A 62-year-old man with leg swelling and dyspnea undergoes CTPA. The radiologist reports a saddle embolus at the pulmonary artery bifurcation with bilateral lower lobe segmental PE. Which finding on CTPA best discriminates massive PE from submassive PE in this patient?

Explanation

## Massive vs. Submassive PE: CTPA Discriminators ### Definition and Hemodynamic Basis **Key Point:** Massive PE is defined by hemodynamic instability (shock, hypotension). Submassive PE shows RV strain (RV dilatation on imaging) without hemodynamic collapse. The RV/LV ratio on CTPA is the best imaging discriminator. | Parameter | Massive PE | Submassive PE | | --- | --- | --- | | **Hemodynamics** | Shock, SBP < 90 mmHg | Normotensive | | **RV/LV ratio** | > 0.9 (often > 1.0) | > 0.9 (RV strain present) | | **RV dysfunction** | Severe + hemodynamic collapse | Isolated (no shock) | | **Thrombus burden** | Central (saddle, main PA) | Lobar/segmental | | **Troponin/BNP** | Elevated | Elevated | | **Prognosis** | In-hospital mortality 30–50% | In-hospital mortality 2–8% | ### Critical Distinction **High-Yield:** RV dilatation (RV/LV > 0.9) indicates RV strain but does NOT define massive PE. **Massive PE requires hemodynamic instability + RV dilatation.** Submassive PE has RV dilatation without shock. The **combination of RV/LV ratio > 0.9 AND absence of hemodynamic collapse** is the CTPA finding that distinguishes submassive from massive PE. Both show RV dilatation; the difference is clinical (presence/absence of shock). **Clinical Pearl:** A patient with a saddle embolus may be either massive or submassive depending on hemodynamics. CTPA cannot assess blood pressure — that is a clinical finding. However, severe RV dilatation (RV/LV > 1.0) in a hemodynamically stable patient indicates submassive PE at high risk for decompensation. **Mnemonic:** **RV strain = RV/LV > 0.9.** Massive = RV strain + shock. Submassive = RV strain without shock. [cite:Harrison 21e Ch 297]