Ann Thorac Surg 2004;78:1064-1066
© 2004 The Society of Thoracic Surgeons
Case report
Morphological and functional magnetic resonance imaging after heterotopic heart transplantation
Konstantin Nikolaou, MDa,*,
Marion Weis, MDb,
Stefan O. Schoenberg, MDa,
Bruno Reichart, MDb,
Maximilian F. Reiser, MDa
a Clinical Radiology, University of Munich, Grosshadern, Germany
b Cardiac Surgery, University of Munich, Grosshadern, Germany
Accepted for publication June 23, 2003.
* Address reprint requests to Dr Nikolaou, Department of Clinical Radiology, University of Munich, Grosshadern, Marchioninistr. 15, D-81377 Munich, Germany
konstantin.nikolaou{at}ikra.med.uni-muenchen.de
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Abstract
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In patients with severe congestive heart failure, a marked elevation in pulmonary vascular resistance limits the success of orthotopic cardiac transplantation, providing the rationale for heterotopic transplantation. In the case reported, cardiac anatomy and function of two hearts in the same chest were imaged using magnetic resonance imaging (MRI). MRI offers a high-resolution, three-dimensional, noninvasive technique to visualize the complex anatomy after heterotopic heart transplantation, providing information of morphologic and functional parameters at the same time. The challenge of sufficient electrocardiogram triggering, hindered by two hearts with electrophysiological activity in the same chest, can be overcome using new real-time techniques.
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Introduction
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Heart transplantation has become an established treatment modality for end-stage heart disease of different etiology with several thousand worldwide reported transplantations annually. Use of the heterotopic heart transplantation technique, ie, transplantation of a human heart into the right thoracic cavity, leaving the native, left thoracic heart in place, has remained limited with less than 1% of all performed heart transplantation procedures [1]. The presence of significant elevation of pulmonary vascular resistance is a major risk factor for death after orthotopic heart transplantation. Therefore, in case of pulmonary hypertension and raised pulmonary resistance, heterotopic heart transplantation can be performed [2]. In the case reported, a patient after heterotopic heart transplantation had to undergo additional cardiac surgery for increasing anginal complaints. Magnetic resonance imaging (MRI) is becoming the method of choice for many cardiac applications, and can provide complex information on anatomy, morphology, and functional parameters at the same time [3]. Additionally, a real-time interactive imaging approach enables acquisition of morphologic and functional parameters, even if electrocardiogram (ECG) triggering is hindered due to two beating hearts in one chest.
A 67-year-old male patient, who underwent heterotopic heart transplantation 11 years ago, was referred for cardiac MRI for increasing complaints of angina pectoris. The reason for this kind of surgery was a fulminant pulmonary embolism with acute cardiac decompensation. At the time point of first surgery, a combined heart and lung transplantation was not indicated for this patient due to his age and due to the high pulmonary vascular resistance as a sequel to the fulminant pulmonary embolism. Under these circumstances, a supporting heart was implanted in the right thoracic cavity, connecting the two aortas, the left atrium, the right atrium, and the pulmonary artery trees. The clinical indication for the first MR study was clarification of the rapid clinical deterioration with signs of heart failure, to confirm patency of all anastomoses, to examine the left ventricular myocardial function of both the native and the transplant heart, and to exclude chronic rejection due to possible transplant vasculopathy.
The patient was in bad clinical condition at the time point of the first MRI examination, needing intensive care and artificial respiration. Initially, morphologic sequences including noncontrast-enhanced single-shot turbo spin-echo (HASTE) acquisitions and three-dimensional, contrast enhanced gradient-echo acquisitions (FLASH) were performed, demonstrating the patency of all anastomoses and a significant dilatation of the native's heart left ventricle (Fig 1). These morphologic acquisitions were performed without ECG gating; however, artificial respiration was suspended for the duration of the acquisitions (up to 20 seconds) to ensure motion free imaging without breathing artifacts. Additionally, functional imaging of both hearts was performed, using real-time techniques during free breathing of the patient. These real-time MRI sequences are performed without ECG gating or suspension of the artificial respiration, as, due to the rapid imaging capability, a sufficient spatial resolution and image contrast can be achieved [4]. Functional real-time MRI proved insufficient left ventricular function of the native heart, due to constant ventricular fibrillation, and a combined severe aortic and mitral valve insufficiency could be demonstrated (Fig 2). As a consequence, cardiac output of the transplanted heart was significantly reduced due to a regurgitation of the insufficient aortic valve of the native heart.
