YOU have been doing your usual 10-kilometre run and feel absolutely well with no chest pain - does it mean that it is impossible that you may have significant blockage of your heart arteries?
Jim Fixx, the American fitness guru who ignited the running revolution, shared the belief of an American pathologist, Thomas Bassler, that any non-smoker fit enough to run a marathon in less than four hours would never suffer a fatal heart attack. Unfortunately, at the age of 52, Mr Fixx died of a massive heart attack while running. The autopsy revealed that there was severe blockage of all three major arteries of the heart.
It is a common myth that if you are able to exercise actively without symptoms, you will not have heart disease. It is not uncommon for patients to vehemently deny that they have no symptoms whatsoever except for the few days prior to seeing the doctor and yet they have severe blockage of their major heart arteries and the heart muscle shows evidence of previous heart attacks. In some, the heart is so swollen and the heart function is so poor, one wonders how they could be asymptomatic with such severe heart disease.
In a 1970 Heart journal publication by Stowers, about one-third of patients who had an acute heart attack did not have preceding chest pain. In another study, "Women's Early Warning Symptoms of Acute Myocardial Infraction" published in Circulation journal in 2003, only about 30 per cent had preceding chest pain in the month before the acute heart attack.
The most frequent symptoms during a heart attack were shortness of breath (58 per cent), weakness (55 per cent), and fatigue (43 per cent). Chest pain was absent in 43 per cent of the women during the acute heart attack. From these and other studies, there is definite data to show that there are some patients who may have severe blockage of the heart arteries and even heart attacks, and yet have no chest pain.
While Jim Fixx believed that exercise would provide immunity from heart disease, another American nutritionist research pioneer, Nathan Pritikin, espoused dietary measures for the prevention of heart disease. Mr Pritikin was of the view that many runners on the average American diet will continue to die during or shortly after long-distance events and many of these men had died because they had wrongly believed that anyone who could run a marathon in under four hours and who was a non-smoker had absolute immunity from having a heart attack.
He believed that diet was an extremely important factor for heart-disease prevention. Mr Pritikin was diagnosed with narrowing of his heart arteries at the age of 41 and embarked on a dietary programme in the era preceding the availability of cholesterol-lowering drugs. He started with a total cholesterol of 300 mg/dl and brought it down to 120 mg/dl through a combination of diet and exercise. When he died, an autopsy study of his coronary arteries showed the near absence of atherosclerosis. We now know from multiple studies that cholesterol lowering can reduce the risk of a heart attack.
A 2012 Mayo Clinic article by O'Keefe reviewed about 50 studies published between 1991 and 2012 on the impact of extreme endurance exercise on the heart. The data suggested that extreme endurance exercises, such as marathons, ultramarathons, triathlons and extremely long distance bicycle races, can cause transient volume overload of the upper and right lower heart (ventricle) chambers, with transient reduction in right ventricular pump function and evidence of heart damage on blood testing, all of which return to normal within one week.
In some individuals, repeated physical strain on the heart may lead to patchy scarring of the heart, resulting in an increased likelihood of abnormal heart rhythms, including a five-fold increase in atrial fibrillation, an abnormal heart rhythm which is associated with an increased stroke risk.
One study showed that about 12 per cent of healthy marathoners had evidence of patchy scarring of the heart muscle. In addition, the incidence of coronary heart disease was significantly higher in marathon runners than in controls during a two-year follow-up.
The potential risk of chronic extreme endurance exercise was again brought into the limelight by the untimely death of Micah True, a renowned ultramarathoner, who died while running last year. An autopsy revealed enlargement of the left ventricle, the main pumping chamber of the heart, associated with thickening of the left ventricular wall, a condition called cardiomyopathy.
Heart disease can be asymptomatic and heart attacks may also occur without any chest pain. Hence, being able to run a marathon without symptoms does not mean that there is no underlying heart disease. Chronic repetitive endurance exercise can be detrimental to the heart and can sometimes lead to sudden death. Those who perform chronic endurance exercise should seek the advice of their physician and may require assessment of their heart.
However, heart muscle scarring due to chronic endurance exercise cannot be detected by routine ultrasound tests and will require special tests, such as magnetic resonance imaging of the heart with gadolinium contrast. Exercise alone does not provide immunity to heart disease but when combined with dietary measures will result in lowering of cholesterol which can potentially be beneficial.
Finally, remember that the benefit of running an ultramarathon is no better than that of moderate exercise of 30 to 60 minutes. Investing in excessive endurance exercise is associated with diminishing returns.
- Dr Lim is medical director at the Singapore Heart, Stroke & Cancer Centre. He is also editor-in-chief, Heart Asia (a journal of the British Medical Journal Publishing Group); chairman, scientific advisory board, Asia Pacific Heart Association; and honorary professor and senior medical adviser, Peking University Heart Centre
This series is brought to you by Heart, Stroke and Cancer Centre. It is produced on alternate Saturdays.