Insights Into Marathoners' Hearts: Don't Believe the Hypertrophy

Shelley Wood

November 27, 2006

November 27, 2007 (Chicago, IL) - Dr Stephan Möhlenkamp tells the story of running tests on a fit, asymptomatic, 57-year-old marathon runner as part of a communitywide screening study. The runner had completed a marathon several days previously and felt fine, if a bit stiff, but tests showed he actually had acute ST-elevation MI, moderate three-vessel disease, and required urgent revascularization.

The findings prompted Möhlenkamp and colleagues to initiate a study specifically of "master" (>50 years) marathon runners, to screen for asymptomatic disease. As he explained to heartwire , "We were puzzled and started to ask, is this guy one in a million that we see, or is this part of a bigger story? What is the extent of atherosclerosis and cardiovascular disease in master marathon runners?"

For their study, Möhlenkamp and colleagues have enrolled more than 100 male marathon runners over the age of 50 and performed traditional risk-factor analyses on all of them, as well as ECG, echocardiography, MRI, and coronary artery calcium (CAC) scans. All of the men had run at least five marathons in the past three years.

Subclinical atherosclerosis despite excellent Framingham risk scores

Earlier this month, Möhlenkamp and colleagues presented CAC scan findings from the Masters Marathon Study at the American Heart Association (AHA) 2006 Scientific Sessions. They reported that while the runners had completed, on average, 20 marathons over the past nine years and had significantly better risk-factor profiles compared with age-matched controls (lower BMI, blood pressure, and LDL; higher HDL), their CAC burden was no different. For the cohort as a whole, Framingham risk scores were approximately 50% lower than in age-matched controls; however, among age-matched controls who were also matched by Framingham risk score, CAC scores greater than 100 were much more common, pointing to a higher incidence of subclinical atherosclerosis despite rosy risk-factor profiles.

"Despite this favorable risk profile, the extent of subclinical atherosclerosis was significantly higher as compared with age- and risk-factor-matched controls from the general population," the investigators concluded. "The unexpectedly high coronary atherosclerotic burden may in part account for some of the exercise-related cardiovascular events in advanced-age marathon runners."

MRI studies hint at adverse adaptive changes

This week, at the Radiological Society of North America (RSNA) 2006 Meeting in Chicago, study investigators presented MRI findings from the same cohort, now expanded to 110 male marathoners, on average 57 years old. As Möhlenkamp explained to heartwire , some degree of left ventricular (LV) hypertrophy is expected in extremely fit subjects, a phenomenon dubbed athlete's heart. But what he and his colleagues--including Dr Torleif A Sandner (University Hospital, Munich, Germany), who presented the results--wanted to find out, particularly given findings from the CAC scans in their marathon runners, was whether some of the changes occurring in older marathoners might not merely be physiologic adaptation to endurance exercise.

What they found is that while LV volumes and LV ejection fractions were comparable to studies of nonathletic men of the same age, LV mass as measured by MRI was significantly higher. Moreover, increased LV mass appeared to correlate with CAC scores.

"When we measured LV mass, we found that those marathon runners with a mass above 150 g had a significantly higher coronary artery calcium score than those below," Möhlenkamp told heartwire . "Usually you would think in a marathon runner that they may have some degree of LV hypertrophy, so an increase in myocardial mass. But what has never been shown, as far as I know, is that this may in fact be associated with the amount of coronary artery calcium, so the big question is, is this 'athlete's heart' or is it early disease?"

He continued, "We believe this is the first evidence that not all of the increase in LV mass is an adaptation to long-term training. In some runners it may be evidence for early cardiovascular disease."

Möhlenkamp pointed out that while some of the marathoners may have been lifelong athletes, others might have gotten into sports much later in life, in some cases after decades of riskier lifestyles. "You might look at these patients and think, sure, there's increased mass because they're runners, but in fact, in some of them, this may be an early sign of some response to earlier risk-factor exposure," he said.

It's impossible to measure previously increased risk-factor profiles in someone who may have lowered their risk-factor profile through lifestyle changes, he stressed. "I can measure blood pressure, lipid profile, ask about symptoms and lifestyle, but all this doesn't tell me much because he's been running for 10 years," Möhlenkamp explained. "If I look at his echo or MRI and I see increased muscle mass, I'd think sure, he's been running for 10 years, and I put everything down to running for 10 years when in fact we have some initial evidence now that at least in some master marathon runners, if you focus just on the MRI scan, some of these subjects with increased myocardial mass have in fact early cardiac disease."

Outcome data needed

Möhlenkamp was careful to stress that he wasn't so much advocating MRI as a standard test to screen older athletes, but rather that MRI, in this study, had illuminated an aspect of cardiovascular risk that might not have previously been appreciated. "I'm very careful about making a strong statement. At this point, the fact is just that there is a mismatch between the risk-factor profiles and the amount of CAC, as we presented at the AHA. And now, as we're showing at the RSNA, a muscle mass above 150 g means you have a higher likelihood, that's statistically significant, of having a higher calcium burden than if you have a muscle mass below 150 g. At this point this just adds to the puzzle: what we will need is outcome data--we'll have to wait five years to really know whether it is the risk factors that predict outcome, or the atherosclerosis burden, or the muscle mass. Any of these variables in the marathon runners could predict outcome."

The complete contents of Heartwire , a professional news service of WebMD, can be found at www.theheart.org, a Web site for cardiovascular healthcare professionals.

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