“Recently there have been reports of apparently fit individuals suffering a sudden heart attack while exercising on a treadmill or performing some other form of vigorous exercise. This sounds counterintuitive, since exercise is known to promote cardiac fitness and prevent heart attacks. While the specific circumstances of prior health status and intensity of exercise undertaken are likely to vary across such cases, there are some general facts which will help to explain this apparent paradox,” says Prof K. Srinath Reddy, a cardiologist, epidemiologist and president, Public Health Foundation of India (PHFI).
UNDERSTANDING PLAQUE RUPTURE
Explaining these sudden episodes, Dr Reddy says, “Heart attacks are caused when there is a sudden blockage of blood supply in one of the coronary arteries that supplies blood to the heart muscle. Chronic obstruction of 70 per cent or more in a coronary artery produces angina or chest pain on exertion, since available blood supply does not meet the increased oxygen demand of the exercising body and straining heart. However, a heart attack (acute myocardial infarction) can occur when soft plaques that form in the coronary arteries rupture and cause a large clot to form. This may come without any prior warning symptoms. Even plaques of 30 per cent can rupture and set up the formation of a large obstructive clot.”
So how are plaques formed? “Plaques form in the coronary arteries due to injury caused to the blood vessel lining, by factors causing inflammation. High blood pressure, smoking, diabetes, unhealthy diets, stress, inadequate sleep or recent infection do that. Fat in the circulating blood then deposits at the site of injury to grow the plaque. Each of those chronic causes of inflammation can also acutely precipitate a plaque rupture leading to a heart attack, if there is a sudden or severe rise in one or more of those factors. Vigorous exercise too can cause plaque rupture or trigger electrical disturbances in the heart leading to cardiac arrest,” adds Dr Reddy.
EARLY MORNING SURGE
Most of these episodes happen early morning. “Usually there is an early morning surge of blood pressure, which is part of our evolutionary biology. Blood clotting tendency, too, is higher at that time. If a person who has some underlying coronary risk factors, has not slept well, is dehydrated and steps up to do vigorous exercise, plaque instability can lead to rupture and trigger large clot formation,” explains Dr Reddy.
EXERCISE ISN’T BAD
This does not mean exercise is bad for the heart. “It is essential to detect and control the risk factors which build and rupture plaques in the coronary arteries. Care and caution are all the more needed in Indians who have an ethnic susceptibility to experiencing a heart attack at younger ages than other population groups, for several reasons,” says Dr Reddy.
Sudden cardiac death during strenuous exercise like vigorous treadmill or snow shovelling occurs in the background of known heart blockages or more often occult coronary artery disease or blockage of heart arteries that are yet undiagnosed. If a patient is revived in such a situation, he carries a better outcome as compared to sudden arrest at rest where the heart is usually weak (heart failure),” says Dr Suman Bhandari Visiting Consultant, Interventional Cardiology, Fortis Escorts Heart Institute
“When treadmill is done at very high speed and /or inclination, there is a double impact, that is the heart rate and blood pressure, which is a determinant of the oxygen demand in the heart. High mets (metabolic equivalent) during higher speed and for prolonged periods can cause undue stress on a compromised heart circulation in a setting of heart blockages. They cause sudden arrhythmia, undue low blood pressure or a heart attack. Such people need to be evaluated urgently with coronary angiography and should have appropriate revascularisation, for example, stenting procedure as per current guidelines,” adds Dr Bhandari.