Biomedical subjects
Publications and source records attributed to J L Wilkinson.
The angiographic and haemodynamic findings in 2 cases of Pompe's disease (glycogenosis type II) indicated an abnormal trabecular pattern, not previously reported, on the left ventricular angiogram of both patients. This feature may be helpful in distinguishing Pompe's disease from other forms of myocardial abnormality.
Two pathological specimens are described in which a bizarre distortion of atrioventricular and ventriculoarterial relations existed. In both cases anterior and leftward displacement of the tricuspid valve coexisted with rightward displacement of the infundibular regions and semilunar valves. Abnormal expansion of the AV canal, possibly secondary to malrotation of the cardiac tube, is considered as a possible cause of the anomaly. One of the hearts showed severe subpulmonary stenosis produced by a valve-like structure which was well differentiated, with a complete annulus and chordae tendineae that inserted in a parachute-like fashion on the infundibular septum. The morphology of this structure was clearly different from that fo the fibrous tags described in other anomalies. Its origin is uncertain. These anomalies have important implications in relation to the nomenclature and classification of congenital heart malformations, and illustrate the value of recent modifications of the segmental approach.
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Two cases are described of a most unusual variant of two-chambered right ventricle. In both the ventricular septal defect was between the distal chamber of the right ventricle and the left ventricle. However the extensive dividing 'septum' between proximal and distal parts of the right ventricle converted the latter, haemodynamically, into part of the left ventricle. In the first case the distal chamber supported the aorta in the left anterior position, the pulmonary artery arising from the proximal part of the right ventricle. In the second the pulmonary artery arose from the distal chamber and the aorta from the proximal chamber. Though in both the ventriculoarterial connection was double outlet right ventricle, functionally there was arterial concordance in case 1 and discordance in case 2. A further disconcerting feature was the resemblance of the distal right ventricular chamber to the rudimentary chamber of a univentricular heart of left ventricular type.
Three hearts are described in which a fibrous membrane was interposed between the right atrium and a formed but hypoplastic right ventricle, which possessed recognisable inlet, trabecular, and infundibular components. In these hearts the distribution of the conducting tissue was as expected for concordant atrioventricular connections, and contrasts with that seen in the classical type of 'tricuspid atresia'. The distinctive morphological and histological features of these specimens lend further support to our view that the majority of cases of atresia of the right atrioventricular orifice should be regarded as coming within the designation of 'the univentricular heart'.
Anatomical studies were made on 114 necropsy specimens of atrioventricular defects with atrioventricular concordance. The malformation is characterised by disproportion between the ventricular inlet and outlet dimensions and a malorientation of the aortic valve relative to the atrioventricular valve or valves. Associated with this there is a characteristic 'scopped-out' appearance of the muscular ventricular septum, gross abnormalities of the membranous components of the septum as compared with the normal heart, and narrowing of the aortic outflow tract. Hearts with these anatomical features can be divided into partial and complete forms depending on the morphology of the atrioventricular annuli. In the partial form the septal leaflets are conjoined to give separate mitral and tricuspid orifices, the conjoined leaflets being displaced into the ventricles and usually attached to the crest of the septum. In the complete form, anterior and posterior components of the 'septal' leaflets are separate, so that a single valve orifice connects the atrial to the ventricular chambers. Further subdivision of the complete form, apart from the morphology of the anterior leaflet, is dependent upon the presence or absence of an ostium primum atrial septal defect.
Anatomical studies were made on 70 necropsied hearts with atrioventricular defects from patients with situs solitus and atrioventricular concordance, all having a common atrioventricular orifice. The arterial connections were concordant in 68 and were double outlet right ventricle in two; cases with arterial discordance (transposition) or single outlet of the heart were excluded. It proved possible to subdivide the hearts, depending on the morphology of the valve leaflets. Five leaflets were distinguished by the commissural pattern and their insertion to major papillary muscles. They were a posterior bridging leaflet, right and left lateral leaflets, and right and left anterior leaflets. Subdivision was made on the basis of the disposition of the anterior leaflets. In six hearts the left anterior leaflet was committed to the left ventricle and the right anterior leaflet to the right ventricle, the commissure between them being on the crest of the ventricular septum. In 39 hearts there was minimal bridging of the left anterior leaflet so that it extended between the anterior papillary muscle of the left ventricle and the medial papillary complex of the right ventricle. In eight hearts the right margin of the left anterior leaflet was attached to an apical papillary muscle, while in 17 hearts it was attached to the anterolateral papillary muscle of the right ventricle. As the bridging of the left anterior leaflet increased, so the size of the right anterior leaflet decreased, but in all hearts both leaflets were identified. These findings were compared with previous classifications of complete atrioventricular defects.
