Ultrasound of the Heart (SDL)

What set up equipment is required for echocardiography of the heart? Describe:

• Patient Preparation

• Patient Positioning

• Equipment Needed

Patient preparation:

• Clip over apical beat

• The apical beat (or apex beat) in a dog is the point of maximum intensity (PMI) of the heartbeat, felt as a pulsation on the lower-left chest wall, typically behind the left elbow at the 5th or 6th intercostal space. It represents the apex of the left ventricle striking the chest wall during contraction.

• Apply water & gel

Patient position:

• Right then left lateral recumbency

• Scan from below patient

- Hypostatic congestion in dependent lung

• Hyperinflation in upper lung

• Heart pushes lung out of the way

Equipment:

• Phased array / microconvex transducer

• ECG leads to determine the state of the cardiac cycle during the exam

What is B-mode Echocardiography?

• What is the importance of performing standardized views?

“Brightness”(B)-mode echocardiography: is a real-time, two-dimensional (2D) ultrasound imaging technique that maps cardiac structures using grayscale pixels, where brightness corresponds to echo intensity.

Why bother with standard views?

• Orientation!

• Systematic examination

• Repeatable images

• Easier to interpret normal v abnormal

• Standard measurements of cardiac structures

• Comparison with published images

• Remote diagnoses

• Follow up scan (progression / resolution)

• Guide M Mode & Doppler measurements

Describe the orientation of standard right parasternal views of the heart.

• SHORT AXIS

• Orientation: The ultrasound beam is aligned perpendicular to the long axis of the heart, roughly parallel with IC space, usually with the marker pointing toward the dog's right shoulder (craniodorsal).

• Gives view of the short axis

• LV = mushroom shape

Describe key features of the following structures when viewed in the Right Parasternal Short Axis View.

• Left Ventricle

• Mitral Valve (Fishmouth)

• Heart Base (Aorta, Pulmonic Trunk & Left Atrium)

The above are the three

• Left Ventricle + papillary muscles

  • Transducer near apical beat

• Mitral Valve (Fishmouth)

  • More cranial-dorsal view

• Heart Base (Aorta, Pulmonic Trunk & Left Atrium)

Describe the orientation of standard right parasternal views of the heart.

• LONG AXIS

Transducer rotated 90 degrees, parallel to long axis and at right angle with IC space

• Views displayed with base to right, and apex to the left

• Pericardium appears hyper echoic - adhered to outside of heart

Describe key features of the following structures when viewed in the Right Parasternal Long Axis View.

• Left Ventricle and Left Atrium

  • Chordae Tendinae

• Left Ventricle and Aorta

• Hyper echoic strands = chordae tendinae

Describe key features of the following structures when viewed in the Left Parasternal Long Axis View.

Left lateral recumbency - mobile apex closer to thoracic wall

1. Four Chambers

2. Five chambers

Summarize the standard Parasternal views that can be visualized.

RPS Short axis views

1. Left ventricle (Mushroom)

2. Mitral valve ("Fishmouth")

3. Heart base (Aorta, Pulmonic trunk & Left atrium)

RPS Long axis views

1. Left ventricle & left atrium

2. Left ventricle & aorta

LPS views:

• 4 chamber view

• 5 chamber view

• Aortic valve / outflow tract

What is “M-mode / Time-Motion Mode” echocardiography?

• Standard B-mode images

• Position cursor line through image, when activates means:

• Movement of structures against time is displayed on screen and constantly updated

• ECG - allows identification of stage of cardiac cycle

• Objective measurements

• Lumen = usually inside

Describe what features of the heart can be visualized in M-mode

1. Cardiac Wall thickness:

• RPS short axis through LV

• Interventricular septum

• Left ventricular free wall

• Published values for thickness for breeds and species

2. LV function:

• RPS short axis through LV

• LV Lumen diameter

• Same trace as wall thickness

Shortening fraction: gives information on the contractility ability of the left ventricle - measures the percentage decrease in left ventricular (LV) diameter during systole, representing systolic function

• LVEDD - LVESD × 100

LVEDD

• Normal range : Dogs: 25 - 45% Cats : 30 - 55%

• RPS long axis through LV & LA - taken using B-mode

• LV Lumen diameter

• End diastole image stopped - MV open / max area

• End systole image stopped - MV closed / min area

Ejection fraction: also gives information on LV contractility and function, should be more accurate than shortening fraction

• Difference between areas

• Normal >50%

3. Left ventricular dilation: gives information on LV volume overload or dilation

• RPS short axis "Fishmouth" view

• Demonstrates movement of mitral valve leaflets

• M & W shapes of the leaflets

• LV wall

E -point to septal separation (EPSS): E-point to septal separation (EPSS) is an M-mode echocardiographic measurement that provides a rapid, reliable, and mostly objective assessment of left ventricular (LV) systolic function.

