Cardiology Lecture Notes: Sensing Blood Flow with Echocardiography

Introduction to Echocardiography

• Dr. David Baker, cardiologist at Royal Prince Alfred Hospital.
• Lecture focuses on sensing blood flow using echocardiography.
• Emphasis on interactive learning with questions encouraged throughout the session.

Team Introductions

• Gareth Foote from Philips (providing assistance and volunteering for echocardiogram).
• Rachel Healyer, Chief Sonographer at RPA.

Lecture Overview

• Principles of echocardiography (building on previous introductions).
• Physics of ultrasound and image creation.
• Doppler imaging principles and technology.
• Live echocardiogram demonstration with Rachel and Gareth:
  • Heart anatomy and movement.
  • Blood flow and physiology.
• Haemodynamic principles for clinical decisions (medication, surgery).
• Normal vs. Abnormal Echo Results
  • Normal echo example with Gareth.
  • Abnormal echo examples to follow.

What is Echocardiography?

• Imaging the heart using ultrasound.
• Clinical applications:
  • Diagnosing heart failure and valvular issues.
  • Monitoring treatment effectiveness (medications, surgery).
  • Guiding procedures (aortic valve replacement, fluid drainage).
• Essential tool for cardiologists, often used as an extension of a physical exam.

What is Ultrasound?

• Sound waves inaudible to humans (frequency > 20 kHz).
• Clinical range: 1.5 to 15 MHz (very short frequency sound waves).
• Ultrasound Machine Components
  • Transducer probe with piezoelectric crystal to emit sound waves into the body.
  • Machine converts reflected sound waves into electrical signals, then images.
• Longitudinal sound waves transmit through body tissues and reflect back.
• Technology History
  • Developed around 1920s for military use.
  • Applied in medicine around 1950s.

Basic Properties of Sound Waves

• Longitudinal waves traveling through a medium.
• Frequency: How often a wave goes through a full revolution.
• Wavelength: Distance between peak to peak of a wave.
• Relationship Between Frequency and Wavelength
  • High frequency = short wavelength.
  • Low frequency = long wavelength.

Clinical Ultrasound Trade-Off

• High frequency: Better resolution (spatial resolution).
• Low frequency: Deeper penetration.
• Compromise for cardiac imaging due to depth; posterior heart can be 15-20 cm deep.
• Speed of Sound
  • Speed of sound in the human body is constant.
  • Allows calculation of distance based on reflection time and known frequency.

Piezoelectric Crystals

• Special crystals inside the transducer probe.
• Properties:
  • Electrical current $\rightarrow$ sound wave emission.
  • Sound wave reception $\rightarrow$ electrical current.

Ultrasound Image Grading Scale

• Anechoic: Very black, low-density (fluid, blood); no sound reflection.
• Isoechoic: Mid-grayscale, medium-density (muscle, tissues).
• Very bright: High-density (bone); reflects a lot of sound; bone reflects most of the sound waves off the anterior part of the bone.
• Shadow effect: Bone reflection obstructs visualization of what's behind it; no sound wave penetration through bone creating a shadow effect.
• Importance for probe placement between ribs to avoid bone interference.

Historical Forms of Ultrasound

• A-mode (Amplitude Mode):
  • Transducer held straight down imaging through heart
  • Displays amplitude spikes of returning signals; denser structures create larger spikes.
  • Limited clinical usefulness.
• B-mode: (Brightness Mode):
  • Applies grayscale to amplitude and depth information to create a basic picture using one line.
  • Still difficult for clinical interpretation.
• M-mode (Motion/Movement Mode):
  • Clinically useful early form; uses B-mode over time (x-axis).
  • Displays movement of structures over time.

Live Ultrasound Demonstration (M-Mode)

• ECG displayed (green line) for cardiac cycle gating (systole vs. diastole).
• Y-axis shows depth (0 cm at skin, 15 cm deep).
• X-axis shows time.
• Two-dimensional image shows line being used for M-mode.

M-Mode Image Interpretation

• Skin reflects ultrasound strongly (white).
• Subcutaneous tissue allows sound penetration.
• Right Ventricle: Anterior heart structure; blood appears black/anechoic.
• Interventricular Septum: Movement shows contraction in systole and relaxation in diastole.
• Left Ventricle: Blood appears black.
• Mitral Valve: Thin structures with significant movement; M-shape.
  • Closed in systole, opens in diastole.
  • Anterior and posterior mitral valve leaflets visible.
• Posterior Wall of Left Ventricle: Contracts in systole, relaxes in diastole.
• Pericardium: Bright and fibrous; reflects a lot of echo.

