Adverse Outcomes Associated with Pre-Existing and New-Onset Atrial Fibrillation in Patients with Acute Coronary Syndrome: A Retrospective Cohort Study.

Introduction: Atrial fibrillation (AF) often occurs in patients with acute coronary syndrome (ACS). It remains unclear whether pre-existing or new-onset AF confers different risk in patients with ACS.

Methods: We conducted a retrospective cohort study using Taiwan's National Health Insurance Research Database. Patients who were hospitalized with a primary diagnosis of ACS from 2005 to 2009 were studied. Major outcomes were mortality, heart failure, and combined ischemic stroke/systemic embolism (IS/SE). The date of the first ACS diagnosis was defined as the index date. Pre-existing AF was defined as AF occurring before the index date. New-onset AF was defined as AF that started after or at the same time as the ACS diagnosis.

Results: Among 6663 patients with ACS, 488 (7.3%) had pre-existing AF and 479 (7.2%) had new-onset AF. Compared to patients with pre-existing AF, those with new-onset AF were younger, less likely to have co-morbidities, and more likely to receive evidence-based therapy. The un-adjusted risks of adverse outcomes in both groups were similar. Compared to pre-existing AF, new-onset AF was significantly associated with a higher adjusted risk of death (hazard ratio 1.27, 95% confidence interval 1.06-1.52) and IS/SE (hazard ratio 1.49, 95% confidence interval 1.01-2.20). The significant associations between new-onset AF and adverse outcomes were more likely to be observed in elderly patients with ACS.

Conclusions: New-onset AF during ACS was associated with a significantly increased risk of adverse outcomes, especially in the elderly patients.