Atrioventricular block in patients with thyroid dysfunction: prognosis after treatment with hormone supplementation or antithyroid medication

Background: Hypothyroidism is a reversible cause of atrioventricular (AV) block. Few reports have described reversible AV block caused by hyperthyroidism. However, it is unknown whether patients with AV block are expected to have a benign course after the initiation of appropriate therapy for thyroid dysfunction.

Methods: The study group consisted of patients with II or III degree AV block and bradyarrhythmia (≤40bpm) excluding patients with myocardial infarction, electrolyte abnormalities, digitalis toxicity, and vasovagal syncope. Thyroid dysfunction is diagnosed when thyroid stimulating hormone and thyroxine levels are not in defined normal ranges. AV block was determined by surface electrocardiogram (ECG). The cause and effect relation between AV block and thyroid dysfunction was evaluated.

Results: Of 668 patients, 29 (4.3%) had hypothyroidism (19 overt) and 21 (3.1%) had hyperthyroidism (8 overt). The most frequent ECG finding was complete AV block (27 of 50 patients). Ten patients had bradyarrhythmia and 13 had second-degree AV block. Euthyroid state was achieved in 10 hypothyroidic (34%) and in 7 hyperthyroidic patients (33%) with hormone replacement and antithyroid therapy, respectively, during the follow-up period (≤21 days). Thyroid dysfunction was found to be not related with AV block in 40 patients (80%). However, in 4 of 10 patients with AV block related to thyroid dysfunction the resolution of AV block occurred after the placement of pacemaker (>21 days). Overall, 44 of 50 (88%) patients with AV block in association with thyroid dysfunction were implanted with a permanent pacemaker. Of 6 patients who did not receive a pacemaker, 2 had complete AV block and 4 had bradyarrythmia.

Conclusion: AV block associated with thyroid dysfunction needs great attention regardless of type of the thyroid disease. Patients with II and/or III degree AV block in the setting of thyroid dysfunction almost always need permanent pacemaker insertion even after normalization of thyroid status.