MRI is a type of body scan that uses magnets and computers to provide high-quality images based on varying characteristics of the body's tissues. The technology allows physicians to study the heart's overall structure and functioning continuously in three dimensions. MRI addresses another critical issue in assessing patients with acute coronary syndrome: time. Patients can be scanned in under 40 minutes; if severe blockages are found, they could receive vital treatment to restore blood flow, such as clot-busting drugs, angioplasty, or coronary artery bypass surgery. Current recommendations are for such therapies to begin within one hour from the start of a heart attack for optimal effectiveness.
EKG records the electrical activity of the heart to detect abnormal heart rhythms, some areas of damage, inadequate blood flow, and heart enlargement. Like MRI, EKG is noninvasive. Because of its low degree of sensitivity, however, EKG immediately diagnoses only about 10 percent of patients with acute coronary syndrome. It is not uncommon for an EKG to appear normal during a heart attack or an episode of unstable angina.
Patients suspected of having a heart attack that is not confirmed by an EKG typically have their blood tested for enzymes or other substances ("markers") that indicate permanent damage to the heart tissue. Because the markers are not evident in the blood until several hours after a heart attack, patients whose EKG appears normal may need to stay in the hospital for 12 to 24 hours to ensure the blood test is accurate. Furthermore, because the blood test detects only permanently damaged tissue, it does not detect unstable angina.
Unstable angina can be considered an "impending heart attack." Heart attacks are caused by a blood clot from a tear or break in fatty deposits (plaque) that have built up inside a coronary artery; when the blood clot suddenly cuts off most or all blood supply to the he
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NIH/National Heart, Lung, and Blood Institute