Seventeen cases are described in which both atria connect directly to a chamber with right ventricular characteristics. The atria connected through separate atrioventricular valves in six hearts and a common valve in 11. All hearts had a posterior rudimentary chamber. The septum which separated it from the main chamber was directed to the crux of the heart. Ten hearts were from patients with atrial situs solitus and seven from patients with atrial situs ambigous. Arterial connections were concordant in three cases, had a double outlet from the main ventricular chamber in nine and single outlet of the heart in five. The patent artery always arose from the main chamber, with pulmonary atresia in three and aortic atresia in two. This and other studies indicate that double inlet atrioventricular connection does not predict the morphology of the main chamber. Although usually associated with a main chamber of left ventricular type, it may also be associated with a main chamber having right ventricular characteristics. Both types should be considered as univentricular hearts; the posterior chamber in hearts of right ventricular type are analogous to the anterior chamber in univentricular hearts of left ventricular type and are a rudimentary chamber rather than a hypoplastic ventricle. In the right ventricular form of univentricular heart, the trabecular zone of the rudimentary chamber is of left ventricular type.
The cardiac specialized conduction tissue was studied by serial sectioning in 13 cases of situs ambiguus. In four cases of right isomerism, we found paired sinus nodes in relation to a crista terminalis, and in each case a sling of conduction tissue between two atrioventricular nodes was present regardless of the ventricular morphology or cardiac position. In the cases with left isomerism, the sinus node was hypoplastic and abnormally located. We saw two types of atrioventricular conduction systems. In the three cases in which the morphologically right ventricle lay to the right of the morphologically left ventricle (presumed d-loop), a single atrioventricular bundle arose from a normally located atrioventricular node. In the five cases in which the morphologically right ventricle lay to the left of the morphologically left ventricle (presumed l-loop) and in the one case with a univentricular heart, paired atrioventricular nodes were present, linked or potentially linked by a sling of conduction tissue.
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Four specimens of univentricular hearts of the right ventricular type, three with two atrioventricular valves and one with a common valve, have been examined histologically to identify the atrioventricular conduction system. Three of the specimens were initially thought to have only one chamber within the ventricular mass, a chamber which had a right ventricular trabecular pattern. On detailed examination and with removal of blocks of tissue for histologic study, a second, rudimentary chamber was found in the posterior ventricular wall. This chamber had a trabecular zone of the left ventricular type and was connected with the main chamber only via a small defect in the septum which separated the two chambers. In all four cases the connecting atrioventricular node was dound in normal relationship to atrial markers and the penetrating bundle descended onto the posterior wall of the main chamber. In three cases it ran along the crest of the septum between the main chamber and rudimentary chamber, in relation to the septal defect. In two cases left bundle branch tissue was identified running into the rudimentary chamber. This pattern of conducting system is different from that previously identified in other varieties of univentricular heart and again underlines the importance of intraoperative mapping of the conduction system during surgery of the univentricular heart.
A simple system for the analysis and classification of the univentricular heart is described. The basis of this approach is the use of a step by step sequential nomenclature with attention paid to the morphology, connexions and relationships of each cardiac segment in turn. Three major morphological types of univentricular heart are identified and these may be distinguished, by their characteristic trabecular patterns, into hearts of left ventricular type, right ventricular type and indeterminate type. With the exception of the last it is usual for a rudimentary second chamber to be present upon the use of a clear definition of "ventricle", depending on readily ascertainable anatomical characteristics. Each morphological type of univentricular heart may be associated with a wide variety of different connexions and intracardiac relationships and it is neither possible nor desirable to describe these in terms of a rigidly structured classification. Adherence to the simple semantic framework outlined would resolve much of the confusion and controversy which exists in relation to the univentricular heart.
22 specimens of univentricular hearts of right ventricular type were examined morphologically. 6 hearts were sectioned for study of the conducting tissue. All the specimens had rudimentary second chambers, which were frequently so small as to have been overlooked, both angiographically and at initial morphological study. The segmental connexions and intracardiac relationships varied widely. Examples were found with 2 atrioventricular valves, a common valve and with absence of either the right or the left atrio-ventricular connexion. In some cases straddling of an atrioventricular valve was observed. The rudimentary chambers always lay posteriorly but varied between a position to the left of the ventricle and one to the right. The septum between ventricle and rudimentary chamber ran to the crux of the heart in all but 2 instances. In most specimens both great arteries arose from the ventricle (double outlet ventricle), so that the rudimentary chamber was solely a trabecular pouch. 4 hearts had concordant arterial connections with the aorta arising from a posterior "outlet" chamber. Pulmonary atresia was found in 5 cases and aortic atresia in 2. The conduction system originated from a normally placed atrioventricular node in 4 out of 6 cases and was related to the trabecular septum in 5. The penetrating bundle usually descended onto the crest of the septum at the "crux" of the heart and bifurcated astride it. In 2 cases with an absent atrioventricular connexion the penetrating bundle originated from an abnormally placed node and in one of these specimens a sling of conducting tissue was identified with dual pathways.
