The Mitral Valve in Endocardial Cushion Defects

Abstract

Since 1957, 29 cases of endocardial cushion defect have been operated upon in this hospital. They included an appreciable number of the more complex forms of the anomaly, and in these, as has been the experience of other workers (Cooley, Latson, and Keats, 1958;Kiely et al., 1958;Gerbode et al., 1961, andScott, Hauck, andNadas, 1962a), the over-all mortality was distressingly high. There were, however, a number of deaths among the apparently simple cases. Reviewing the causes of death in these "simple" cases suggested that persistence of mitral incompetence had played a dominant role. Difficulty was experienced in repairing the mitral valve because the anatomy was more complicated than had been expected, and of a kind not previously stressed.The problems presented by these patients prompted us to review the group as a whole for there appeared to be a lack of correlation between the clinical evaluation and the findings at operation. We considered it desirable to clarify the anatomy of the lesion and the adequacy of methods for its assessment and treatment, paying particular attention to the mitral valve and the ways in which its form and function might best be determined. TERMINOLOGY AND CLASSIFICATIONThe term "endocardial cushion defect" covers a wide range of embryologically related congenital cardiac anomalies from the so-called simple ostium primum at one end of the scale to the complete atrio-ventricular canal at the other. There appears to be little virtue in considering either of these two extremes as separate entities since this leaves a large group of intermediate forms unclassified, and implies that there is a clear-cut distinction between groups, which is fallacious. While no classification is entirely satisfactory, for practical purposes we use that of Campbell and Missen (1957) who grouped them in three grades of increasing complexity.The embryological development of the endocardial cushions and the part that they play in the final formation of the central portions of the heart have been clearly outlined by van Mierop and his colleagues (1962). Briefly, the endocardial cushions are a dorsal (posterior) and ventral (anterior) mass of mesenchyme which grow, fuse, and become so modelled that they divide the atrio-ventricular canal into two orifices-the mitral and tricuspid valves. At the same time, however, they contribute to the atrio-ventricular septum and membranous septum as well as to the valve cusps and their chordae. Each endocardial cushion provides two half leaflets, and on the right side there is an additional contribution from the conus septum. The distribution of these elements in the mature heart is shown superimposed on photographs of the right and left sides of a normal child's heart in Fig. 1.

Left ventricular angiocardiography in atrioventricular defects.

“…Separate left atrial injection is considered to be obligatory for the confirmation of these lesions. We did not find angiocardiography was reliable for the diagnosis of 455 tricuspid valve abnormality, which is contrary to the experience of others (Omeri et al, 1965).…”

“…Using the venous route to the left ventricle has been a deliberate policy, and unlike Omeri et al (1965) we did not find this interfered with assessment of mitral valve anatomy. Larger catheters, No.…”

Electrocardiographic correlation of anatomical and haemodynamic data in ostium primum atrial septal defects.

“…Left atrial enlargement did not indicate mitral insufficiency (Al Omeri et al, 1965;Blondeau et al, 1966). Biatrial enlargement, however, was only seen in cases with moderate to severe mitral incompetence.…”

“…It has been previously assumed (Al Omeri et al, 1965;Fernandez-Caamano et al, 1966) that a high qR complex in the left praecordial leads was a good guide to the presence of mitral regurgitation. We have found this criterion very useful but not completely reliable.…”

“…In the absence of left ventricular hypertrophy, considerable right ventricular hypertension may be suspected when the mean QRS axis is shifted to the right or inferior quadrants (Al Omeri et al, 1965), or when the R/S ratio in V6 is less than 1.…”