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A survey of thyroid function test abnormalities in patients presenting with atrial fibrillation and flutter to a New Zealand district hospital.

AIM
Subclinical and overt hyperthyroidism is a known trigger of atrial fibrillation and flutter (AF). We wanted to see if thyroid function tests (TFT) were being requested appropriately in patients with atrial fibrillation or flutter at North Shore Hospital, and how common subclinical or overt hyperthyroidism was in our local inpatient population presenting with AF.


METHOD
Clinical data on 250 patients admitted to North Shore Hospital with a history of AF was retrospectively analysed, including prior history of thyroid dysfunction, measurement of TFT and their results at the time of admission, subsequent management of subjects with abnormal TFT, and the association of amiodarone treatment or use of radiocontrast with TFT derangements.


RESULTS
Of the 250 patients analysed, only a small (7.2%) proportion had known thyroid dysfunction prior to admission, most of whom had hypothyroidism on thyroxine replacement. Although the majority (77%) of AF patients had had TFT checked either at the time of admission or in the prior 6 months, a significant proportion (23%) had not. Of the patients in whom TFT were performed, 82% were normal. Abnormalities included subclinical hyperthyroidism (2.1%), overt hyperthyroidism (3.1%), subclinical hypothyroidism (11%), and overt hypothyroidism (1.6%).


CONCLUSION
Despite a relatively low frequency, hyperthyroid conditions in patients presenting to North Shore Hospital with AF were sufficiently prevalent to continue recommending TFT assessment in these patients. Although the majority of AF patients were being adequately screened with TFT, a significant proportion was not, and those with abnormalities were not well followed up.