Nikaidoh procedure for the correction of transposition of the great arteries, ventricular septal defect and pulmonary stenosis.

(Figure 2). Given the Mobitz II second degree AVB and the bifascicular block, a bi-chamber pacemaker was implanted. Acquired AVB in young patients is a very exceptional disorder. The patient presented here had two factors that might account for the AVB: radiotherapy and hypothyroidism.1,2,4,5 Atrioventricular block secondary to hypothyroidism4 is an unusual entity that is due to the myxedematous infiltration of the conduction tissue and which presents as one more symptom amongst many, in which the onset of AVB is relatively early, even during phases of subclinical hypothyroidism. The localization of the block is mainly supra-Hisian6 (first degree or Mobitz I AVB) and in many cases it can be successfully reverted with replacement therapy.4 In patients with AVB and a history of radiotherapy, biopsy studies reveal a severe, progressive fibrosis5 of the conduction tissue as the main cause of the block. The history of radiotherapy usually dates back a long time (15-20 years), which can thus sometimes make the association with AVB more difficult to suspect.1,2 The electrophysiologic study enabled the block to be localized as infra-Hisian in most published reports.5 Its evolution is irreversible and requires implantation of a pacemaker. The progressive nature of the block seen on the evolution of the electrocardiograms, the absence of other symptoms and signs of hypothyroidism, the normal thyroid function with replacement therapy and the infraHisian localization all point to the radiation as the most likely cause. Although this type of radiotherapy is no longer used, many patients have received it over the past decades. Periodic electrocardiograms are therefore recommended in the follow-up of these patients, bearing in mind the slow but progressive evolution of the fibrosis and the AVB. The case presented here poses the differential diagnosis between 2 unusual etiologies of AVB and stresses the importance of regular electrocardiograms and a good clinical history for a correct diagnosis.