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DOI: 10.1148/rg.275065107
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RadioGraphics 2007;27:1297-1309
© RSNA, 2007

EDUCATION EXHIBIT

Cardiac CT of the Transplanted Heart: Indications, Technique, Appearance, and Complications1

Naama R. Bogot, MD, Ronen Durst, MD, Dorith Shaham, MD, and Dan Admon, MD

1 From the Departments of Radiology (N.R.B., D.S.) and Cardiology (R.D., D.A.), Hadassah–Hebrew University Medical Center, POB 12000, Jerusalem 91120, Israel. Presented as an education exhibit at the 2005 RSNA Annual Meeting. Received May 30, 2006; revision requested January 9, 2007, and received February 5; accepted February 8. Supported in part by a grant from Hadassah–Hebrew University Medical Center. All authors have no financial relationships to disclose. Address correspondence to N.R.B. (e-mail: naamab{at}hadassah.org.il).


   Abstract
Top
 Abstract
LEARNING OBJECTIVES FOR TEST...
 Introduction
 CT of the Transplanted...
 Conclusions
 References
 
Effective antirejection therapy and infection control have significantly improved the long-term survival of heart transplant recipients, but coronary allograft vasculopathy remains an important limiting factor. Most heart transplant recipients undergo annual coronary angiography for the detection of allograft vasculopathy, which is often clinically silent. Angiography allows detection of vasculopathy only indirectly, with depiction of the lumen, and does not depict the wall thickening and intimal hyperplasia that typify this disease; the procedure also is invasive and is associated with a 1%–2% risk of complication. In contrast, electrocardiographically gated multidetector computed tomography (CT) can provide a comprehensive and noninvasive evaluation of the transplanted heart in a single study. Cardiac CT enables evaluation of the coronary artery lumen and wall and thus may be used for screening, diagnosis, grading, and follow-up of coronary allograft vasculopathy. It also may be used to detect other posttransplantation complications, such as malignancy and infection, and to assess cardiac and vascular anastomoses and cardiac function. However, special strategies may be needed to reduce the transplant heart rate so as to obtain images of diagnostic quality.

© RSNA, 2007


   LEARNING OBJECTIVES FOR TEST 2
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 Abstract
 LEARNING OBJECTIVES FOR TEST...
Introduction
 CT of the Transplanted...
 Conclusions
 References
 
After reading this article and taking the test, the reader will be able to:


   Introduction
Top
 Abstract
 LEARNING OBJECTIVES FOR TEST...
 Introduction
CT of the Transplanted...
 Conclusions
 References
 
In recent years, heart transplantation has evolved as the procedure of choice for end-stage heart disease. Approximately 2200 cardiac transplantations are performed in the United States and 4000 are performed worldwide each year (1–3). Advances in surgical techniques, immunosuppressive therapy, and control of infection and rejection have led to improvements in the long- and short-term survival of heart transplant recipients, with 1-year, 3-year, and 10-year survival rates exceeding 85%, 80%, and 50%, respectively (3). Assuming a 50% survival at 10 years, more than 11,000 heart transplant recipients are currently alive in the United States alone.

However, transplanted hearts are vulnerable to coronary allograft vasculopathy, a multifactorial disease that is caused partly by rejection and that manifests as accelerated arteriosclerosis (4,5). Coronary allograft vasculopathy, which is characterized by wall thickening and diffuse narrowing of the lumen, is often clinically silent in the denervated transplanted heart. In many patients, its first manifestation may be sudden death due to a catastrophic cardiac event.

To detect early-stage coronary artery lesions in transplant recipients and prevent adverse outcomes, the current standard of care is annual coronary angiography (5). However, angiography has limitations in heart transplant recipients: It does not allow direct visualization of wall thickening and intimal hyperplasia, which are characteristics of coronary allograft vasculopathy, and it has lower sensitivity than intravascular ultrasonography (US) for the detection of coronary allograft vasculopathy (6–8). However, intravascular US is invasive and is not routinely performed at annual follow-up examinations. Patients also must undergo routine repeated cardiac function evaluations (9,10). In this regard, the results of experience and many recent validating studies indicate that electrocardiographically gated multidetector computed tomography (CT) may be useful as a single noninvasive test for evaluation of the coronary arteries, heart chambers, and cardiac function, because it is capable of providing all the required diagnostic information about the transplanted heart.

