Atrial Fibrillation Burden on a 14-Day ECG Monitor: Findings from the GUARD-AF Trial Screening Arm

The "burden" of atrial fibrillation (AF) detected by screening likely influences stroke risk, but the distribution of burden is not well described. Determine the frequency of AF and the distribution of AF "burden" found when screening individuals age ≥70 years with a 14-day ECG monitor. Cohort study of the screening arm of a randomized AF screening trial among those age ≥70 without a prior AF diagnosis (2019-2021). Screening was done with a 14-day continuous ECG patch monitor. Analyzable patches were returned by 5,684 (95%) of screening arm participants; median (quartile 1, quartile 3) age 75 years (72,78), 57% female, and median CHA2DS2-VASc score 3 (2, 4). AF was detected in 252 participants (4.4%); 29 (0.5%) had continuous AF and 223 (3.9%) had paroxysmal AF (PAF). Among those with PAF, the average indices of AF burden were of low magnitude with right-skewed distributions: Median % time in AF was 0.46% (0.02, 2.48%), or 75 (3, 454) minutes and median longest episode was 38 (2, 245) minutes. The upper quartile threshold of 2.48% time in AF corresponded to 7.6 hours. Age >80 years was associated with screen-detected AF in our multivariable model, OR 1.46 (95% C.I.: 1.06, 2.02). Most AF detected in these older patients was very low burden. However, one-quarter of those with AF had multiple hours of AF, raising concern about stroke risk. These findings have implications for targeting populations for AF screening trials and for responding to heart rhythm alerts from mobile devices.