Prevalence of Cardiac Arrhythmias in Hypothyroid and Euthyroid Patients

The thyroid functions as a regulator of cardiac function and rhythm through genomic and nongenomic actions of triiodothyronine (T3) in cardiac myocytes. Atrial fibrillation is a common complication of thyrotoxicosis. Hypothyroidism is not considered a risk factor for arrhythmias despite well-known EKG changes in this condition. This case control study was conducted to analyze the differences, if any, in the prevalence of cardiac arrhythmias between hypothyroid patients and euthyroid controls. Three hundred and four consecutive patients admitted at our medical center for a period of one year were included in the study. The study population was divided into 2 groups (age, gender and race matched): patients with hypothyroidism and euthyroid subjects as a control group. Major arrhythmia data were obtained from telemetry recordings and from known past medical history. There were 152 subjects in each arm of the study. The mean age was 61.9 years. Mean TSH in hypothyroid group was 40.4 mIU/l (95% CI 33.3-47.5) (range 10.09-304, SE 3.62) and in euthyroid group was 0.89 mIU/l (95% CI 0.82-0.96). Chi-square analysis revealed a higher prevalence of ventricular tachycardia (p=0.04) and any ventricular arrhythmia in the hypothyroid group (p=0.007). This relatively large case control study revealed a statistically higher prevalence of ventricular arrhythmias in hypothyroidism. Our study has thrown light on the prevalence of arrhythmias in hypothyroidism and the observation of increased ventricular arrhythmias necessitates future large scale prospective studies to better define the risk of such ventricular arrhythmias and the effects of thyroid supplementation on this risk.