Infrahisian atrioventricular block secondary to radiotherapy.

Radiotherapy and hypothyroidism are unusual causes of acquired atrioventricular block (AVB). Thoracic radiotherapy used for the treatment of different neoplasms may cause adverse cardiac1,2 and endocrinologic3 events, attributed to fibrosis of the conduction tissue and the thyroid gland, respectively. The infra-Hisian localization of an AVB is uncommon in young patients, but nevertheless of great clinical importance, given its prognostic implications. We report a patient with infraHisian AVB and hypothyroidism, both of which had developed progressively 17 years after receiving radiotherapy for a Hodgkin lymphoma. The patient was a 36-year-old woman, with a history of Hodgkin lymphoma diagnosed at the age of 19 years and treated with chemotherapy, Mantle-type radiotherapy (48 Gy) and an autologous bone marrow transplant, which had been in complete remission for 15 years. In 2000 she was diagnosed with hypothyroidism, attributed to glandular fibrosis resulting from the radiotherapy. Since 2003 she had required replacement therapy, with good subsequent control. She was referred to the cardiology service due to palpitations lasting several hours associated with situations of emotional stress, of sudden onset and gradual end. Physical examination, laboratory tests (including the thyroid profile), and an echocardiogram were all normal. An electrocardiogram showed sinus rhythm with first degree AVB, left posterior hemiblock and right bundle branch block, with a clear progression of the conduction disorder as compared with an electrocardiogram done 6 years previously (Figure 1). The Holter showed a Mobitz II second degree AVB during the moments of maximum heart rate and a 2:1 AVB during an episode of clinical palpitations. The electrophysiologic study showed severe involvement of the infra-Hisian conduction (HA, 67 ms; HV, 68 ms), with frequent P waves spontaneously blocked at the infra-Hisian level LETTERS TO THE EDITOR