Blog | Tuesday, December 20, 2011

Research suggests more damaging effects of endurance exercise on the heart


Dear Endurance Athletes,

Accept an apology in advance. You have endured so much from me.

Sorry.

Let's at least start by agreeing that I can't control the data.

Yes, you guessed it. There is unfortunately more bad news pertaining to the deleterious effects of endurance exercise on the human heart.

Again, I am sorry. Maybe re-phrasing the previous sentence will soften the blow. How about this: "Yet another study on endurance athletes suggests that exercise, like everything else in life, has an upper limit."

Here goes, buckle up.

The study titled, "Exercise-induced right ventricular dysfunction and structural remodeling in endurance athletes" was published last week in the European Heart Journal.

Researchers from Belgium and Australia enrolled 40 long-term endurance athletes in a study looking at heart function after an endurance race. All subjects were long-term exercisers and were accomplished athletes with above average fitness. They were elite.

By measuring cardiac enzymes (heart injury) and taking ultrasounds (directly seeing heart function) immediately after four different length races (marathon through 'ultra-triathlon'), researchers were able to measure the acute effects of extreme exercise on the heart. MRI scans performed a week later assessed for cardiac scar tissue. (The presence of scar in heart muscle portends trouble because it disrupts electrical signals.)

The main findings:
--Compared to pre-race measures, right ventricular (RV) function diminished post-race, whereas LV function remained normal.
--Blood levels of cardiac enzymes increased post race and these rises correlated with the amount of RV impairment.
--The degree to which RV function decreased correlated with increasing race length and an athletes' VO2 max.
--12% of athletes had scar detected on MRI scans at one- week post-race. Those with scar reported greater cumulative exposure to exercise and had more RV abnormalities post race.

Ouch!

The authors rightly conclude: "Intense exercise causes dysfunction of the RV, but not the LV. Although short-term recovery appears complete, chronic changes may remain in many of the most practiced athletes."

My take:

I'm not an alarmist, but this study scares me.

First, there are (general) rules in medicine. One in cardiology, electrophysiology in particular, holds that RV damage is not good. Diseases that affect the RV tend to cause electrical instability that may increase the risk of sudden death. (Medical people call such a process, arrhythmo-genic.)

I'm not saying that exercise-related stunning of the heart and scar formation causes sudden death. I'm just pointing out that things that mess with the RV should not be called meek. If I was writing an academic piece, it would read, "The findings of this well-done study are hypothesis-generating and warrant further prospective investigation."

Second, the data fits a pattern: Longer races and fitter athletes (who are able to sustain higher outputs longer) release more cardiac enzymes and sustain greater RV dysfunction. Those with the greatest exercise history and those who sustain post race RV damage are at greatest risk of developing scar. More was worse.

Third, the findings fit nicely with prior studies. Marathon rats who ran themselves silly, like the subjects in this study, showed similar scar patterns. Also, numerous prior studies in humans (published in peer-reviewed journals) have shown similar patterns of heart injury immediately post race. Other more recent MRI-imaging trials also confirm the presence of scar tissue in the hearts of endurance athletes.

Fourth, and most frightening, in the discussion section the researchers comment on the possibility that heart damage accumulated from long-term exercise may persist even after de-training.

Conclusion

Exercise remains the most effective and safest means to prevent and treat heart disease. The overwhelming majority exercise far too little. In fact, I believe the U.S. suffers from severe exercise-deficiency.

That said, however, accumulating data suggest at least the possibility of an upper limit of what the human heart can sustain.

Each study on extreme exercise has its limitations. This one is small. It's not randomized. And, studying exercise is tough because of the many confounding variables: genetic make-up of individuals, the presence of underlying diseases, and self-reporting of exercise amounts are just a few of many examples. But when taken together en bloc, these ominous trials grow harder for the naysayers to dismantle.

All this is reassuring to masters of the obvious. As it looks like optimal health is born and nurtured through balance.

And there's little about running marathons or slogging through Ironmans that could be called balanced. Fun maybe, for some.

Balanced? Heart-healthy? No way.

This post by John Mandrola, MD, appeared at Get Better Health, a network of popular health bloggers brought together by Val Jones, MD. Better Health's mission is to support and promote health care professional bloggers, provide insightful and trustworthy health commentary, and help to inform health policy makers about the provider point of view on health care reform, science, research and patient care.