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Hyperthyroid Atrial Fibrillation: Does It Matter for Stroke Risk?

patients found hyperthyroidism not to be independently predictive of stroke by multivariate analysis [13] . The prothrombotic state in hyperthyroidism has a biological basis. Many derangements in the coagulation system such as increased factors VIII and X activity, shorter activated partial thromboplastin time, higher fibrinogen levels and increased synthesis of acute phase reactants have been described [14] . Moreover, D-dimer level, a marker for fibrinolysis, has been found to be significantly higher in hyperthyroidism and to correlate with disease severity. D-dimer level was also identified as a predictor of thromboembolic events in AF [15] . In the present report, the authors studied 62 patients with hyperthyroid AF, comparing them to two control groups: non-thyroid AF (n = 107) and hyperthyroidism without AF (n = 100); all prospectively followed for a mean of 34 months. The authors found that the annual incidence of ischemic stroke was highest among hyperthyroid AF patients at 7.6% versus 3.6 and 0.7% in the non-thyroid AF and hyperthyroidism without AF groups, respectively [1] . Although the study groups were matched for stroke risk according to the CHA 2 DS 2 -VASc score, the Cox proportional hazards analysis indicated that hyperthyroid AF patients were at significantly higher stroke risk than non-thyroid AF patients with a hazard ratio of 3.2 (95% CI 1.01–5.59, p = 0.04), indicating that hyperthyroid AF is predictive of stroke risk above and beyond the CHA 2 DS 2 -VASc score. The study by Chen et al. [1] has many strengths, including consecutive patient selection and prospective followIn a recent issue of Cardiology , Chen et al. [1] reported on hypercoagulable state and stroke risk in hyperthyroid atrial fibrillation (AF). The existing evidence is not completely settled as to whether hyperthyroid AF is associated with a hypercoagulable state and constitutes an excess stroke risk, since the existing studies are small and observational in nature. This is reflected in discordant published guidelines [2, 3] and an inadequate adjudication of stroke risk in hyperthyroid AF as assessed by the CHADS 2 and CHA 2 DS 2 -VASc scores [4, 5] . Thus, the present study is quite relevant as the authors prospectively compared stroke risk in a cohort of patients with hyperthyroid AF to two control groups: non-thyroid AF and hyperthyroid patients without AF. In this editorial comment, we examine the internal and external validity of this study and weigh-in on the controversy of stroke risk and recommendation for anticoagulation in hyperthyroid AF. It is well established that patients with hyperthyroidism are at significant risk for AF. However, stroke risk among hyperthyroid AF patients remains controversial. Many reports indicate that hyperthyroidism alone is associated with an increased stroke risk, with a reported incidence ranging from 2.4 to 26.7% [6–11] . Furthermore, strokes have even been observed with sinus rhythm and in young adults with hyperthyroidism and no other risk factors [6, 9, 12] . A study by Sheu et al. [12] suggested that thyrotoxic patients (without AF), as compared to euthyroid individuals, are at increased risk for ischemic stroke with a hazard ratio of 1.44. On the other hand, the Swedish Atrial Fibrillation cohort study of 182,678 AF Received: November 26, 2013 Accepted: November 27, 2013 Published online: February 12, 2014