Coping With a Heart Attack
A heart attack, known medically as a myocardial infarction, occurs when a blood clot blocks one of the coronary arteries (see Figure 9). Each coronary artery supplies blood to a specific part of the heart’s muscular wall, so a blockage causes pain and malfunction in the area that the affected artery serves. Depending on the location and the amount of heart muscle involved, this malfunction can seriously interfere with the heart’s ability to pump blood. Also, some of the coronary arteries supply areas of the heart that regulate heartbeat, so a blockage sometimes causes potentially fatal abnormal heartbeats called cardiac arrhythmias.
Most people are familiar with the classic description of a heart attack: crushing chest pressure; pain radiating to the neck, jaw, back, or arm; sweating and shortness of breath; sudden “indigestion” that isn’t relieved by antacids. While some women do experience these classic symptoms, the warning signs of a heart attack may be significantly different in women than in men (see Table 7).
If you experience these symptoms or others that indicate you may be having a heart attack, call your doctor immediately and go to the nearest emergency room. Chew an aspirin on the way to help reduce your blood’s tendency to clot. Every second counts. In one landmark study, people who received treatment within one to two hours were only half as likely to die as those who were treated four to six hours after the onset of symptoms. The primary goal in treating most heart attacks is to unblock the artery and restore blood flow to the heart as fast as possible with medication or surgery. Doing so will minimize the damage to the heart tissue.
Figure 9: Your heart’s “weakest links”
Blockage can occur in any of your coronary arteries. Two common sites are the right coronary artery (A) and the left anterior descending artery (B). When blockages occur in these locations, heart damage can result in the adjoining areas (shown shaded).
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 7)
- suggestive ECG abnormalities
- blood tests that reveal elevated levels of the blood chemicals troponin or creatine kinase-MB (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.
Table 7: Common symptoms of a heart attack
|Learn the symptoms of a heart attack and seek help immediately if you think you are having one. Although the most common sign of a heart attack in both men and women is chest pain or discomfort, other symptoms tend to vary depending on your gender.|
Emergency room staff often do an immediate ECG; sometimes this is even done in the ambulance during the ride to the hospital. In many cases (but not all), the ECG helps to determine whether you are having a heart attack, and if so, what type of heart attack.
One such type is a full-thickness or transmural heart attack, meaning it involves the full thickness of the heart’s muscular wall. Generally, this type of heart attack produces an injury current that shows up on an ECG as an ST segment elevation (see Figure 10). Cardiologists call this kind of attack an ST-elevation myocardial infarction, or STEMI.
A partial-thickness heart attack, or non-ST-elevation myocardial infarction (non-STEMI), produces different ECG 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 heart attack, and it can sometimes mimic a full-thickness heart attack. More often, however, the ECG abnormalities that accompany a heart attack are atypical, subtle, or even absent. That’s why doctors always use blood tests to confirm a heart attack diagnosis.
Figure 10: Types of heart attacks
Doctors analyze ECG 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 the baseline (right). However, ECG patterns are seldom so clear, and blood tests and other indicators will confirm a diagnosis.
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 will probably test your blood for either troponin I or troponin T, which are proteins that begin to rise within minutes to hours after a heart attack. Troponin levels usually increase sharply about four to six hours after heart muscle has been damaged, reach peak levels in 10 to 24 hours, and return to normal 10 to 14 days later. Another protein in the blood, creatine kinase-MB, also rises in response to heart tissue damage within six hours of a heart attack. It reaches peak levels at about 18 hours and returns to normal in two to three days. Troponin has emerged as the preferred test for heart attacks at most hospitals. Compared to creatine kinase-MB, it is less likely to cause false positives (that is, to mistakenly identify a heart attack when one has not occurred), and it remains elevated for a longer period of time.
Two-thirds of Americans can’t identify the signs of a heart attack and say what needs to be done when one strikes.