Complete heart block following therapeutic irradiation of the left side of the chest.

Two female patients had received therapeutic irradiation of the left side of the chest for adenocarcinoma of the left breast and 18 and 23 years later, respectively, developed atrioventricular block. Both patients had early and late cutaneous reactions, as well as fibrosis of the left lung, lymphedema of the left arm, and pathologic rib fractures but had no signs of recurrence of the carcinoma. One patient developed signs of congestive heart failure while the electrocardiogram revealed second and third degree atrioventricular block; subsequent pacemaker implantation relieved the congestive heart failure. In the second patient, fatigue was the only symptom leading to the diagnosis of transient second and third degree atrioventricular block; this symptom subsided after pacemaker implantation. Based on reports of radiation-induced cardiac damage, it is assumed that the heart block in these two patients might have been due to postirradiation fibrosis of the atrioventricular node, either direct or mediated by fibro-occlusive changes in the coronary vessels.