Following a brief introduction listing the salient aspects of heart transplantation as they pertain to children, there is a detailed section on assessment of the explanted heart with special reference to cardiomyopathy and congenital heart disease. This is followed by a section on the implanted heart that deals with the problems of acute cellular rejection, chronic allograft vasculopathy and post-transplant lymphoproliferative disorder. Particular attention is paid to endomyocardial biopsy in these assessments. The chapter closes with sections on re-explant and on post-mortem assessment of the transplanted heart.
Cardiac transplantation is usually considered when heart disease is so severe that life expectancy is estimated to be less than two years and the quality of life is unacceptable . Paediatric cardiac transplantation is becoming increasingly frequent. The International Society for Heart and Lung Transplantation (ISHLT) Registry now lists an accumulation of almost 14 000 cases . About 90% of paediatric heart transplants are done for cardiomyopathy (dilated cardiomyopathy being the most frequent) and complex congenital heart disease, usually after failure of conventional surgery or other forms of treatment . Congenital heart disease accounts for about two-thirds of transplants in infants, and cardiomyopathy a similar proportion in adolescents. As a group, children transplanted for congenital heart disease fare less well than those transplanted for cardiomyopathy . Single ventricle with prior palliation, and especially the failing Fontan, carry the highest risk for transplantation and are least amenable to bridging with mechanical circulatory support .
Mechanical circulatory support is now common before transplant (bridge to transplant). More than half of all children (excluding infants) with dilated cardiomyopathy are now bridged to transplant on some form of mechanical support device, most commonly a ventricular assist device (VAD). Mechanical support is less frequent in children with congenital heart disease, and this is particularly the case in infants. VAD outcomes are significantly better in patients weighing more than 5 kg (25% mortality) compared to those weighing less than 5 kg (64% mortality) . Achieving effective anticoagulation in the smallest children is also very difficult . Only 12% of infants with congenital heart disease are bridged to transplant on some form of mechanical support. In this age group extracorporeal membrane oxygenation (ECMO) is more commonly employed than a VAD . Overall, VADs permit satisfactory support for children with advanced heart failure of many causes until transplantation and children bridged with VADs have comparable long-term post-transplant survival to those undergoing primary heart transplantation .
Around 684 paediatric heart transplants were carried out worldwide in 2015 and registered with the ISHLT . Only 22 centres in the world perform more than 10 paediatric heart transplants annually . There were 37 paediatric heart transplants in the United Kingdom in the financial year 2014/2015 [8.] Infants account for around 20% of paediatric heart transplants worldwide . The number of suitable donors is limited.
Mechanical circulatory support is not without its problems. ECMO is not a long-term support but is an option for several weeks. The morbidity of ECMO is substantial, often tracheostomy is required, there is commonly renal dysfunction requiring haemofiltration and muscle weakness postoperatively leads to delayed mobilisation.
In the period before the introduction of VAD (pre-2004) the one-year survival of paediatric patients listed for transplant was 74%. Since 2005, the figure is 86% . The earliest VADs such as Berlin Heart EXCOR were paracorporeal, pneumatic, pulsatile pumps with a range of cannula and pump sizes. They are non-portable and require the patient to remain in hospital. There is a substantial risk of complications that may be catastrophic, most notably neurological, respiratory, bleeding and multiorgan failure . More recently, continuous flow pumps such as HeartWare have become available that can be implanted and mean that the patient can leave hospital to await a suitable donor.
Actuarial graft survival for newborn heart transplant recipients is 59% at 25 years. Survival has improved in the most recent era. Cardiac allograft vasculopathy is the most important late cause of death with an actuarial incidence at 25 years of 35%. Post-transplant lymphoma is estimated to occur in 20% of infant recipients by 25 years. Severe chronic renal disease (grade 3 or worse) is present in 31% of survivors . The percentage of re-transplants has been relatively stable over time, comprising 5% of all paediatric heart transplants in 2015 .
