The incidence and prognostic significance of new-onset atrial fibrillation in patients with acute myocardial infarction and left ventricular systolic dysfunction: a CARISMA substudy.

Background: The incidence and risk associated with new-onset atrial fibrillation (AF) occurring after discharge in patients with acute myocardial infarction (MI) remains unknown.

Objective: This study sought to describe the incidence and clinical risk associated with postdischarge new-onset AF in post-MI patients with left ventricular systolic dysfunction.

Methods: The population included 271 post-MI patients with left ventricular ejection fraction ≤ 40% and no history of previous AF from the Cardiac Arrhythmias and Risk Stratification after Acute Myocardial Infarction (CARISMA) study. All patients were implanted with an implantable cardiac monitor and followed up every 3 months for 2 years. Major cardiovascular events were defined as reinfarction, stroke, hospitalization for heart failure, or death.

Results: The risk of new-onset AF is highest during the first 2 months after the acute MI (16% event rate) and decreases until month 12 post-MI, after which the risk for new-onset AF is stable. The risk of major cardiovascular events was increased in patients with AF events ≥ 30 seconds (hazard ratio [95% CI] = 2.73 [1.35 to 5.50], P = .005), but not in patients with AF events lasting <30 seconds (hazard ratio [95% CI] = 1.17 [0.35 to 3.92], P = .80). More than 90% of all recorded AF events were asymptomatic.

Conclusion: Using an implantable cardiac monitor, the incidence of new-onset AF was found to be 4-fold higher than earlier reported. In the study population, in which treatment with beta-blockers was optimized, the vast majority of AF events were asymptomatic, emphasizing the importance of using continuous monitoring for studies concerning AF in heart failure patients. A duration of 30 seconds or more identified clinically important AF episodes documented by an implantable cardiac monitor.