Atrial fibrillation diagnosed at different phases of myocardial infarction are all associated with excess risk
Authors: Torok S , Yip Lundstrom L , Leosdottir M , Hofmann R , Jernberg T , Svensson P 
Published: November 2023

Abstract

Background
Atrial fibrillation (AF) in patients with myocardial infarction (MI) is associated with higher mortality and cardiovascular complications such as hospitalisation due to heart failure and ischaemic stroke. It is unknown whether the association with poor outcomes is general or specific for AF diagnosed before, at or during follow-up after an MI.

Purpose
The aim of this study was to investigate the occurrence of AF, and its clinical correlates at different stages in patients with acute MI. In addition, we also explored whether any association between AF and mortality, incident heart failure or stroke differed for AF diagnosed at these stages.

Methods
Patients attending cardiac rehabilitation after MI in Sweden 2006-2020 were identified in the Swedish registry for cardiac disease SWEDEHEART. The patients were divided into groups with sinus rhythm at hospitalisation and follow-up (reference group), AF at MI hospitalisation including prior and new-onset AF during MI hospitalisation, and late-onset AF diagnosed at cardiac rehabilitation follow-up visits during the first year post-MI. All patients were followed until 2020-12-31 and the groups were compared regarding overall mortality, hospitalisation due to heart failure, and stroke using log-rank test and Cox-regression adjusted for age in cubic splines and sex.

Results
Overall 104,325 patients (26% female) between 18-80 years old were investigated. 4731 patients presented with AF at admission for MI (4.5%) and 2,119 (2%) had a persistent AF at discharge. Out of these, 139 had new-onset AF at MI. STEMI was more common in patients with new onset AF compared to those with a history of AF before MI (40.3% vs 31.7%, p=0.013). During the one-year follow-up period after index MI 448 patients had a new-onset AF which was associated with older age, NSTEMI, reduced ejection fraction and more extensive coronary artery disease at the index MI. The association between AF diagnosed at the different phases of MI with outcomes are illustrated in figure 1. During a median follow-up of 7.0 years, patients with AF at MI had a higher mortality (33.3% vs 14.2%, p&lt;0.001), more hospitalisations due to heart failure (25.6% vs 6.7%, p&lt;0.001) and stroke (8.0% vs 3.9%, p&lt;0.001) compared to patients with SR. Patients with new-onset AF at MI had a similar risk for these outcomes compared to patients with a history of AF at MI. Patients with late-onset AF during the one-year follow-up period after index MI also had higher mortality (28.3% vs 12.2%, p&lt;0.001) and more hospitalisations for heart failure (21.9% vs 5.6%, p&lt;0.001) but not stroke (4.2% vs 3.9%, ns) compared to patients that remained in SR.

Conclusion
In patients attending cardiac rehabilitation after MI, chronic AF, new-onset AF at MI and late-onset AF were associated with increased risk for mortality, heart failure hospitalisations and stroke. Hence, AF should be considered a severe risk factor in patients with MI irrespective of time of occurrence.AF at MI