ECG Findings in Pulmonary Embolism
The most common ECG findings in pulmonary embolism (PE) are sinus tachycardia and atrial fibrillation, while more severe cases may show signs of right ventricular overload including T wave inversions in leads V1-V4, QR pattern in V1, S1Q3T3 pattern, and incomplete or complete right bundle branch block. 1
Common ECG Findings in PE
Most Frequent Findings
- Sinus tachycardia (present in about 40% of patients) 1
- Atrial fibrillation or other atrial arrhythmias 1
- Nonspecific ST-segment and T-wave changes 1
Signs of Right Ventricular Strain (More Common in Severe PE)
- T wave inversions in leads V1-V4 1
- QR pattern in V1 1
- S1Q3T3 pattern (S wave in lead I, Q wave in lead III, and inverted T wave in lead III) 1
- Incomplete or complete right bundle branch block 1
Other Possible Findings
- Right axis deviation 1
- Clockwise rotation 2
- S-wave notch in lead V1 2
- QTc prolongation 2
- Transient junctional rhythm or sinus arrest (in cases with syncope) 2
Diagnostic Value of ECG in PE
It's important to note that ECG has limited standalone diagnostic value for PE 3. The 2019 ESC guidelines emphasize that ECG signs of right ventricular strain are usually found in more severe cases of PE, while milder cases may only show sinus tachycardia 1.
Recent research indicates that among traditional ECG signs, only the S1Q3T3 pattern (LR+ 2.07) and liberal right ventricular strain pattern (inverted/flattened T-waves in ≥2 inferior and ≥2 anterior leads, LR+ 4.75) modestly increase the post-test probability of PE 3.
Clinical Correlation
ECG findings should always be interpreted in the context of:
- Clinical presentation (dyspnea, chest pain, syncope)
- Risk factors for venous thromboembolism
- Other diagnostic tests (D-dimer, imaging)
Pitfalls to Avoid
Relying solely on ECG for diagnosis: A normal ECG does not rule out PE, and many PE patients have normal ECGs or nonspecific changes 1, 3
Misinterpreting ECG changes: Similar ECG patterns can be seen in other conditions causing right heart strain
Overlooking subtle changes: Some PE-related ECG findings may be transient or subtle
Focusing only on classic patterns: While S1Q3T3 is well-known, it's not the most common finding in PE 3
Remember that definitive diagnosis of PE requires pulmonary perfusion imaging, typically with CT pulmonary angiography 1. ECG findings should prompt further diagnostic evaluation rather than being used as a standalone diagnostic tool.