Can an EKG detect a previous heart attack? How it works

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An EKG is a test that measures a person’s heart rhythm and electrical activity.

During an EKG, medical professionals attach special sensors to a person’s skin. These sensors record the heart’s electrical activity, including the electrical impulses the heart produces with each beat.

A machine records and processes this information. It provides a readout of the wave patterns that specialists analyze.

Learn more about an echocardiogram.

According to a 2023 review, heart attacks can appear on an EKG.

How heart attacks show up on EKGs is a complicated and technical matter. However, EKGs can identify some tell-tale signs of a heart attack in the form of ST elevations. In people with acute coronary syndrome, ST segment depressions may signal an obstructed artery.

These patterns involve the following EKG results:

• ST: This is when the ST segment of the EKG is abnormally low. This ST segment represents the changes that occur when electrical activity flows out of the ventricles, also known as depolarization. The ventricles are the two lower chambers of the heart. When they depolarize, they contract.
• T waves: T waves represent how the ventricles regain their electrical charge after having lost it. This is known as repolarization. De Winter T waves are a type of down-sloping T wave.
• R waves: Another way that EKG measures the extent of ventricle depolarization.
• aVF: This is an abbreviation for “augmented vector foot.” This EKG pattern comes from a lead that medical professionals attach to the left leg. It records electrical activity related to the bottom of the heart.

Learn more about what an abnormal EKG means.

EKGs may be able to detect previous heart attacks. However, an EKG is not the most reliable way to detect previous heart attacks.

According to a 2018 review, EKGs can detect previous heart attacks around 48.4% of the time. They can also detect the absence of any previous heart attack 83.5% of the time.

Ultimately, EKGs are more helpful in determining that someone has not had a previous heart attack.

Learn about blood tests for diagnosing a heart attack.

EKGs may also help predict future heart attacks.

One 2019 study found that EKGs can indicate patterns of heart activity that represent risk factors for heart attacks. EKGs can detect these patterns even in people who have no other obvious heart attack risk factors.

Another 2019 study suggests that EKG data can sometimes produce more accurate predictions of future heart attacks than predictions based on medical history.

Learn more about whether an EKG can predict a heart attack.

According to the American Heart Association (AHA), silent heart attacks are heart attacks with atypical, minimal, or absent symptoms, such as:

• indigestion
• a feeling of having a strained chest or upper back muscle
• long lasting and excessive fatigue

The AHA estimates that around 20% of all heart attacks that occur in the United States each year are silent.

Learn more about silent heart attacks here.

EKGs are not the only tests available for diagnosing heart attacks.

According to the National Institutes of Health (NIH), doctors can also use some blood tests to detect heart attacks, such as tests that check for troponin, a protein the body releases when heart muscle cells die during a heart attack.

Doctors can also use heart imaging tests to determine whether someone’s heart is functioning correctly. These tests include echocardiograms and computed tomography (CT) scans.

Learn more about heart CT scans.

EKGs work by measuring the electrical signals in a person’s heart. They can detect heart attacks as they are happening by picking up on abnormalities in ventricle depolarization and repolarization.

Evidence suggests that EKGs can detect previous heart attacks. However, they are much more reliable at detecting the absence of previous heart attacks. They can also help to assess the risk of future heart attacks.