Clinical Diagnosis with M-Mode

• Example: Large mass in left atrium prolapsing through mitral valve in diastole.
• Left Atrial Myxoma: Tumor in left atrium.
  • Can obstruct blood flow or cause strokes.

Two-Dimensional (2D) Doppler Imaging

• Uses an array of sound waves in a 2D plane.
• B-mode image not over time.
• Updates information over time to create a more detailed image.
• Three-Dimensional (3D) Imaging now available.

Doppler Imaging Principles

• Uses the Doppler effect to assess blood flow.
• Provides information on direction, speed, and turbulence of blood flow.
• Used in pathology like valvular stenosis or regurgitation.

Doppler Effect Explanation

• Sound of ambulance demonstrates Doppler shift.
• Frequency changes relative to stationary observer if the sound source is moving.
• Approaching ambulance: Frequency increases (shorter wavelength, higher pitch).
• Receding ambulance: Frequency decreases (longer wavelength, lower pitch).

Doppler Application in Ultrasound

• Probe emits sound wave; reflection from blood cells or valves changes if moving.
• Change in frequency detects direction and speed of movement.

Types of Doppler

• Continuous Wave Doppler
  • Measures high velocities (e.g., aortic stenosis).
  • Uses two crystals: continuous transmission and reception.
  • Cannot determine location along the line of sound.
• Pulsed Wave Doppler
  • Measures precise velocity at a specific point.
  • Uses single crystal: transmits, stops, and waits for the signal.
  • Limited by aliasing at certain velocities.
• Color Doppler
  • Assigns color to velocity, direction, and turbulence of blood flow.
  • Blue: Blood moving away from probe.
  • Red: Blood moving toward probe.

Live Case Demonstration: Basic Echocardiography

Patient Positioning and Echo Windows

• Patient lies on left side (left lateral position) with arm above head.
  • Brings heart closer to chest wall.
  • Spreads out rib spaces for better images.
• Echo window: Area of body providing good images (avoid ribs, air-filled stomach).
• Parasternal Long Axis View:
  • Standard first image.
  • Probe along left sternum, top pointing toward left shoulder.
  • Images long axis of the heart through mitral and aortic valves.

Image Orientation and Anatomy

• Top of screen = skin surface.
• Yellow dots = centimeter marks.
• Focal point adjusts resolution.
• Right Ventricle: Most anterior.
• Interventricular Septum:
• Aortic Root and Valve: Opens in systole, closes in diastole.
• ECG for reference.
• Left Ventricle:
• Mitral Valve: Closes in systole, opens in diastole.
• Anterior Septum.
• Posterior wall, Pericardium fibrous sac surrounds the heart. Fibrous= a lot of reflection.

Mitral Valve Dynamics

• Mitral valve separates the two chambers of the heart.
• Blood flows back to the left atrium from the pulmonary veins.
• Blood flow is based on pressure, and pressure gradients.
• Systole: Mitral valve closes, left atrium dilates, and fills with blood.
• Diastole: Left ventricular pressure drops, mitral valve opens.
  • (E Wave): Early diastolic filling.
• Atrial Contraction (A Wave): Additional filling due to atrial systole.
  • Significant for cardiac output (20% reduction in atrial fibrillation).
• Bi-leaflet valve: Anterior leaflet larger than posterior.
• Chordae tendineae: Attach mitral valve to papillary muscles; preventing prolapse of valve

Right Ventricular Inflow View

• Probe tilted anteriorly towards right side shows tricuspid valve and right atrium.

Right Ventricular Outflow View

• Move probe upward toward the top of the heart.
  Right ventricle exits into the pulmonary artery.

• Pulmonary valve semilunar.

• Images pulmonary trunk (main pulmonary artery) and right pulmonary artery.
  Aortic valve visible in middle, but not always clear.

Color Doppler on Pulmonary Valve

• Shows blood flow direction.
• Systole: Blue jet shows blood flowing away from probe into pulmonary artery.
• Diastole: Valve closed.
  *Trivial pulmonary regurgitation. Tiny blood squeak goes back from the pulmonary artery back to the right ventricle.

Color Doppler on Aortic and Mitral Valves

• Confirms competence and proper opening.
• Red color indicates planar blood flow in one direction.
• Turbulent flow shows mixed colors (blue and red).

M-Mode of Aortic Valve

Two-Dimensional (2D) Measurements

Measure diameter within root of the heart and measure thickness of the ventricle to asses for any defects or disease.

Parasternal Short Axis View

• Rotate probe 90 degrees from long axis view.

• Left Ventricle:

  • Bullet-shaped (circular).

• High-pressure ventricle.

  • During squeezing, pressure hits 120 mmHg.

• Normal thickness: 8-9 mm.

