23-49: Pulmonary Embolism

Maite A. Huis in ‘t Veld; Amal Mattu; R. Jason Thurman

ECG Findings

Sinus tachycardia, nonspecific ST-T changes.
Precordial T-wave inversions.
Prominent S wave in lead I, Q wave in lead III, and inverted T wave in III (S₁/Q₃/T₃).
Incomplete or complete RBBB, P pulmonale (lead II).
Rightward axis.
ST-segment elevation (especially in leads V₁, aVR) and ST-segment depression may occur in cases of large pulmonary emboli.

No ECG pattern is diagnostic for pulmonary embolism. Small-to-moderate emboli may not affect the ECG.
With large emboli, increased resistance to pulmonary arterial flow produces right ventricle overload and dilation.
Increased right atrial pressures may produce P pulmonale (tall P waves > 2.5 mm in lead II) or atrial dysrhythmias.

Sinus Tachycardia and S1Q3T3 Pattern in a Patient with Acute Pulmonary Embolism. (ECG contributor: James V. Ritchie, MD.)

S wave is apparent in lead I (blue arrowhead), Q wave in lead III (black arrowhead), and inverted T wave in lead III (blue arrow).

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