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Lesson

PE and Right-Heart Strain on ECG

11 min Cardiac & ECG Skip to quiz

Objective: Use the ECG as one clue to possible pulmonary embolism. The tracing does not prove or clear the clot. Do not start a fibrinolytic from this lesson.

Why this matters

Pulmonary embolism is a clinical suspicion, not an ECG diagnosis. The tracing can show the right ventricle under pressure. You may see sinus tachycardia, anterior T-wave changes, a new right bundle branch block, or S1Q3T3. S1Q3T3 means a large S in lead I, a Q in lead III, and an inverted T in lead III. Many patients with a clot have none of those findings.

Use the ECG so you do not miss right-heart strain. Do not call every anterior T-wave change a simple anterior heart attack. The hospital still has to image the clot.

Key points
  • The story is sudden shortness of breath, pleuritic pain, syncope, or unexplained hypoxia, plus a reason to suspect a clot. The ECG only supports that story.
  • S1Q3T3 does not prove PE. Its absence does not clear PE. PE means pulmonary embolism.
  • Give oxygen if the sat is low. Get a 12-lead. If the blood pressure is low, keep fluids cautious and follow protocol. Go to a hospital that can diagnose PE. This lesson does not give a fibrinolytic recipe.
Verbalize
  • This may be PE. The ECG does not make the diagnosis.
  • The sat is low, so I am giving oxygen. The blood pressure is soft, so fluids stay cautious and follow protocol.
  • I am not starting a fibrinolytic from this lesson.

Clinical sequence

  1. Give oxygen if the sat is low. A normal sat does not erase a strong story.
  2. Get a 12-lead. Look for tachycardia, T-wave inversion in the right to mid chest leads, a new right bundle branch block, and S1Q3T3. Also look for STEMI, because the two stories can look alike. STEMI means an ST-elevation heart attack.
  3. If the blood pressure is low, think obstructive shock. Keep fluids cautious. A large bolus can worsen a failing right ventricle. Follow protocol.
  4. Say the suspicion on the radio, including the risk story and the vital signs. Go to a hospital that can CT or otherwise diagnose PE, unless a closer hospital is required because the patient is unstable.
  5. Read PE field suspicion for the clinical frame. This lesson is only the ECG piece.

Teaching points

  • The 2026 AHA/ACC pulmonary embolism guideline is a hospital diagnosis pathway. The field job is suspicion, oxygen, monitoring, and not harming the right ventricle with a casual fluid bolus.
  • Right-heart strain on the ECG is a clue. Echocardiography and CT are not field tests in most systems.
  • Do not give a fibrinolytic from this page. If a system has a protocol for arrest or near-arrest PE, that protocol owns the drug.

Common errors

  • Clearing PE because S1Q3T3 is absent.
  • Calling every anterior T-wave change an occlusion and giving nitro to a hypotensive patient.
  • Giving a large fluid bolus into a strained right ventricle.

Practice

One-minute check

Sudden dyspnea, saturation 88 percent, pressure 88 systolic, and anterior T-wave inversion. Say what you transmit, what you do with oxygen, and what you do not bolus.

Sources & Further Study

Named guidelines for further study. They are not clinical orders and do not replace your protocol or medical direction.

Education only. Apply learning within your protocols and medical direction. This is not clinical care guidance.

Check Your Understanding

Questions drawn only from this lesson. After you check, the key is highlighted. Education practice — not a certification exam.

1. An S1Q3T3 pattern on the 12-lead means:
2. The field plan for suspected PE in this lesson is:
3. A normal ECG in a patient with sudden dyspnea and risk for clot:
4. Anterior T-wave inversion and a new right bundle branch block in this context should be:
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