SCN5A and atrial fibrillation: Within the ion channel scores, variants in the SCN5A gene that lengthened P-wave duration and PR interval were associated with a lower risk of AF and SVT, in keeping with the anti-arrhythmic action of flecainide, which, by blocking Nav1.5 (the sodium channel encoded by SCN5A), prolongs the PR interval and prevents AF and SVT recurrence.