A. Combination with partial persistence of the truncus arteriosus communis. The defects coming under this head show usually very great deficiency of the organ and its great vessels, although the heart itself in rare instances shows the proper arrangement of the cavities and their valves. The persistence of the truncus art. comm. may be complete or partial; the defect consists in the total absence or arrest of growth of the septum of the truncus, which partitions it into two portions. Normally, the two septa grow simultaneously and meet at the base of the heart. In cases of persistence of the truncus art. comm. the upper septum fails to develop. In incomplete division of the truncus the pulmonary artery suffers more than the aorta, and the former is always narrower than its fellow-vessel. This difference varies greatly. The valves of the pulmonary artery often fail entirely, and the ductus art. Botalli is many times absent.
B. Combination with cor biloculare.—Here we have a heart consisting of two cavities—one auricle and one ventricle—where no partitioning has taken effect. The defect results from the failure of the septum ventriculorum to grow; and with this, as in the former division, comes also a more or less complete failure of the septum trunci art. comm.
C. Combination with single ventricle and divided auricles (cor triloculare biatriatum).—In the cases of single ventricle with more or less complete division of the auricles the pulmonary artery generally shows narrowing to a greater or less degree; it may still be pervious, although its orifice is closed, or it may be throughout entirely obliterated. The valves may be entirely wanting. The duration of life is very short, though in a very few with effective compensatory changes it may be prolonged very considerably.
D. Combination with divided ventricle and a single auricle (cor triloculare biventriculare).—In strictness, this defect is nothing more than an open foramen ovale with some deficiency of the pulmonary artery; but, in reality, the heart is much more malformed. The whole septum atriorum is wanting; the superior or descending vena cava is doubled—one entering the left part of the common auricle, the other opening more to the right. The ventricular septum shows a greater or less defection, the pulmonary artery is narrowed, and the aorta arises from both ventricles or wholly from the right one.
E. Combination with special anomalies in the position of both the great arterial trunks.—Here come a variety of anomalies in the arrangement of the aorta and the pulmonary artery in relation to their respective ventricles and to themselves.
a. In transposition of the great arteries, the aorta arising from the right ventricle and the pulmonary artery from the left cavity, either there comes a general transposition of all the viscera or the heart alone is reversed. Very rarely in transposition of the vessels the septum ventriculorum is closed, commonly open, and although the size of the vessels may be normal, usually their relation and position continue reversed throughout their course. In cases where the pulmonary artery is narrowed the duration of life is short. b. The pulmonary artery may arise from the left ventricle and the aorta from both ventricles; or, c, the aorta may come wholly from the right ventricle, and the pulmonary artery from both cavities; the latter vessel may be narrowed or show its normal width or even be considerably dilated. d. Both the great vessels may arise from the left ventricle, very much dilated, with the aorta in front of the pulmonary artery and the latter narrowed. e. The relation of the great arteries may be found reversed—i.e. the aorta in front and the pulmonary artery behind, and the aorta spring from both ventricles and the pulmonary from the right alone.
F. Combination with primary defects of other valvular orifices of the heart.
a. The tricuspid valve may be quite rudimentary, producing by the regurgitation thus allowed, especially when combined with pulmonary stenosis, great dilatation of the right auricle. When the pulmonary artery is narrowed the septum ventriculorum remains open; the aorta carries the blood, distributing it to the lungs by an open ductus arteriosus Botalli or a collateral circulation. The collateral circulation is less developed the greater the width of the pulmonary artery. The foramen ovale may close in such a case, but when it remains open the relief to the over-distended right auricle is very great.
b. Many cases of congenital stenosis and atresia of the right auriculo-ventricular orifice are reported in which the condition of the pulmonary artery is not described. In fact, it is a difficult matter to determine if the auriculo-ventricular narrowing is a primary one. Its defective size may be merely, as it were, a rudimentary condition, a failure to enlarge through disuse. When the pulmonary orifice is closed and the right ventricular cavity remains small, the tricuspid orifice is naturally small in size. There are, however, undoubted cases of tricuspid narrowing with or without stenosis of the pulmonary artery; the defect consists in a primary contraction of the fibrous ring or in the union by partial adhesions of the leaflets.
Malformations affecting primarily the Left Side of the Heart.