A blood clot in the lungs is called a pulmonary embolism. It can affect heart function by making the right side of the heart work harder, because it blocks blood flow in the lungs.

PE can be life threatening, but it is often treatable if diagnosed early.

An electrocardiogram (ECG) is one of several tests that doctors might use to learn more information about a PE. An ECG is a noninvasive screening that involves electrodes placed on the skin that can monitor the heart’s electrical activity and pick up any deviations from the heart’s usual rhythm.

If a patient has other symptoms, an electrocardiogram can show problems in the heart that could suggest a PE. It could show problems with the right ventricle.

Reading an ECG

The pattern of electrical activity in the heart is represented by an electrocardiogram. The waves have five key points labeled P, Q, R, S, and T.

The distances between the points and their positions above and below the baseline show the speed and rhythm of the beating heart. They show the strength and pace of the electrical impulses moving through the heart muscle.

The PQRST waves can tell doctors a lot about your heart. If your heart rate is slow or elevated, an electrocardiogram can show.

The limbs and chest have escopies that measure different information. Each lead is important in showing a complete picture of how electrical impulses move through the heart.

ecg reading of a typical sinus rhythm
Illustration by Maya Chastain

An ECG cannot, by itself, diagnose a pulmonary embolism. A 2017 study suggests that about 25 percent of ECG results appear standard in people with a blood clot in their lungs.

An electrocardiogram can uncover some of the more common conditions.

Sinus tachycardia

Sinus tachycardia is one of the more common arrhythmias associated with PE. Sinus tachycardia occurs when the sinus node emits electrical impulses that make the heart beat too fast. Sinus tachycardia is present in about 30 percent of PE cases.

The underlying cause of sinus tachycardia can be treated, whether it is a PE, anemia, or another cause.

Right bundle branch block

A blockage of electrical signals in the right side of the heart is called a right bundle branch block (RBBB). A PE could cause an RBBB by causing the right ventricle to work unusually hard.

The electrical signals from the right atrium to the right ventricle are carried by the special fibers in the right bundle branches.

The presence of RBBB suggests a large blood clot.

Right ventricular strain

Right ventricular (RV) strain means there’s a problem with the muscle in the heart’s right ventricle. A 2019 study suggests that an ECG indicating RV strain in people with shortness of breath is “highly suggestive” of a PE.

Right atrial enlargement

The right side of the heart can become enlarged if the blood flow from the right side to the lungs is made more difficult by a blood clot in the lungs. The changes can make the heart less effective in pumping blood out of the body.

Atrial fibrillation

One of the most common arrhythmias, atrial fibrillation (AFib), can be both a result and a cause of PE, according to a 2017 review.

Someone with a blood clot in the heart is at higher risk of having a blocked arteries in the lungs. If a clot forms in the lungs, the heart could work harder, which could cause the start of a disease called afib.

Pulmonary embolism and the S1Q3T3 pattern

The S1Q3T3 pattern is a common ECG finding when a PE is present. But it does not always indicate PE.

The pattern shows an electrocardiogram reading.

  • A wave in lead 1.
  • A wave in lead 3.
  • An upside-down T wave in the lead.

The pattern suggests that the right side of the heart is not strong.

Certain ECG anomalies associated with PE, such as an S1Q3T3 pattern with RBBB, may also be reflected in cor pulmonale. This is a disease of the right ventricle that may or may not be triggered by PE.

An electrocardiogram is not a must for a PE, but it can give doctors more information.

A doctor will look at your medical history and symptoms to determine if you have a PE. An electrocardiogram can give clues as to how the heart is functioning.

If anomalies show up on an ECG, they may indicate the severity of a PE and help determine whether emergency treatment is necessary.

A 2017 review of studies found that ECG anomalies predicted a negative outcome for PE patients. Those with S1Q3T3 patterns or signs of RBBB were more likely to die in hospital. Sinus tachycardia and AFib were the strongest predictors of 30-day mortality.

An electrocardiogram is a relatively easy test to perform. When there is a suspicion of cardiovascular trouble, doctors often request an electrocardiogram. The test has steps.

  1. A doctor, nurse, or technician will place a small device on your body.
  2. “The heart’s electrical activity is transmitted to the monitor.”
  3. The information is converted into waves.
  4. Doctors can usually get a hard copy of the patterns from the printed ones.
  5. Your doctor will look for signs of irregular rates or rhythms.

“The procedure can be done in a few minutes. It is painless and doesn’t require any special preparation.”

Why is pulmonary embolism so difficult to diagnose?

The symptoms of a PE, such as chest pain, are common in other cardiovascular conditions, making it difficult to diagnose.

“Standard screenings like an electrocardiogram or chest x-ray can’t tell whether a blood clot is present in the lungs. They can help create a comprehensive assessment of a person’s heart and lung health.”

What tests do doctors use to diagnose pulmonary embolism?

A 2021 study suggests that computed tomographic pulmonary angiography is the “gold standard” test used to diagnose a PE. The screening combines a CT scan with an angiogram.

A computed tomograph, orCT, scans can create cross-sectional images of your body. An angiogram uses a contrast dye to show the flow of blood.

Some tests can identify the location of a blood clot. Others help to evaluate how the heart and lungs work. These tests can reveal the severity of the PE or rule out a particular cause of symptoms.

There are a number of tests used to diagnose a PE.

Can I take an ECG at home?

There are a variety of at-home ECG monitors you can purchase. There are also portable monitors, such as a Holter monitor, that a doctor can prescribe to track your heart’s electrical activity 24/7.

These devices can be helpful in picking up unusual heart rhythms when you are away from the doctor, but they cannot detect a PE.

A PE can cause a variety of problems. It is possible to get an accurate diagnosis as soon as possible.

An arrhythmia can be determined with an electrocardiogram. It is part of a comprehensive evaluation of your heart and lung health.

If your doctor suspects a PE, a painless, painless electrocardiogram can give them vital information about your heart function and any other problems that may arise from a blood clot in the lungs.