Univentricular heart of left ventricular type is defined as the condition in which the entirety of atrial inputs is committed to a main chamber exhibiting trabecular pattern of left ventricular type, usually in the presence of another chamber in the ventricular mass which has a right ventricular trabecular pattern. This condition can occur with two atrioventricular valves, a common atrioventricular valve, a straddling atrioventricular valve or with absence of the right or left atrioventricular connexions. The hallmark of univentricular heart of left ventricular type is absence of the inlet septum, which normally separates the inlet portions of the two ventricles and which in the normal heart carries the atrioventricular conduction bundle. In univentricular heart of the left ventricular type, as a consequence of its absence, an abnormal disposition of the atrioventricular conduction tissues is found. An anterior or lateral atrioventricular node is present from which the prenetrating bundle descends onto the trabecular septum separating main chamber from rudimentray chamber. The topographical relationship of the bundle particularly with respect to the outflow tract of the posterior great artery from the main chamber, depends on the position of the rudimentary chamber. In atrial situs solitus, a left-sided rudimentary chamber will be associated with a long bundle in close proximity to the ostium of the posterior great artery from the main chamber. In contrast, in the heart with a right-sided rudimentary chamber the bundle will stay remote from the posterior outflow tract. The position of the rudimentary chamber will also alter the site of the ventriculotomy for any proposed corrective surgery and, hence,, alter the relationship of the bundle relative to the outlet foremen, as viewed by the surgeon. The general disposition of the atrioventricular conduction system in univentricular heart of left ventricular type is not altered by the type or mode of the atrioventricular connexion, nor by the type of the arterial connexion.
The ventricle morphology is described in hearts in which the entire atrial inputs are committed to a single chamber in the ventricular mass, this being considered the criterion for definition of the univentricular heart. Such a definition does not exclude from the univentricular category hearts with two chambers in their ventricular mass providing that the second chamber does not receive a direct atrial input. Three types of ventricular morphology were identified: hearts with a main chamber of left ventricular pattern and a rudimentary chamber of right ventricular pattern; hearts with a main chamber of right ventricular pattern and a rudimentary chamber of left ventricular pattern and hearts with a sole chamber in their ventricular mass of indeterminate pattern. Hearts may also exist of right or left ventricular type without rudimentary chambers. Variation was noted in type and position of the rudimentary chambers. Chambers of either right or left ventricular type were found supporting either or both great arteries (outlet chambers), and also without a direct outlet (trabecular pouches). Right ventricular rudimentary chambers were usually anterior but could be right or left sided; left ventricular chambers were posterior but again could be right or left sided. Hearts with these ventricular morphologies possessed either double inlet atrioventricular connexions, or absence of the right or left atrioventriuclar connexion. In double inlet ventricles, cases were observed with two valves, a common valve, one imperforate valve, and with straddling atrioventricular valves. A straddling valve was also found in hearts with absence of one atrioventricular connexion. Further variation was found in the pattern of arterial connexions. It is concluded that ventricular morphology is an important feature of the iniventricular heart but must be considered in the context of other important and variable features.
Diagnosis of the univentricular heart and recognition of its most important variations depends on the establishment of atrial situs, the demonstration of the type and mode of the atrio-ventricular connexion, the identification of the presence or absence of a rudimentary chamber, the establishment of its morphology, together with that of the main chamber, and classification of the arterial connexion. A logical means of demonstrating these features is presented, depending on bronchial visualization, one or possible two injections of contrast medium into the main chamber, followed if necessary by selective injection into the rudimentary chamber, and in exceptional cases, demonstration of the atrial septum by atrial injection. The advantagess of cranio-caudal tilt and oblique projections are discussed in detail.
There are three main reasons why there are problems concerning the nomenclature of the univentricular heart. The first is that different authorities have used the same term to describe different varieties of the univentricular heart. The second is that many of the terms used in categorisation of these anomalies are derived from embryological concepts which are more or less speculative. The final reason, perhaps the major one, is that there is a lack of definition of a ventricle. Consequently there is no consensus as to precisely what constitutes a "univentricular" heart. Many of the heart described as "single" or "common" ventricle possess two chambers within their ventricular mass. For such hearts to be univentricular it is evident that one of these chambers cannot be a ventricle. Yet definitions have yet to be provided to distinguish ventricles from rudimentary chambers. The solutions to these problems can be produced firstly by using descriptive terms for categorisation of univentricular hearts which do not have multiple meanings. Secondly, the problems concerning usage of embryologic terms can be easily circumvented by eschewing all embryologic considerations in naming these malformations. The problem of definition of a ventricle is best solved by considering normal ventricles as possessing three portions -- an inlet portion, a trabecular portion and an outlet portion. It may then be proposed that the minimal requirements for a ventricle are that it possesses at least an inlet and a trabecular portion. Chambers without inlet portions are rudimentary chambers. Either ventricles or rudimentary chambers may possess a trabecular pattern of right or left ventricular type. Tue univentricular heart may then be categorised as composing all anomalies which have a sole chamber in their ventricular mass together with all anomalies which possess a rudimentary chamber.
One of mono-zygotic twins who had the asplenia syndrome with severe cardiac malformations is described, the other twin being normal. This is the first documented case of situs ambiguus in mono-zygotic twins. The relationship of situs ambiguus to situs inversus, which has previously been described in a number of mono-zygotic twin pairs (some concordant and some discordant) is unclear.