ESR1 and atrial fibrillation: However, the cfDNA variant development assessed retrospectively in this study showed the appearance and even increase in AF of PIK3CA E726K (Oct 2015 9.8%; June 2016 38.3%), PIK3CA H1047R (Oct 2015 11.4%; June 2016 39.0%), ESR1 Y536S, ESR1 Y537S, ESR1 539S and one ESR1 intronic variant (AF of all ESR1 variants: Oct 2015 4.1%; June 2016 14.0%) in this time frame.