging, they may be associated with elevated flow velocities.
• Epicardial echocardiography can be used to assess pulmonary vein anastomoses when TEE imaging has been suboptimal.
• The right PA anastomosis can usually be visualized with TEE, but the left is often not seen.
• The ME ascending aortic SAX view (with gentle anteflexion of the transducer) usually provides the best view of the right PA (Figure 11-7).
• Before chest closure, LV filling and systolic function, RV function, and TR severity should be reassessed.
• The pleural spaces and pericardial space should be assessed to ensure there are no fluid collections amenable to surgical drainage.
• It is also the authors routine practice to reassess RV function and TR after the chest is closed, particularly in patients with prior RV dysfunction, because there is sometimes a tamponade effect from chest closure (especially if the implanted lungs are a large size relative to the patient’s chest cavity), resulting in deterioration of RV function.
• In the presence of increased preoperative pulmonary vascular resistance and RV hypertrophy, post implantation right ventricular outflow tract obstruction may occur. This is a result of the now normalized pulmonary vascular resistance and is accentuated by hypovolemia (Figure 11-8).
Figure 11-5 The donor lung. The white arrows show the orifices of the pulmonary veins surrounded by the LA cuff.
Key Points Transesophageal Echocardiography Assessment Post-Implantation Lung Transplant
• RV function. Sequential assessment is important. Reassess after chest closure because RV function can deteriorate.
• Anastomoses (Figure 11-9)
• Pulmonary veins: evaluate left- and right-sided veins after reperfusion (after both lungs are reperfused in BLT). Assess dimensions (2D imaging) and flow patterns (color flow and spectral Doppler) to rule out obstruction. Echocardiographic signs of obstruction include narrow vessel diameter on 2D imaging (e.g., <0.5 cm), elevated flow velocities (e.g., >100-140 cm/s), and turbulence on color flow imaging, particularly if associated with pulmonary edema.
Acquisition, Analysis, and Pitfalls: Procedure Performed with Cardiopulmonary Bypass
• The pre-bypass assessment should be undertaken as for part A discussed previously (see “Acquisition, Analysis, and Pitfalls: Initial Assessment after Anesthetic Induction”). In addition, epiaortic ultrasound may be used in older patients to assess the ascending aorta for the presence of atheroma and to select a suitable cannulation site.
• The pleural and pericardial spaces should be assessed post-CPB, because bleeding is usually more significant in patients whose procedure is undertaken utilizing CPB. The pericardium may be left open, in which case, bleeding will tend to accumulate in the pleural cavities.
1 Stehlik J, Edwards LB, Kucheryavaya AY, et al. The Registry of the International Society for Heart and Lung Transplantation: Twenty-seventh official adult heart transplant report—2010. J Heart Lung Transplant. 2010;29:1089-1103.
2 Christie JD, Edwards LB, Kucheryavaya AY, et al. The Registry of the International Society for Heart and Lung Transplantation: Twenty-seventh official adult lung and heart-lung transplant report—2010. J Heart Lung Transplant. 2010;29:1104-1118.
3 Venkateswaran RV, Townend JN, Wilson IC, et al. Echocardiography in the potential heart donor. Transplantation. 2010;89:894-901.
Excellent review of what to look for in assessing a donor heart for transplant suitability.
4 Asante-Korang A. Echocardiographic evaluation before and after cardiac transplantation. Cardiol Young. 2004;14(Suppl 1):88-92.
5 Romano P, Mangion JM. The role of intraoperative transesophageal echocardiography in heart. Echocardiography. 2002;19:599-604.
Two nice reviews of what to look for in children and adults after cardiac transplantation.
6 Chumnanvej S, Wood MJ, MacGillivray TE, Melo MF. Perioperative echocardiographic examination for ventricular assist device implantation. Anesth Analg. 2007;105:583-601.
7 Augoustides JG. Perioperative echocardiographic assessment of left ventricular assist device implantation: Additional causes of inflow cannula obstruction. Anesth Analg. 2008;106:673-674.
Two nice reviews of the specifics in the examination of patients with assist devices.
8 Michel-Cherqui M, Brusset A, Liu N, et al. Intraoperative transesophageal echocardiographic assessment of vascular anastomoses in lung transplantation. A report on 18 cases. Chest. 1997;111:1229-1235.
9 Huang YC, Cheng YJ, Lin YH, et al. Graft failure caused by pulmonary venous obstruction diagnosed by intraoperative transesophageal echocardiography during lung transplantation. Anesth Analg. 2000;91:558-560.
10 Myles PS, Marasco S. Misleading turbulent flow through pulmonary venous anastomoses during lung transplantation. Anesth Analg. 2008;107:1504-1505.
11 McIlroy DR, Sesto AC, Buckland MR. Pulmonary vein thrombosis, lung transplantation, and intraoperative transesophageal echocardiography. J Cardiothorac Vasc Anesth. 2006;20:712-715.