The article describes the indications for performing cardiac CT in heart transplant recipients, the unique challenges of performing cardiac CT of the transplanted heart, and strategies that may be used to overcome those challenges. The typical posttransplantation appearance of the heart, including vascular anastomoses, is reviewed. The clinical manifestations, CT appearance, and standard follow-up of coronary allograft vasculopathy are described. Additional roles for cardiac CT in the evaluation of cardiac function and the diagnosis of other common complications of heart transplantation also are discussed.


   CT of the Transplanted Heart
Top
 Abstract
 LEARNING OBJECTIVES FOR TEST...
 Introduction
 CT of the Transplanted...
Conclusions
 References
 
Technological advances in multidetector CT have made it an important imaging modality for noninvasive cardiac evaluation (11,12). Multidetector CT allows visualization of the coronary artery walls and lumen (11). Therefore, it can be used for detection and characterization of the luminal narrowing and wall thickening that occur with occlusive coronary artery disease, including coronary allograft vasculopathy (13,14). CT also is useful for assessing cardiac function; it enables direct evaluation of cardiac chambers, valves, and great vessels in a single examination (15,16). Furthermore, cardiac CT enables visualization of portions of the mediastinum, lungs, pleura, and chest wall and thus may allow the detection of other transplantation-related complications, such as malignancy or infection (17).

We have found cardiac CT useful for a wide variety of indications in heart transplant recipients, including annual screening to detect coronary allograft vasculopathy; selection of patients for revascularization; evaluation of indeterminate findings on coronary artery angiograms; frequent monitoring of patients with borderline lesions at critical locations (Fig 1); patency assessment after revascularization (Fig 2); evaluation of cardiac function and wall motion; and calcium scoring. Cardiac CT may be useful also for cardiac donor evaluation before organ harvesting.


Figure 1A
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  		Figure 1a.  Coronary angiogram and corresponding CT image obtained in a 56-year-old man 12 years after transplantation. (a) Angiogram shows focal dilatation of the left main coronary artery (arrow) with an apparent dissection, a critical finding that necessitates close follow-up. (b) Baseline CT image obtained for follow-up helps confirm the presence of focal dilatation (arrow) but shows no intimal flap and thus helps exclude dissection.

 

Figure 1B
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  		Figure 1b.  Coronary angiogram and corresponding CT image obtained in a 56-year-old man 12 years after transplantation. (a) Angiogram shows focal dilatation of the left main coronary artery (arrow) with an apparent dissection, a critical finding that necessitates close follow-up. (b) Baseline CT image obtained for follow-up helps confirm the presence of focal dilatation (arrow) but shows no intimal flap and thus helps exclude dissection.

 

Figure 2
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  		Figure 2.  CT performed for stent patency assessment in an 84-year-old man 21 years after transplantation. Curved multiplanar reformatted image of the left main and left anterior descending arteries helps confirm stent patency but shows soft plaque at the distal end of the stent (arrow) and diffuse concentric wall thickening (arrowheads), features typical of coronary allograft vasculopathy.

 
CT of the transplanted heart essentially does not differ from standard cardiac CT; for the most part, comparable study protocols are used. The same principles of data acquisition apply, including low spatial resolution, high temporal resolution, and retrospective electrocardiographic gating (18).

Heart Rate Control
Cardiac CT of the transplanted heart poses a unique technical challenge. After transplantation, the heart is usually denervated and the resting heart rate typically is elevated to 80–100 beats per minute (19). To achieve sufficient image quality for reliable detection of coronary artery stenoses, the heart rate should ideally be reduced to 65 or fewer beats per minute (20,21). Images obtained at higher heart rates are often degraded by motion artifacts, which may hinder assessment of the coronary arteries, particularly the right coronary artery (Fig 3).


Figure 3A
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  		Figure 3a.  A comparison of cardiac CT images demonstrates the importance of an average heart rate of 65 beats per minute or less for obtaining images with adequate diagnostic quality. (a) Curved multiplanar reformatted image of the right coronary artery in a patient with a heart rate of 63 beats per minute demonstrates a slight irregularity at the vessel origin, a finding suggestive of coronary allograft vasculopathy. (b) Curved multiplanar reformatted image of the right coronary artery in a patient with a heart rate of 87 beats per minute does not allow accurate evaluation of the patency of a stent (arrow).