14.2 Assessment of the Explanted Heart
Explanted hearts are submitted for histological examination. Prior valve harvesting renders the assessment more challenging but does not preclude it (Figure 14.1). It is becoming increasingly common to receive explanted hearts with attached VADs. The hearts are generally received unfixed, and it is prudent to snap freeze a piece of atrial myocardium before formalin fixation in case genetic testing is required at a later date. The heart should then be placed in a large volume of formalin and fixed for at least 24 hours to facilitate dissection.
Figure 14.1 Explanted heart with dilated cardiomyopathy received in multiple pieces following valve harvest. This is a somewhat extreme case. Nevertheless, the anatomy can be described with some confidence. There is left ventricular dilatation and there is no obvious focal abnormality of the myocardium. Such atrioventricular valvar tissue as is present is unremarkable. Adequate histological sampling can be made of the atrioventricular junctions and the ventricular walls.
For the assessment of hearts removed for end-stage dilated, restrictive or hypertrophic cardiomyopathy the most useful approach is a simulated four-chamber cut through the atria and ventricles (Figure 14.2). This gives information about the relative sizes of the atrial and ventricular cavities and allows simultaneous demonstration of all the major structures other than the arterial valves. The arterial valves can be assessed by cutting through the left and right outflow tracts to expose them.
Figure 14.2 Four-chamber cut of heart. This heart was explanted for dilated cardiomyopathy. The arterial valves have been harvested. Nevertheless, the simulated four-chamber cut shows at a glance the typical features of dilated cardiomyopathy with dilated left ventricular cavity and endocardial fibrosis.
If there is a VAD in situ, it will most commonly be in the apex of the left ventricle. With the Berlin heart, a flanged cannula is sewn into the ventricular apex and the cannula extends for 3–5 cm into the ventricular cavity. If sufficient of the aorta is included in the specimen, the aortic cannula (usually right-angled) may be seen sewn into the lateral wall of the aorta (Figure 14.3). The pericardial surface of the heart in such cases shows fibrous pericardial adhesions and the track of the aortic cannula is usually apparent over the anterior surface of the right atrium and right atrioventricular groove (Figure 14.4). For the HeartWare device, the pump itself is usually included in the specimen, together with a variable length of cannula and electrical lead (Figure 14.5). It is more difficult to remove these devices, but cutting through the myocardium until hitting the device and then carefully cutting around the attachment site will usually allow the device to be removed.
Figure 14.3 Ventricular assist device cannulae. A one-year-old infant with myocarditis and heart failure bridged to transplant with a Berlin heart. The explanted heart is cut in a simulated long-axis view. The left ventricle is only mildly dilated but shows dense endocardial fibrous thickening. A cannula is inserted at the left ventricular apex and another in the ascending aorta. Histologically the myocardium showed fibrosis and lymphocytic infiltration. Parvovirus was identified by PCR in fresh myocardium.
(A) A heart explanted from an infant with dilated cardiomyopathy bridged to transplant with a Berlin heart. The epicardial surface of the heart shows haemorrhagic fibrous adhesions in the region of the right ventricular outflow tract, and a right-angled plastic cannula is attached to the aorta. There is some irregularity of the epicardium over the left ventricular apex where the ventricular cannula is inserted.
(B) The epicardial surface of the base of the explanted heart in a two-year-old with operated hypoplastic left heart. The arterial pedicle consists of a large pulmonary trunk surgically anastomosed to a diminutive aorta. There are fibrous adhesions over the epicardium and a smooth shallow groove running from top left to lower midfield and representing the track of the cannula of a left VAD. The cannula was removed before submission of the specimen.
Figure 14.5 HeartWare left VAD. Explanted heart from a ten-year-old with dilated cardiomyopathy. The heart has undergone valve harvest before receipt. A HeartWare device is inserted in the apex of the left ventricle. The electrical lead can be seen to the left of the pump chamber. The metal cannula is inserted into the left ventricular cavity.
Histological sampling of the explanted heart requires myocardium from both atria and ventricles, interventricular septum, papillary muscles of the mitral valve and the arterial valves (if present) . A section through the atrioventricular junctions will normally encompass the main right and left coronary arteries together with the coronary sinus.
