Valve lesions and anaesthetics Flashcards
What percentage of people over 65 have aortic stenosis
65%
What is the prevalence and relevance of a congenital bicuspid aortic valve
2% prevalence –> earlier development of aortic stenosis
Classify severity of aortic stenosis based on peak gradient and valve area
Mild:
<20 mmHg and > 1.5cm^2
Moderate:
20 - 50 mmHg and 0.8 to 1.5 cm^2
Severe:
>50 mmHg and < 0.8 cm^2
Thereafter LVF ensues and the pressure gradient gets less indicating LVF
What is the normal valve area of the aortic valve
2.6 to 3.5 cm^2
When do patients present with symptoms in AS
When the stenosis is severe –> if the valve is not replaced the life expectancy is 2 to 5 years
What are the symptoms of aortic stenosis
Forward - Backward - outward
Forward - Fixed CO state and low LV compliance due to concentric hypertrophy. During exercise CO can not be increased to compensate for peripheral vasodilation –> SYNCOPE
Backward - Concentric hypertrophy leads to increased LVEDP required to maintain cardiac output –> LVEDP is transmitted backwards into the pulmonary circulation –> pulmonary congestion. Development of dyspnoea indicates that the LV is decompensating and starting to dilate –> DYSPNOEA
Outward - LV hypertrophy –> greater muscle mass –> greater O2 demand. Neovascularization is not as fast as hypertrophy and O2 supply is compromised. Calcification and distortion of coronary ostia may also contribute to impaired blood and hence O2 supply –> ANGINA
What is the nature of the murmur auscultated in aortic stenosis
Ejection systolic murmur that often radiates to the carotids
Describe the findings related to the apex beat in AS
Heaving apex, undisplaced (concentric hypertrophy)
Describe the pulse in AS
Slow rising
When should a patient with AS be referred to cardiology
Type of surgery
Patient symptomatic
Severity of AS
Consideration by cardiology for cardiac catheterization ± valve replacement
AS vs normal patients - what is the % of ventricular filling done by atrial contraction
Normal patients 20% of filling
AS patients 40% of filling
Why should tachycardia be avoided in aortic stenosis
Reduces time for diastolic filling time and therefore coronary perfusion time –> worsens ischaemia
Why should bradycardia be avoided in aortic stenosis
Stiff LV cannot increase SV to compensate
Increase LV filling time –> longer diastole –> increase ventricular wall tension and reduction of coronary perfusion
What is the effect of reduced SVR in AS
Reduced coronary perfusion (fixed output state) coronary perfusion relies on systemic BP
Considering the dramatic effect of propofol on the BP during induction in patients with AS, how should this be treated?
Noradrenalin or phenylephrine –> vasopressors is first line to increase SVR without causing tachycardia
Is spinal anaesthesia commonly practice in AS
NO. High potential for hypotension and vasodilation caused by rapid onset of SNS blockade
What is a good approach to a patient for emergency surgery with an ejection systolic murmur on initial examination
? ECG abnormal with LVH
? Syncope
If yes to both assume severe AS
If no then unlikely that they have significant AS
Describe the pathophysiology of AS
Stenosed valve obstructs blood from LV Increased LV wall tension Concentric LV hypertrophy Poor LV compliance requires higher LVEDP LV dilatation
During a preoperative assessment of a 75-year-old gentleman for an anterior resection you find an ejection systolic murmur on examination. Which of the following investigations would you like to carry out? A. ECG B. Exercise tolerance test C. Echocardiography D. Chest x-ray E. Cardiac catheterization
A. Correct. There may be evidence of LV hypertrophy.
B. Incorrect. AS is a contraindication to performing an exercise tolerance test.
C. Correct. An echo will define the murmur in terms of type of lesion and severity.
D. Correct. A chest x-ray may show the calcified valve, aortic root dilatation, LA enlargement and/or interstitial oedema.
E. Correct. This gives a more accurate indication of the severity of the AS. However this will be requested by a cardiologist not an anaesthetist.
Summarize the perioperative management issues associated with AS
Prevent tachycardia Prevent bradycardia Maintain normotension Maintain preload Maintain afterload
Classify the clinical presentation of mitral regurgitation
Acute (rare)
- Rapid decompensation often requiring surgical intervention
- MI/Ischaemia or endocarditis
Chronic (more common than acute MR)
- Rheumatic fever
- Degenerative disease
- LV dilatation from any cause (HPT/IHD)
Describe the pathophysiology of Mitral Regurgitation
Regurgitant mitral valve –> Increase LA volume –> LA dilation + AF –> Pulmonary venous congestion –> Increased PA pressure (Chronic HPV secondary to fluid transudation into alveoli)
How is severity of mitral regurgitation assessed
- Size and volume of the regurgitant jet as it appears on ECHO
- Pulsed wave Doppler is used to look for flow reversal in the pulmonary veins - indicates severity
- Regurgitant fraction > 0.6
What is regurgitant fraction and how is it calculated and interpreted
Regurgitant fraction =
Regurgitant SV/Systemic SV
RF < 0.3 mild
RF > 0.6 severe
