The Right Ventricle and Small Pulmonary Arteries in Aneurysmal Dilatation of the Left Atrium

were collected together and analysed by Bramwell and Duguid (1928). They concluded that two main factors were concerned in the aetiology of this con- dition. A "passive factor" was gross fibrosis of the wall of the left atrium: this was usually, but not always, due to chronic rheumatic heart disease that had predominantly affected this chamber. An "active factor" was increased flow of blood into the inelastic fibrous left atrium commonly from a hypertrophied left ventricle through an incompetent mitral valve. They stated that " one cannot fail to be impressed by the fact that the condition is so constantly associated with great ventricular hypertrophy," and this applied in their collected series of cases not only to the left ventricular hypertrophy associated with mitral incompetence but also to right ventricular hypertrophy. Of the 20 cases in their series the state of the right ventricle at necropsy was specified in 13, and in 10 of these it was said to be hypertrophied. Wood (1954) also stated that "mitral incompetence is a more important cause of left atrial dilatation than mitral stenosis ". In the face of these data and opinions we thought it would be of interest to see how many of our cases coming to necropsy, with extreme dilatation of the left atrium, had mitral incompetence, right ventricular hypertrophy, and pulmonary vascular disease.