Aortic Stenosis

• Aortic stenosis is the narrowing of the aortic valve, which restricts blood flow from the LV into the aorta during systole. Over time, this increases afterload leading to LV hypertrophy and eventually angina, syncope, and/or signs of heart failure. 

• Causes of AS include:
  • Age-related calcific degeneration (most common in older adults)
  • Bicuspid aortic valve (especially in younger patients)
  • Rheumatic heart disease

• On physical exam, AS presents with a crescendo-decrescendo systolic murmur, best heard at the right second intercostal space with radiation to the carotids. Signs of severe AS may include a delayed carotid upstroke (pulsus parvus et tardus - weak and slow rising pulse), narrowed pulse pressure, soft/absent S2, and sustained apex beat.

• On POCUS, colour doppler can be used to assess for turbulent flow, measure flow velocity across the narrowed valve, and assess for secondary changes.

• POCUS can estimate AS severity by assessing valve area, peak velocity (Vmax), and mean pressure gradient. Here, we focus on Vmax, a reliable indicator when performed accurately. Continuous Wave (CW) Doppler is used because it measures high velocities without artifacts, unlike pulsed wave Doppler. 

1. Turn On CW Doppler: Place the marker within the aortic valve.
2. Trace the parabolic waveform under aortic valve measurement
3. Vmax Interpretation: The more severe the stenosis, the faster blood flows through the valve.
   • Mild AS: < 3 m/s 
   • Moderate AS: 3–4 m/s
   • Severe AS: > 4 m/s 
   • Critical AS: > 5 m/s (or > 4 m/s with symptoms) 

💡 Tip: In low-flow states, these velocity measurements may be unreliable. Always pair doppler findings with valve appearance (e.g., thickening, calcification) and clinical signs/symptoms.