FELLOW SCHOOL:BASICS OF ECHOCARDIOGRAPHY

JULY 9, 2014

OBJECTIVES OF THIS TALK:

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Review basics of echocardiography and physics behind it

Orient new fellows to reading echoes and basic interpretation and image acquisition

Review a normal echo

WHAT THIS TALK ISN’T…

In depth discussion of echocardiography physics Discussion on how to assess low output aortic

stenosis, differentiating constriction from restriction, or how we assess for dysynchrony

In other words, this is echo 101, getting you through your first day or two….

Why do we perform echoes?

LV systolic and diastolic function

RV function

valvular anatomy / pathology / function

Aortic pathology

Pericardial disease

Intracardiac shunts

Endocarditis

Intracardiac thrombus

Volume status (IVC, RA pressure assessment)

Pulmonary hypertension

Mechanical support assessment (LVAD, etc)

Hemodynamic assessment (Tamponade, constriction, restriction)

Etc.

How does an ultrasound wave turn into a picture on a screen? Based on fundamental principle of constant

speed of sound in a given medium (1540 m/sec in tissue or 1.54 mm/usec)

Ultrasound wave that is received by the transducer at time (t) after the ultrasound wave was emitted from crystal, the echo traveled 1.54 x (t) mm, but the object it bounced off of is 0.77 mm (t) away from transducer (round trip)

This alone can be a full day of lectures…. Beyond the scope of this talk

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How does it work?

How do we do it?

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NORMAL ECHO

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980200396 - normal

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M MODE:

X axis is time, Y axis is depth from transducer.

‘ice pick’ in the heart

PROS: High temporal resolution CONS: Loss of 2D imaging

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CJ Doppler

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Continuous Wave Doppler:

Doppler is based on physics principal of an echo returning from a moving object (red blood cell) creates a shift in frequency

CW is simplest form of Doppler – one crystal continually sending signal, another receiving

Pros: accurately assess high velocity jets; Confidently obtain the highest velocity in any given plane

Cons: Cannot pinpoint where along the plane the highest velocity occurs (for example, in AS: is it at the valve, HOCM, subvalvular membrane?? Don’t know with CW)

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CONTINUOUS WAVE DOPPLER (CW):

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Pulse wave doppler:

Intermittent / episodic emission of echo pulses from a crystal with reception of signal intermittently

PROS: Obtain a velocity at a specific point in space (ie, in the LVOT or RVOT)

CONS: Unable to accurately measure high velocities; aliasing occurs at the Nyquist limit (important concept)

Nyquist limit = ½ PRF

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PULSE WAVE DOPPLER (PW):

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Cos 20 = 0.94 Cos 30 = 0.86

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Example of aortic stenosis:

True gradient across aortic valve is mean of 43 mm Hg

Transducer is parallel to flow. Will measure gradient at 43 (severe AS)

Transducer is 20 degrees off. Will measure gradient at 40 (still severe)

Transducer is 40 degrees from parallel. Will measure at 33 (moderate).

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NOW BACK TO COLOR DOPPLER…

This is a form of pulsed wave Doppler (with all of the pros and cons)

However, the cons can actually be used to your benefit (ie, Nyquist limit, aliasing, and PISA calculation…)

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Example of exceeding Nyquist limit:

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Tissue Doppler:

Same principal as PW, change the settings to focus on velocity of tissue and filter out blood velocity

Visualize the S wave (systolic contraction), E wave (early diastolic relaxation), A wave (atrial relaxation)

Used most commonly for assessment of diastolic dysfunction, LV relaxation, and RV systolic function.

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RV SYSTOLIC FUNCTION ASSESSMENT:

Due to abnormal shape of RV, much more difficult to assess RV size/systolic function compared to LV

S wave normal: > 10 cm/s TAPSE normal: > 1.6 cm

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IVC assessment:

Estimate of RA pressure

If doesn’t fit either of these paradigms, the pressure is intermediate: 8 mm Hg (5-10 mm Hg)

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IVC Collapse? RA pressure

< 2.1 cm Yes 3 (0-5) mm Hg

> 2.1 cm No 15 (10-20) mm Hg

EF ASSESSMENT:

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SIMPLIFIED BERNOULLI EQUATION:

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The change in velocity of blood from a high pressure system (ie, RV or LV) to a low pressure system (ie, RA or LA) is directly proportional to the difference in pressure.

Due to nearly all of the other variables being very negligible to the equation, can easily simplify to:

Change in P = 4V2

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RV systolic pressure assessment:

P = 4V2

Can calculate the difference between RV and RA with CW signal: we know the velocity through the TV with CW

Take that number, put in our above equation. This only accounts for difference between RV

and RA, so need to add the RA pressure to get the RV pressure

RV systolic pressure = 4 (peak TV vel)2 + RA pressure

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CONTINUITY EQUATION: Conservation of mass/energy Flow is constant, so if area decreases, velocity

proportionally increases

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Goal: want A2 You know V1 (LVOT PW) You know V2 (AoV CW) You can calculate A1:

Measure LVOT diameter (usually about 2 cm) Area = pi*r2

Area = 3.14 x ~1 Because the number is squared, biggest area of

error is measurement of LVOT

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In our patient:

A2 (aortic valve area) =

A1 (area LVOT) x V1 (LVOT) /

A2 (AoV velocity)

LVOT measured 1.8 cm So A1 = 3.14 x 0.92 = 2.54 V1 = 0.8 V2 = 1.15 A2 = 2.54 x 0.8 / 1.15 A2 = 1.8 (no AS)

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There is much more to learn, but start with the basics to build a foundation.

Then read, learn, and put to use the more complex cardiac assessments that can be performed by echo (diastolic dysfunction, segmental wall motion abnormalities, VTI, PISA, CO calculation, QP/QS calculation, speckle, strain, etc, etc, etc)

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950017202 – MVP with MR

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