Despite the poor diagnostic accuracy of ECG in detecting pulmonary embolism, it can still be useful in ruling out acute MI in patients with symptoms of PE, which can mimic those of acute myocardial infarction. 

Acute PE shows ST elevation in leads V₁ and III. Acute MI of the inferior walls often presents with significant ST elevation in leads II, III, and aVF. An older infarction presents with Q waves. Acute right ventricular overload from a PE may present with a Q wave in lead II, but that is extremely rare.

PE can also be a result of cardiac arrhythmias and conduction disturbances. An ECG can be used to reliably diagnose arrhythmias and blockages and adds to the clinician’s suspicion that the patient has developed a PE as a result.

An ECG suggestive of right ventricular overload offers a clue to clinicians who can then decide whether to order a spiral CT or ventilation/perfusion scan. 

ECG results can also be useful after treating a PE. Regression of the ECG findings of right ventricular overload indicates the treatment has been successful.