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[Prolonged hyperthyroidism and recurrent atrio-ventricular block]
Insights
This case study highlights a rare instance of severe atrio-ventricular block in a hyperthyroid patient. Normalization of heart conduction after thyroid recovery suggests a link between hyperthyroidism and cardiac conduction disorders.
Area of Science:
- Cardiology
- Endocrinology
Background:
- Hyperthyroidism is associated with various cardiac manifestations, but severe atrio-ventricular (AV) block is uncommon.
- While mild AV conduction abnormalities (grade 1 AV block) occur in 6-8% of hyperthyroid patients, higher grades are rare.
- Existing case reports often involve confounding factors, making isolated thyrotoxicosis as a cause of conduction disorders exceptional.
Abstract:
The authors report the case of a patient with hyperthyroidism who had three episodes of grade 2 and 3 atrio-ventricular block over a 6-year period. After he recovered from hyperthyroidism, the atrio-ventricular conduction returned to normal and remained so throughout a 5-year follow-up. A grade 1 atrio-ventricular block is found in 6 to 8 p. 100 of hyperthyroid patients, but grade 2 and 3 blocks are rare in such patients. Case reports in which thyrotoxicosis alone seemed to be responsible for disorders of conduction are exceptional; frequently, other factors likely to induce such disorders were present. In 90 p. 100 of the cases hyperthyroidism was due to Graves' disease; it lasted for more than one year and thyrotoxicosis was often severe. These facts suggest the possibility of a thyrotoxic myocarditis and/or an autoimmune focal myocarditis. Although rare, atrio-ventricular block in hyperthyroid subjects is a possibility that warrants electrocardiographic monitoring, notably when negative dromotropic drugs are prescribed.