 

Figure 3B
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  		Figure 3b.  A comparison of cardiac CT images demonstrates the importance of an average heart rate of 65 beats per minute or less for obtaining images with adequate diagnostic quality. (a) Curved multiplanar reformatted image of the right coronary artery in a patient with a heart rate of 63 beats per minute demonstrates a slight irregularity at the vessel origin, a finding suggestive of coronary allograft vasculopathy. (b) Curved multiplanar reformatted image of the right coronary artery in a patient with a heart rate of 87 beats per minute does not allow accurate evaluation of the patency of a stent (arrow).

 
In the general population, premedication with ß-blockers helps reduce the heart rate and achieve improved image quality (22). However, ß-blocker pharmacodynamics are altered in the denervated transplanted heart because the medication cannot exert a direct effect through the sympathetic nervous system. As a result of denervation, the drug acts only through the humoral system, and the response to ß-blockers is decreased and delayed in heart transplant recipients (4,19).

Romeo et al reported that within 1 hour after oral administration of 100 mg of metoprolol to their patients, a heart rate of 70 or fewer beats per minute was achieved (13). However, in our experience, heart transplant recipients may need prolonged ß-blocker loading at higher doses to reduce the heart rate to an adequate level. In some cases, it may be necessary to administer either repeated 50-mg doses of metoprolol, beginning in the evening before the CT examination and continuing until a cumulative dose of 200 mg is reached, or a single intravenous dose of 50–100 mg of esmolol, a potent and fast-acting ß-blocker, immediately before CT.

Posttransplantation Cardiac Anatomy and CT Appearance
To avoid mistaking normal anatomy for a pathologic entity, radiologists must be familiar with the full range of normal cardiac appearances after transplantation. Orthotopic cardiac transplantation, the surgical technique of choice, involves replacement of the recipient’s heart with a healthy donor allograft. The recipient’s heart is removed through a median sternotomy, and cuffs of the ascending aorta and pulmonary artery are left in place. Atrial anastomoses traditionally have been created by using the Lower and Shumway technique (biatrial anastomosis) (Fig 4) (23). With this technique, the posterior halves of the recipient’s left and right atria are retained, and anastomoses with the anterior parts of the donor’s atria are created; thus, the normal atrial anatomy is not preserved. Enlargement of the left atrium is a normal posttransplantation appearance and must not be mistaken for abnormal atrial dilatation (Fig 5).


Figure 4
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  		Figure 4.  Schema of orthotopic cardiac transplantation with the Lower and Shumway technique shows the intraoperative appearance of the native and donor hearts before the creation of anastomoses of the right atrium (RA), left atrium (LA), aorta (AO), and pulmonary artery (PA). IVC = inferior vena cava, LV = left ventricle, SVC = superior vena cava.

 

Figure 5A
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  		Figure 5a.  Axial (a) and sagittal oblique (b) cardiac CT images show a normal left atrial anastomosis (arrows) that simulates abnormal dilatation of the left atrium (LA). The donor left atrium was incised and sutured to the recipient posterior atrial wall and pulmonary veins.

 

Figure 5B
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  		Figure 5b.  Axial (a) and sagittal oblique (b) cardiac CT images show a normal left atrial anastomosis (arrows) that simulates abnormal dilatation of the left atrium (LA). The donor left atrium was incised and sutured to the recipient posterior atrial wall and pulmonary veins.

 
The more recently developed bicaval technique (Fig 6) may result in longer donor heart ischemic time but is associated with improved transplantation outcomes because of a significant decrease in the incidence of conduction abnormalities, which were relatively common with the use of the biatrial technique (24). With the bicaval technique, the recipient’s right and left atria are excised, while inferior and superior caval cuffs, the posterior wall of the left atrium, and the pulmonary vein openings are left intact. The inferior and superior venae cavae from the donor are sutured to the corresponding recipient cuffs, and the donor’s left atrium is sutured to the posterior wall of the recipient’s native left atrium (as in the biatrial technique). The surgery is completed with end-to-end anastomoses of the ascending aorta and main pulmonary artery (Figs 6, 7). A size mismatch between the recipient and donor vessels can create the appearance of redundancy or stenosis at these locations (Fig 7) (17,25). The transplanted heart is typically rotated clockwise in the axial plane (Fig 8). The recipient’s pericardium is opened during explantation of the native heart and is left open. A size discrepancy between the recipient pericardial sac and the transplanted heart may cause an enlarged pericardial silhouette on chest radiographs during the initial postoperative period (13,39); however, there should be no unusual appearance of the pericardium in the long term.


