A 52-year-old man with chronic hypertension presents with a systolic murmur best heard at the right upper sternal border. Regarding the physiological mechanisms of systolic murmurs, all of the following are correct EXCEPT:

Explanation

## Physiological Mechanisms of Systolic Murmurs ### Classification by Timing and Mechanism **Key Point:** Systolic murmurs are classified as either **ejection** (crescendo-decrescendo) or **regurgitant** (holosystolic/pansystolic) based on the underlying hemodynamic mechanism. ### Ejection Murmurs (Crescendo-Decrescendo) **High-Yield:** Ejection murmurs occur when flow through a narrowed orifice increases during early-to-mid systole, then decreases as ventricular pressure falls. This creates a diamond-shaped envelope on phonocardiography. **Examples:** - **Aortic stenosis** — narrowed aortic valve; murmur at right upper sternal border, radiates to carotids - **Aortic sclerosis** — thickened but non-stenotic aortic valve; similar murmur but no hemodynamic obstruction - **Pulmonary stenosis** — narrowed pulmonary valve; murmur at left upper sternal border ### Regurgitant Murmurs (Holosystolic/Pansystolic) **Key Point:** Regurgitant murmurs persist throughout systole because the pressure gradient between the high-pressure chamber and low-pressure chamber remains constant. **Examples:** - **Mitral regurgitation** — LV pressure > LA pressure throughout systole → holosystolic murmur at apex, radiates to axilla - **Tricuspid regurgitation** — RV pressure > RA pressure throughout systole → holosystolic murmur at left lower sternal border - **Ventricular septal defect** — LV pressure > RV pressure throughout systole → holosystolic murmur at left lower sternal border ### Why VSD Timing is Critical **Clinical Pearl:** The VSD murmur is holosystolic (throughout systole), NOT early diastolic. The left-to-right shunt occurs during systole when LV pressure exceeds RV pressure. The statement that the murmur is "louder in early diastole" is **physiologically incorrect** — VSD produces no diastolic murmur. | Murmur Type | Timing | Mechanism | Location | Example | |---|---|---|---|---| | Ejection | Crescendo-decrescendo (early-mid systole) | Flow through narrowed orifice | Right upper sternal border | Aortic stenosis | | Regurgitant | Holosystolic (entire systole) | Constant pressure gradient | Apex (mitral) or left lower border (tricuspid/VSD) | Mitral regurgitation | | Diastolic | Early diastole or mid-diastole | Inflow obstruction or regurgitation | Apex (mitral stenosis) or left lower border (pulmonary regurgitation) | Mitral stenosis | **Warning:** Do not confuse the timing of the murmur with the timing of the shunt. VSD shunt is systolic (when LV > RV), and the murmur is therefore holosystolic. There is no diastolic component.