Screen-Detected Atrial Fibrillation and "Micro-Atrial Fibrillation" and Risk of Cardiovascular Events after Myocardial Infarction in Elderly Patients.

Background: Incident atrial fibrillation (AF) occurs in 5-10% of patients after acute myocardial infarction (AMI) and is associated with adverse outcomes. Guidelines now recommend screening for AF in all elderly patients. However, the relevance of screen-detected AF and short episodes of irregular supraventricular ectopic beats ("micro-AF") after AMI is unknown.

Objectives: The objective of the study was to investigate the value of 2-week intermittent ECG screening to detect incident AF and "micro-AF" in elderly patients 12 months after an AMI and its association with risk of cardiovascular events.

Methods: This was an investigator-initiated, multicenter sub-study of the OMega-3 fatty acids in Elderly patients with Myocardial Infarction (OMEMI) trial, in Norway. Women and men aged 70-82 years, with a recent AMI, were recruited during 2012-2018. All participants had a 12-lead ECG performed at 3, 12, and 24 months. Patients without AF 1 year after the index AMI underwent 2 weeks of intermittent 30-s "thumb ECG" screening. Incident AF and "micro-AF" (episodes of ≥3 consecutive irregular supraventricular ectopic beats) were registered, and the association with risk of major cardiovascular events (MACEs; nonfatal AMI, stroke, coronary revascularization, hospitalization for heart failure, or all-cause death) was analyzed with logistic regression.

Results: Among 1014 patients (198 [28.7%] women), 255 (25.1%) had known AF or AF identified at baseline. New-onset AF was detected clinically or at study visits in 39 (3.8%) patients. By screening participants without AF (n = 567), unknown AF was identified in 4 (0.7%) and "micro-AF" in 27 (4.8%) patients. Among 43 patients with incident AF, 21 (48.8%) experienced a MACE, which was significantly higher than those without AF (n = 114, 15.9%; p < 0.001), driven by a higher risk of AMI or revascularization. Nine (33.3%) patients with "micro-AF" and 75 (13.9%) without "micro-AF" experienced a MACE (p = 0.002), explained mostly by a higher risk of heart failure hospitalization (p < 0.001). Using patients without AF and "micro-AF" as reference, "micro-AF" was associated with an intermediate risk of MACE (OR 2.8; 95% CI 1.2-6.4) and new-onset AF with a high risk of MACE (OR 5.3; 95% CI 2.8-10.0).

Conclusions: Two-week intermittent ECG screening identified few cases of new-onset AF but a substantial number of patients with "micro-AF." "Micro-AF" was associated with an increased risk of major cardiovascular events, albeit with an intermediate risk compared to those with new-onset AF.