Segmental model of LV

There is a 16 segment model and a 17 segment model

16 segment model:

There are 6 basal, 6 mid and 4 apical segments
The naming is from anteroseptal and continues anticlockwise

Basal
1- Anteroseptal
2- Anterior
3- Lateral
4- Posterior
5- Inferior
6- Septal

Mid
7- Anteroseptal
8- Anterior
9- Lateral
10- Posterior
11- Inferior
12- Septal

Apical
13- Anterior
14- Lateral
15- Inferior
16- Septal


In the transgastric view one can see all the segments at a particular level.
Visualising apical segment is difficult in TOE.

Segments seen in different views:
1- Long axis view are – (130)
Anteroseptal – 1, 7 – LAD territory
Posterior – 4, 10 – LCX territory

2- 2-C view are – (90)
Anterior – 2, 8 and 13 – LAD territory
Inferior – 5, 11 and 15 – RCA territory

3- 4- C View – (10)
Lateral – 3, 9 and 14 are seen – LCX territory.
Septal – 6, 12 and 16 are seen – LAD territory

Segmental Blood supply:
1- LAD territory includes –
Septal (6, 12, 16)
Anteroseptal (1, 7)
Anterior (2, 8, 13)

2- LCX territory –
Lateral (3, 9, 14)
Posterior (4, 10)

3- RCA territory –
Inferior (5, 11, 15).




17 segment model:

Basal
1- Anterior
2- Anteroseptal
3- Inferoseptal
4- Inferior
5- Inferolateral
6- Anterolateral

Mid
7- Anterior
8- Anteroseptal
9- Inferoseptal
10- Inferior
11- Inferolateral
12- Anterolateral

Apical
13- Anterior
14- Septal
15- Inferior
16- Lateral
17- Apical

There are segments at three levels. The naming progression is clockwise.

Imaging Artifact

Artifacts: Any structure in an ultrasound image that does not have a corresponding anatomic tissue structure.
Classification:
1. Missing structures
2. Degraded images
3. Falsely perceived images
4. Structures with misregistered location.
Missing structures:
Reasons:
Reduced resolution – To improve resolution increase the frequency, bring your area of interest into focal zone and decrease the overall gain
Acoustic shadowing – change the window.
Degraded images:
Reverberations – they are secondary reflections that occur along the path of sound pulse. They occur as a result of ultrasound bouncing between the structure and another reflecting surface. The reflecting surface may be the near side of the object, a second object or the transducer itself. The repeated journey produces two or more additional signals which are equally spaced, twice the distance as the original signal. Some times the reverberations are merged together and appear as a single solid line away from the transducer – comet tail/ring down.
Enhancements – reciprocal of image shadowing. If the intervening tissue has low acoustic impedence then the structures beyond appear to be enhanced because the sound signal is minimally attenuated. This can be adjusted by reducing the time gain compensation.
Noise – has many causes – excessive gain, cautery etc.
Falsely perceived objects:
This can be due to refraction or reverberation. Examples include:
Mirror images – Common place of occurrence is descending aorta- called as double barrel aorta. This is believed to be due to aorta-lung interface. Seen at twice the distance from the transducer as the original image.
False dissections
Line artifacts – type of reverberation artifact. Can be identified at twice the distance similar to mirror images. They mimic false intimal flaps. They can be detected as false flaps when they have indistinct borders, do not display rapid oscillatory motion and are located twice the distance from the LA wall. In addition colour Doppler does not show any interruption of flow pattern. Artifacts are more likely if the aortic diameter is >5cm and atrial-aortic ratio ≥0.6.
Reverberation artifacts are also described in the LAA mimicking thrombi. To differentiate -
Thrombus
Artifact
Confined to cavity
Not always
Has an attachment
None
Uniform consistency
Non- uniform
Texture different to LA
Similar
Twice the distance from Coumadin ridge.

Misregistered locations:
Range ambiguity – results in the display of correct structures in the wrong location. It occurs with high PRF(Pulse Repetition Frequency). This results in deeper structures appearing closer. When an unexpected object is seen in the cardiac chamber, it is due to range ambiguity.
Side lobes – are additional multiple beams emerging from the transducer in a diverging manner. Displayed as a curved line and always have a common radius from the transducer. They cross anatomical walls and cavities without regard for natural borders. They disappear with adjustment of depth/angle of the transducer.

Anatomic Pitfalls

Crista terminalis: Structure between smooth and trabeculated parts of RA. It is seen at the junction of SVC and RA. It is visualized in the bicaval view.
Eustachian valve: Valve of the IVC. It is seen in 4C / Bicaval view in 25% population at the junction of RA and IVC. It can be confused with thrombus.
Thebesian Valve: Valve of the coronary sinus. It may make coronary sinus cannulation difficult.
Chiary network: Mobile, filamentous structure seen in RA. It is probably a remnant of sinus venosus derived structures. It is associated with PFO, paradoxical embolism and interatrial septal aneurysm.
Coronary Sinus: Seen in 0 degree view as an echo free space just above tricuspid valve in the RA. If >1cm – possibility of persistent LSVC. It can also be seen in 90 degree 2-C view.
Persistent LSVC: drains into coronary sinus. It can be seen between LAA and descending aorta. It can also be seen between LAA and LUPV. In this setting it can be misinterpreted as a cyst or abscess. It should have colour flow in it. Agitated saline injection into left upper extremity vein should opacify coronary sinus and RA to confirm the diagnosis.
Trabeculations: More characteristic of RA and RV. They are caused by muscle bundles on the endocardial surface.
Pectinate Muscles: series of parallel ridges coursing along anterior surface of RA and LA.
LA is entirely smooth except for LAA.
Coumadin ridge: Junction of LAA and LUPV
Persistent LSVC drains into coronary sinus and leads to its dilatation.

