Atrial Fibrillation in Acute MI

ABSTRACT & COMMENTARY

Synopsis: Atrial fibrillation remains a common complication of acute myocardial infarction in the thromboly-tic era and is associated with an increased risk of a complicated hospital course and a worse outcome.

Source: Crenshaw BS, et al. J Am Coll Cardiol 1997;30:406-413.

Crenshaw et al examine in this paper the clinical significance of atrial fibrillation (AF) in the setting of acute myocardial infarction (MI). They performed a retrospective study in the GUSTO-I trial on 40,891 patients who were enrolled between December 1990 and February 1993. Patients who were receiving chronic warfarin anticoagulation were excluded from GUSTO-I, so it may be assumed that many patients with well-established AF before their infarction were excluded. This study identified 1026 patients with AF at study entry and 324 who developed AF later in their hospital course. Patients with any AF were older, had higher heart rates and Killip classes, but were less likely to be current smokers and had lower systolic blood pressures at entry. Similar relationships were seen in both the patients who had AF at presentation and those who developed the arrhythmia later in their course. In a subgroup of more than 22,000 patients who had angiography, patients with AF had more extensive CAD. Three-vessel disease was present in 28% of those with AF vs. only 16% of those without AF. Poor reperfusion and a lower left ventricular ejection fraction (49% vs 52%) were also noted in those with AF. The presence of AF was associated with several adverse outcomes including in-hospital mortality (14% vs 6%), one-year mortality (22% vs 8%), stroke (3% vs 1%), and sustained ventricular tachycardia or VF (30% vs 11%). Crenshaw et al conclude that AF remains a common complication of acute MI in the thrombolytic era, and AF is associated with an increased risk of a complicated hospital course and a worse outcome. Crenshaw et al suggest that patients with AF should be managed aggressively with consideration of early angiography and revascularization, anticoagulation, and cardioversion.

COMMENT BY JOHN P. DiMARCO, MD, PhD

This paper shows that AF remains an important complicating factor in patients with acute MI. About 10% of MI patients will have AF during their hospital course, and about 75% of these will develop the arrhythmia after admission. AF is strongly associated with some of the other mortality risk factors previously described in this study (Circulation 1995;91:1659-1668) including age, heart rate, systolic blood pressure, and Killip class, but not with site of infarction. When angiographic variables were analyzed, AF was clearly shown to be associated with inadequate reperfusion and ventricular dysfunction. Patients with AF were also at risk for more serious arrhythmias including sustained ventricular tachycardia, ventricular fibrillation, AV block, and asystole.

Unfortunately, retrospective database studies cannot provide guidelines for better management. Although it is tempting to believe that antiarrhythmic drug therapy might decrease the incidence of AF and improve outcomes, it is perhaps equally possible that adverse electrophysiologic or hemodynamic responses to drug therapy might actually increase mortality. The role of beta- adrenergic blocking agents is also not well addressed in this study. Beta blockers might both decrease the incidence of AF and help control ventricular rate should the arrhythmia occur. The former question might be addressed by retrospective analysis of data from randomized trials on early beta-blocker usage in MI, but these data are not available.

At present, AF during MI should probably be managed using the standard treatment guidelines. Unstable patients should be cardioverted and an antiarrhythmic drug started to prevent future episodes. The optimal agent is uncertain, but this reviewer prefers amiodarone. Stable patients should have their rates controlled and be anticoagulated. Discussions about cardioversion can be made later in their hospital course.