Friday, Jun 22, 2018
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Better tests diagnose heart attacks faster

“You had a heart attack.”

These words, pronounced 1.1 million times each year in the United States, have serious medical, psychological, and practical implications for men and women diagnosed with the nation's No. 1 killer disease.

People who imagine themselves invulnerable suddenly become aware of a close encounter with death. They bear the psychological burden of having a potentially fatal disease. And there are practical considerations that may affect an individual's ability to buy life, health, and disability insurance; continue in a job and find future employment, and much more.

If estimates are correct, a quarter fo a million more Americans will hear those words every year.

No, the number of heart attacks has not suddenly surged. The heart attack is being redefined.

Doctors are adopting a new official definition of the heart attack. It will identify many minor heart attacks that previously were dismissed as indigestion, anxiety, virus infections, or a bad bout of angina. Angina is the chest pain that often occurs in patients with atherosclerosis, the artery-clogging disease that causes most heart attacks.

Advances in the technology for diagnosing heart attacks that occurred during the 1990s forced cardiologists to consider changing the traditional definition.

Myocardial infarction (MI), the medical term for a heart attack, literally means “heart muscle death.” Most MIs occur when a clot forms in the coronary arteries, which carry blood to the heart's muscular walls.

If blood flow is not restored quickly with clot-busting drugs, angioplasty, or bypass surgery, heart muscle cells supplied by the blocked artery die. The dead cells break open, pouring enzymes and other contents into the blood. Blood tests used to diagnose heart attacks in hospital emergency rooms search for those enzymes.

A human heart weighs 7 to 15 ounces (200 to 425 grams or 200,000 to 425,000 milligrams) and is about the size of an individual's fist. One gram is about 1/28 of an ounce. Traditional blood tests worked well in identifying relatively big areas of dead tissue. For instance, doctors defined a “small” heart attack as the death of up to 10 per cent of the heart's main pumping chamber.

By the late 1990s, however, a new blood test proved effective in identifying minute areas of dead muscle, weighing less than 1 gram or 1,000 milligrams. The test detects “cardiac troponin,” an enzyme found only in heart muscle. It gets into the blood only when heart muscle dies.

In 1999, the American College of Cardiology and the Joint European Society of Cardiology appointed an expert panel of doctors to re-examine the definition of an MI. Late in 2000, the panel concluded that the existing definition was outdated. It recommended that the test for cardiac troponin be added to the criteria used to decide if a person has had a heart attack.

Those criteria include elevation in another muscle enzyme called CK-MB, changes in the patient's electrocardiogram, and symptoms such as crushing chest pain, sweating, and nausea.

Doctors in some parts of the United States already had begun using the cardiac troponin test before it officially was added to the defining signs of an MI.

A University of Michigan study estimated that the new criteria would result in diagnosis of about 250,000 additional MIs in the United States annually. Many more MIs will be diagnosed worldwide as more doctors embrace cardiac troponin as one defining sign of a heart attack.

More people with small MIs that were previously undetectable will be brought under medicine's protective medical shield. Its framework of drugs, surgery, and lifestyle changes offer the promise of preventing a second - and perhaps more serious - heart attack.

Michael Woods is the Blade's science editor. His column on health and science issues appears each Monday. Email him at

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