## Discriminating Features: Dilated vs Restrictive Cardiomyopathy ### Key Structural Difference **Key Point:** The hallmark of restrictive cardiomyopathy is **preserved or mildly reduced ejection fraction WITH restrictive filling pattern**, whereas dilated cardiomyopathy presents with **severe systolic dysfunction (reduced EF) and dilated LV cavity**. ### Comparative Table | Feature | Dilated Cardiomyopathy | Restrictive Cardiomyopathy | | --- | --- | --- | | **LV Size** | Dilated (LVEDD >55 mm) | Normal or mildly enlarged | | **EF** | Severely reduced (<35%) | Preserved or mildly reduced (>40%) | | **Filling Pattern** | Normal or impaired relaxation | Restrictive (↑E/A ratio, ↓DT) | | **Wall Thickness** | Thin, dilated | Normal or thick (infiltrative) | | **LA Size** | Mildly enlarged | Markedly enlarged | | **Doppler E/A** | <1 (impaired relaxation) | >2 (restrictive) | ### Why This Matters Clinically **High-Yield:** The **echocardiographic pattern** is the single most discriminating feature: - **Restrictive:** Normal cavity size + restrictive physiology (E/A >2, short deceleration time <160 ms, dilated LA) - **Dilated:** Enlarged cavity + reduced EF (often <30%) + impaired relaxation pattern **Clinical Pearl:** Both conditions cause diastolic dysfunction and elevated filling pressures, so symptoms (dyspnea, orthopnea) and BNP elevation overlap significantly. However, the **EF and cavity size** on echocardiography are mutually exclusive discriminators. ### Why S3 Gallop Is Not the Best Answer Both dilated and restrictive cardiomyopathy can produce a prominent S3 gallop due to rapid ventricular filling from elevated end-diastolic pressure. This is a shared finding, not a discriminator. ### Why Dilated LV Is Not the Best Answer This describes dilated cardiomyopathy itself, not a feature that distinguishes one from the other. The question asks for the **discriminating feature**—the finding that tells them apart.
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