Figure 6A
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  		Figure 6a.  Orthotopic cardiac transplantation with the bicaval technique. Schemas show the intraoperative appearance of the native and donor hearts before (a) and after (b) the creation of anastomoses of the left atrium (LA), inferior vena cava (IVC), superior vena cava (SVC), aorta (AO), and pulmonary artery (PA). LV = left ventricle, RA = right atrium.

 

Figure 6B
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  		Figure 6b.  Orthotopic cardiac transplantation with the bicaval technique. Schemas show the intraoperative appearance of the native and donor hearts before (a) and after (b) the creation of anastomoses of the left atrium (LA), inferior vena cava (IVC), superior vena cava (SVC), aorta (AO), and pulmonary artery (PA). LV = left ventricle, RA = right atrium.

 

Figure 7A
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  		Figure 7a.  Anastomoses of pulmonary artery and aorta. (a) Axial CT image shows a normal appearance of the pulmonary artery anastomosis, with surgical clips visible at the site. The asterisk indicates the donor pulmonary artery. (b) Axial CT image in another patient shows an appearance of pulmonary artery redundancy at the anastomosis site (arrows), an appearance produced by a size mismatch between the donor and recipient pulmonary arteries. (c) Coronal CT image in a third patient shows a donor aorta that is narrower than the recipient aorta, a feature that simulates an aortic aneurysm but that has no clinical significance.

 

Figure 7B
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  		Figure 7b.  Anastomoses of pulmonary artery and aorta. (a) Axial CT image shows a normal appearance of the pulmonary artery anastomosis, with surgical clips visible at the site. The asterisk indicates the donor pulmonary artery. (b) Axial CT image in another patient shows an appearance of pulmonary artery redundancy at the anastomosis site (arrows), an appearance produced by a size mismatch between the donor and recipient pulmonary arteries. (c) Coronal CT image in a third patient shows a donor aorta that is narrower than the recipient aorta, a feature that simulates an aortic aneurysm but that has no clinical significance.

 

Figure 7C
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  		Figure 7c.  Anastomoses of pulmonary artery and aorta. (a) Axial CT image shows a normal appearance of the pulmonary artery anastomosis, with surgical clips visible at the site. The asterisk indicates the donor pulmonary artery. (b) Axial CT image in another patient shows an appearance of pulmonary artery redundancy at the anastomosis site (arrows), an appearance produced by a size mismatch between the donor and recipient pulmonary arteries. (c) Coronal CT image in a third patient shows a donor aorta that is narrower than the recipient aorta, a feature that simulates an aortic aneurysm but that has no clinical significance.

 

Figure 8A
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  		Figure 8a.  Position of the native heart and transplanted heart in the axial plane. (a) Axial CT image shows the normal orientation of a native heart. (b) Axial CT image shows marked clockwise rotation of a transplanted heart with a left atrial anastomosis (arrows) that simulates atrial enlargement.

 

Figure 8B
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  		Figure 8b.  Position of the native heart and transplanted heart in the axial plane. (a) Axial CT image shows the normal orientation of a native heart. (b) Axial CT image shows marked clockwise rotation of a transplanted heart with a left atrial anastomosis (arrows) that simulates atrial enlargement.

 
Heterotopic cardiac transplantation, which is reserved for patients with severe pulmonary hypertension or a significant size mismatch, accounts for less than 0.3% of heart transplantations (2,4). In this procedure, the donor heart is placed side by side with the recipient heart, with multiple anastomoses.

Coronary Allograft Vasculopathy
Coronary allograft vasculopathy is a diffuse process that often manifests with concentric narrowing of the vessel lumen rather than focal luminal constriction. Because it is clinically silent in the denervated transplanted heart and may be overlooked at coronary angiography, it is a leading cause of death in heart transplant recipients.

The most common causes of early posttrans-plantation mortality include rejection and acute right ventricular failure, which occurs frequently in patients with severe pulmonary hypertension (26). Following discharge from the hospital, in the 1st year after transplantation, infection due to immunosuppressant therapy is the major cause of mortality (4). After the 1st year, coronary allograft vasculopathy is the leading cause of death, followed by malignancy (4).

Coronary allograft vasculopathy is a unique form of atherosclerosis that results from chronic immune-mediated injury to the transplanted heart, combined with multiple nonimmunologic factors (Fig 9) (7,27). Coronary allograft vasculopathy causes endothelial damage, which often results in luminal narrowing, myocardial ischemia, and ultimately graft failure (2,28). The estimated risk for the development of coronary allograft vasculopathy in heart transplant recipients is 10% per year.


