A 72-year-old man with a history of recent hip fracture (immobilized for 2 weeks) presents with sudden-onset dyspnea, tachycardia (HR 118 bpm), and hypoxemia (SpO₂ 88% on room air). CTPA is performed and shows a large filling defect in the right main pulmonary artery extending into the right lower lobe segmental arteries. The right ventricle appears dilated. Which of the following CT findings would best indicate hemodynamic compromise and guide the decision for thrombolysis?

Explanation

## CT Signs of Hemodynamically Significant PE **Key Point:** The **right ventricular to left ventricular (RV:LV) diameter ratio >0.9** on the four-chamber view of CTPA is the most important CT indicator of **RV strain and hemodynamic compromise**. This finding correlates with elevated pulmonary vascular resistance and predicts worse prognosis. ### RV Dilatation and Hemodynamic Significance | Finding | Ratio | Clinical Significance | Prognosis | |---------|-------|----------------------|----------| | **Normal RV** | RV:LV <0.9 | No RV strain | Good | | **Mild RV dilatation** | RV:LV 0.9–1.0 | Borderline RV strain | Intermediate | | **Moderate RV dilatation** | RV:LV 1.0–1.5 | Significant RV strain | Poor | | **Severe RV dilatation** | RV:LV >1.5 | Cardiogenic shock risk | Very poor | **High-Yield:** RV dilatation on CTPA is a **surrogate marker for hemodynamic compromise** and is used to: 1. Identify **intermediate-risk or high-risk PE** (not just massive PE) 2. Guide the decision for **thrombolysis or catheter-directed intervention** 3. Predict **30-day mortality** (RV dilatation increases mortality 2–3 fold) ### Measurement Technique **Mnemonic: RV:LV Ratio — **R**ight ventricle, **V**ersus, **L**eft ventricle, **R**atio at the **4**-chamber view** 1. Identify the **four-chamber view** on axial CTPA (or reconstruct coronal/sagittal) 2. Measure the **maximum short-axis diameter of the RV** (perpendicular to the interventricular septum) 3. Measure the **maximum short-axis diameter of the LV** (at the same level) 4. Calculate **RV:LV ratio = RV diameter ÷ LV diameter** 5. **RV:LV >0.9** indicates hemodynamic compromise **Clinical Pearl:** RV dilatation on CTPA correlates with: - Elevated **troponin** and **BNP/NT-proBNP** (biomarkers of myocardial injury) - **Systolic BP <90 mmHg** or drop >40 mmHg (cardiogenic shock) - **Reduced ejection fraction** on echocardiography ### Thrombolysis Decision-Making ```mermaid flowchart TD A[Acute PE diagnosed on CTPA]:::outcome --> B{Hemodynamic stability?}:::decision B -->|SBP <90 mmHg or shock| C[Massive PE]:::urgent B -->|SBP ≥90 mmHg| D{RV dilatation + elevated troponin/BNP?}:::decision C --> E[Thrombolysis or embolectomy]:::action D -->|Yes| F[Intermediate-risk PE]:::outcome D -->|No| G[Low-risk PE]:::outcome F --> H{Consider thrombolysis}:::decision H -->|High bleeding risk| I[Anticoagulation alone]:::action H -->|Low bleeding risk| J[Thrombolysis + anticoagulation]:::action G --> K[Anticoagulation]:::action ``` **Warning:** RV dilatation alone (without hemodynamic instability or biomarker elevation) does NOT automatically mandate thrombolysis. The decision depends on the **combination of RV dilatation + hemodynamic status + biomarkers**. [cite:Harrison 21e Ch 298; European Society of Cardiology PE Guidelines 2019]