Assessment of fibrosis
Structure of the coronary arteries
Assessment of elastic tissue deposition in endocardial fibrosis
Special Diagnostic Investigations (Including Electron Microscopy)
Electron microscopy will confirm the presence of large numbers of mitochondria, many abnormal in the mitochondrial cardiomyopathies.
The specific details of the various forms of cardiomyopathy are covered in more detail Chapter 7. Below are listed those features of most relevance in assessing the explanted heart.
The heart is enlarged, dilated and globular (Figure 14.6)
The heart weight is increased
The heart usually shows extensive endocardial fibrosis in the left ventricle sometimes up to several millimetres in thickness.
The right ventricle may be secondarily dilated but rarely shows any significant degree of endocardial fibrosis
If a VAD has been implanted, the ventricular cavity may have undergone remodelling and not be so markedly dilated (Figure 14.7)
Figure 14.6 Dilated cardiomyopathy. Idiopathic dilated cardiomyopathy. An explanted heart from a 15-year-old. The left ventricular cavity is dilated and shows mild fibrosis of its endocardium. The interventricular septum is bowed to the right. The atria, atrioventricular valves and right ventricle appear unremarkable.
Figure 14.7 Remodelled dilated cardiomyopathy with VAD. Explanted heart from a two-year-old with dilated cardiomyopathy. There is a left VAD cannula inserted in the apex. The endocardium of the left ventricle is thickened and fibrotic. The left ventricular cavity is not especially dilated, and it is possible that the unloading of the ventricle by the assist device has allowed for remodelling and reduction in the cavity diameter.
Fibrosis of the myocardium – particularly papillary muscles of the mitral valve
Multiple spotty foci of fibrosis; this raises the possibility of previous myocarditis
Myocyte nuclear enlargement and hyperchromasia
Stretched and wavy myofibres
Epicardium showing inflammatory cell infiltrate or fibrosis
Secondary degenerative changes sometimes present in the valves in the form of thickening of the leaflets
Dilation of atria with endocardial fibrosis
Left ventricular endocardium thickened by laminar elastic tissue
An increase in endocardial smooth muscle fibres in left atrial endocardium, also frequently thickened sometimes with prominent smooth muscle (Figure 14.8)
If a left VAD has been inserted, a large cannula is present at the apex of the left ventricle usually with surrounding myocardial necrosis and inflammatory infiltration, haemorrhage, and fibrosis and dystrophic calcification (Figure 14.9).
Figure 14.8 Endocardial smooth muscle. A section from the right atrium of a child with dilated cardiomyopathy caused by mutation in RBM20. The atrial myocardium is visible at the upper part of the field. The endocardium is greatly thickened by fibrous and elastic tissue and shows numerous bundles of longitudinally disposed smooth muscle cells. Smooth muscle bundles may be seen in the endocardium of the normal atria or ventricles but are commoner with cardiomyopathy.
(A) The cannula insertion site of this explanted heart shows fibrosis with loss of cardiac muscle. Dystrophic calcification is evident in the myocardium at the lower right of the field.
A form of dilated cardiomyopathy of unknown cause
Not widely recognised and poorly understood
In children, half of cases show associated cardiac abnormalities such as VSD, polyvalvar dysplasia and pulmonary stenosis
A striking morphology affecting predominantly the left ventricular myocardium imparting a spongy appearance reminiscent of the developing embryonic heart.
The ventricular cavity extends almost to the epicardial surface among a myriad of thin muscular trabeculations; the normal compact layer separating the muscular trabeculations of the ventricular lining from the epicardium is reduced in thickness (Figure 14.10).
Figure 14.10 Left ventricular non-compaction. A two-year-old with non-compaction of the left ventricular myocardium and restrictive physiology. The explanted heart underwent valve harvest before receipt. The simulated four-chamber view shows a left ventricle with marked fibroelastic thickening of its endocardium and multiple invaginations into the myocardium almost to the epicardial surface.
Papillary muscles of the mitral valve are poorly developed. VERY USEFUL often prominent endocardial fibroelastosis.