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Fig 1. (A) Presurgical coronal, noncontrast enhanced single-shot turbo spin-echo images demonstrating the connection of the two aortas (arrow) of the patient's native heart in the left thoracic cavity and the transplanted heart in the right thoracic cavity. (B) Axial image showing a patent anastomosis of the pulmonary artery trunc (arrow). (C) Coronal contrast-enhanced gradient-echo sequence visualizes the connection of the left (long arrow) and right atria (short arrow) of the two hearts. (D) Global dilatation of the left native heart is found (arrow), due to a combined aortic and mitral valve insufficiency.
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Fig 2. Presurgical real-time functional sequences during free breathing of the patient clearly demonstrate a significant regurgitation during diastole in the region of the aortic valve of the left heart (arrow), proving aortic valve insufficiency.
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Based on these MR findings, surgery was performed, occluding the aortal valve of the native heart permanently using a Dacron patch. Twenty-eight weeks post surgery a second MR examination was performed to exclude formation of thrombotic material in the native heart, to prove the impermeability of the surgically closed valve, and to assess the left ventricular function of the transplanted heart. Successful occlusion in the region of the aortic valve was demonstrated, without regurgitation, and formation of thrombotic material could be excluded (Fig 3). At the second MRI examination, ECG triggering of the transplanted heart succeeded, placing the ECG leads over the right side of the thorax. ECG-triggered, steady-state free precession (SSFP) functional imaging of the transplanted heart proved a significantly improved ejection fraction with a nearly normal ejection fraction of 47% and only slightly increased end-systolic volume (Fig 4).
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Fig 3. Postsurgical coronal contrast-enhanced gradient-echo image depicting the surgical occlusion of the aortic valve using a Dacron patch (arrow). Formation of thrombotic material in the left ventricle could be excluded. The structure at the base of the heart (arrowhead) corresponds to a papillary muscle.
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Fig 4. Postsurgical functional SSFP images of the right transplant heart during end-systole (A) and end-diastole (B) demonstrating an adequate left ventricular function of the transplanted heart with an ejection fraction of 47%. (SSFP = steady-state free precession.)
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Comment
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The presence of significant elevation of pulmonary vascular resistance is a major risk factor for death after orthotopic heart transplantation [5]. The discarded recipient's right heart, acclimated to pulmonary hypertension, is often stronger than its nonconditioned donor replacement. In case of pulmonary hypertension and raised pulmonary resistance, heterotopic heart transplantation can be performed. The aim of such a heterotopic heart transplantation is auxiliary cardiac support. Recent studies have demonstrated cardiac improvement in patients supported with a ventricular assist device, suggesting that reverse remodelling, myocardial recovery, and a gradual decrease of the pulmonary vascular resistance are possible [6]. Heterotopic heart transplantation in carefully selected recipients can allow safer transplantation in patients with elevated pulmonary resistance, can increase the donor pool by allowing use of smaller hearts and nonideal donors, and may reduce the mortality on the transplant waiting list by providing earlier transplantation.
The surgical approach for patients with such a complex cardiac anatomy will be dependent on the primary disease and specific morphologic and functional parameters. Monitoring of this unusual clinical setting of two hearts beating independently in one chest requires special acquisition techniques. Conventional imaging approaches such as ultrasound imaging are often impaired and hindered by the complex postsurgical anatomical situs. Important information that have to be obtained by imaging are: presence of proximal pulmonary artery and intracavitary thrombi; patency of foramen ovale with right to left shunting; presence of atrial septal or ventricular septal defects, and others [7]. In recent years, the technological developments in MRI have made it possible to perform routine cardiovascular imaging, including evaluation of wall motion, perfusion, and viability at rest and under stress [8]. One of the most spectacular technical innovations was the introduction of real-time applications, updating the imaging sequences constantly, without the necessity of apnea or ECG synchronization [9]. In conventional cardiac MRI, cine (gated and breathheld) scanning techniques can achieve high temporal and spatial resolution, but are often complicated by arrhythmia and patient difficulty with long or multiple breathholds. Real-time imaging, which is performed independent of respiratory and cardiac motion, is robust to both arrhythmia and patient shift. Implementation of real-time cardiac MR imaging can significantly decrease the time required for a complete functional cardiac examination and enables cardiac MRI in intensive care patients, as in the case reported.
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Acknowledgments
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The authors want to thank Frank Stadie, Wolfgang Klinger, Anja Struwe, and Carola Schmid from the Department of Clinical Radiology, Ludwig-Maximilians-University of Munich, for their support in performing the studies.
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References
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Abstract
Introduction
