Atrial fibrillation and arterial embolism in hyperthyroidism.

Atrial fibrillation or flutter was present in 70 of 381 patients with uncontrolled hyperthyroidism; return to stable sinus rhythm occurred in 39 with antithyroid and antiarrhythmic treatment. One third of the patients who reverted did so in the first week of treatment while still hyperthyroid. As expected, reversion was more likely in younger patients, and in those with arrhythmia of recent onset, without evidence of other heart disease. Eight patients with arrhythmia had proven (five) or probable (three) major arterial embolic episodes. Four of these eight patients died. Embolism tended to occur at an early stage, during uncontrolled hyperthyroidism, in patients with both atrial fibrillation and cardiac failure. These findings suggest that prophylactic anticoagulation may be appropriate in this high risk group, although more extensive studies are necessary before effective prevention of embolism can be claimed.