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Wednesday, January 17, 2018

Mayo study: higher cardiorespiratory fitness associated with lower risk of atrial fibrillation

Data and analysis continues to address the issue of exercise level and risk of atrial fibrillation (AF)-sometimes referred to as the U-shaped curve controversy.

Hussain et al (1) published a follow-up study on 14,094 selected subjects who had been referred to Mayo Clinic for exercise stress testing. These were from a much larger group from whom those with a history of heart failure, atrial fibrillation or flutter or stroke were excluded.The average follow-up was 14 years and the outcomes of interest were incident atrial fibrillation ,stroke and death.
They divided the subjects into 4 groups based on functional cardiorespiratory capacity as estimated by their performance on the Bruce protocol stress test.

Those subjects in the highest exercise performance category showed no increase in the risk for AF.

The authors concluded:

"...better cardiorespiratory fitness is associated with lower risk of incident AF, stroke and mortality. Similarly risk of stroke and mortality in patients with AF is also inversely associated with cardiorespiratory fitness."

They also commented that the reduction in these risks with increasing exercise capacity  "may be a direct physiological effect of exercise and physical activity or a consequence of a lower burden of cardiovascular risk factors" I would add "or both".

This is  another coarse grain study which will not settle the U shaped curve argument.I think often these "controversies " just dwindle away rather than get settled. The etiology of AF and stroke with AF involves a complex array of numerous possible input variables and here we look at the effect of  only one such variable ( exercise capacity-as a surrogate for exercise level) on the outcome (s) but at least  long time endurance exercisers may find some solace here. Critics can justifiably point out that a number of potentially confounding variables were not available  for analysis including, smoking history,alcohol use,and actually exercise habits.

Again quoting  Simon (2) ".. a man hears what he wants to hear and disregards the rest"





1) Hussain,N Impact of cardiorespiratory fitness on frequency of atrial fibrillation , stroke,and all cause mortality. AJC Jan 1, 2018. vol 121 issue 1, p 41-49

2) Simon, P .Lyrics from the song ,The Boxer, 1969


H/T "notes from DR RW"

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