Right Heart

Quantitative and Semi quantitative Echo

Pressure and flow cannot be measured by echo.
Velocities can be estimated from Doppler effect. Dimensions can be measured by 2-D imaging.
Volumes and flows can be derived from this.
Pressure gradient across a restrictive orifice can be estimated using simple Bernoulli equation(P=4V2).
The rate of change of pressure gradient - pressure half time - can be used to estimate the orifice size in MS and AR. (orifice area = 220/PHT)

PISA & JETS:

Fluid speeds up as it approaches narrow orifices. This results in characteristic appearances proximally and distally.

Proximally more than one PISA - Proximal Isovelocity Surface Area - may be visible in colour flow doppler. The dimensions of PISA can be used to estimate valve orifice.

Distally a jet is formed. This jet entrains mass and its volume increases. The area of the jet seen with colour flow is assumed to be proportional to the volume. But jet area may vary from plane to plane as it is only 2-D.
Also jets may be free or confined.
Free jet is unaffected by the boundaries of the chamber.
If the jet is close to the walls of the chamber, its volume is confined due to Coanda effect. Reliance on jet size will lead to underestimation of lesion severity.

Jets in the vicinity are affected by each other. Jets in the same direction result in accentuation and those in the opposite direction attenuate.

The intensity of the flow signal obtained with CW doppler depends on:
1. Gain setting
2. Number of blood cells from which echo beam has reflected.

VELOCITY, FLOW & AREA:
If we assume laminar flow in a cylinder of constant diameter, then velocity

V = s/t

where
s - distance covered
t - time taken to cover the distance

Volume is cross section area x length
ie CSA x s

Flow = Rate of change of volume
= CSA x s/t
= CSA x V

So Q = CSA x V

V can be estimated from doppler.
Obtaining CSA is more difficult. Planimetry can be difficult. So from 2-D dimensions CSA is calculated approximately applying standard geometric formulae.

But the fact is:
1. Flow is not laminar.
2. Flow does not have flat profile.
3. FLow is pulsatile.

Velocity-time integral (VTI) gives the distance travelled by blood over any particular period.

V=s/t
so
s = Vxt.
= Vmean x time.









Mean flow Qmean = CSA x Vmean
Maximum flow Qmax = CSA x Vmax
Stroke volume SV = CSA x VTI.
Cardiac output CO = SV x HR.

The sites of obtaining the velocity spectra are:
1. CW doppler across aortic valve
2. PW doppler positioned in LVOT
3. PW across competent mitral valve.

The CSA can be derieved from the following equations:
1. Aortic valve. Measure intercommisural length "s".
CSA = 0.433xs2.

2. Mitral annulus. Measure radii r1 and r2.
CSA = π r1 x r2

3. LVOT. Measure diameter.
CSA = π x r2


Principle of continuity of flow:

In the absence of shunts, net forward SV in any one part of the circulation must equal net forward SV in any other part.

This can be used to calculate orifice areas of stenotic or regurgitant valves.

Adjacent structures in same phase or non adjacent structures in differnt phase of circualtion can be used.
1. LVOT and AV can be used to calculate AV valve area.
Qav = Qlvot
CSA av x Vmax-av = CSA lvot x Vmax-lvot

CSAav= CSAlvot xVmax-lvot/Vmax-av.

Similarly

CSAav = CSAlvot x VTIlvot/VTIav

Doppler velocity index Vmax-lvot/Vmax-av is also used as a simple index of severity of stenosis.

2.MV doppler in diastole and AV doppler in systole can be used in a similar way.

If one of the structure is normal the area of other can be derieved.

Thoracic Aorta

Mitral Valve

Diastolic Dysfunction

Diastole has 4 phases:

1. Isovolumetric relaxation
2. Early filling
3. Diasatsis
4. Atrial systole

LA to LV gradient is the driving force for LV filling.

