Heart transplantation
Assessment of potential recipients
Echocardiography forms an integral part of the assessment of patients with end-stage heart failure who are being considered for cardiac transplantation Echocardiography provides information on systolic and diastolic ventricular function, cardiac output, pulmonary arterial pressure, valvular function, and the presence of an intracardiac thrombus or a patent foramen ovale (PFO). Under most circumstances, assessment with transthoracic echocardiography (TTE) is adequate. Transesophageal echocardiography (TEE) assessment is occasionally required when transthoracic views are inadequate or when magnetic resonance imaging is contraindicated, such as in patients with a pacemaker or an implantable cardioverter defibrillator.
End-stage ischemic heart disease and dilated cardiomyopathy are the most common indications for heart transplantation. Patients with these conditions frequently also have mitral and tricuspid regurgitation, pulmonary hypertension, and pleural effusions, which can be also readily assessed with echocardiography.
Assessment of the donor heart before organ retrieval
Echocardiography to assess the function of the donor heart is a critical part of assessment of suitability for transplantation. A careful assessment of valvular function, left and right ventricular function, and segmental wall motion abnormalities (SWMAs) is indicated, taking into account intravascular volume status and inotropic therapy. Because donors are intubated and invasively ventilated, TEE is the examination of choice. TEE is more likely to result in a complete assessment than TTE but also results in more abnormal studies. Appropriate interpretation of ventricular function in potential donors requires an operator experienced in performing echocardiograms in the setting of brainstem death. For this reason, there is an advantage in the retrieval team taking a portable TEE machine during the retrieval and performing an echocardiogram themselves.
Ventricular function
Left ventricular (LV) dysfunction is the most common reason for not using a potential donor heart. SWMAs are common in patients with intracranial pathology and brainstem death, occurring in 20% to 42% of cases. SWMAs often involve multiple coronary artery territories, usually without associated coronary artery disease. Apical LV function is often preserved, possibly due to the lower number of sympathetic nerve endings in that region. LV dysfunction seen on echocardiography in patients with brainstem death does not correspond to any pathologic abnormality on postmortem examination, and even donor hearts with severe SWMAs may improve rapidly following transplantation. Thus, the presence of multiple wall motion abnormalities in an otherwise eligible donor should not be a contraindication to donation. Dobutamine stress echocardiography may be useful to help distinguish those patients with transient abnormalities of function (in whom SWMAs resolve with dobutamine) from those with fixed impairment, although this is not usually done in clinical practice. Biomarkers such as an elevated troponin and B-type natriuretic peptide are of uncertain clinical utility. Intensive donor management with fluid and inotrope titration over several hours results in improved cardiac function (detected by sequential echocardiography) in more than 75% of donors.
LV hypertrophy is another common finding in donor hearts assessed for transplantation. Although LV hypertrophy resolves in most cases, an LV wall thickness of 1.4 cm is associated with a lower long-term survival and a higher incidence of allograft vasculopathy. As hypovolemia can cause “pseudohypertrophy” (see Chapter 19 ), care should be taken to ensure that LV wall thickness is assessed when the donor is euvolemic. Careful assessment of right-heart function is also important, as right ventricular (RV) dysfunction can be masked by tricuspid regurgitation.
Valvular abnormalities
The most common valvular abnormality found in donor hearts pretransplantation is mitral regurgitation. Mild central mitral regurgitation in an anatomically normal valve should not be a contraindication to donation. In one study, 12 of 16 (75%) cases of mitral regurgitation identified pretransplant had fully resolved at long-term follow-up. If structural abnormalities of the mitral leaflets are identified in the donor, bench repair of the mitral valve (MV) may be performed before transplantation.
Although tricuspid regurgitation is uncommon pretransplant, it is the most common post-transplant valvular abnormality. Prophylactic tricuspid valve repair results in lower long-term cardiac-related mortality and a lower incidence of new tricuspid regurgitation. Given this, the presence of significant tricuspid regurgitation in a pretransplant echocardiogram should not be an absolute contraindication to donation.
Patent foramen ovale
A careful examination for the presence of a PFO (see Chapter 14 ) should be performed. Although a PFO or small atrial septal defect (ASD) is not a contraindication to transplantation, it is useful information to have should ventricular function deteriorate and mechanical circulatory support be required (see Chapter 16 ).
Assessment of the recipient’s native heart before cardiopulmonary bypass
The severity of pulmonary hypertension should be evaluated by Doppler interrogation of the tricuspid regurgitant jet, as pulmonary vascular resistance (PVR) may have increased since the patient last underwent an echocardiogram or right-heart catheter study. The presence and severity of aortic atheroma should be assessed in case an intra-aortic balloon pump (IABP) is required postoperatively. Finally, the presence of pleural effusions should be noted, as these can be drained during surgery. More detailed examination of the native heart is not warranted.
Assessment of cardiac function immediately after transplantation
Before separation from cardiopulmonary bypass (CPB), with the heart ejecting and filled, the adequacy of deairing, ventricular function, and the presence of any gross valvular abnormalities should be assessed. Once the patient has separated from CPB, a complete examination of the heart should be performed, including an assessment of preload, systolic function, diastolic function, and surgical anastomoses and a quantification of any valvular abnormalities.
