What specific finding on an ECG is most suggestive of acute pulmonary embolism?

The specific finding on an ECG that is most suggestive of acute pulmonary embolism (PE) is the S1Q3T3 pattern. This pattern consists of a deep S wave in lead I, a Q wave in lead III, and an inverted T wave in lead III. While the S1Q3T3 pattern is not highly sensitive or specific for PE (meaning it is not always present in patients with PE and can be seen in other conditions), it is a classic ECG finding that should raise suspicion for PE, especially in the appropriate clinical context. The S1Q3T3 pattern is thought to result from acute right ventricular strain caused by the sudden increase in pulmonary artery pressure associated with PE. The S wave in lead I represents right ventricular enlargement, the Q wave in lead III indicates right ventricular ischemia or infarction, and the inverted T wave in lead III reflects repolarization abnormalities due to right ventricular strain. Other ECG findings that may be seen in PE include sinus tachycardia (rapid heart rate), right axis deviation, incomplete or complete right bundle branch block, and T wave inversions in the anterior precordial leads (V1-V4). However, the S1Q3T3 pattern is the most classically associated with acute PE.