Risk factors for atrial fibrillation in a patient with hypothyroidism:
(1) high doses of thyroxine replacement
(2) myxedematous cardiomyopathy
(3) cardiac surgery (with risk for postoperative atrial fibrillation)
(4) subclinical hypothyroidism with high-normal free T4 concentration
(5) comorbid cardiac disease from other cause
(6) advanced age
Criteria for euthyroid state: serum TSH from 0.45 to 4.49 mIU/L
Criteria for subclinical hypothyroidism:
(1) serum TSH >= 4.5 mIU/L (elevated)
(2) free T4 within the normal reference range
It may be necessary to monitor free T4 in patients with hypothyroidism and to keep the serum levels below the mean for the reference range.