Left ventricular function
A degree of LV systolic dysfunction is usual early after heart transplantation due to the combined effects of brain death in the donor and poor myocardial protection during retrieval and implantation. This usually resolves over the first few hours to days following transplantation. A restrictive pattern (see Chapter 8 ) of diastolic filling is common in the early period following heart transplantation and usually persists for several weeks. A subgroup of heart transplant recipients has persistent long-term restrictive filling patterns. These patients have more heart failure symptoms and more episodes of acute rejection.
Right ventricular function
RV dysfunction is common early after transplantation due to the combined effects of brain death in the donor, poor myocardial protection during retrieval and implantation, acute-on-chronic elevated PVR in the recipient, any size mismatch between the donor and the recipient, and the potential for gas emboli to the anteriorly positioned right coronary artery. Acute RV dysfunction due to stunning or gas embolism usually presents at the time of separation from CPB and resolves over minutes to hours. Chest closure can precipitate severe hypotension due to RV compression, so it is useful to keep the TEE probe in situ until after this time. RV failure may also develop a few hours after surgery due to an acute (on chronic) increase in PVR (e.g., due to atelectasis, fluid overload, or acute lung injury resulting from the systemic inflammatory response syndrome).
Atrial anastomoses and pulmonary veins
The left atrial (LA) suture line may appear as an echodense ridge in the atrium ( Figure 15-1 ). The left atrium may have an “hourglass” shape and have an increased longitudinal dimension. Residual native atrial tissue can create the appearance of an unusual echo-free space behind the heart or give the impression of an inverted LA appendage. If the LA suture line is too tight, it can result in acquired cor triatriatum and a midatrial stenosis.
The right atrial (RA) suture line is not often seen, particularly with the current “bicaval technique,” in which the anastomosis is performed at the level of the vena cavae (as opposed to the older “biatrial technique,” in which a cuff of native right atrium is anastomosed to the donor right atrium).
The pulmonary veins should be interrogated with color and spectral Doppler to ensure there is no obstruction to flow. However, this complication is less likely than following lung transplantation.
Assessment of early hemodynamic instability
Common causes of hemodynamic instability early after cardiac transplantation are hypovolemia, vasoplegia, LV and RV dysfunction, and cardiac tamponade.
Because the donor heart is placed in a large pericardial sac, a relatively large volume of blood is able to be accommodated for the same degree of cardiac compression compared with other types of cardiac surgery. However, this is offset by the bleeding that is common following heart transplantation. Furthermore, early in the postoperative period, ventricular function is typically impaired; therefore, the heart is very sensitive to the compressive effects of pericardial blood. Bleeding from the LA suture line may cause regional tamponade behind the left atrium (see Figure 19-7 ).
In one study of 88 patients after heart transplantation, 31 developed moderate or large pericardial fluid collections and 3 developed cardiac tamponade requiring immediate intervention. All other pericardial effusions resolved spontaneously within 3 months.
Late assessment following cardiac transplantation
Pericardial fluid collections
Chronic pericardial effusions are common in patients following heart transplantation and may indicate acute rejection. In one study of 264 consecutive heart transplants, pericardial effusions were present in 26% of patients in whom there was no biopsy evidence of acute rejection but present in 49% of patients with biopsy-proven acute rejection.
Cardiac tamponade may complicate endomyocardial biopsy and should always be considered in patients who develop hemodynamic instability following this procedure.
Tricuspid regurgitation
Tricuspid regurgitation is common following heart transplantation. In one study, “clinically significant” tricuspid regurgitation was present in 36% of patients assessed beyond 1 year after transplant. In an earlier study by the same authors, moderate or severe tricuspid regurgitation was identified in 17% of patients assessed beyond 1 year after transplant.
Tricuspid regurgitation that occurs early (days to weeks) after heart transplant is often due to elevated PVR or fluid overload. Tricuspid regurgitation that occurs later (weeks to months) may indicate acute rejection or valvular injury from endomyocardial biopsy. The incidence of tricuspid regurgitation is also influenced by surgical technique, occurring less with the newer bicaval anastomosis technique than with the older biatrial technique (described earlier).
Regardless of the cause, persistent moderate or severe tricuspid regurgitation is associated with adverse outcome (RV failure, renal impairment, and reduced functional status) and increased mortality. Significantly decreased survival has been shown for patients with moderate or severe tricuspid regurgitation detected by intraoperative TEE.
Acute rejection
All patients undergo regular endomyocardial biopsies to diagnose acute rejection, with the first biopsy usually performed 2 weeks after transplantation. In the early stages of acute rejection, patients typically are asymptomatic and have normal LV systolic function. Indices of diastolic function are frequently abnormal, with a short isovolumetric relaxation time (IVRT) and a short E wave deceleration time (i.e., a restrictive pattern) being characteristic. However, these patterns lack sufficient sensitivity to be clinically useful for diagnosing acute rejection.
Other echocardiographic abnormalities that may be seen in acute rejection include pericardial effusions, valvular regurgitation, and ventricular hypertrophy and dilation.
Detection of cardiac allograft vasculopathy (chronic rejection)
The primary cause of long-term mortality in cardiac transplant recipients is allograft vasculopathy. This typically presents late, and coronary angiography is insensitive for the detection of clinically significant disease. The presence of a new SWMAs is specific for coronary vasculopathy and is predictive of mortality.
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