Prevalence and relevance of H558R in the efficacy and toxicity of flecainide in patients with atrial fibrillation: a cohort study

BACKGROUND: The SCN5A gene polymorphism histidine-558-to-arginine (H558R) has been associated with atrial fibrillation (AF) and may affect the therapeutic effects of flecainide. This study aimed to assess the prevalence of the H558R polymorphism in a European cohort of patients with AF and examine its association with flecainide's effects on AF recurrence and toxicity. METHODS: This cohort study included patients diagnosed with AF and prescribed flecainide between 2017 and 2021 in a regional health area. Patients without the polymorphism (H558R-/-) were compared with heterozygous patients (H558R+/-) for a primary outcome of combined 6-month AF recurrence or toxicity. Secondary analyses evaluated the long-term outcomes and compared the prevalence of H558R in the AF cohort to a general population sample (n=3401). RESULTS: A total of 104 patients were enrolled, with 57% H558R-/-, 37% H558R+/- and 6% H558R+/+. The prevalence of the H558R polymorphism was significantly higher in the AF cohort than in the general population (43.27% vs 24.37%, prevalence ratio 1.78, 95% CI 1.41 to 2.23, p<0.01). H558R+/- patients had a significantly lower risk of 6-month AF recurrence or toxicity (p=0.023, risk ratio 0.423, 95% CI 0.189 to 0.947), corresponding to an absolute risk difference of 21.5%. These findings were similar in the multivariable analysis. In long-term follow-up, H558R+/- patients continued to demonstrate a lower risk of AF recurrence or toxicity (p=0.039, HR 0.53, 95% CI 0.276 to 0.999). CONCLUSIONS: The H558R polymorphism is more prevalent in patients with AF compared with the general population and its presence is associated with a more favourable response to flecainide treatment.