The heart is enlarged and the heart weight increased
There is hypertrophy of the ventricular myocardium (Figure 14.11)
May be confined to the septum but usually involves all of the left ventricle
Whorling of the myocardium may be evident macroscopically (Figure 14.12)
May be myocardial fibrosis
Impact lesions of the left ventricular outflow endocardium are unusual in children
There may be regional myocardial necrosis (Figure 14.13)
Figure 14.11 Hypertrophic cardiomyopathy. Explanted heart of a 14-year-old with hypertrophic cardiomyopathy (MYBPC3 mutation). A short-axis cut towards the apex demonstrates asymmetrical hypertrophy of the left ventricular myocardium affecting the septum and inferior wall with relative sparing of the anterior wall.
Figure 14.12 Hypertrophic cardiomyopathy – whorling. A short-axis cut at mid-ventricular level in the same heart as in Figure 14.11. The close-up view of the myocardium of the anterior interventricular septum shows the whorled arrangement of the muscle with streaky pale areas of fibrosis. The endocardium is normal.
Figure 14.13 Hypertrophic cardiomyopathy – necrosis. A 15-year-old with hypertrophic cardiomyopathy (MYH7 mutation) who collapsed with chest pain and was supported on a left ventricular assist device before undergoing heart transplant. A short-axis cut of the heart shows severe concentric hypertrophy of the left ventricular wall with extensive haemorrhagic infarction.
Hypertrophic myocyte nuclei
Myofibre disarray – usually very extensive
In hypertrophic cardiomyopathy due to structural gene mutations many of the intramural cardiac coronary arteries will show dysplastic features
In hypertrophic cardiomyopathy secondary to mitochondrial disorders giant mitochondria in the form of rounded eosinophilic cytoplasmic inclusions approximately one-third the diameter of an erythrocyte may be visible within the myocyte cytoplasm
There is usually associated myocardial fibrosis with endocardial fibroelastic thickening, but not as prominent as in dilated cardiomyopathy (Figure 14.14)
(A) Myocyte disarray shows myocytes with hyperchromatic nuclei and swirling and interdigitating cytoplasm.
(B) Fibrosis – this trichrome-stained section shows extensive interstitial fibrosis surrounding individual myocytes and accentuating the normal fascicular pattern.
(C) Dysplastic intramyocardial artery – the elastin-stained section shows the marked irregularity of the vessel wall. The lumen is irregular in profile, the intima shows irregular elastin deposition and the muscular coat is focally thinned. The adventitia is fibrous.
The atria, particularly the right atrium, are dilated (Figure 14.15)
Because the atria are rarely received intact in explanted hearts, this feature may sometimes be difficult to appreciate
The heart shows thickened ventricular myocardium
Figure 14.15 Restrictive cardiomyopathy. Explanted heart from a three-year-old with restrictive physiology. The heart is cut in a simulated four-chamber view and shows dilatation of both atria and ventricles and thickening of both ventricular walls There is mild endocardial fibrosis in the left ventricle. The histology was not specific.
Frequently myocyte disarray identical to that in hypertrophic cardiomyopathy
Small vessel dysplasia
Frequently interstitial fibrosis, often pericellular
May be myocyte vacuolation
May be cytoplasmic inclusions (Figure 14.16)
Figure 14.16 Restrictive cardiomyopathy. Explanted heart from a 12-year-old with familial restrictive cardiomyopathy. Histologically there are hypereosinophilic smudgy inclusions within myocytes. On cross section these inclusions are rounded, but on longitudinal section they were wavy and extended for considerable distances within the myofibres. They showed no staining with PAS, Luxol fast blue or Congo red, and immunohistochemistry for desmin did not stain them. Ultrastructurally they consisted of fibrillary material suggestive of myofibrillary myopathy. A sibling who also developed cardiomyopathy had a similar histological picture.
Hypertrophic cardiomyopathy is commoner in infants than dilated cardiomyopathy
The hypertrophy may be extreme
There may be an ICD lead or pacing lead (Figure 14.17).
(A) Fourteen-year-old with dilated cardiomyopathy. The explanted heart shows a very dilated left ventricle with mild left ventricular endocardial fibrosis. There is patchy fibrosis evident in the outer one-half of the wall of the left ventricle and septum. An ICD lead is in situ at the apex of the right ventricle.
