For the unfit, marathons may endanger the heart

About 10 years ago, as Eric Larose was nearing the finish line of a marathon in Quebec City, a young runner, apparently healthy and fit, collapsed and died of a heart attack.

"Very eerie," Larose recalls.

It was not an isolated event. Other seemingly healthy runners have died suddenly in other marathons.

Larose was intrigued.

"How is it that someone with no known health defects suddenly dies during an event that's supposed to encompass the fittest people?" he wondered. As a marathoner himself, he found the phenomenon "worrying."

Digging through the scientific literature, he discovered that the risk of sudden cardiac death jumps sevenfold for those engaged in vigorous prolonged exercise.

"We know that running is good for you and will reduce the risk of a cardiovascular event over a lifetime by two- or threefold," says Larose, 41, a cardiologist and clinical researcher at the Quebec Heart and Lung Institute and assistant professor of medicine at Laval University.

"So there's a disconnect between the long-term benefit of exercise, which no one disputes, and the temporarily increased risk that occurs while doing prolonged strenuous exercise."

Larose decided to study this disconnect. Specifically, he wanted to find out how exercise can harm you and under what circumstances.

Or, as Larose puts it: "How can somebody without known cardiovascular disease actually damage the heart during a marathon?"

He presented a summary of his findings last month at the Canadian Cardiovascular Congress. In a nutshell: The hearts of marathon runners show some of the same signs of distress evident in the initial phase of a heart attack.

"In the early stages of a heart attack, the signs you see resemble what we found in our study subjects," Larose told me by telephone. He hastened to add: "The damage was not permanent."

For the study, Larose and his colleagues recruited 20 amateur runners, all free of cardiovascular disease as determined by a stress test on a treadmill. They ranged in age from just over 20 to just under 60 and represented a broad span of experience and fitness. Some were running their first marathon; the most seasoned was running his 30th. Fourteen of the 20 were male.

The runners' fitness was measured six weeks before the 2008 Quebec City Marathon, when they presumably were in peak condition. The fitness yardstick was V02 max, the so-called gold standard. This test, usually administered on a treadmill, determines the body's maximum capacity to transport and use oxygen during exertion that fully taxes the aerobic energy system.

Simultaneously, the condition of their hearts was inspected via MRI. Images of the heart were taken again immediately after the marathon and yet again three months later.

Larose and his research team were monitoring several things: impaired heart function; signs of injury, such as inflammation and swelling (edema); and blood flow to the heart muscle (perfusion of the myocardium).

The findings? Parts of the runners' hearts were swollen and inflamed, and function fell in more than half the regions of the heart, an effect possibly associated with the observed drop in blood supply and nourishment of the heart muscle. In addition, the enzyme troponin, which rises in response to heart strain, spiked.

"These are the same signs you see in various diseased states," Larose says, "in hearts that are in distress and suffering."

Significantly, the researchers saw no evidence of cell death or scarring. Says Larose: "There were definitely signs of injury but no loss of heart tissue." Ergo, no permanent damage.

If the injury is temporary, you may reasonably wonder, why fret?

Larose explains: "The temporary damage you see in other diseased states is associated with increased arrhythmia and cardiac events. The heart is not only a muscle, it's also an electrical system. If you injure the cells, they can go haywire, and electricity is not conducted properly. That's why a heart in a relatively disease-free state can go into sudden cardiac arrest."

None of Larose's study subjects had a heart attack or "cardiac event." But the rigors of the marathon affected them differently. The determining factor: fitness.

The most fit runners had less to no injury; the least fit had more.

In some cases, the damage was so widespread that it extended to the entire left ventricle.

Would a heart show the same damage after an all-out 800-meter run, or a mile?

"We don't know," Larose says. "But running a marathon is probably the most extreme thing most of us will ever do, and the sheer duration of the effort is a major issue. The longer it took to run the marathon, the more injury we saw."

The take-home message: "If you're not properly trained for a marathon," Larose says, "you should be aware that you may be at increased risk."