Transeosophageal ECHO

Transeosophageal ECHO

18/03/09

Beique, F et al (1996) ‘Equipment in Anaesthesia – An introduction to transoesophageal echocardiography: basic principles’ CJA Review Article – page 252 – 277

Dr Chris Horrocks Tutorial – 19/3/09

GENERAL

- allow real time anatomical and physiological assessment of cardiac status

- probes (single, bi, omiplane and epivascular)

- very expensive equipment

- very expensive but reusable

INFORMATION GATHERED

- anatomy (heart, valves, great veins, aorta)

- preload (volume status)

- contractility (left and right systolic and diastolic function)

- regional wall motion abnormalities

- abnormal masses (i.e. vegetations)

- peri-cardial/pleural/aortic collections

- pressure gradients (across valves and chambers) -> remember NOT pressures as you can’t measure pressures with sound waves!

- using Doppler -> Q

PHYSICS

- sound waves via piezoelectric crystals -> electrical current -> produces and senses vibrations

- remember that sound waves can get bounced and also that if you seen something -> you need to ensure its not artefact by looking in two views

- crystals produce 2-3 wavelengths (short burst) and then listens for a comparatively long time

- remember: time is proportional to distance

- speed of sound in soft tissue = 1540m/s

- 4-7 MHz

- frequency can be adjusted based on what you are looking for

- resolution is directly proportional to frequency (but you loose tissue penetration = depth)

- attenuation of U/S signal is proportional to distance travelled and medium travelling through (air = worse, H2O = best )

MODES

- M, 2D, Doppler (spectral, colour flow)

2D-mode

- multiple beams across a single plane

- resolution can be altered by changing the number of crystals being recruited and narrowing the area being studied

- goals in examining in cardiac surgery = assessment of ventricular function, volume and area that is being repaired

- there are over 20 views

- 5 that should be mastered by a novice

- 0º = U/S ray coming out horizontal from probe

- 90º = U/S ray coming out vertical from probe

- 180º - U/S ray coming out horizontal from probe (opposite from 0º)

- long axis = view structure side on

- short axis = view structure end on

- movements of the probe:

1. advance/withdraw

2. turn left/right

3. ante/retrovert

4. rotate (0-180º)

5. flex left/right

M-mode

- M = motion

- an amalgamation of A and B modes which represent lines and dots depending on the echogenic density of the medium through which the U/S wave is travelling.

- M mode displays this in real time

- it provides the highest resolution across a specific line

- used with colour flow Doppler to define timing of an abnormal flow within the cardiac cycle

- allow precise measurement of changes in cavity size, wall thickness and wall motion

- also the best at looking @ anatomical structures (vegetations, thrombus and valve dysfunction)

See Figure 3 in Article

LEARNING VIEWS

Mid Oesophagus (30cm)

- Four Chamber view (0º) - ventricular function, valvular function and atrial abnormalities, Doppler interrogation of MV and TV, pericardium

- AV short axis (30º) - “Mercedes Benz” sign of AV, interatrial septum, coronary ostia, LVOT, PV

- Two Chamber view (90º) - left atrial appendage, inferior and anterior LV walls, MV and transmitral flow and coronary sinus

- Long Axis (130º) - LA, LV, AV, MV and proximal aorta

Transgastric (40cm)

- Short Axis Mid Papillary View (0º) - LV function, RWA, RV function, tamponade (can look at this view and get a lot of information – kissing sign = decreased preload, collapsing ventricle = decreased after load, RWA = ischaemia, pericardial fluid = tamponade)

EXPERT VIEWS

Upper Oesophagus (20cm)

- Aortic Arch Long Axis (0º) - PA bifurcation, aortic root

- Aortic Arch Short Axis (90º) - aortic arch, PA, PV, left brachiocephalic vein

Mid Oesophagus (30cm)

- 5 chamber view (0º) - LA, LV, RA, RV and LVOT

- Right Ventricular Inflow Tract & Coronary Sinus (60-90º)

- Right Ventricular Inflow and Outflow Tracts (from 90º, rotate to right)

- Bicaval (80-110º) - RA, right atrial appendage, atrial septum, venae cavae and LA (PFO and ASD)

Deep Transgastric (45cm)

- long axis (0º and anteflex) - LOVT, AV, ascending aortic arch, aortic outflow velocities

And there are many others!

