Summary

High-risk pulmonary embolism (PE) is associated with several ECG findings that indicate right ventricular (RV) strain and acute load on the right heart. The most concerning findings include sinus tachycardia, the S1Q3T3 pattern, right bundle branch block (RBBB), T-wave inversions in the right precordial leads, and right axis deviation.

At a Glance

ECG Finding	Explanation
Sinus tachycardia	Most common, nonspecific sign of increased sympathetic tone.
S1Q3T3 pattern	Prominent S wave in lead I, Q wave and inverted T wave in lead III; reflects acute RV strain.
Right bundle branch block (RBBB)	Indicates conduction delay in the right ventricle, which may occur with RV dilation.
T-wave inversions in precordial leads (V1–V4)	Suggests ischemia or strain in the right ventricle due to increased afterload.
Right axis deviation	Reflects altered electrical activity secondary to an enlarged or pressured right ventricle.

Explanation

In the setting of a high-risk PE, the abrupt increase in pulmonary vascular resistance results in RV dilation and dysfunction, which then manifests on the ECG. Although findings such as sinus tachycardia are nonspecific, the combination of S1Q3T3, new RBBB, right axis deviation, and T-wave inversions in the anterior leads raises a red flag for RV strain. Recognizing these ECG patterns can aid in the rapid assessment of patients with a suspected PE, prompting further confirmatory imaging and urgent management.

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