Mitral atresia and occlusive left atrial thrombus.

Mitral atresia and occlusive left atrial thrombus Sir, I have been studying the Case Report on page 649 of the September I969 issue of the British Heart Journal. I would like to suggest a completely different interpretation of the anatomy. I think that the fundamental lesion may be a single atrium with atrioventricular communis, and that the 'left atrium' is actually a common pulmonary vein which drains by a small orifice ('the ASD') into the left side of the common atrium. The mitral and tricuspid valves are represented by a common atrioventricular valve, well seen in Fig. 3A. If my interpretation is correct, there is no mitral atresia, and the case can be described as cor triatriatum sinister with atrioventricularis com-munis and single atrium. We are indebted to Professor R. Hudson for his embryological interpretation, which we consider most attractive. It seems to us, nevertheless, that the foramen ovale can be recognized in the 'interatrial septum' (Fig. 3A), indicating that interatrial septation occurred. Instead of considering the 'single atrium' possibility suggested, we could theorize that the diaphragm of 'cor triatriatum' descended and covered the 'ostium primum' and the mitral part of the AV valve, the tricuspid part taking over the feeding of both ventricles. The 'accessory chamber' would occupy the whole left atrium. This would nicely explain the semicircular band in the lower part of the septum (Fig. 3A) which could represent the edge of the septum primum, covered by the diaphragm with the central orifice. It should also be noted that the presence of the left atrial appendage (Fig. 3B) does not seem to favourthe left cavity being an 'accessorychamber', though we do not consider this to be a strong point. It is possible that related cases could shed light on the validity of this new concept, and support the naming of the malformation as 'Stenosis of the common pulmonary vein and AV communis', with or without 'single atrium'. For the present, it appears to us justifiable to use the description 'Mitral atresia and overriding tricuspid valve, with AV type of defect', implying that the mal-formation, despite its two distinct anatomical and ontogenic facts, shares the basic clinical, haemo-dynamic, and anatomical features of the anatomo-clinical group of mitral atresias.