Aim of this study was to evaluate the effectiveness and safety of oral anticoagulant therapy in patients with atrial fibrillation and hyperthyroidism compared to those presenting the same cardiac disorder, but with normal thyroid function.
Material and methods: The study included 61 patients admitted to the Endocrinology Department in Elias Hospital between January 2011October 2011 with mean age of 64 years: 25 patients had primary hyperthyroidism and atrial fibrillation, 36 patients had atrial fibrillation with normal thyroid function, used as a control group. The patients were followed during the hospitalization (mean period 10 days) regarding the thyroid function tests (TSH, Free T4) the international normalized ratio (INR) and the dose of oral anticoagulant taken (acenocumarol).
Results: All patients (20 women and 5 men) in the hyperthyroid group had a supressed TSH (below 0.01 UI/l) and a near upper limit values of free T4. They were recently diagnosed with either Gravess disease (18 pts) or toxic multinodular goiter (7 pts) and received antithyroid therapy at admitance in the hospital. The acenocumarol dose at the admitance was an average of 0.36±0.19 mg daily with an average INR of 1.8±1.1.
In the control group (23 women and 13 men refeered for thyroid disfunction but proved to have normal TSH and free T4 and no history of thyroid disfunction), the average dose of accumarol was 0.71±0.2 daily at the admitance with an average INR of 2.16±0.6.
We found a significantly lower dose of acecumarol needed in the hyperthyroid patients (0.3 comparing to 0.7 mg) comparing to controls with no significant differences in the INR values between groups. Taking into account the dynamic of the INR values during the follow up, we found a significantly higher variations of the INR values in the hyperthyroid group (from 1.8 to 2.7 average). In this group we have noticed 5 cases of minor adverse effects comparing to none in the control group during the follow up period.
Conclusion: Achieving and maintaining target levels of efficiency and safety of oral anticoagulant treatment throughout the hyperthyroidism might be more difficult due to important fluctuations of INR values during the antithyroid treatment.
Therefore hyperthyroid patients require more frequent monitoring of INR because imbalances especially in the sense of overdose are unpredictable and can have serious consequences.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.