Is It A Heart Attack - Dealing With A Heart Attack: Heart Disease

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Is it a heart attack?

Physicians or emergency room staff must first determine whether you are having a heart attack, an episode of angina, or something completely unrelated to the heart (see "Chest pain"). The American College of Cardiology recommends that a diagnosis of heart attack be made when two of the following three criteria are met:

• compatible symptoms (see Table 9)

• suggestive EKG abnormalities

• blood tests that reveal elevated levels of the blood chemicals creatine kinase-MB or troponin (see "Blood tests").

Because heart attacks are sometimes hard to distinguish from other causes of chest pain, your physician may also order additional tests, such as echocardiography, nuclear scans, and cardiac catheterization, before making a diagnosis.

EKG patterns

Emergency room staff often do an immediate EKG; sometimes this is even done in the ambulance during the ride to the hospital. The EKG helps, in many cases (but not all), to determine whether you are having a heart attack, and if so what type of heart attack.

One type is a full-thickness heart attack, also known as a transmural heart attack. When such heart attacks follow the rules, they produce an injury current that shows up on an EKG as an ST segment elevation (see Figure 6). Cardiologists call this kind of heart attack an ST-elevation myocardial infarction, or STEMI.

A partial-thickness heart attack, or non-ST-elevation myocardial infarction, produces different EKG changes — or at least, it should. Instead of becoming elevated, the ST segment is depressed, or lowered.

To complicate matters, angina often produces exactly the same changes as a partial-thickness (non-STEMI) heart attack, and it can sometimes mimic a full-thickness (STEMI) heart attack. More often, the EKG abnormalities that accompany a heart attack are atypical, subtle, or even absent. That's why doctors always use blood tests to diagnose heart attacks.

Figure 6: Types of heart attacks Doctors analyze EKG patterns to help determine what type of heart attack you are having. In an ST-elevation heart attack, which requires the most aggressive treatment, the ST segment is usually above the baseline (middle). In a non-ST-elevation heart attack, the ST segment is below baseline (right). However, EKG patterns are seldom so clear, and blood tests and other tests will confirm a diagnosis.

Blood tests

When heart cells die, they release enzymes, the chemicals that trigger vital tissue functions. Some of these enzymes are specific to the heart and aren't produced in any other tissue in large quantities. Doctors measure the blood levels of these enzymes at intervals over time.

Because dying heart cells release different enzymes at different rates, the blood tests can help pinpoint the time the heart attack occurred — information that is particularly useful when symptoms are vague. In addition, the more cells that die, the higher the blood levels of these different enzymes. Doctors can use this information to estimate the amount of heart tissue that has been destroyed.

If doctors suspect that you are having a heart attack, they usually test the blood, either for a specific form of the enzyme creatine kinase (known as creatine kinase-MB) or for two forms of a chemical called troponin (troponin-T and troponin-I). The level of creatine kinase-MB goes up when there has been damage to heart tissue. It rises within 6 hours of a heart attack, reaches peak levels at about 18 hours, and returns to normal within 2–3 days. Testing for this enzyme is useful for the many people who arrive at the hospital several hours after the onset of a heart attack. Abnormally high levels of troponins are also evidence of a heart attack because these proteins begin to rise within minutes to hours after a heart attack. Troponin levels usually increase sharply about 4–6 hours after heart muscle has been damaged, reach peak levels in 10–24 hours, and return to normal 10–14 days later.

Last updated:	May 03, 2007