(B) The myocytes contained giant mitochondria in keeping with mitochondrial cardiomyopathy (Masson’s trichrome stain).
The myocytes may appear swollen, with perinuclear clearing and replacement of cross striations by fine eosinophilic granules representing increased numbers of mitochondria (Figure 14.17B)
Frozen sections of myocardium may show reduction in oxidative enzymes
Cardiac mitochondria are more numerous than usual and on electron microscopy show abnormalities of size or structure with abnormal internal structure
If a VAD has been employed for any length of time, abnormal mitochondria may be more difficult to identify
NB It is doubtful if the disease occurs much below the age of 10 years.
Fatty replacement of the right ventricular myocardium extending from epicardium to endocardium
Usually affects the so-called triangle of dysplasia that encompasses the anterior wall of the right ventricular outflow tract and apex and the posterobasal wall of the right ventricle (Figure 14.18A)
Sparing of the muscular trabeculations
May affect the left ventricle or interventricular septum
Fibrosis may be obvious macroscopically
There is thinning of the wall, which may bulge to form aneurysmal protrusions
(A) Explanted heart from a 15-year-old with ARVC. The simulated four-chamber cut shows fatty replacement of much of the free wall of the right ventricle by adipose tissue. The right ventricle is dilated. There is some patchy infiltration also of the left ventricular myocardium. There is endocardial fibrosis over the posterior wall of the right ventricle, the interventricular septum and in the free wall of the left ventricle.
(B) A histological section taken from the right ventricular wall shows extensive fatty replacement of the right ventricular myocardium. The residual myocardium towards the endocardial surface shows fibrosis.
Characterised pathologically by fatty and fibrous replacement of the right (and sometimes the left) ventricular myocardium (Figure 14.18B)
Fibrosis is predominantly epicardial based in the right ventricular wall
CAUTION – may see fatty replacement in the normal right ventricular myocardium, particularly in obese subjects
18.104.22.168 Ventricular Assist Device (Berlin Heart or HeartWare)
Mechanical circulatory support is frequently used to bridge infants and children to cardiac transplant. When a ventricular assist device (VAD) is used as a bridge to transplant, the explanted heart contains a large cannula in the apex of the left ventricle, and if the aorta is also received, a cannula will be present here also. Sometimes both right and left ventricular assist devices are used. The typical specimen shows:
Cannula in apex of left ventricle
Cannula in aorta (Figure 14.3)
Cannulation site shows:
confluent myocyte necrosis
granulation tissue (Figure 14.9)
acute and chronic inflammatory cell infiltration
foreign body giant cell reaction
fibrosis in older cases
Figure 14.19 Myocarditis. Explanted heart from a four-week-old with Enterovirus myocarditis. The four-chamber cut of the heart shows extensive areas of necrosis of the left ventricular free wall, the crest of the interventricular septum and the anterior papillary muscle of the tricuspid valve. The necrotic areas are bright yellow with a dusky rim.
Hearts post myocarditis often show areas of myocardial necrosis and even dystrophic calcification, but otherwise resemble dilated cardiomyopathy (Figure 14.19).
It is very unusual to see a heart in the setting of congenital heart disease that has not undergone some transcatheter or surgical intervention, therefore knowledge of both the anatomy of congenital heart disease and its treatment is essential in assessment.
The most common conditions encountered are failed Fontan (see section Failing Fontan) and Norwood (see below) operations for hypoplastic left heart syndrome.
In assessing these hearts, therefore, not only is the original pathology present, but also the secondary pathology associated with surgery and its effects, and also cardiac failure. With the exception of the neonate with hypoplastic left heart syndrome, most children with congenital heart disease undergoing transplantation have had multiple previous surgical palliative and corrective operations, which adds to the complexity of the explanted specimen.
22.214.171.124 Technical Considerations
Many of the materials used in these operations can be sectioned histologically. Sutures may have to be removed to preserve quality of sections, but Gore-Tex can be easily sectioned and does not present a technical problem. There is frequently calcification, and some material may require a short period of decalcification before processing and sectioning. There may be artificial or biological valves.
