Subacute Bacterial Endocarditis
A 36 year old man had a persistent low grade fever following an influenza-like illness 6 months prior to admission. On examination his temperature was 38.8_C, pulse rate 138 per min., and there was a loud apical systolic murmur transmitted to the axilla. The spleen was palpable and the fingers mildly clubbed. There was microscopic haematuria. Blood cultures grew non-haemolytic Streptococci.
The heart has been opened to display the left atrium, mitral valve and left ventricle. The chambers are dilated and the ventricular myocardium is hypertrophied. There is patchy mild thickening of the mitral valve cusps, and irregular friable vegetations are present on both cusps, associated with focal destruction of the underlying valve tissue. The endocardium lining the posterior wall of the left atrium is wrinkled and thickened, the changes extending to the mitral valve ring. Ante-mortem thrombus is adherent to this area, which is known as MacCallum's patch. Some of the cordae tendinae of the mitral valve are shortened and thickened. This is a case of subacute bacterial endocarditis.
MacCallum's patch is an irregular area of thickening in the posterior wall of the left atrium, usually due to previous severe acute rheumatic endocarditis involving the sub-endocardial connective tissue at this site. The factors which predispose to infective endocarditis are:(1) Conditions which result in bacteraemia or septicaemia. (2) Previous damage to the endocardial surface of the heart, particularly the valves. The most common cause of this is rheumatic heart disease.(3) Immune deficiency. In this case, there is evidence of previous acute rheumatic carditis (the changes seen in the mit mitral valve, cordae tendinae and endocardium of the left atrium.)