Prognostic significance of incident atrial fibrillation following STEMI depends on the timing of atrial fibrillation.

Atrial fibrillation (AF) is associated with short-term mortality after ST-elevation myocardial infarction (STEMI), but there is limited data on the temporal association between AF and mortality after STEMI. A total of 830 patients were included (age: 62 ± 12 years, 76 % male). Patients with new-onset AF < 30 days after STEMI were divided among three subgroups: AF on the day of admission, AF 24-72 h and AF > 72 h after admission. Thirty-day mortality was assessed by telephone and via the municipal population registry. Twenty patients died < 30 days after admission. In 41 patients, AF was detected on the day of admission, in 14 patients 24-72 h after admission and in 18 patients > 72 h after admission. Mortality was higher in patients with AF on the day of admission (7.3 vs 2.2 %, p = 0.036) and 24-72 h after admission (14.3 vs 1.4 %, p < 0.001), but not in patients with AF > 72 h after admission (0 vs 1.1 %, p > 0.999). Age (odds ratio (OR) 1.123, p < 0.001), Killip class (adjusted OR 8.341, p < 0.001), AF on the day of admission (OR 3.585, p = 0.049) and 24-72 h after admission (OR 11.515, p = 0.003) were, amongst other variables, associated with an increased 30-day mortality. In conclusion, only new-onset incident AF during the first 72 h after admission was associated with 30-day mortality in STEMI patients.