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: To investigate the value of two-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 substudy 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 one year after the index AMI underwent 2 weeks of intermittent 30-second ‘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 (MACE; non-fatal 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.
