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Ann Thorac Surg 1998;66:621-626
© 1998 The Society of Thoracic Surgeons
a Department of Paediatrics, Imperial College School of Medicine at National Heart and Lung Institute, London, England, United Kingdom
Address reprint requests to Prof Anderson, Department of Paediatrics, Imperial College School of Medicine at National Heart and Lung Institute, Dovehouse St, London SW3 6LY, UK
Presented at the Workshop on "One and One-Half Ventricle Repairs," Gubbio, Italy, Dec 6–7, 1996.
Abstract
Background. The surgical option of biventricular repair requires two ventricles, each fully capable of supporting the systemic or pulmonary circulation. The morphologic substrates that may preclude some hearts from biventricular repair need to be assessed.
Methods. Heart specimens were reviewed to assess the morphologic mechanisms that produce an unbalanced ventricular mass and to identify features that would, potentially, be a contraindication for biventricular repair.
Results. Hearts with solitary and indeterminate ventricles, and hearts with essentially solitary ventricles, often have associated abnormalities of venoatrial connections and arrangement of the atrioventricular valves. In the majority of hearts with univentricular atrioventricular connections, the rudimentary and incomplete ventricle of either right or left morphology may be too small to support either the systemic or the pulmonary circulation. Straddling with overriding of the atrioventricular valve, unbalanced atrioventricular septal defect, and gross hypoplasia of one of the ventricles in hearts with biventricular connections are other mechanisms producing ventricular imbalance, which could preclude biventricular repair.
Conclusions. The morphologic mechanisms that result in ventricular imbalance are mainly related to the sizes and morphology of the ventricles, septal malalignment, valvar morphology, and component make-up of the ventricles. These features will influence decision-making in considering the option of biventricular repair.
In our review discussing the morphologic definition of ventricles [1], we made the point that all chambers within the ventricular mass possessing an apical trabecular component could logically be described as ventricles. We also emphasized that full description of such ventricles required information concerning all their features, namely component make-up, morphology, and, most importantly, size. It is the feature of size that is key in determining the nature of the ventricular mass in hearts unsuitable for biventricular correction. The obvious answer to the question posed in all those hearts that have one big and one small ventricle, when the small ventricle is overly hypoplastic, and those few hearts in which there is a truly solitary ventricle. The latter hearts can be dealt with simply and briefly. The hearts that possess one big and one small ventricle pose greater problems for at least two reasons. First, there are several morphologic mechanisms that produce an unbalanced ventricular mass. Not all disqualify automatically the heart from the surgical option of biventricular correction. Second, there is no way that the morphologist can predict, based on studies of autopsied hearts, the critical size of a ventricle that automatically rules out its capacity to support the systemic or pulmonary circulation. As yet, the answer to this conundrum has also defeated the best efforts of the echocardiographers, although strides have been made in providing guidelines that point to the minimal size required of the left ventricle to support the systemic circulation in the setting of critical aortic stenosis [2–4]. In this review, therefore, we will concentrate on those morphologic mechanisms that result in ventricular imbalance, hoping that the ever-increasing sophistication of cross-sectional echocardiography [5] will soon permit those morphologic features properly to be assessed during life.
Hearts with a solitary and indeterminate ventricle
Such hearts are exceedingly rare. When found, almost always they possess double inlet to, and double outlet from, a ventricle of indeterminate apical trabecular pattern. The very coarse apical trabeculations extend throughout the apical component, and almost always are continuous with the tension apparatus of both atrioventricular valves or, more frequently, a common atrioventricular valve. The potential for septation of such a ventricle, which must always be considered as a potential possibility, is then further eroded in most instances by the fact that the majority of patients in the category have isomeric atrial appendages, adding the increased problem of grossly abnormal venoatrial connections. In such cases, further to compound the potential surgical difficulties, there is usually a gross abnormal disposition of the conduction system [6]. Taken together, these problems rule out the options not only for biventricular repair, but also those of creating a half-ventricle.
