Isolated acute myocardial infarction of papillary muscles of the heart. Clinicopathological study of 9 cases.

Nine cases are reported of isolated acute myocardial infarction of the papillary muscles, revealed by gross histochemical reaction (nitro-BT method) and verified histologically.In 7 cases the infarction was localized to the posterior, in 2 cases to the anterior papillary muscles.The clinicopathologicalfindings are described and the pathogenesis of this type of acute myocardial infarc- tion is discussed.In our series, papillary muscle dysfunction caused by isolated acute myocardial infarction of papillary muscles led to acute backwardfailure in 8 out of 9 cases.In 5 of 7 cases with acute myocardial infarction of posterior papillary muscles, electrocardiograms were available, and in 3 of these a third-degree atrioventricular block developed.One case with acute myocardial infarction of anterior papillary muscles developed second-degree atrioventricular block.In cases with acute backward failure andlor atrioventricular block, isolated acute myocardial infarction of papillary muscles should be considered and, if necropsy is performed, the nitro-BT method is recommended.It has been shown in experimental studies (Salis- bury, Cross, and Rieben, I963; Bailas, I965; Mittal et al., I97I) and in clinical and clinicopathological investigations (Arosemena, Moller, and Edwards, I967; Heikkila, I967; Shelburne, Rubinstein, and Gorlin, I969; Forrester et al., I97I) that the papil- lary muscles of the left ventricle of the heart are of great importance in maintaining normal haemo- dynamic conditions.Papillary muscle dysfunction with mitral incom- petence and acute heart failure is caused most often by acute myocardial infarction.Acute myocardial infarction of papillary muscles is frequently part of a transmural infarct (DePasquale and Burch, I966; Heikkila, I967; Brand, Brown, and Berge, I969) while isolated acute myo- cardial infarction of one or both papillary muscles of the left ventricle has rarely been described (Lotti, Zucker, and Bernstein, I966).The nitro-BT method was introduced by Nachlas and Shnitka (I963).In an experimental study in dogs, they showed that ligation of a coronary artery produced a pronounced fall in the content of de- hydrogenases in the myocardium supplied by the