1. IVRT:
- prolonged by impaired active relaxation as in ischaemia
- shortened by raised LA pressure
It is normally less than 100 ms

2. Early filling:
Pressure gradient is greatest during this phase.
So 80% of filling occurs.

The main determinants of filling are:
a.LA pressure
b.Rate of active relaxation
c.Myocardial elastic recoil

3. Diastasis:
Most complicated phase
As the gradient reduces the filling diminishes
The main determinant of filling: LV chamber compliance

LV compliance is in turn determined by:
a.intrinsic myocardial stiffness
b.ventricular mass
c.pericardial restraint
d.RV Volume
e.LV Volume

4. Atrial systole:
increases trans-mitral gradient and accounts for 15-20 % of normal filling.
In conditions of impaired active relaxation the contribution is higher as in AS.

Diastolic dysfunction is divided into:

Active - affects early active relaxation(IVRT and first part of early filling) due to delayed re-uptake of calcium - thus prolongs relaxation
Examples include ischemia, hypertension, AS and HCM
Passive - affects later passive filling phase (later part of LV filling, diastasis and atrial systole) and it is due to reduced chamber compliance.
Examples include amyloidosis and myocardial fibrosis
The natural history of abnormal relaxation is to progress to reduced chamber compliance.

Echocardiographic assessment:
1. 2-D
2. M-mode
3. Transmitral doppler
4. Pulmonary venous doppler
5. Newer - Colour M-mode
- Tissue doppler imaging

2-D:
Look for hypertrophy in trans gastric mid SAx view at end diastole
concentric - wall thickness increased out of proportion to chamber size - due to pressure overload. This may be asymmetrical, affecting anterior septum in prefrence.
eccentric - wall thickness increased in proportion to chamber size
Thickening of anterior septum is best assessed in mid oesophageal long axis view. But do not do M-mode as it inveriably cuts the septum obliquely.
Normal thickness:
Male 1.3 and 1.2 cm
Females 1.2 and 1.1 cm. (Septum normally thicker than rest of the ventricle)

Trans mitral doppler:
Position of sample volume - level of open leaflet tips in diastole.
Normal waveforms:
Has 2 peaks - E and A.
E - due to early diastolic filling.
A - due to atrial systole
With age E max reduces while A max increases and become equal after 60 years.
Emax reduces from 0.70 m/s to 0.55 m/s
Amax increases from 0.35 m/s to 0.55 m/s.



Variables that can be measured include:
1. IVRT -
2. Emax
3. Evti
4. Edec
5. Amax
6. Avti
7. E/A ratio

Three abnormal pattern have been identified.
1.Impaired relaxation
2.Pseudonormalisation
3.Restrictive filling.

Impaired relaxation:

With impaired relaxation IVRT is prolonged.
E max is reduced.
E dec is increased.
Relaxation is complete late so filling occurs late in the atrial systole period. Thus E/A ratio is smaller than 1.
Again low LA pressure exaggerates these findings while increasing LA pressures minimises this.

Systolic L V function

Ultrasound

The audible range is 20 to 20,000 Hertz(20kHz). This is because the middle ear acts as low pass filter.Any sound wave having a frequency more than 20,000 is termed ultrasound. (Any frequency below 20Hz is infrasound). The velocity of sound in any given medium is constant. It is determined by the properties of the medium rather than the sound wave itself. The velocity is 0 in vacuum, increases with stiffness and against the density of the propogated medium. So it is slower in air than in water and in non-porous solid medium. It is 343 m/s in air and 1540 m/s in the tissues.

Transmission: Sound is transmitted as longitudinal waves in gaseous and liquid medium. In solids it is propogated as both longitudinal and transverse waves.

Valve Pathology And Anaesthesia

Mitral Stenosis
Mitral Regurgitation

Echocardiography

Ultrasound
DOPPLER
TOE Views
Imaging Artifact
Anatomic Pitfalls
Systolic L V function
Segmental model of LV
Diastolic Dysfunction
Mitral Valve
Aortic valve and LVOT
Thoracic Aorta
Right Heart
Quantitative and Semi quantitative Echo

Aortic valve and LVOT

LVOT has 3 components:
1. Subvalvular LVOT - from free edges of mitral leaflets to aortic annulus
2. Aortic Valve
3. Aortic root and proximal ascending aorta.

Aortic annulus is made by 3 cords.
Aortic valve has 3 leaflets - Right, Left and Non-coronary. Each leaflet is is separated by commmisures.