• Right Ventricle:
  *Lower pressure system.

• Pressure hits 30.

  • Wraps around left ventricle.

• Very thin- walled.
  *Pressure in the right ventricle is very low. 3 millimeters.

• Tricuspid Valve and Pulmonary Artery are not close to each other.

Mercedes Benz Sign:

• There is usually 3 cusps on the aortic valve. This is the open position of the aortic valve.
• The non-coronary leaflet, the right coronary leaflet , and the left coronary leaflet. Use NRL to remember which way to assign them.

Aortic valve is identical to the pulmonary valve. Use your semi-lunar to tell them apart. *
There are no chordae tending on the Aortic and Pulmonary valve.

You can sometimes see the tram tracks of the coronary vessels.
Right coronary comes off the right coronary cusp.
Interatrial septum- connects the right with the left atria.
Tricuspid valve feeds into the right ventricle.
Often you find a squeak in the Tricuspid area from backflow.
Isolation angle- measure the blood flow using a line.
Can measure what the velocity is down those lines.
You measure that at the line of velocity.* *
Continuous Wave Dopler- Measuring what the velocity is along that line.
Can be similar to M-Mode but is giving you information about the line and how it is updating in the X axis.
If there is a leaky Tricuspid valve, the blood will go from the Tricuspid valve to the right atrium.* *
See a white envelope created due to the tricuspid regurgitation.
You can take that velocity and see the pressures of the pulmonary hypertension.* *
Measure this line to get the maximum velocity.* *
Showed different windows throughout the heart to try to asses the heart.* *
Assessment of the heart to make sure each part is moving correctly.* *
Each heart is supplied with blood and the heart moves and contracts from this. Is also known as the coronary vessel.* *
If a person is experiencing a lack of blood flow through a specific coronary artery, the parts of that part of the heart are affected which in turn makes it difficult to more which indicates to have a heart attack or medical problems.* *
The different differences between the right and left ventricle is that the right heart is complex with many different pieces connected. There are a lot of fibrous connections that do that.* *
The right ventricle is far more trabecular and so is the papillary muscles.* *
We also want to see the Apical four chamber here.* *
Looking directly under the nipple pointing to the heart.* *
You can see all four parts of the heart in this specific position.* *
You can now distinguish which side is left and right of the heart. And where the trabeculations and the mitral valve is.
The tricuspid valves will always point to the bottom of the apex.* *
What needs to know about flow of the right chamber and the left chamber.* *
Left atrium: is on the posterior of the heart.* *
The Transesophageal Echo.* *
Using the esophagus to get to the back of the heart.
Looking at the interatrial septum.* *
Structures come anteriorly with the heart.* *
Hook sack hangs off the left Atrial Appendage.* *
Slow blood clots occur in these appendages.* *
Pulmonary blood veins are very important.* *
The difference between the E or A wave. and the ECG during diastole is the wave from the arteries which has an S and D wave.* *
P wave: which will get atrial contraction. Called the atrial reversal.
From the four-chamber view.* *
Five chamber view.
Take hand and face it forward. Then have your left thumb show where the aorta comes from. And then your other point where the Pulmonary artery is.
Showed a 5- chamber again to show the structure.* *
The Aortic valve works in the other side.* *
Measure velocity in this five-chamber view using a continuous wave to meausure the area along the line.* *
Water the garden. You put your thumb over to make it smaller so it goes faster. That’s just like what is happening with a velocity of the small heart valve. This gives a direct relationship.
A mean peak gradient means a lot about how the pressure is happening throughout the stenosis. *
Can then be taken to three which helps see each part.* *
We can also do the subcostal view to show all the other pieces to the heart.* *
Has to lower her view because the heart is further away.
Use the liver to go under.
Shows the ventricle in and how it works.
Where and how the Tricuspid valve works and what structures are entering the right atrium. the SVC and the IVC.* *
the superior and inferior venacava. Can use each one to identify the structures.* *
Blood is getting sucked into the heart by taking a deep breath. Compression. Lower pressure. Which will create an increase the pressure inside the chest or throax.* *
Compress the inside.* *
The properties of the echo are important.* *
If there any kind of vessels that are cutting over the middle then it becomes important to learn.* *
Showed all the supercostyl and all the differences.* *
Where the vessels are located within the heart and how that effects everything. Velocity with the Doppler. Etc.* *

Clinical Applications of Doppler Echocardiography Equations and principles.

Cardiac output=

• stroke volume times the heart rate.
• Area=\pi r^2.
• Flow times area= Velocity.

Bernoulli Equation:

• $Pressure Gradient = 4 \times Velocity^2$.
  Continuous: you can get an idea how high the pressure is to the heart.