Flag on the Field for Atrial Fibrillation in Retired NFL Players

Patrice Wendling

July 26, 2019

As National Football League (NFL) training camps begin in earnest this week, the conversation will undoubtedly turn to the long-term health of players and the debilitating brain disorder, chronic traumatic encephalopathy. Now, research suggests these elite athletes also may be at increased risk for atrial fibrillation (AF) and conduction abnormalities decades after leaving the sport.

Former NFL players had nearly six times higher adjusted odds of AF than nonelite athletes from the Dallas Heart Study (DHS)-2 after controlling for age, hypertension, diabetes, body mass index (BMI), and race.

AF was previously undiagnosed in 65% of former NFL athletes, and most (53%) had a CHA2DS2-VASc score of 2 or more — a solid indication for oral anticoagulation based on their stroke risk, according to the study, published in the August 6 issue of the Journal of the American Heart Association.

"In these particular people, we shouldn't make assumptions that just because they were an elite athlete, they cannot have any cardiac disease," lead author Dermot Phelan, MD, PhD, Heart and Vascular Institute, Cleveland Clinic, said. "In fact, in this particular case, it's possible that the fact that they were an elite athlete makes them at risk of having asymptomatic atrial fibrillation because the heart doesn't increase in rate as much."

People who go into AF tend to become tachycardic and their heart rate accelerates often up into the 150s, so they are aware of it, whereas NFL players with AF at the time of screening had an average resting heart rate of 77 beats per minute (bpm), he explained. Heart rate was higher in NFL players without than with previously unknown AF (84 vs 66 bpm), but almost all had a heart rate of less than 100 bpm and all were asymptomatic.

"The majority of the time, their heart rates were less than a 100 beats per minute, so they were not aware they were in atrial fibrillation," Phelan said. "This was a new, surprising diagnosis for most."

It is well recognized that long-term participation in endurance sports is associated with an increased risk for AF, but little is known about how strenuous strength training affects the heart. Research indicates former NFL players have lower overall and cardiovascular mortality than the general population, but because athletes tend to live healthier lifestyles than the average person, there may be a bias known as the "healthy worker hire effect," suggested Phelan. Moreover, recent work shows former NFL players have significantly higher rates of mortality from all causes, cardiovascular disease, and neurodegenerative diseases than Major League Baseball players.

"So this is a population that we do have some concerns about," he told theheart.org | Medscape Cardiology. "We show in a prior paper an increased risk of aortic dilation and now an increased risk of atrial fibrillation. So I think it's just important that we remain vigilant in monitoring these people closely."

CV Scrutiny

Working in association with the NFL Player Care Foundation, the researchers, led by Philip Aagaard, MD, Cleveland Clinic, screened 484 former NFL players (mean age, 55.9 years) who had participated in at least one NFL game (average, 7 years) and 925 DHS-2 nonelite athletes (mean age, 53.9 years).

The 460 former NFL players with complete data were older and had higher BMIs, but the DHS-2 group had more risk factors for AF and conduction disease, such as history of smoking, hypertension, hyperlipidemia, diabetes, coronary artery disease, and heart failure. AF was present in 23 people in the NFL group (15 previously unknown) and five in the DHS-2 group (all previously known).

The NFL group had 5.7 times higher odds of AF than the DHS-2 group in stepwise multivariate analysis (odds ratio [OR], 5.7; 95% CI, 2.1 -15.9) and 4.86 greater odds after propensity score matching (95% CI, 1.54 - 15.4).

Retired NFL players had an eightfold higher prevalence of paced rhythms (2.0% vs 0.25%; P < .01). They were also twice as likely to have first-degree atrioventricular block (18.0% vs 9.0%: P < .001) and premature ventricular contractions (3.9% vs 1.8%; P = .01) and had longer PR intervals (179 vs 167 ms; P < .001) and QRS intervals (96 vs 93 ms; P < .001).

Selection Bias?

The study is suggestive of an association between strength training and AF but it's not definitive, Paul D. Thompson, MD, Hartford Hospital, Connecticut, who chaired a 2015 scientific statement on CV abnormalities in competitive athletes, told theheart.org | Medscape Cardiology.

"One of the main problems, which they dismiss but which we need to at least keep in mind, is that the football players volunteered to come into the study," Thompson said. "So if you had some suspicion that something was the matter with you or you felt a little palpitation, maybe you would be more likely to volunteer."

"The other thing that was a little strange was the number of people who had paced rhythms, so that means these people have already had pacemakers put in and that suggests to me, a little bit, that these people were self-selecting in," he said.

Thompson also noted that there was no relation between AF and years of NFL participation, although the authors point out that the players likely accumulated at least 1500 hours of exercise throughout their careers — a threshold beyond which AF risk is thought to increase.

Commenting further, "I would have expected football players to have a lot more AFib than a comparison group because they're just bigger and so they're much more likely to have sleep apnea," he said. "They point out that the BMIs were not that different, but the BMIs were bigger in the athletes and the athletes were older."

"I think what you can take away is that there may be some relationship between strength training and atrial fibrillation but you wouldn't bet your house on it from this study," said Thompson.

Phelan said American football players have been shown to have a higher risk for obstructive sleep apnea but, unfortunately, they didn't have the data to follow-up. Use of performance-enhancing drugs or anabolic steroids, another risk factor for AF, was also unknown.

"I suspect that that is a major role in this whole story, that perhaps sleep apnea is a driving force in it," he said. "Now the difference in BMI, however, was there, but we're talking about not a huge difference. We're talking about a BMI of 32.3 vs 30.5, so I don't think that is enough on its own to account for the significant difference in atrial fibrillation we were seeing."

Phelan noted that the number of paced rhythms in the study was very small. "I think that was something that was interesting, thought provoking, and requires more data, but I don't think that was really the main finding in this study."

"Could there be a selection bias? There absolutely could," he said. "We recognize that in the paper but it also applies to the Dallas Heart Study. People volunteered to participate in both. But most of these were asymptomatic and most of them had fewer risk factors for atrial fibrillation than the Dallas Heart Study did."

Ideally, Phelan would like to follow American football players longitudinally from their time in college to well after their NFL career and identify risk factors for AF. They hypothesize that the stress on the heart of a strength-trained elite athlete is unique from that of an endurance athlete, where the main hemodynamic stress is high flow.

"The stress in the strength-trained athlete is different; they are primarily getting spikes in afterload," he said. "Every time they lift, every time they hit — particularly, for example, linemen when they're hitting — they're getting spikes in their blood pressure. So increases in afterload, which tend to translate into changes that we see more like in hypertensive heart disease, where you get some more concentric hypertrophy of the ventricle. And that can translate into worsening diastolic function that we have seen in American-style athletes, which increases the size of the left atrium and certainly can increase the risk of atrial fibrillation."

In adjusted multivariate analysis that included only former NFL players, larger left atrial volume index (OR, 3.1) and higher BMI (OR, 1.1) independently predicted higher odds of AF, whereas black race was protective (OR, 0.1).

Study coauthor David McNamara, MD, MPH, is supported by the National Heart, Lung, and Blood Institute. The remaining authors and Thompson report having no relevant disclosures.

J Am Heart Assoc. 2019;8:e012531. Full text

Follow Patrice Wendling on Twitter: @pwendl. For more from theheart.org | Medscape Cardiology, join us on Twitter and Facebook.

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