Bit · Cardio
Aortic Stenosis vs HOCM (murmur with manoeuvres)
Two systolic murmurs that sound similar but respond oppositely to manoeuvres. The pivot is what happens with Valsalva.
Mechanism
Both produce a systolic ejection murmur heard at the upper sternal border. The mechanism is opposite:
- Aortic stenosis (AS) — a fixed obstruction at the aortic valve. The amount of murmur depends on how much blood crosses the narrowed valve. More preload → more flow → louder murmur. Reducing preload (Valsalva, standing) makes it softer.
- HOCM (hypertrophic obstructive cardiomyopathy) — a dynamic outflow obstruction caused by septal hypertrophy + systolic anterior motion (SAM) of the mitral valve. The obstruction worsens when the LV is smaller (less stretch on the outflow tract). Reducing preload (Valsalva, standing) makes the murmur louder. Increasing preload or afterload makes it softer.
Same direction of change: AS gets louder with more preload; HOCM gets louder with less preload.
Differentiator Table
| Manoeuvre | What it does to LV size | Aortic stenosis murmur | HOCM murmur |
|---|---|---|---|
| Valsalva (strain phase) | ↓ Preload → smaller LV | Softer | LOUDER |
| Standing from squatting | ↓ Preload → smaller LV | Softer | LOUDER |
| Sudden squatting | ↑ Preload + ↑ Afterload | Louder | Softer |
| Passive leg raise | ↑ Preload | Louder | Softer |
| Handgrip / sustained isometric | ↑ Afterload | Softer | Softer |
| Inspiration | ↑ Right-sided preload | No major change | No major change |
The Pivot
One question almost always answers it:
- What happens with Valsalva? Murmur gets quieter → AS. Murmur gets louder → HOCM. (HOCM is the only common left-sided systolic murmur that gets louder with Valsalva.)
Other helpers: AS classically has a crescendo-decrescendo murmur radiating to the carotids, with a delayed carotid upstroke (pulsus parvus et tardus). HOCM is more likely to give a bisferiens (double-peak) carotid pulse and a fourth heart sound.
NBME-Style Stem
A 16-year-old boy collapses during basketball practice but recovers spontaneously. On examination, a harsh systolic murmur is heard at the lower left sternal border. The murmur becomes louder when he stands up from a squatting position and softer when he squats. Which of the following is the most likely diagnosis?
Concept Anchor
Aortic stenosis is a fixed pipe — more flow makes more noise. HOCM is a collapsing pipe — less filling lets it collapse more, making more noise. The Valsalva response is the cleanest single test in cardiac auscultation.