Cardiac Intensive care

Most patients in cardiac intensive care are post surgery. The type of surgery may be CABG, valve repair/replacement, heart or lung transplant. Ocassionally patients may be admitted for preop stabilisation.

Hand Over following CABG:
1. Know the number of grafts done.
2. Whether radial artery was used.
3. Pre -op LV function. Intraop TOE finding
4. Bypass and cross clamp time
5. Intraop hemodynamic instability
6. Ease of coming off bypass
7. Post bypass supports - pharmacological, mechanical and electrical(pacing)
8. Underlying rhythm.
9. Plan

Things to do on arrival:
1. Connect to ventilator and confirm air entry and ventilator settings
2. Do 12 lead ECG
3. Monitor bleeding - inform surgeons if >400ml in first hour, >250 in next three hours.
4. See the blood gas and adjust ventilation
5. Fill in the drug chart.
6. Go through the clinical notes - co-existing illness, medications, allergies.

Acute lung Injury

• The use of high tidal volume and high respiratory rate are independent predictors of acute lung injury in patients with severe brain injury. In this patient population, alternative ventilator strategies should be considered to protect the lung and guarantee a tight CO2 control.
• Early acute lung injury/acute respiratory distress syndrome is characterized by decreased plasma levels of protein C and increased plasma levels of plasminogen activator inhibitor-1 that are independent risk factors for mortality and adverse clinical outcomes. Measurement of plasminogen activator inhibitor-1 and protein-C levels may be useful to identify those at highest risk of adverse clinical outcomes for the development of new therapies.

Transfer of Critically ill

Usually these patients are ventilated and on cardiovascular support. It involves lot of gadget to transfer these patients.

For an uneventful transfer be it intra- or inter hospital transfer the following tips will help:

1. Adequate oxygen supply - twice that required for the journey
2. Fully charged ventilator
3. Fully charged monitor - minimum monitoring should include ECG, SPO2, BP either IBP/NIBP, ETCO2.
4. Adequate nitric oxide if used. Proper connectors should be ready.
5. Emergency Drugs- Atropine, Adrenaline(1/1000 and 1/10000 dilutions), metaraminol(1mg/ml in 10 ml), saline flushes should be present atleast.
6. Anaesthetic drugs - Muscle relaxant(paralyse a ventilated patient before transfer), Fentanyl/Alfentanil or morphine infusion(if already on that in ICU).
7. Fluids - Colloids - Gelofusine, hetastarch, blood(if low Hb)
8. Minimise things to be transferred - like KCl, Actrapid or frusemide infusion.
9. Adequate staff to transfer.

Endoscopic Coronary Artery Bypass Graft

Goals:
1. Normotensive
2. Normothermic
3. Maintain normal electrolytes
4. Avoid tachycardia or bradycardia

Approach:
Left thorocoscopic for dissection of left internal mammary artery.
Left parasternal thoracotomy in 4th intercostal space for LIMA to LAD aastamosis.

Requirements:
1. Venous access and radial arterial line in right hand
2. One lung ventilation. Left lung can be collapsed either with double lumen tube or use of broncial blocker with single lumen tube.
3. Left internal jugular access.
4. External warming device.
5. Perfusionist fully prepared for CPB if required.
6. Heparin just before clamping the LIMA, half to full dose depending on the local practice.
7. Post op pain relief - PCA morphine is what we ususlly follow. Other options include - thoracic epidural, PCA alfentanil.

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.

DOPPLER

Three types:
1. Continuous wave
2. Pulsed wave
3. Colour flow

Signal processing controls:
1. Doppler reciever gain
2. Wall filter
3. Velocity scale
4. Baseline shift
5. Sample volume size
6. Color threshold
7. Steering angle
8. Color box size and position
9. Variance
10. Color inversion
11. Color maps

Doppler effect:
The apparent change in the frequency of waves due to relative motion of the source and observer. Christian Johann Doppler described this in 1842. The apparent frequency increases if source is moving towards (red-shift) and decreases if moving away (blue-shift). The difference between the transmitted frequency and the received frequency is known as Doppler Shift. This can be calculated from Doppler equation.

fD = f0[v/c-v]

fD - Doppler frequency
f0 - Transmitted frequency
v - Velocity of the source
c - Speed of propagation of the wave in the medium.

In echocardiograpgy doppler shift occurs twice. First when the wave travels from transmitter to the scatter and second when it reflects and travels back to the receiver.

So,

fD = f0[2v/c-v]

As c>>>v c-v ≈ c

Then,


fD = 2f0v/c

Then the velocity of the scatter can be derived from

v = fD c / 2 f0

If the scatter is moving at an angle θ, then

v = fD c / 2 f0 cos θ

This angle is known as the crossing angle. The error is negligible if this angle is less than 20 degrees.