ECG Diagnosis: Pulmonary Embolism

Figure 1.

12-lead ECG from a 68-year-old woman with new onset dyspnea on exertion.

Demonstrates sinus tachycardia, prominent S wave in lead I, with Q wave and T wave inversion in lead III (S₁Q₃T₃ sign), with inverted T waves in leads V₁-V₆. ST-segment elevation in leads aVR and V₁ is also present. A computed tomography angiogram of the chest was performed, which demonstrated multiple, bilateral pulmonary emboli (PE).

The S₁Q₃T₃ sign (prominent S wave in lead I, Q wave and inverted T wave in lead III) is a sign of acute cor pulmonale (acute pressure and volume overload of the right ventricle because of pulmonary hypertension) and reflects right ventricular strain.¹ This electrocardiogram (ECG) finding is present in 15% to 25% of patients ultimately diagnosed with pulmonary emboli (PE).² Any cause of acute cor pulmonale can result in the S₁Q₃T₃ findings on ECG, including PE, acute bronchospasms, pneumothorax, and other acute lung disorders. Other ECG findings noted during the acute phase of a PE include new right bundle branch block (complete or incomplete), rightward shift of the QRS axis, ST-segment elevation in V₁ and aVR, generalized low amplitude QRS complexes, atrial premature contractions, sinus tachycardia, atrial fibrillation/flutter, and T wave inversions in leads V₁-V₄. ² The ECG is often abnormal in PE, but findings are neither sensitive nor specific for the diagnosis of PE.³ The greatest utility of the ECG in a patient with suspected PE is ruling out other life-threatening diagnoses (eg, acute myocardial infarction).