How do they calculate: 1. Valve area 2. Mean AV gradient 3. Max AV gradient
2/14
Essential Principles: 1. The effective orifice area is always smaller than the anatomical orifice area
This effective orifice area is what is calculated
It is the key determinant of survival 2. Continuity equation
Conservation of mass
3/14
Continuity equation:
A2 X V2 = A1 x V1
(AVA) x (AV VTI) = (LVOT CSA) x (LVOT VTI)
AVA = [(LVOT CSA) x (LVOT VTI)]/ AV VTI
4/14
We need to measure 3 of 4 variables
The 4th is unknown and is the AV effective orifice area
A1: LVOT cross sectional area
Measure at level of cusp insertion
Inner edge to inner edge
Mid systole
5/14
Measuring V1 - LVOT VTI
6/14
LVOT VTI
Pulse wave doppler!
Remember - Shave the whiskers!
7/14
And lastly measure V2: AV VTI
Continous wave doppler!
Tracing the doppler envelope also calculates Mean and Max gradients using the simplified Bernoulli Equation
8/14
And to explain:
9/14
How can you make sure you have the seen the maximum gradient?
1. Focused AV 5ch view 2. Right parasternal view
10/14
Focused AV 5ch:
Slide probe laterally, in the same ribspace - towards the axilla to line up the cursor
11/14
Right parasternal:
1. Lie the patient in the RIGHT lateral position 2. Obtain standard PLAX view in right lateral position 3. Follow the path of the ascending aorta across the sternum 4. Rock medially + tail up
Probe now faces down the ascending aorta through the AV
12/14
Once Identified - use the pedoff probe to assess
And for those of you who still auscultate the precordium you would have heard the elusive 'tumour plop'....of course you would.
But lets get back to the basics of M- Mode use in the PLAX view
2/6
Firstly the AV:
Here is a normal m-mode image through the AV during the cardiac cycle - note: 1. How systole and diastole are identified by ECG 2. Opening of the RCC and NCC to form the 'envelope' 3. Symmetry of the envelope 4. Closure line at end syst.
3/6
Compare this to m mode in severe AS where there is no identifiable opening of the cusps:
1 Welcome to #researchmethodologies with @DrAoifeBee
Kaplan-Meier (KM) curves are a wonderfully informative way of presenting survival outcomes over time. But how do we interpret them? Survival analysis determines the probability of a binary outcome (aka an event or a failure)
2/15
Survival means the event being studied has not occurred yet - the patient is still alive if you’re analysing mortality, the baby has not been delivered if analysing births, the patient has not yet met whatever criteria you have decided constitutes an event in your study.
3/15
In medical research, the binary outcome of interest is commonly survival vs death though other outcomes/events can be used. KM curves are a visual way of showing the fraction of patients living over time after a treatment, or lack of treatment if in a control group.