Echocardiography

Objective 1.1.1 — Understand the physics of ultrasound, echocardiographic views and modes, Doppler imaging, contrast studies, stress echocardiography, and TEE indications and hazards.

An echocardiogram (Echo) is a type of ultrasound that creates a real-time image of the cardiovascular system. It is the most commonly used and comprehensive cardiac imaging method — non-invasive and inexpensive.

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Physics of Ultrasound

Ultrasound uses high-frequency sound waves (≥ 20,000 Hz) transmitted through a medium and sent and received through a transducer. The beam can be directed and focused.

Key Terms

Reflection

Reflection depends on:

• The degree of difference between the two media (greater density difference → greater reflection)
• The angle of the interface relative to the transducer — the closer to 90°, the greater the amount of sound reflected back

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Echocardiography Overview

Echocardiography is based on standard ultrasound principles:

• High-frequency sound waves are emitted from piezoelectric crystals housed in a transducer
• Sound waves interact with internal structures and are reflected back to the transducer, producing an image

Two Primary Methods

Transducer

• Consists of many small, carefully arranged piezoelectric elements interconnected electronically
• Each element is coupled to electrodes that transmit current to the crystals and record the voltage generated by returning signals
• Sends and receives the ultrasound beam

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2-D (Two-Dimensional) Echocardiography

Two-dimensional imaging uses multiple emitting and receiving elements in the transducer to generate moving images in real time. It is excellent for basic cardiac morphology and functional assessment.

Standard Transducer Positions

Echos begin with transthoracic 2-D scanning from four standard positions:

Patient Positions

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Parasternal Views

The normal echocardiographic examination starts in the parasternal position (3rd or 4th left intercostal space), with the patient in the left lateral decubitus position.

Parasternal Long Axis View

Represents a sagittal or coronal section of the heart — bisects the heart from base to apex.

• The ultrasound beam is parallel with a line joining the right shoulder to the left flank
• Structures visible:
  • Aortic root and aortic valve leaflets
  • Mitral valve leaflets and chordal/papillary muscle attachments
  • Left ventricle

Parasternal Long Axis — RV Inflow

Obtained by tilting the transducer inferomedially (pointing down) and rotating slightly clockwise.

• Provides views of the RV and RA
• Good for identifying tricuspid valve regurgitation

Parasternal Short Axis View

Perpendicular to the long axis view — analogous to slicing bread across the loaf.

• Obtained by rotating the transducer clockwise from the long axis position
• The transducer notch is pointed superiorly toward the right supraclavicular fossa

Short Axis Levels (base to apex)

"Fish Lips" — the appearance of the open mitral valve leaflets in the parasternal short axis view at the basal level.

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Apical Views

The point of maximal impulse (PMI) is located by palpation and used as the starting point for apical views. Images are displayed as if viewing the heart from the apex up through to the base. The patient remains in the left lateral decubitus position.

Apical Four-Chamber View

• Visualizes all four chambers simultaneously
• Greatest benefit: identifying the relative sizes of the ventricles
• The apex is closest to the transducer; the atria are furthest away

Apical Long-Axis (Five-Chamber) View

• Obtained with a slight clockwise rotation of the transducer from the four-chamber view
• Adds the aortic root and aortic valve to the four-chamber view
• Identifies the aortic outflow tract

Apical Two-Chamber View

• Obtained with further clockwise rotation
• Provides an additional wall-motion perspective

All three apical views are essential for analysis of regional myocardial contractility — particularly for stress echocardiography.

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Subcostal Position

In patients with COPD or emphysema, hyperinflated lungs obliterate the standard ultrasonic window. The subcostal position is used to avoid imaging interference.

• Transducer is placed in the midline or slightly to the patient's right, with the transducer groove pointed toward the patient's spine
• Tilting the transducer inferiorly, with the head toward the patient's right, visualizes:
  • Liver parenchyma
  • Hepatic vessels
  • Inferior vena cava (IVC)
• Combined with color Doppler → helps identify regurgitation and right heart dysfunction

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Suprasternal View

The transducer head is positioned in the suprasternal notch for visualization of the aortic arch.

• Primary use: examine the great vessels
• Long-axis view: ascending aorta and aortic arch
• Short-axis view: obtained by rotating the transducer clockwise so the notch faces posteriorly toward the patient's trachea
• May be uncomfortable on the patient's throat

Structures Visualized

• Ascending aorta
• Aortic arch
• Brachiocephalic vessels
• Descending thoracic aorta

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M-Mode

M-Mode (motion mode) records detailed motion of cardiac structures over time.

• Vertical axis: distance (depth)
• Horizontal axis: time
• Can only be measured through 2-D imaging

Uses

• Measurement of cardiac dimensions
• Detection of subtle motion abnormalities of specific cardiac structures
• Detection of valvular dysfunction — primarily mitral and aortic valves
• Assessment of ventricular dimensions

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Doppler & Color Flow Imaging

Doppler Effect

The increase in sound frequency as a sound source moves toward the observer, and the decrease in frequency as the source moves away from the observer.

In echocardiography, the moving target is red blood cells.

• Blood cells moving toward the transducer → higher frequency
• Blood cells moving away from the transducer → lower frequency

Doppler echocardiography measures blood flow velocities in the heart and great vessels.

Color Flow Imaging

Color flow imaging is based on pulsed wave Doppler principles (a single transducer crystal fires a sound wave and receives it back). The echo machine automatically assigns colors to different velocities and directions of blood flow.

BART — Blue Away, Red Towards

• Red = flow moving toward the transducer
• Blue = flow moving away from the transducer
• Green = turbulent flow

• Color Flow Doppler Echocardiography

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Contrast Studies (Bubble Study)

Contrast echocardiography (also called a Bubble Study) is primarily used to identify intracardiac shunts.

• Agitated saline is injected, producing small bubbles visible on ultrasound
• Most common use: identify shunting through the patent foramen ovale (PFO)

Interpretation

• Bubble Study — Contrast Echocardiography

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Stress Echocardiography

The most common indication for stress echocardiography is evaluation of myocardial ischemia or coronary artery disease (CAD).

• Images are obtained before and after stress
• Many echo machines allow side-by-side comparison of pre- and post-stress recordings
• Allows identification of differences in regional wall motion between pre and post stress

Stress Modalities

Exercise-induced regional wall motion abnormalities can be detected a few minutes after exercise. These abnormalities are due to ischemia causing abnormal contractility.

• Stress Echocardiography Overview

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Transesophageal Echocardiogram (TEE)

TEE is a semi-invasive procedure using a modified gastroesophageal endoscopy probe with an ultrasound transducer at the tip placed into the esophagus.

Procedure

• Patient is positioned in the left lateral decubitus position
• Patient is lightly sedated and given topical numbing agents (e.g., lidocaine) before probe insertion
• Fasting is required — higher likelihood of pulmonary aspiration
• Careful guidance is needed to avoid tracheal intubation during esophageal intubation

Indications

Hazards