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How can an EKG tell a doctor if I'm having a heart attack?

An EKG shows the electrical activity generated by the heart. When there are changes in the electrical complexes, an EKG can show your doctor if the changes are indicative of an acute myocardial infarction (heart attack).

To confirm the diagnosis of a heart attack (or myocardial infarction), a doctor will require blood tests and/or an EKG.

During a heart attack, the EKG shows a series of abnormalities. The first abnormality is called a hyperacute T wave. This T wave shows up on the test as taller and more pointed than a normal T wave. The abnormality only lasts for a short time. Then elevation of the ST segment occurs. Elevation of the ST segment is the hallmark abnormality of an acute myocardial infarction - a heart attack. The ST segment elevation happens when a lack of blood flow and oxygen is actually injuring the heart muscle. This is also called a current of injury. Not long after come T wave inversions. When the heart muscle cells actually die over time, these abnormalities are replaced with Q waves.

It is important to know that not everyone with a heart attack has an abnormal EKG. In as many as 40 percent of patients, the initial EKG may not show ST elevation in patients having a heart attack. When a Q wave develops after a heart attack, it is known as a Q-wave myocardial infarction and usually corresponds to a transmural myocardial infarction (this means the heart muscle wall?s entire thickness has died). When a Q wave does not develop after a heart attack, it is called a non-Q-wave myocardial infarction and usually corresponds to the less severe non transmural heart muscle death, also called a subendocardial myocardial infarction. This means heart muscle just below the inner lining of the heart has died.

EKGs can not only tell a doctor if a heart attack is present but can also show the approximate location of a heart attack - often including which artery is involved.

The heart has an electrical conduction system. An EKG is a test that checks to see if that electrical conduction system is working properly. An EKG has the ability to take the electrical impulses in the heart and put them into a tracing that is shown on paper. This tracing can indicate whether the heart is working properly.

When a person is having a heart attack the physician will perform an EKG. The EKG can show if there are any problems with the heart and if a person is having a heart attack. If a person is having a heart attack the EKG shows certain changes. These changes can tell the physician if the person is having a heart attack right now, or if it has happened in the past. The changes can also tell the physician the location of the heart attack.

The unfortunate thing is that not all patients having a heart attack will show immediate changes on the EKG. The physician will normally order blood tests and a EKG to check if a person is having a heart attack. The EKG and a positive sign in the blood test will help the physician diagnose the heart attack.

In many cases (but not all), the electrocardiogram (ECG) helps determine whether you are having a heart attack and, if so, what type of heart attack.

One 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 that shows up on an ECG as an ST segment elevation. 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.
Kenneth Zelnick, MD, of Westside Regional Medical Center explains how doctors read EKGs and identify heart attacks. Learn more about how special segments in the EKG can inform doctors in this video.
How Can an EKG Help Identify a Heart Attack?

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.