The same anatomic considerations also rule out the even rarer cases of hearts with solitary and indeterminate ventricle in which there is absence of one atrioventricular connection. On the basis of the above discussion, we can also rule out all those hearts in which, in clinical terms, there seems to be a solitary right or a solitary left ventricle. In these hearts, a rudimentary and incomplete ventricle is almost always found on histologic examination. Such a ventricle is self-evidently incapable of being incorporated in any proposed surgical repair. One lesion that might be considered to lend itself to biventricular repair, and that warrants discussions in this setting, is the heart with a huge ventricular septal defect, in other words, the "type C" single ventricle in the categorization of Van Praagh and colleagues [7]. In reality, these hearts possess a rim of apical ventricular septum, which separates the apical components of the morphologically right and left ventricles [8]. The conduction axis descends from a regular atrioventricular node when such hearts are found with concordant atrioventricular connections, but would be abnormal in the setting of discordant or ambiguous and biventricular connection. These hearts would lend themselves to biventricular repair in the absence of confounding features such as a complexly malformed common valve or gross abnormalities of the pulmonary arterial pathways.
Hearts with an unbalanced ventricular mass
There are several combinations to be discussed in this section, and the constraints of space mean that the coverage of each specific entity must be relatively brief. We will be particularly brief when describing those hearts, therefore, that automatically rule out biventricular repair, spending somewhat more time on those situations where the decision-making is more complex.
Hearts with univentricular atrioventricular connection
The group of hearts with univentricular atrioventricular connection, of course, includes those already discussed with a solitary and indeterminate ventricle. In the context of the unbalanced ventricular mass, however, we are concerned with all those hearts possessing one big and one small ventricle in consequence of the atrial chambers being connected to the dominant ventricle, either because of double inlet or because one atrioventricular connection is absent (Fig 1). Some rare hearts with univentricular connection to a dominant left ventricle, and with concordant ventriculoarterial connections, possess a rudimentary and incomplete right ventricle of sufficient dimensions that it might appear "normal" in size [9]. Other hearts with tricuspid atresia occurring in the context of absence of the right atrioventricular connection have, in the past, been corrected surgically by incorporating the rudimentary right ventricle within the pulmonary circulation [10]. Such incorporation can encourage growth of the rudimentary right ventricle. This setting is produced when the ventricular septal defect is of good size and there is no obstruction within the pulmonary arterial pathways (so-called type 1C in the alphanumeric classification for tricuspid atresia). Nowadays, however, this surgical option seems to have fallen into disrepute in favor of the cavopulmonary connection. The possibility for such repair, nonetheless, is worthy of consideration. Similarly, some hearts with double-inlet left ventricle still lend themselves to biventricular surgical repair by means of septation. The hearts with left-sided rudimentary right ventricles, discordant ventriculoarterial connections, and naturally occurring subpulmonary stenosis stand out as a group in which septation provided good surgical results [11], but groups working in Japan have continued to explore the option of septation with surgical results comparable with those obtained using univentricular options [12]. The requisites for such repair are two unobstructed atrioventricular valves and the potential readily to septate the systemic and pulmonary circulations. This combination is produced most immediately by the entity discussed above (so-called type A3 in the alphanumeric classification popularized from the Mayo Clinic [7], or in the so-called Holmes heart [concordant ventriculo-arterial connections with right-sided rudimentary right ventricle]). The frequent finding of a restrictive ventricular septal defect in the latter setting is an obvious surgical problem. With increasing experience with the double switch procedure, nonetheless, and recognizing the ingenuity of cardiac surgeons, it is likely that a larger proportion of patients with double-inlet ventricle could become candidates for biventricular repair. The majority of hearts with univentricular atrioventricular connection, however, have rudimentary and incomplete ventricles of either right (Fig 2) or left (Fig 3) morphology, which cannot be incorporated into a biventricular repair because not only are they incomplete and rudimentary but they are also too small to support either the systemic or the pulmonary circulation.
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Hearts with intact ventricular septum and critical stenosis or atresia of the outflow tracts
In this, the final group of hearts that has ventricular hypoplasia as one of its characteristic components, the afflicted ventricle is usually normally constructed, but has cavitary hypoplasia either because of hypertrophy of its walls or else because the entire ventricle is small. It is mural hypertrophy leading to cavitary hypoplasia that is the problem in critical pulmonary stenosis or pulmonary atresia existing in the setting of an intact ventricular septum. In pathologic terms, these hearts constitute an anatomic spectrum, with the right ventricular cavity usually being of normal dimensions in the setting of a critically stenotic valve, showing minimal hypoplasia with an imperforate valve, but becoming severely compromised when the mural hypertrophy squeezes out not only the apical trabecular component but also the cavity of the infundibulum, producing, in effect, muscular atresia [21]. It is within this spectrum that hearts will be found that will lend themselves to the one and a half ventricular repair. We will discuss the morphology more fully in a subsequent review within this supplement [22].
