How useful is thyroid function testing in patients with recent-onset atrial fibrillation? The Canadian Registry of Atrial Fibrillation Investigators.
BACKGROUND
Patients with recent-onset atrial fibrillation often undergo routine thyroid function screening to rule out thyroid disease as a cause of atrial fibrillation.


METHODS
Patients with recent (< 3 months) onset of documented atrial fibrillation or flutter were enrolled in the Canadian Registry of Atrial Fibrillation from outpatient clinics, emergency departments, and hospital wards across Canada. Seven hundred twenty-six patients underwent baseline thyroid function screening and were assessed for presence of clinical thyroid disease. Serum thyrotropin level (TSH) was measured in 707 patients (97%), and thyroxine level (T4) in 407 patients (56%).


RESULTS
A TSH level less than 0.1 mU/L was present in 5 patients (0.7%). A TSH level less than normal but more than 0.1 mU/L was present in 34 patients (4.7%). No patient had definite hypothyroidism (TSH > 20 mU/L), but 56 patients (7.7%) had an elevated TSH level that was less than 20 mU/L. During 1.7 years of follow-up, only 7 patients were found to have clinical hyperthyroidism, and 11 patients (1.5%) had hypothyroidism. Logistic regression analysis showed that palpitations (odds ratio, 4.9; 95% confidence interval, 1.7-14.0) and asymptomatic presentation (odds ratio, 5.5; 95% confidence interval, 1.9-16.2) were risk factors for low TSH level, and increasing age (odds ratio, 1.32 every 10 years; 95% confidence interval, 1.01-1.66) was a risk factor for high TSH level. The positive predictive value of palpitations and asymptomatic presentation for low TSH level were 9% and 8%, respectively.


CONCLUSIONS
An abnormal TSH level is common in patients with recent-onset atrial fibrillation. However, clinical thyroid disease is uncommon. Routine TSH screening of patients who have atrial fibrillation has a low yield and may be better applied to those patients at higher risk of having undiagnosed clinical thyroid disease.
Krahn
A D
AD
University of Western Ontario, London.
Klein
G J
GJ
Kerr
C R
CR
Boone
J
J
Sheldon
R
R
Green
M
M
Talajic
M
M
Wang
X
X
Connolly
S
S
D001281:Atrial Fibrillation / Q000097:blood / Q000209:etiology* / Q000503:physiopathology; D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D013959:Thyroid Diseases / Q000097:blood / Q000150:complications*; D013960:Thyroid Function Tests; D013972:Thyrotropin / Q000097:blood; D013997:Time Factors
D013972:Thyrotropin