Background: Supraventricular tachyarrythmias(SVT), especially atrial fibrillation, are among the  most prevalent arrhythmias. Atrial fibrillation could be found in patients with hyperthyroidism. The role of thyroid disorders in other supraventricular tachyarrythmias is not clear. Thus, this survey was  designed to determine the relationship between serum TSH as the marker of thyroid function and supraventricular tachyarrythmias in Shaheed Beheshti hospital in Zanjan.

 Materials and methods: This case-control study was conducted on 100 patients with SVT including:  atria! fibrillation, flutter, PSVT, MAT and atrial tachycardia, and 100 normal age and sex-matched controls. Serum TSH was measured by immunoradiometric assay and if revealed to be abnormal  serum free T4 and free T3 were also measured by radioimmunoassay in the same laboratory centre.  Data were analyzed by t-test and Chi-square test and odd's ratios were calculated.

 Results: TSH abnormality was detected in 18% of patients and 7% of controls (p<0.05). Overt  hyperthyroidism was detected in 9% of cases and 1% of controls (p<0.01). Differences between two  groups for hypothyroidism and subclinical forms of thyroid dysfunctions were not statistically  significant. Odd's ratio for hypothyroidism in patients with AF was 2.6 and for hyperthyroidism in AF  was 11. Odd's ratio for hyperthyroidism in PSVT was 8.5, but this ratio was not significant in general  population.

 Conclusion: TSH abnormality is more prevalent in SVT. In case of lack of suggestive symptoms or signs of thyroid dysfunction, we recommend thyroid function tests only for patients with AF. For patients with PSVT further studies with greater sample size are recommended.