745-4 Sudden “Arrhythmic” Death in Young People with Apparently Normal Heart

The aim of the present study was to assess whether and how often the ultimate diagnosis of structural heart disease underlying sudden cardiac arrest depends on histologic examination of the myocardium and specialized conduction system. Among 186 cases of consecutive sudden cardiovascular death in young people (≤35 yrs) studied from 1979 to 1994, in 59 (32%) gross examination failed to show any cardiac cause of sudden death such as obstructive coronary atherosclerosis, congenital coronary anomaly, cardiomyopathy, valve disease and aortic dissection. The grossly normal heart group consisted of 40 males and 19 females, aged 4–35 yrs (mean 23.7); 27 patients experienced warning symptoms and signs consisting of syncope in 12, ECG abnormalities in 16, and arrhythmias in 11. None had been diagnosed while alive. Detailed histologic study, including examination of ordinary ventricular myocardium as well as serial sections of specialized conduction system, disclosed: 1)focal myocarditis in 17 patients; 2) conduction system abnormalities leading to heart block in 6 patients (sick sinus syndrome in 1, lipomatous discontinuity between the atrial myocardium and the atrioventricular node in 2, sclerotic interruption of His and bundle branches in 2, and longitudinal dissociation of the His bundle in 1). and to ventricular pre-excitation in 15 (atrioventricular by-pass fibers in 9, nodoventricular Mahaim fibers in 4, atriofascicular tract in 1, AV nodal hypoplasia in 1); 3) focal fibrousfatty replacement of the right anterior wall and infundibulum in 5 patients. Sudden death remained unexplained in 16 cases. In conclusion, gross heart features were normal in nearly one third of the young sudden cardiovascular death victims; in 73% of them, however, there was histopathologic evidence of concealed “arrhythmogenic” substrates mostly consisting of conduction system pathology and focal myocarditis