Figure 9
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  		Figure 9.  Diagram shows the multiple factors that contribute to the development of coronary allograft vasculopathy (7). CMV = cytomegalovirus infection.

 
The disease process in coronary allograft vasculopathy differs from that in classic atherosclerosis both anatomically and histologically (28). Luminal narrowing typically begins in the distal small coronary arteries and progresses proximally to the epicardial vessels. Collateral vessels are remarkably absent. Pathologically, there is diffuse concentric atherosclerotic narrowing rather than the focal, patchy, and often eccentric disease that typifies classic atherosclerosis, in which collateral vessels are common (Fig 10) (28).


Figure 10A
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  		Figure 10a.  Typical and atypical coronary allograft vasculopathy. (a) Curved multiplanar reformatted image from cardiac CT in a 56-year-old man 12 years after transplantation shows diffuse concentric wall thickening (arrowheads) of the right coronary artery, a finding typical of coronary allograft vasculopathy. (b) Axial oblique maximum intensity projection image from cardiac CT in a 47-year-old man 12 years after transplantation demonstrates the left main and left anterior descending coronary artery with partially calcified plaque at the bifurcation (arrowhead), a finding typical of classic atherosclerosis.

 

Figure 10B
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  		Figure 10b.  Typical and atypical coronary allograft vasculopathy. (a) Curved multiplanar reformatted image from cardiac CT in a 56-year-old man 12 years after transplantation shows diffuse concentric wall thickening (arrowheads) of the right coronary artery, a finding typical of coronary allograft vasculopathy. (b) Axial oblique maximum intensity projection image from cardiac CT in a 47-year-old man 12 years after transplantation demonstrates the left main and left anterior descending coronary artery with partially calcified plaque at the bifurcation (arrowhead), a finding typical of classic atherosclerosis.

 
Coronary allograft vasculopathy is usually clinically silent and therefore presents a diagnostic challenge; because of continued denervation in 70%–90% of cardiac grafts, any occurrence of myocardial ischemia in those grafts is asymptomatic (29). Affected patients rarely complain of angina. They might manifest sequelae of coronary artery disease, including signs of congestive heart failure or loss of allograft function, or they may experience arrhythmias or sudden death (30). Early diagnosis of coronary allograft vasculopathy is important because the prevention of impending catastrophic events is feasible in some patients through revascularization—either percutaneously with balloon angioplasty and with or without stent implantation, or by means of bypass surgery. Revascularization is performed primarily in hearts with focal disease and good distal flow, but unfortunately these conditions are present in few transplant recipients (3,4).

Annual surveillance with coronary angiography is the current standard of care, but angiography has intrinsic limitations for the detection of coronary allograft vasculopathy, which often manifests with diffuse luminal narrowing rather than focal constriction. Angiography depicts the lumen alone and cannot directly portray wall thickening and intimal hyperplasia. An experienced angiographer may overcome some of these limitations by actively seeking signs of coronary allograft vasculopathy instead of stenosis in heart transplant recipients; nevertheless, in instances of positive vessel remodeling (characterized by dilatation of the atherosclerotic vessel) or diffuse concentric intimal hyperplasia, the disease process may be underestimated or overlooked (4,31,32). Indeed, there have been multiple reports about the relative insensitivity of coronary angiography compared with that of intravascular US for coronary allograft vasculopathy detection (8,32,33). In addition, coronary angiography is associated with a 1%–2% complication rate (34,35).

Intravascular US allows measurement of the luminal diameter as well as the thickness of the intima and media, and thus it is more sensitive than coronary angiography for the detection of nonocclusive coronary allograft vasculopathy and for monitoring progression (28,36). However, intravascular US is invasive and must be preceded by coronary angiography, is limited to the large proximal arteries, and is time consuming and costly; therefore, it is difficult to perform the examination on an annual basis (28).

Multidetector CT with the use of an intravascular contrast material enables the noninvasive visualization of coronary vessels, including the lumen and wall (11). In addition, CT provides high-resolution depiction of soft tissue, which allows the direct assessment of any atherosclerotic thickening and plaque burden in the vessel wall (37). Thus, CT combines the advantages of angiography for lumen imaging and of intravascular US for coronary wall imaging, and it may have the potential to surpass coronary angiography in the diagnosis of coronary allograft vasculopathy (Fig 11). Using a 16-channel multidetector CT scanner to evaluate the utility of CT for the detection of coronary allograft vasculopathy, Romeo et al reported a sensitivity of 83%, specificity of 95%, positive predictive value of 71%, and negative predictive value of 95% for the detection of coronary artery stenoses greater than 50% in a prospective 53-patient series (13). Similar findings were reported by Carrascosa et al (38).