Perhaps the group of hearts that raises the most problems concerning the ability of a ventricle to support the circulation on account of its size is the one found with critical aortic stenosis and an intact ventricular septum. These hearts are closely related to the hypoplastic left heart syndrome and, with the latter syndrome, there is no question of biventricular repair. Indeed, the larger question is whether the dominant right ventricle in such lesions is itself capable of sustaining the systemic circulation after an eventual Fontan procedure. The hypoplastic left heart syndrome, in its pure form, is found with aortic atresia. The mitral valve, however, can be absent, along with the left atrioventricular connection, or it can be stenotic. When the valve and connection are absent, the left ventricle is no more than a virtual slit. Sometimes the cavity is discovered only after histologic examination. When the mitral valve is patent but stenotic and miniaturized, the left ventricular cavity is not only hypoplastic, but is lined by a thick fibroelastotic layer. Such a picture can also be found in the setting of critical aortic stenosis, and the fibroelastosis can also be seen when the left ventricle is somewhat dilated. Such findings constitute a bad prognostic sign and are a poor indicator of success for any attempted biventricular repair. It is in those circumstances where the left ventricle is of marginal size but shows no evidence of fibroelastosis that the real problems arise. In this setting, it is probably the structure of the deformed valve that is of most significance. A large proportion of valves in autopsy series show the so-called unicuspid and unicommissural arrangement [23]. The leaflets are hinged in truly annular fashion when showing this deformity (Fig 6). Mere incision of the diaphragmatic obstruction may relieve the stenosis, but is unlikely to produce a competent valve. If biventricular repair is deemed acceptable, with the size of the left ventricle taken into account, the abnormal architecture of the valve suggests that a Ross procedure combined with the biventricular approach may well offer the best chance of success [24].
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The primary morphology that rules out biventricular repair for the overall spectrum of congenitally malformed hearts is, obviously, the exceedingly rare situation in which a solitary chamber exists within the ventricular mass. Far more frequently, biventricular repair will be excluded because of the combination of one big and one small ventricle. This can be produced by abnormal segmental combinations, such as double-inlet ventricle or absence of one atrioventricular connection (see Fig 1), or by hypoplasia of one ventricle in the setting of critical stenosis or atresia of its outflow tract. Ventricular imbalance exists in other circumstances such as atrioventricular septal malalignment. Biventricular repair may also be excluded simply because of complications occurring in pathways of flow when both ventricles are of good size, such as double-outlet right ventricle with noncommitted ventricular septal defect. In all these settings, anatomic analysis needs to include assessment not only of the size, but also the component make-up of the chambers within the ventricular mass. It is the tripartite approach to evaluation [1] that we find always to be of value in these circumstances.
Acknowledgments
This work was supported by the British Heart Foundation.
References
ventriclular repair. Ann Thorac Surg 1998;66:673-677.This article has been cited by other articles:
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  E. M. Delmo Walter, P. Ewert, R. Hetzer, M. Hubler, V. Alexi-Meskishvili, P. Lange, and F. Berger Biventricular repair in children with complete atrioventricular septal defect and a small left ventricle Eur. J. Cardiothorac. Surg., January 1, 2008; 33(1): 40 - 47. [Abstract] [Full Text] [PDF]
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 L. Kiraly, M. Hubay, A. C. Cook, S. Y. Ho, and R. H. Anderson Morphologic features of the uniatrial but biventricular atrioventricular connection J. Thorac. Cardiovasc. Surg., January 1, 2007; 133(1): 229 - 234. [Abstract] [Full Text] [PDF]
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 A. Fraisse, P. J. del Nido, J. Gaudart, and T. Geva Echocardiographic characteristics and outcome of straddling mitral valve J. Am. Coll. Cardiol., September 1, 2001; 38(3): 819 - 826. [Abstract] [Full Text] [PDF]
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