• Distance between valve and IVS

• Normal <7mm

4. Measurement of left atrial size: Left atrial enlargement:

• RPS short axis through heart base

• End systole

• Left atrium diameter

• Aorta diameter

• Mercedes - Benz sign

Ratio LA : Aorta

Dogs 1:1-1.4

Cats 1: 1.2-1.7

What is the doppler ultrasound and what are the main types?

• Frequency of beam changes when it encounters moving objects eg RBCs, allows assessment of the movement of blood through the heart

Types of Doppler:

• Colourflow - flow through heart as areas of color

• Spectral - depicts blood flow as a graph, 2 types:

• Pulsed wave

• Continuous wave

How does the doppler ultrasound allow for assessment of blood flow?

• 1. Direction:

• if moving towards or away from transducer

• 2. Velocity:

• Beam parallel with direction movement = most accurate measurement

• 3. Uniformity:

• laminar v turbulent

Describe the key features of colorflow doppler echocardiography.

• B-mode images guide the Doppler “Gate” placement

LPS 4/5 chamber views

• Aorta (downward, blood depicted blue), MV & TV (Toward transducer (blood pictured red)

• RPS SA heart base view

• Pulmonic trunk (Away from transducer, blue)

Conventional Coloring System

• BART system

• Blue = Depicts blood going away from transducer

• Aortic / Pulmonic outflow

• Red = Depicts blood going towards transducer

• Mitral / Tricuspid inflow

Valvular incompetence - indicated by opposite color of flow in the wrong direction, turbulent flow - mosaic or multi-colored appearance

• Screens large areas of blood flow through heart to identify abnormalities

Describe key features of the spectral doppler, specifically the pulsed wave.

• Specifically the LPS 4 chamber view.

Colorflow guides placement of the spectral doppler cursor box of areas of normal or abnormal inflow/outflow. Activation of pulsed wave produces a trace of blood flow through the box against time.

Pulsed Wave

• Mitral / Tricuspid flow up screen towards transducer, normal flow characterized by peaks of flow above baseline are normal

• LPS 4 chamber view

• E and A peaks

• E = early peak

• A = atrial peak

• Can measure velocity of flow by measuring the peaks

  • E and A peaks in pulsed-wave Doppler echocardiography represent velocities of blood flow across the mitral valve, used to assess left ventricular diastolic function. The E-wave (early) indicates passive, rapid filling of the left ventricle, while the A-wave (atrial) represents active filling caused by atrial contraction.

Describe key features of the spectral doppler, specifically the pulsed wave.

• Specifically the LPS 5 chamber view?

• Aortic / Pulmonic Flow

• Aorta most visible on - LPS 5 chamber view

• Pulmonic valve most visible - RPS SA heart base

• Flow away from transducer = below baseline

• Single peak with black outline below the baseline - indicates normal laminar flow

How is regurgitant flow through the Aorta/pulmonic valves on the spectral doppler, specifically the pulsed wave doppler identified?

Best assessed during diastole between peaks of normal outflow

Wrong direction

• Aorta / Pulmonic - above baseline - present in diastole

• MV / TV - below baseline - present in systole

• Envelope 'filled in' = turbulent flow

  • Normally should be filled with black

• Velocity = height / depth of peak

• Simplified Bernoulli equation:

  • p₁-p₂=4V² - can be used to calculate pressure difference between the valves

How is regurgitant flow through the Aorta/pulmonic valves on the spectral doppler - specifically the continuous wave doppler.

Continuous wave Doppler

• Unlimited velocity measurement, good for areas exceeding pulsed wave - good for stenosis and high blood flow

• Pulsed wave - limitations on max velocity of flow it can measure

• Does not assess uniformity

• Used to measure high flow rates in aortic / pulmonic stenosis

Summarize the different ultrasound modes and they main uses.

B (Brightness) Mode:

Standard views - RPS / LPS

• Identify physical changes + subjective function of heart

• Identify marked functional changes

• Objective measurements - such as size

• Guide M-Mode / Doppler cursor placement

•M (Motion) Mode

• Objective measurement of LV function & chamber size

•Doppler: Objective assessment of blood flow through the heart

• Colourflow - direction & uniformity of flow, no flow velocity, mainly to guide placement of spectral doppler

• Pulsed Wave - direction, uniformity and limited velocity, identifies regurgitant and turbulent flow

• Continuous Wave - direction, limited uniformity but unlimited velocity (Can be used when pulse wave is limited by velocity)