Transoesophageal Echocardiography

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 OBTAINED

  • 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)
  • pericardial/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

v = f x lambda

v = velocity
f = frequency
lambda = wavelength

  • 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 traveling.
  • 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

Doppler Shift (Fd) = observed frequency – original frequency

V = Fd x speed of sound / 2 x generated frequency x Cos ɵ

V = velocity of RBC
Fd = Doppler shift
Speed of sound = 1540m/s
2 = because Doppler shift occurs twice
Generated frequency = between 3.7-7 MHz
ɵ = the angle between the interrogating U/S beam and direction of blood flow (should ideally be <20º -> blood moving directly towards or away from probe)

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

CCC 700 6

Critical Care

Compendium

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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