Future AF Risk Falls At Optimal, Not Highest, Fitness Levels

Pam Harrison

March 23, 2015

KUOPIO, FINLAND — The risk of future atrial fibrillation (AF) plummets with increasing cardiorespiratory fitness (CRF)—up to a point, suggests a new analysis based on a large cohort of middle-aged men in Finland[1]. The benefit was seen within an optimal range of fitness, but the risk decrease reversed direction and started to climb in the most highly trained men, those considered "the fittest of the fit."

As for the latter finding,"Endurance athletes and individuals who have extreme levels of physical fitness have a higher incidence of atrial arrhythmias, so this effect has been seen before," Dr Hassan Khan (Emory University Hospital, Atlanta, GA) told heartwire from Medscape.

"But that represented only a small subset of the cohort, those in the highest quartile of cardiovascular fitness, Khan said. "In general, there was a very nice relationship that showed improving the overall level of fitness decreases the risk of atrial fibrillation in the overall population," he said.

The study was published online March 14, 2015 in Heart Rhythm.

Subjects were participants in the Kuopio Ischaemic Heart Disease Risk Factor Study, a longitudinal population-based study designed to investigate risk factors for cardiovascular disease (CVD), atherosclerosis, and related outcomes. The current analysis was based on 1950 men from that study.

Maximal oxygen uptake was used as a measure of CRF and was assessed by using a respiratory gas-exchange analyzer during a cycle ergometer exercise test. Incident AF was identified through a comprehensive review of hospital discharge diagnoses, inpatient physician claims data, and ECG studies. The mean age of participants at baseline was 52.6 years, while the mean VO2max was 30.3 mL/kg/min.

"During an average follow-up of 19.5 years . . . there were 305 incident AF cases," investigators write. Overall, a nonlinear association was observed between CRF and incident AF rates per 1000 person-years of follow-up.

For the first quartile of CRF indicating the lowest level of fitness, AF rates were 11.5 per 1000 person-years of follow-up (95% CI 9.4–14.0); for the second CRF quartile, AF rates were 9.1 per 1000 person-years of follow-up (95% CI 7.4–11.2). For the third CRF quartile, AF rates were 5.7 per 1000 person-years of follow-up (95% CI 4.4–7.4); for the fourth, or fittest, quartile AF rates were 6.3 per 1000 person-years of follow-up (95% CI 5.0–8.0).

CRF by Quartile and AF Incidence

CRF (mL/kg/min (mean) Events Hazard ratio (95% CI) (adjusted for age only) P
Q1: 20.3 91/488 ref ref
Q2: 27.7 90/487 0.74 (0.55–0.99) 0.049
Q3: 32.6 56/488 0.54 (0.39–0.75) <0.001
Q4: 40.6 68/487 0.67 (0.48–0.95) 0.025

As the authors point out, the age-adjusted hazard ratio (HR) comparing the top CRF quartile to the bottom was indeed 0.67, but this HR was attenuated to 0.98 (95% CI 0.66–1.43) when further adjusted for CVD risk factors.

Findings were comparable across age, body-mass index, history of smoking, diabetes, and CVD status at baseline.

"Unfortunately, it is not possible to precisely relate physical fitness with level of activity or exercise done per week," Khan told heartwire in written correspondence.

"What this work shows is an echo of earlier work showing that better physical fitness is a marker of better health and improved outcomes such as less atrial fibrillation, and physicians should encourage patients to exercise more as suggested by current AHA recommendations."

LEGACY Trial

The Long-Term Effect of Goal Directed Weight Management on an Atrial Fibrillation Cohort (LEGACY) study, presented last week at the American College of Cardiology (ACC) 2015 Scientific Sessions, showed that those patients who achieved at least a 10% weight loss at 1 year had a greater reduction in severe symptoms of AF than participants who lost less weight.

Khan said he has been following the LEGACY trial and agrees that weight loss may have an important role in reducing the burden of AF, as seen among patients who lost the most weight in the LEGACY trial.

"From our own work, we could see a strong negative correlation of body-mass index with levels of CRF," Khan said. "And these findings again suggest that people who are overweight have lower levels of CRF and thus are at higher risk of AF.

So the data are consistent, he said, that "physical activity and weight loss improve CRF and thereby lower the risk of AF," Khan said.

The study was supported by the Academy of Finland, the City of Kuopio, and the Finnish Medical Foundation, as well as the Finnish Cultural Foundation. The authors report they have no relevant financial relationships.

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