Figure 11A
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  		Figure 11a.  Comparison of images from cardiac CT and coronary angiography in a 55-year-old man 7 years after transplantation. (a) Curved multiplanar reformatted image demonstrates mild concentric wall thickening and luminal narrowing of the left anterior descending artery (small arrows), as well as mild narrowing of the left main coronary artery (large arrow), findings that were markedly underestimated on the basis of the conventional coronary angiogram (b).

 

Figure 11B
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  		Figure 11b.  Comparison of images from cardiac CT and coronary angiography in a 55-year-old man 7 years after transplantation. (a) Curved multiplanar reformatted image demonstrates mild concentric wall thickening and luminal narrowing of the left anterior descending artery (small arrows), as well as mild narrowing of the left main coronary artery (large arrow), findings that were markedly underestimated on the basis of the conventional coronary angiogram (b).

 
However, current CT technology has several disadvantages (37). In comparison with conventional coronary angiography, CT has lower temporal and spatial resolution; in comparison with intravascular US, it has reduced spatial and contrast resolution. These limitations may be overcome with the continuing evolution of CT technology.

Grading of Coronary Allograft Vasculopathy
At present, there is no universally accepted scale for grading cardiac CT findings. A three-point scale based on the vessel morphologic characteristics at coronary angiography was developed by Gao and colleagues (39). Grade A corresponds to discrete proximal tubular stenosis, grade B to diffuse concentric narrowing, and grade C to irregular diffuse concentric narrowing with occluded branches. This grading system could be adapted for application to CT coronary angiography with the use of multiplanar reformatted images (Fig 12) and maximum intensity projection images. Further studies are warranted to define and evaluate a comparable scale and to compare findings at grading with CT coronary angiography with those at grading with standard coronary angiography.


Figure 12A
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  		Figure 12a.  Multiplanar reformatted CT images obtained for grading of coronary allograft vasculopathy show type A vasculopathy, with a discrete tubular stenosis (arrowhead in a) in the middle of the left anterior descending artery; type B vasculopathy, with diffuse concentric narrowing of the right coronary artery (arrowheads in b); and type C vasculopathy, represented in c by a narrow and irregular circumflex artery with no side branches and in d by an irregular right coronary artery with a wavy contour and lack of distal outflow. The lack of distal outflow is the most ominous finding for prognosis.

 

Figure 12B
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  		Figure 12b.  Multiplanar reformatted CT images obtained for grading of coronary allograft vasculopathy show type A vasculopathy, with a discrete tubular stenosis (arrowhead in a) in the middle of the left anterior descending artery; type B vasculopathy, with diffuse concentric narrowing of the right coronary artery (arrowheads in b); and type C vasculopathy, represented in c by a narrow and irregular circumflex artery with no side branches and in d by an irregular right coronary artery with a wavy contour and lack of distal outflow. The lack of distal outflow is the most ominous finding for prognosis.

 

Figure 12C
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  		Figure 12c.  Multiplanar reformatted CT images obtained for grading of coronary allograft vasculopathy show type A vasculopathy, with a discrete tubular stenosis (arrowhead in a) in the middle of the left anterior descending artery; type B vasculopathy, with diffuse concentric narrowing of the right coronary artery (arrowheads in b); and type C vasculopathy, represented in c by a narrow and irregular circumflex artery with no side branches and in d by an irregular right coronary artery with a wavy contour and lack of distal outflow. The lack of distal outflow is the most ominous finding for prognosis.

 

Figure 12D
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  		Figure 12d.  Multiplanar reformatted CT images obtained for grading of coronary allograft vasculopathy show type A vasculopathy, with a discrete tubular stenosis (arrowhead in a) in the middle of the left anterior descending artery; type B vasculopathy, with diffuse concentric narrowing of the right coronary artery (arrowheads in b); and type C vasculopathy, represented in c by a narrow and irregular circumflex artery with no side branches and in d by an irregular right coronary artery with a wavy contour and lack of distal outflow. The lack of distal outflow is the most ominous finding for prognosis.

