Atrial Fibrillation Increases Heart Attack Risk

A new analysis of a large patient cohort concludes that atrial fibrillation (AF) is associated with an increased risk of just 1 of the 2 major types of heart attack — but the association is strong enough to increase the overall heart-attack risk by 63%.

Researchers, who published their findings in Circulation, analyzed records from 14,462 participants the Atherosclerosis Risk in Communities (ARIC) study, which began in 1987 and followed patients until 2010. They used electrocardiogram results and discharge papers to determine which patients had AF. Then, they let an independent adjudication committee tally heart attacks and determine whether each heart attack was a ST segment elevation myocardial infarction (STEMI) or a non-ST segment elevation myocardial infarction (NSTEMI).

Some 1,374 heart attacks took place during the study period, 829 of them NSTEMI, 249 of them STEMI, and 296 of them unclassifiable. Multivariable adjusted analysis found that AF, which was diagnosed in 1,545 patients, was associated with a 63% greater risk of any type of myocardial infarction (95% confidence interval [CI], 1.32-2.02). Subgroup analysis showed an even greater risk for women with AF.

That said, AF was not associated with any increase in STEMI risk. To the contrary, it was associated with a lower STEMI risk, though not to a significant degree (hazard ratio [HR], 0.49; 95% CI, 0.18-1.34). The entire connection between AF and heat attack stemmed from the strong connection between AF and NSTEMI (HR, 1.80; 95% CI, 1.39-2.31).

The finding is, to some degree, good news for people with AF. NSTEMI, which accounts for about 2/3 of all heart attacks, is the less severe type of heart attack. It occurs when a blood clot partially clogs a coronary artery and damages part of the heart muscle served by that artery. STEMI occurs when a blood clot fully clogs the artery and damages all the tissue it serves.

The study authors believe their findings suggest that the link between AF and heart attack is more likely explained by factors that would increase the heart’s demand for oxygen, like a sudden increase in beats per minute, than factors that would sometimes cause a complete blockage, such as the migration of a blood clot from the heart and into the artery.

“These results have important implications for management of the risk of heart attack in people with atrial fibrillation,” said lead author Elsayed Z. Soliman, MD, director of the Epidemiological Cardiology Research Center at Wake Forest Baptist Medical Center, in a news release that accompanied publication of the study results. “For example, blood thinners that are commonly prescribed to people with a-fib to prevent stroke may not be as effective in in preventing heart attacks in this population.”

The new study was a follow-up to earlier research by Soliman and his team, research that used the same cohort to estimate that AF was associated with a 70% increase in the risk of heart attack. Many prior studies had established that a person who suffers a heart attack faces an increased risk of developing AF, but Soliman’s earlier study, which was published in 2013, was the first large study to conclude that people with AF face a greater risk of heart attack.