12. AS

Question 0

Pathophysiology of AS

Answer 0

• slow increase in afterload on the ventricle
• concentric hypertrophy occurs to normalize wall stress
• hypertrophy leads to decreased compliance and ultimately fails
• patients require:
  
  • atrial kick (afib can producedecompensated HF)
  • high preload

Question 1

AVR at time of CABG if:

Answer 1

• moderate AS, even if asymptomatic

Question 2

Methods to evaluate AS

Answer 2

Peak velocity (m/s)
Normal: 4

Mean gradient (mmHg)
Mild: 40

Valve area (cm^2)
Normal: 2.5-3.5
Mild: >1.5
Mod: 1-1.5
Severe: <1

Question 3

AS Assessment, Bernoulli equation for pressure gradients

Answer 3

Peak gradient
= 4 x (aortic peak velocity)^2

Mean gradient
= 2.4 x (aortic peak velocity)^2

Peak gradient with significant LVOT velocities (>1.5 m/s)
- seen in LVOT obstruction and high output states (ie AR)
- prevents overestimation of pressure gradient
= 4 x [(aortic peak velocity)^2 - (LVOT peak velocity)^2)]

Question 4

TEE pressure gradient vs cath

Answer 4

• TEE measures instantaneous gradient between LVOT and aorta
  
  • tends to be higher than peak-to-peak gradient
• Cath measures peak-to-peak gradient (max pressure in LV, then max pressure in aorta separately)

Question 5

Pitfalls of peak velocity and pressure gradient by Bernoulli in measuring AS

Answer 5

• hyperdynamic states (volume overload LV) produces high velocity unrelated to valve area
• patients with poor contractility are unable to produce high velocities, so AS severity will be underestimated

Question 6

Doppler CW profile of MR can be confused for:

Answer 6

AS

• both negative, peak in mid systole and high velocity
• MR jet should start earlier in systole since alert atrial pressure is lower than aortic

Question 7

Assessment of AS in low cardiac output state

Answer 7

1. Dobutamine stress
   - dobutamine 5-10 mcg/kg/min
   - increase in CO with constant valve area suggests valve disease
   - increase in CO with increase in valve area suggests myocardial disease
2. Dimensionless index
   - LVOT VTI/AV VTI or LVOT peak velocity/AV peak velocity
   - <0.25 suggests severe AS

Question 8

Assessment of AS with AI

Answer 8

• AI causes hypervolemia of LV and increased forward flow (and velocities) through LV and LVOT
• must use modified Bernoulli that includes LVOT velocity

= 4 x [(aortic peak velocity)^2 - (LVOT peak velocity)^2)]