 
Calcium Scoring
Both electron-beam CT and multidetector CT are used in the general population to detect atherosclerotic coronary heart disease by quantifying coronary artery calcium. Preliminary studies in cardiac transplant recipients showed an increase in coronary calcium over time. High sensitivity and specificity of calcium scoring for the detection of stenoses greater than 50% suggest that calcium scoring may be used for early detection of coronary allograft vasculopathy (Fig 13) (40,41). However, in more recent studies, a relatively high rate of occurrence of significant coronary artery disease was found in patients with normal calcium scores (42).


Figure 13
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  		Figure 13.  Axial image obtained at follow-up CT for calcium scoring in a 54-year-old man 41/2 years after transplantation shows mild calcification in the left anterior descending artery (LAD), a feature not seen at baseline CT for calcium scoring. The total calcium score was 14. (Courtesy of Joseph Shemesh, MD, Sheba Medical Center, Tel Aviv, Israel.)

 
Cardiac Function
Heart transplant recipients also undergo routine evaluations with echocardiography and scintigraphy for the detection of any cardiac allograft dysfunction involving the left and right ventricles (9,10). Multidetector CT technology enables heart imaging during the entire cardiac cycle, provides excellent spatial resolution, and allows image reformation in multiple planes. Dedicated software is used to measure the diastolic and systolic left ventricular volume and to calculate the left ventricular ejection fraction and stroke volume by using the Simson disk method (Fig 14) (43). In studies performed to validate the use of CT for function analysis, a good correlation was found between the results of cardiac function assessments with CT and with standard clinical imaging modalities in patients who were not heart transplant recipients (44–46). Furthermore, cine viewing of the left and right ventricles in the short and long axes enables the analysis of global and regional myocardial wall motion abnormalities. Our initial experience with the use of CT and echocardiography for left ventricular function evaluation in a small sample of heart transplant recipients supports the conclusion that CT may be comparable to echocardiography for evaluating heart function. Further validation is needed.


Figure 14
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  		Figure 14.  Cardiac CT images, obtained for evaluation of left ventricular function in a 47-year-old man 9 years after transplantation, show four-chamber (top row) and two-chamber (bottom row) views in diastole (left column) and systole (right column). The calculated ejection fraction (63.3%) was indicative of normal ventricular contractility.

 
Other Complications
Cardiac CT allows visualization of the great vessels and anastomoses as well as portions of the mediastinum, lungs, pleura, and chest wall, depending on the field of view chosen. CT thus has the potential to depict various transplantation-related complications within a single examination. Infections, particularly nosocomial and opportunistic pneumonia, are major causes of morbidity and mortality in the 1st year after transplantation (2,17,47). An increased risk of community-acquired and opportunistic pulmonary infections persists thereafter because of ongoing immunosuppression. Malignancy, presumably related to immunosuppression, is the second most common long-term cause of mortality in heart transplant recipients (47). Posttransplantation lymphoproliferative disorders, primarily non-Hodgkin B-cell lymphoma, are the most important type of malignancy in this patient group. The tumors may be manifested as a solitary mass, enlarged lymph nodes, or pulmonary nodules (47). Other malignancies that may be depicted at cardiac CT with a limited field of view include lung cancer and thoracic metastases (17,47).


   Conclusions
Top
 Abstract
 LEARNING OBJECTIVES FOR TEST...
 Introduction
 CT of the Transplanted...
 Conclusions
References
 
Heart transplantation is the treatment of choice for end-stage heart failure, but coronary allograft vasculopathy significantly limits the long-term survival of heart transplant recipients. Cardiac CT allows the noninvasive assessment of the coronary artery wall thickness and lumen; therefore, it may be most useful as an adjunct with coronary angiography in screening for coronary allograft vasculopathy and in some instances may surpass angiography. CT has the added advantage of enabling the evaluation of cardiac function, the assessment of cardiac structures (including the great vessels and anastomoses) and adjacent organs, and the detection of common posttrans-plantation complications such as infection and malignancy located within the field of view. Further studies are warranted to evaluate the role of CT as a noninvasive comprehensive screening tool for the follow-up of heart transplant recipients.


   Acknowledgments
 
The authors thank Shifra Fraifeld for her assistance with the manuscript preparation.


   References
Top
 Abstract
 LEARNING OBJECTIVES FOR TEST...
 Introduction
 CT of the Transplanted...
 Conclusions
 References
 

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