In a patient with acute pulmonary embolism, which of the following is the most common electrocardiographic finding?

Explanation

## Electrocardiographic Findings in Acute PE ### Most Common ECG Pattern **Key Point:** Sinus tachycardia with T-wave inversion in the precordial leads (V1–V4) is the most frequently observed ECG abnormality in acute pulmonary embolism, reflecting right ventricular strain. ### ECG Findings in PE — Frequency and Patterns | ECG Finding | Frequency | Mechanism | Clinical Significance | |-------------|-----------|-----------|----------------------| | Sinus tachycardia | 40–50% | Sympathetic activation | Most common | | T-wave inversion V1–V4 | 30–40% | RV strain pattern | Indicates RV dilatation | | S1Q3T3 pattern | 10–15% | Classic but rare | Acute cor pulmonale | | Atrial fibrillation | 5–10% | RV stretch; increased ectopy | Worse prognosis | | ST elevation V1–V3 | <5% | Massive PE with infarction | Uncommon; high mortality | | Normal ECG | 10–15% | Subsegmental PE | Does not exclude PE | ### Pathophysiology of T-Wave Inversion 1. **Acute RV dilatation** → increased RV wall tension 2. **RV ischaemia** → repolarization abnormality 3. **T-wave inversion** appears in **precordial leads (V1–V4)** — the "RV strain pattern" 4. This pattern reflects **acute cor pulmonale** but is **not specific** to PE **High-Yield:** The classic **S1Q3T3 pattern** (S wave in lead I, Q wave in lead III, T-wave inversion in lead III) is pathognomonic for acute cor pulmonale but is present in only 10–15% of PE cases. Do not rely on it for diagnosis. **Clinical Pearl:** A **normal ECG does not exclude PE** — up to 10–15% of confirmed PE cases have normal baseline ECG. ECG is useful for ruling out acute MI (which may mimic PE clinically) and detecting arrhythmias. **Warning:** ~~ST elevation in V1–V3 with reciprocal changes~~ suggests acute anterior MI, not PE. This is a common trap — ST elevation is rare in PE (<5%) unless there is massive PE with infarction. ### ECG Role in PE Diagnosis - **Not diagnostic** — no single ECG pattern confirms PE - **Supportive** — tachycardia + T-wave inversion V1–V4 raises suspicion - **Exclusionary value** — helps rule out MI, pericarditis, pneumothorax - **Prognostic** — RV strain pattern (T-wave inversion V1–V4) indicates haemodynamic compromise [cite:Harrison 21e Ch 297]