Morphology of the functionally univentricular heart

Of all the complex malformations that affect the heart, those that have produced the greatest difficulty, over the years, in terms of logical description and classification are the ones with the circulations supported by a functionally univentricular mass. The problems in description stem from the fact that, although the ventricular mass functions as a singular entity, the majority of lesions falling within this category, from the stance of morphology, possess two ventricular chambers. For many years, and indeed, even now in many centres, the hearts are described as being “univentricular”, or alternatively as “single ventricles”. There is still no consensus as to which particular lesions should be included within this “univentricular” category. The paradigm of the group is usually taken as double inlet left ventricle. 1 In this lesion, the dominant left ventricle is accompanied by a rudimentary second chamber, albeit that arguments continue as to whether the second chamber is an incomplete right ventricle, 2 or simply an infundibulum. 3 Further arguments raged as to whether tricuspid atresia should be included within the univentricular category. 4 , 5 The debate is rationalised when we recognise that all the potentially univentricular hearts are treated nowadays by constructing the Fontan circulation, 6 or one of its variants, 7 as indeed are some unequivocally biventricular hearts. 8 Clarification and simplification of the anatomical arrangement in this functionally univentricular category, as we will show in this review, is provided by rigorous application of the crucial philosophic principle of analysis called the “Morphological Method”, 9 coupled with separate analysis of the ventricular mass and the atrioventricular junctions. 10 , 11