All of the following hemodynamic events occur during ventricular systole EXCEPT:

Explanation

## Hemodynamic Events During Ventricular Systole ### Definition of Ventricular Systole **Key Point:** Ventricular systole spans from the closure of the atrioventricular (AV) valves (mitral and tricuspid) to the closure of the semilunar valves (aortic and pulmonary). During this entire period, the AV valves are CLOSED and the ventricles are contracting. ### Timeline of Systole ```mermaid flowchart LR A["AV valve closure<br/>(S1 sound)"]:::outcome --> B["Isovolumetric<br/>contraction"]:::action B --> C["Semilunar valve<br/>opening"]:::action C --> D["Ventricular<br/>ejection"]:::action D --> E["Semilunar valve<br/>closure<br/>(S2 sound)"]:::outcome style A fill:#e8f4f8 style E fill:#e8f4f8 ``` ### Correct Events During Systole (Options 0, 1, 2) | Event | Mechanism | Timing | |-------|-----------|--------| | S2 production | Aortic and pulmonary valve closure | End of systole | | Ventricular volume ↓ | Ejection of stroke volume (~70 mL) | Throughout ejection phase | | Atrial pressure ↑ | Atria fill from pulmonary veins and SVC/IVC | Throughout systole (AV valves closed) | **High-Yield:** The atria fill during ventricular systole because the AV valves are closed. Atrial pressure rises progressively as blood accumulates from the venous system. This is why the atrial pressure tracing shows a gradual rise during the ventricular systole phase of the cardiac cycle. ### Why Option 3 Is Wrong **Clinical Pearl:** AV valve opening occurs during **ventricular diastole**, not systole. Specifically: - The mitral valve opens when LV pressure falls below LA pressure (early diastole) - Passive filling occurs during the rapid filling phase of diastole - During systole, the AV valves are firmly closed to prevent backflow This is a fundamental timing error — the AV valves are the defining boundary of systole. If they were open, it would be diastole. [cite:Harrison's Principles of Internal Medicine 21e Ch 297]