Published: Nov 4, 2013 | Updated: Nov 5, 2013
By Todd Neale, Senior Staff Writer, MedPage Today

Full Story:  http://www.medpagetoday.com/Cardiology/Arrhythmias/42696

Although myocardial infarction is a known risk factor for the development of atrial fibrillation, the relationship might work the other way around, too, researchers found.

Among patients without a history of coronary heart disease, those with atrial fibrillation were 70% more likely to have an MI through an average of about 7 years of follow-up after accounting for other potential risk factors (HR 1.70, 95% CI 1.26-2.30), according to Elsayed Soliman, MD, of Wake Forest School of Medicine in Winston-Salem, N.C., and colleagues.

“These data … add to the growing recognition of important bidirectional relationships between atrial fibrillation and other cardiovascular comorbidities,” Jonathan Dukes, MD, andGregory Marcus, MD, of the University of California San Francisco, wrote in an accompanying editorial. “Just as ‘AF begets AF,’ we are learning it may also lead to kidney disease, heart failure, and now MI.”

The study included 23,928 black and white participants from the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study who did not have coronary heart disease at baseline; 6.8% had atrial fibrillation detected either with a study-scheduled ECG or through a reported history of a physician diagnosis.

Through an average of 6.9 years of follow-up, there were 648 incident MIs, with a rate twice as high among the patients with atrial fibrillation (12 versus 6 per 1,000 person-years,P<0.001).

The increased risk remained in a fully adjusted model that accounted for sociodemographics, total and HDL cholesterol, smoking, systolic blood pressure, use of blood pressure-lowering drugs, body mass index, diabetes, warfarin use, aspirin use, statin use, history of stroke and vascular disease, kidney function, and C-reactive protein level. The results were not changed substantially by further adjustment for heart failure or stroke events or hospitalization for chest pain.

The relationship between atrial fibrillation and incident MI significantly differed by sex and race (P<0.05 for both interactions).

The risk of MI associated with the arrhythmia was greatest in black men (HR 2.91, 95% CI 1.62-5.23), followed by black women (HR 2.17, 95% CI 1.19-3.98) and white women (HR 2.33, 95% CI 1.27-4.28). The relationship was not significant among white men (HR 0.86, 95% CI 0.58-1.56).

“[W]hether genetic background, emerging risk factors, access to healthcare, awareness, and adherence to medication regimens contribute to these sex and race differences needs further investigation,” the researchers wrote.

Age did not seem to affect the association, but warfarin use did. The risk of MI associated with atrial fibrillation was not significantly elevated in warfarin users (HR 0.76, 95% CI 0.29-1.94), but it was in nonusers (HR 1.92, 95% CI 1.42-2.60), which “accords with previous reports showing that warfarin might provide a protective effect against MI after acute coronary syndromes and in patients with atrial fibrillation who are prescribed anticoagulation for stroke prevention,” the authors wrote.

In discussing the potential mechanisms by which atrial fibrillation might increase the risk of MI, Dukes and Marcus referred to a meta-analysis they conducted to look at the effects of warfarin on MI. In pooled results from trials comparing the anticoagulant with either antiplatelets or placebo, warfarin was associated with a significant reduction in MI.

“Since aspirin, or antiplatelet agents in general, are believed to be particularly effective for preventing spontaneous (type 1) MI (from atherosclerotic plaque rupture leading to thrombus via platelet activation),” they wrote, “evidence in favor of the superiority of warfarin (generally believed to be most effective for stasis-related thrombus formation) likely supports the contention that atrial-sourced thromboemboli are important in atrial fibrillation-associated MI.”

They added that “although the findings of the study … are informative, they do not suggest a change in our atrial fibrillation treatment strategies.”

Soliman and colleagues noted some limitations of the study, including the possibility that some cases of atrial fibrillation were missed, the lack of a systematic assessment of heart failure, the inability to account for atrial fibrillation that developed during follow-up, the inclusion of white and black individuals only, and the potential for residual confounding.

From the American Heart Association:

• Guidelines for the Prevention of Cardiovascular Disease in Women—2011 Update
• 2011 Focused Update on the Management of Patients With Atrial Fibrillation
• AHA Heart Disease and Stroke Statistics 2013 Update

Primary source: JAMA Internal Medicine

That risk was greatest among women (HR 2.16, 95% CI 1.41-3.31) and black individuals (HR 2.53, 95% CI 1.67-3.86), they reported online in JAMA Internal Medicine.