Recently there's been increased emphasis on developing blood tests to detect injury to the heart muscle (myocardium) (mi"o-KAR'de-um) as early as possible among people with chest discomfort or other signs of a potentially serious heart problem. Such signs include shortness of breath, nausea, sweating and lightheadedness. This wide-scale effort has been based on several important local, regional and national goals.

1. Early diagnosis and treatment of people suffering heart attacks (myocardial infarction) (mi"o-KAR'de-al in-FARK'shun) and other serious complications of coronary atherosclerosis (ath"er-o-skleh-RO'sis). (Coronary atherosclerosis is the buildup of fatty plaques in the arteries that supply the heart muscle with blood.)
2. Cost-effective management of people with suspected coronary atherosclerosis who are at risk for heart attacks and death.
3. Early detection of people with non-heart-related illnesses that may warrant further evaluation.

Evaluating those with chest discomfort and a potentially life-threatening heart problem commonly includes four steps.

1. Medical history, including relevant risk factors for coronary atherosclerosis
2. Physical examination
3. Electrocardiogram.
4. Blood tests

Blood tests confirm (or refute) suspicions raised in the early stages of evaluation typically in an emergency room, intensive care unit or urgent care setting. Such tests are sometimes called heart damage markers or cardiac enzymes.

The blood test most commonly used to confirm the existence of heart muscle damage is the creatine kinase (KREE'ah-teen KI'nas), or CK for short. A small fraction of the CK enzyme, CK-MB, is often measured as well. CK-MB shows an increase above normal in a person's blood test about six hours after the start of a heart attack. It reaches its peak level in about 18 hours and returns to normal in 24 to 36 hours. The peak level and the return to normal can be delayed in a person who's had a large heart attack, especially if they don't get early and aggressive treatment.

Tests can measure the level of other cardiac muscle proteins called troponins (tro-PO'ninz), specifically troponin T (cTnT) and troponin I (cTnI). These proteins control the interactions between actin and myosin, which contracts or squeezes the heart muscle. Troponins specific to heart muscle have been found, allowing the development of blood tests (assays) that can detect minor heart muscle injury ("microinfarction") not detected by CK-MB.  Normally the level of cTnT and cTnI in the blood is very low. It increases substantially within several hours (on average four to six hours) of muscle damage. It peaks at 10 to 24 hours and can be detected for up to 10 to 14 days.

AHA Recommendation

Several studies have identified a measurable relationship between cardiac troponin levels and outcome after an episode of chest discomfort. They suggest that these tests may be particularly useful to evaluate levels of risk. In other words. results of a troponin test could help identify people at higher risk for serious heart problems or death. It remains to be proven whether more cost-effective methods of treatment and, eventually, a better outcome will result from routine troponin testing.

• Heart and Stroke Facts
• Heart Attack and Stroke: Signals and Actions (also in Spanish)