Atrial Fibrillation Modifies the Relationship Between Beta Blocker Dose and Physical Capacity After Myocardial Infarction

Background: Atrial fibrillation (AF) is a common arrythmia in post-myocardial infarction (MI) cardiac rehabilitation (CR) cohorts, and beta-adrenergic signaling remodeling and rate-control pharmacotherapy may influence functional capacity. Methods: We retrospectively studied 117 consecutive male post-MI patients referred to outpatient CR. Functional capacity was assessed with a 6 min walk test (6MWT). AF was identified from clinical records, and beta-blocker exposure was unified as carvedilol-equivalent daily dose. Results: Beta-blockers were used in 94.1% of patients and AF was present in 10.3%. Patients with AF were older (72.7 ± 6.6 vs 58.1 ± 9.3 years) and walked shorter distances (430.0 [375.0–497.5] vs. 540.0 [480.0–570.0] m). In the prespecified interaction model, age remained independently associated with lower 6MWT (−4.29 m/year; p < 0.001), AF was associated with lower 6MWT (−137.21 m; p = 0.01), and the beta-blocker dose × AF interaction was positive (+6.78; p = 0.02; R2 = 0.44). Importantly, the beta-blocker dose was not associated with 6MWT in patients without AF, whereas a positive association was observed in AF (B = 7.55, p = 0.04). Conclusions: In this exploratory analysis, AF identified a subgroup with markedly reduced functional capacity in early post-MI CR, supporting the potential of phenotype-informed assessment. Additionally, the association between beta-blocker dose and 6MWT distance differed by rhythm status. These preliminary findings require confirmation in larger prospective cohorts.