2.9 Aortic Stenosis + AVR

Question 1

a) What is the pathophysiology of worsening aortic stenosis? (8 mark)

Answer 1

1. Latent phase:

> > Left ventricular outflow obstruction
due to abnormal valve
(rheumatic fever,
congenital bicuspid valve,
age-related calcification).

2. Compensatory phase:

> > Left ventricle hypertrophies
to overcome outflow obstruction,
maintaining ejection fraction.

> > Consequent increased oxygen demand
but poorer supply and diastolic dysfunction.

3. Decompensation:

> > Subendocardial ischaemia
due to poor oxygen delivery
to hypertrophied myocardium.

> > Increased left ventricular
end-diastolic volume and pressure
result in increased pulmonary capillary pressure
with pulmonary oedema,
mitral regurgitation.

> > Ejection fraction starts to fall
as hypertrophy increases in the face of
worsening outflow obstruction.

4. Symptomatic phase:
   » As blood passes through the narrowed valve,
   it accelerates, gaining kinetic energy.

By the law of conservation of energy,
it therefore loses pressure,
resulting in reduced perfusion pressure
of the coronary arteries,
thus reducing oxygen delivery to an already embarrassed myocardium.

The consequences are
angina,
breathlessness,
syncope,
sudden death.

Question 2

b) Which specific cardiac investigations may be used in assessing the severity of this woman’s disease?
(3 marks)

Answer 2

1. Echocardiography (transoesophageal or transthoracic):

> > Assess valve:
Doppler assessment of peak flow velocity,
mean pressure gradient,
effective orifice area,
presence of regurgitation.

> > Assess consequences of its stenosis:
left ventricular dimensions and function;
mitral valve competence,
left atrium,
pulmonary artery pressure,
right ventricular function,
post-stenotic ascending aortic dilatation.

Left heart catheter study:

> > Retrograde catheterisation of aortic valve
to assess pressure gradient.

MRI:
» To assess the consequences of stenosis.

ECG:
» Will demonstrate the consequences of stenosis:
left ventricular hypertrophy,
ischaemia, arrhythmias.

Question 3

c) Give values for the peak aortic flow velocity, mean pressure gradient and valve area that would indicate
that this woman has severe aortic stenosis. (3 marks)

Answer 3

Peak aortic flow velocity: greater than 4 m/s.

Mean pressure gradient: greater than 40 mm Hg.

Valve area: less than 1 cm2

Question 4

d) What would be your haemodynamic goals for the perioperative management of this patient? (6 marks)

Answer 4

1. > > Maintain myocardial oxygen delivery

with adequate systolic and diastolic
blood pressure within 20% of normal values
(as monitored by invasive BP monitoring).

2. > > Maintain contractility

(balanced anaesthetic technique,
adequate filling as guided by cardiac output (CO) monitoring,
may need inotropic support if
left ventricle is poorly functioning).

3. > > Optimise pre-load with filling
   (guided by CO monitoring).
4. > > Maintain sinus rhythm at a rate of 60–80 bpm

(5-lead ECG,
avoidance of tachycardia by managing pain,
use of beta-blockers,
possible need for pacing post-bypass due
to surgical interruption of conduction pathway).

5. > > Maintain afterload.

Coronary artery filling is dependent
on aortic root pressure
(avoid excessive doses of
intravenous induction agents
or inhalational agents,

may need alpha agonist,
as guided by CO monitoring).