Follow the standard sequential segmental analysis. It is usually possible to determine the atrial situs even if only parts of the atria are attached. The muscular trabeculations and terminal crest identify the right atrium.
It is usually not possible to form any opinion on the pulmonary venous anatomy since the pulmonary veins are never included in the explanted heart. Even the systemic venous anatomy may not be interpretable from the specimen submitted. Usually insufficiency of the atrial septum is included to offer an opinion on it.
Each case must be assessed on its own features when deciding the best method of dissection. I find it useful to cut the hearts in one of the echocardiographic standard planes, but it may sometimes be necessary to dissect in the standard manner following the course of the blood. Photography is important for documenting abnormalities. Video is even better.
Myocardium valves and vessels should be sampled for histology .
The explanted hearts with congenital heart disease show some common features as a group. The majority will have undergone at least one, if not multiple, surgical procedures and, as a result, will show dense pericardial adhesions. This makes recognition of the external topography more difficult. It is important to identify the coronary arteries and assess them. I prefer to dissect the major arteries on the epicardial surface, albeit epicardial fibrosis can make the procedure tedious (Figure 14.20). At the very least they should be probed and palpated. Atriotomy and aortotomy scars and suture lines are almost invariable. The hearts have all been failing and will thus be enlarged, some greatly so. Some have attached permanent pacing leads. The myocardium shows areas of subendocardial fibrosis. The disordered anatomy that has led to heart failure is usually complex to begin with, so hearts with isomerism of the atrial appendages, with congenitally corrected transposition or those requiring Fontan circulation, make up a large share of the explanted hearts.
Figure 14.20 Dissection of epicardial coronary arteries. Explanted heart from an 11-year-old with mitral and aortic stenosis who had undergone Norwood procedure and bilateral Glenn shunt and had failing right ventricle. The Damus–Kaye–Stansel anastomosis is visible, connecting the hypoplastic aorta to the much larger pulmonary trunk. The epicardial coronary arteries have been dissected in the epicardial fat. They show a dominant right coronary artery. The LAD artery delineates the position of the interventricular septum. The circumflex vessel is absent.
126.96.36.199 Some Specific Conditions
Very unusual to get the unoperated heart
Norwood operation with or without Sano modification
The left ventricle is diminutive (Figure 14.21)
Aortic valve atretic or severely hypoplastic and stenotic (Figure 14.22)
Mitral valve atretic or hypoplastic; its papillary muscles are inconspicuous (Figure 14.21)
Usually no VSD
Left ventricular lining shows dense fibroelastic thickening
The myocardium shows myofibre disarray, fibrosis and dysplastic vessels
Damus–Kaye–Stansel anastomosis, or at least part of it, may be included (Figure 14.20)
Fontan anastomoses will not be included
Figure 14.21 Hypoplastic left heart. Explanted heart from a one-year-old with failing stage 2 Norwood. The heart is cut in a simulated four-chamber view and viewed from behind. The right atrium is identified by its muscular trabeculations. Very little of the left atrium is included. The right ventricle occupies most of the ventricular mass. The left ventricle is a little cavity sitting atop the interventricular septum. It has a dense endocardial lining and the mitral valve is hypoplastic and thickened with thickened cords and barely visible papillary muscles. The aortic valve is not visible in this cut but was atretic. The myocardium of the right ventricle is hypertrophied and the septum in particular shows streaky fibrosis. There is fibrosis also of the tips of the papillary muscles of the tricuspid valve.
Figure 14.22 Hypoplastic left heart. Same heart as in Figure 14.20 cut in a simulated long-axis view and viewed from behind. The left ventricle is tiny in comparison to the right. It shows a thick opaque lining. The mitral valve leaflets are thickened and the cords short and thick with diminutive papillary muscles. The left ventricular outflow tract is a narrow conduit of considerably smaller diameter than the aortic lumen and includes part of the membranous septum. The aortic valve leaflets are small and thick. A coronary artery orifice is visible. The right ventricular endocardium is also thickened and opaque.
Tetralogy of Fallot
May be a conduit – frequently shows calcification
The left ventricle may be dilated and fibrotic (Figure 14.23)