Which finding best distinguishes rapid ventricular filling from slow ventricular filling (diastasis) in the cardiac cycle?

Explanation

## Rapid Ventricular Filling vs. Diastasis ### Phase Definitions **Rapid Ventricular Filling (RVF):** - Begins immediately after mitral valve opens (end of IVR) - Ventricle fills rapidly due to large atrio-ventricular pressure gradient - Accounts for ~70% of ventricular filling - Duration: ~0.1 seconds - Flow rate: High (steep diastolic slope on pressure curve) **Slow Ventricular Filling (Diastasis):** - Occurs in mid-to-late diastole - Ventricle fills slowly as pressure gradient decreases - Accounts for ~20% of ventricular filling - Duration: ~0.2 seconds - Flow rate: Low (nearly flat diastolic plateau) ### Key Discriminating Feature | Feature | Rapid Ventricular Filling | Diastasis (Slow Filling) | |---------|--------------------------|-------------------------| | **Blood Flow Rate** | **High/Steep** | **Low/Flat** | | Mitral Valve | Open | Open | | LV Pressure Trend | Falling (but slower than IVR) | Nearly constant (plateau) | | Atrial Pressure | Exceeds LV pressure | Approaches LV pressure | | Sound | S3 gallop may occur (pathologic if late) | Silent | | Proportion of Filling | ~70% of total diastolic filling | ~20% of total diastolic filling | **Key Point:** The **rate of blood flow from atrium to ventricle** is the most direct and physiologically meaningful discriminator. RVF is characterized by a steep inflow curve; diastasis by a nearly flat plateau. This is visible on Doppler echocardiography (E wave vs. A wave) and on ventricular pressure tracings. **High-Yield:** On the pressure-volume loop, RVF occupies the **steep downslope** of the diastolic curve, while diastasis is the **flat plateau** before atrial systole. The slope of the diastolic curve directly reflects filling rate. **Mnemonic:** **FAST vs. SLOW** — Rapid filling is **F**ast (steep slope), diastasis is **S**low (flat plateau). Both have the mitral valve **O**pen, and both are part of **W**enckebachian diastole (the three phases: IVR, RVF, diastasis). **Clinical Pearl:** In restrictive cardiomyopathy and constrictive pericarditis, diastasis is nearly absent—the ventricle fills rapidly early then abruptly stops ("square root sign" on pressure tracing). In normal aging and diastolic dysfunction, RVF is impaired and diastasis is prolonged, shifting filling to atrial systole (increased A wave on Doppler).