IMPROVING IMAGE QUALITY

- increase frame rate = frequency of refreshment of screen

- limit frame = increased definition

- decrease depth = increases quality

- increase gain = power output or strength of the signal (increases will increase artefact however)

- adjustment of dynamic range compression (like adjusting contrast level on a TV)

- adjusting frequency filter to eliminate noise

- the cine loop = allows digital acquisition of and storage of cardiac cycles which are then displayed on the screen (can use full screen, split or quad screen to look @ different views of the heart @ the same time)

- zoom = U/S limited to a specific depth

- B mode colour = changes the grey scale of 2D imaging to various hues of blue, purple, orange or yellow

DOPPLER

- The Doppler shift = frequency shift that take place when RBC is moving towards and then away from transducer

- towards = sound waves compressed -> frequency increases

- away = sounds waves expand -> frequency decreases

Spectral Doppler

- blood flow velocity can be measured using a pulsed wave or continuous wave.

- a spectral tracing derived by Fourrier analysis (time vs spectral tracing)

- the amplitude of the spectral tracing (y-axis) is directly proportional to the measured RBC velocity

- BART = blue away, red towards

- patterns of blood flow can also be determined (laminar to turbulent)

- laminar = well defined flow with pale centre

- see diagram in notes

- Bernoulli equation: change in P = 4V2

PULSED WAVE

- sends a signal and waits for its return before sending another one

- good for looking at an area of interest that is at a specific depth

- cannot measure high velocity turbulent flow (c/o high frequency shifts)

- colour flow mapping = a form of pulsed wave Doppler -> good for illustrating regurgitation and abnormal flow (ASD, PFO, VSD)

CONTINUOUS WAVE

- two different transmitters transmitting and listening

- can measure high velocity flows

- disadvantage is that the transducers cannot differentiate which signals come from which depth -> final analysis = an average of all U/S signals generated by moving RBC’s

CLINICAL APPLICATION = measurement of:

- pressure gradients

- flow velocity

- valve areas

- pressure half time

- regurgitant factions

- Q

- systolic function

- diastolic function

Valves

- stenotic = calculate gradients

- regurgitant = use colour flow mapping

LV Function

- end systolic distance < 4.5cm

- end diastolic distance < 7cm

- wall thickness < 12mm

- transgastric short access to get impression

- fractional shortening (diastolic – systolic diameter of LV)

- fractional area change (diastolic – systolic circumference change of LV) – more accurate

- 2 and 4 chamber area change in systole and diastole = EF

Diastolic Function

- relaxation requires energy (ATP)

- phases of relaxation = isovolumetric relaxation, early filling, diastasis (when LA passively fills LV and then stops), atrial contraction

- transmitral flow velocity

- normal = E > A

- abnormal = A > E

- pseudonormal = E > A (LA dilated to compensated for lack of LV relaxation)

- restrictive = E > A

Regional wall motion abnormalities

- heart divided into 16 parts than can be seen on TOE (+1 = apex which is not seen)

- all can be commented on

- normal

- mild RWMA

- severe RWMA

- akinesis

- dyskinesis (move in opposite direction to where it is meant to be)

ADVANTAGES OVER TTE

- decreased interference from bone or air (exception = left main bronchus -> distal ascending aorta)

Valves - increased resolution (endocarditis, post surgery)

Atrial structures – appendage, septum, pulmonary veins

Thoracic aorta

TTE technically difficult – post cardiac surgery and in ventilated with high PEEP

COMPLICATIONS

- gastrointestinal bleeding

- oesophageal rupture

Jeremy Fernando (2010)