A-fib Identified as a Risk Factor for Incident NSTEMI

A-fib is associated with an elevated risk of incident MI, particularly among women, according to a study published online April 27, 2015, ahead of print in Circulation. When broken down by MI type, however, the relationship applies only to NSTEMI.

Implications:  A-fib Identified as a Risk Factor for Incident NSTEMI“MI is an established risk factor for [A-fib], and based on our findings we now can say that [A-fib] is also a risk factor for MI,” study author Elsayed Z. Soliman, MD, MSc, MS, of Wake Forest Baptist Health (Winston-Salem, NC), told TCTMD in an email.

This bidirectional link, which represents a “paradigm shift in the thinking of the relationship between [A-fib] and its risk factors,” he said, “is intriguing and calls for examining the association between [A-fib] and its other risk factors, such as heart failure and chronic kidney disease.”

The researchers examined data from the ARIC (Atherosclerosis Risk in Communities) study, which follows individuals from 4 US communities: Washington County, MD; the suburbs of Minneapolis, MN; Jackson, MS; and Forsyth County, NC. Their analysis included 14,462 people (mean age 54 years; 56% women; 26% African Americans) who were free from coronary heart disease at baseline in 1987-1989 and were followed through 2010. Overall, A-fib was present in 31 participants at baseline and observed in 1,514 during follow-up.

Over a median follow-up period of 21.6 years, there were 829 NSTEMIs, 249 STEMIs, and 296 unclassified MIs. The age-adjusted rate of total MI was higher among the patients with A-fib than in those without the condition (11.60 vs 3.96 per 1,000 person-years), with greater differences observed among women and African Americans.

After multivariate adjustment, A-fib remained associated with increases in total MI and NSTEMI but not STEMI (table 1). The difference between the risk estimates for NSTEMI and STEMI was significant (P = .004).

Table 1. MI Risk: A-fib vs No A-fib

The links between A-fib and incident MI—both total and NSTEMI—were stronger in women than in men (P < .01 for interaction).

In sensitivity analyses, grouping unclassifiable MIs with either STEMI or NSTEMI did not change the findings.

Potential Mechanisms Explored

A prior study by Dr. Soliman and colleagues using data from the REGARDS cohort showed that A-fib was a risk factor for incident MI, and the current analysis refines those results by MI type. The finding that the association is present for NSTEMI alone may provide insight into potential mechanisms, according to the authors.

This discrepancy “suggests that total occlusion of the coronary arteries via direct thromboembolism, for example, is unlikely to be the mechanism by which [A-fib] leads to MI,” Dr. Soliman told TCTMD in an email. “On the other hand, factors contributing to partial occlusion of the coronary arteries or increased oxygen demand are more likely to explain the link.”

In an accompanying editorial, Michiel Rienstra, MD, PhD, of University Medical Center Groningen (Groningen, the Netherlands), and colleagues discuss the possibility that A-fib and MI are connected by factors associated with underlying vascular disease.

“However, the explanation of shared risk factors, and common pathways, negates the complex relations between [A-fib] and myocardial infarction,” they write, pointing to evidence supporting both MI as a risk factor for A-fib and vice versa.

John P. Erwin III, MD, of Baylor Scott & White Health (Temple, TX), said in an email to TCTMD that the current paper “will heighten our curiosity as to whether there is truly a causative role of A-fib in MI or whether these disease states are merely final common pathways of traditional cardiovascular risk factors and the resultant pathophysiology related to the risk factors themselves.

“This study is another piece of the puzzle,” he continued, “but shows us how far we’ve yet to go in understanding the complex interplay of mechanisms in cardiac diseases and how to best use that knowledge to combat untoward outcomes related to those disease states.”

The Growing A-fib Problem

According to the researchers, the number of patients with A-fib in the United States—estimated at 2.7 to 6.1 million—is expected to double by 2050. Based on the study results, they say, the burden of A-fib-associated morbidity and mortality, including MI, also will increase.

“In an increasingly older population, such as the United States population, this may incur a substantial burden on the healthcare system,” they write. “Efforts to increase awareness and detection of [A-fib], especially in blacks and women, and the development of risk stratification tools to identify [A-fib] patients who are [at] high risk for developing MI are needed.”

In addition, Dr. Soliman called for strategies to reduce MI risk in A-fib patients, noting that “since total coronary occlusion via direct thromboembolism may not be the main mechanism, anticoagulants that are commonly prescribed to people with [A-fib] to prevent stroke may not be fully effective in preventing MI.”


Sources: 
1. Soliman EZ, Lopez F, O’Neal WT, et al. Atrial fibrillation and risk of ST-segment elevation versus non-ST segment elevation myocardial infarction: the Atherosclerosis Risk in Communities (ARIC) study. Circulation. 2015;Epub ahead of print.

2. Vermond RA, Van Gelder IC, Crijns HJ, Rienstra M. Does myocardial infarction beget atrial fibrillation and atrial fibrillation beget myocardial infarction [editorial]? Circulation. 2015;Epub ahead of print.

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Todd Neale is the Associate News Editor for TCTMD and a Senior Medical Journalist. He got his start in journalism at …

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Disclosures
  • ARIC is supported by the National Heart, Lung, and Blood Institute, with additional funding from the American Heart Association.
  • The editorialists report support from the Netherlands Cardiovascular Research Initiative, and Dr. Rienstra reports support from the EHRA academic fellowship program and the Netherlands Organization for Scientific Research.
  • Drs. Erwin and Soliman report no relevant conflicts of interest.

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