Echo Fundamentals

Transthoracic echocardiography uses reflected ultrasound to assess cardiac anatomy, function, blood flow, and hemodynamics. Image interpretation depends on understanding how frequency, depth, resolution, alignment, and loading conditions affect the recorded data.

Ultrasound Physics¶

\[ c = f\lambda \]

\(c\): propagation velocity
\(f\): frequency
\(\lambda\): wavelength

Ultrasound systems assume an average propagation velocity of approximately 1,540 m/s in soft tissue.

Frequency¶

Higher frequency	Lower frequency
Shorter wavelength	Longer wavelength
Better resolution	Lower resolution
Greater attenuation	Less attenuation
Less penetration	Greater penetration

Use the highest frequency that provides adequate penetration.

Reflection and scattering¶

Reflection: returning ultrasound from a tissue interface; the basis of anatomic imaging
Scattering: redirection of ultrasound by small structures such as RBCs; the basis of Doppler imaging
Refraction: change in beam direction across a tissue interface; may create displaced or duplicated structures
Attenuation: progressive loss of signal from absorption, reflection, and scattering

Reflection is greatest when the beam is perpendicular to a tissue interface. Doppler velocity is most accurate when the beam is parallel to blood flow.

Resolution¶

Axial resolution: distinguishes structures parallel to the beam; improves with higher frequency and shorter pulse length
Lateral resolution: distinguishes structures perpendicular to the beam; best at the focal zone
Temporal resolution: distinguishes events over time; improves with a higher frame rate

Improve frame rate by:

Decreasing depth
Narrowing sector width
Reducing line density
Limiting unnecessary focal zones

Imaging Modes¶

2D imaging: primary mode for real-time anatomy
M-mode: very high temporal resolution along a single scan line
Pulsed-wave Doppler: measures velocity at a selected depth but aliases at high velocities
Continuous-wave Doppler: measures high velocities without aliasing but lacks precise depth localization
Color Doppler: displays the direction and mean velocity of flow within a region of interest
Tissue Doppler: measures myocardial velocity

Color-jet area alone should not be used to determine regurgitation severity.

Standard TTE Windows¶

Parasternal¶

Parasternal long-axis
Parasternal short-axis at the aortic valve, mitral valve, papillary muscle, and apical levels
RV inflow
RV outflow

Apical¶

Apical four-chamber
Apical two-chamber
Apical long-axis or three-chamber
Apical five-chamber
RV-focused four-chamber when indicated

Avoid apical foreshortening. The true LV apex should appear narrow rather than rounded.

Subcostal¶

Useful for:

Pericardial effusion
Interatrial septum
Right-heart assessment
IVC and hepatic veins
Abdominal aorta

Suprasternal¶

Used to assess:

Aortic arch
Proximal descending aorta
Arch vessels
Coarctation
Abnormal aortic flow

Doppler Principles¶

Measured Doppler velocity depends on the angle between the ultrasound beam and blood flow:

\[ v_{\text{measured}} = v_{\text{true}}\cos\theta \]

Velocity is most accurate when the beam is parallel to flow. Doppler misalignment causes velocity and pressure-gradient underestimation.

Simplified Bernoulli equation¶

\[ \Delta P = 4v^2 \]

\(\Delta P\): pressure gradient in mm Hg
\(v\): peak velocity in m/s

Continuity principle¶

Flow proximal to an orifice equals flow through the orifice:

\[ \text{CSA}_1 \times \text{VTI}_1 = \text{CSA}_2 \times \text{VTI}_2 \]

Small errors in diameter measurement are magnified because cross-sectional area depends on the radius squared.

Image Optimization¶

Obtain the correct imaging plane.
Reduce depth so the structure of interest fills the display.
Narrow sector width when possible.
Position the focal zone near the structure of interest.
Adjust overall gain and time-gain compensation.
Optimize compression and dynamic range.
Increase frame rate when evaluating rapid motion.
Align Doppler parallel to flow.
Adjust the Doppler baseline and velocity scale.
Confirm abnormalities in multiple views.

Use an ultrasound-enhancing agent when clinically indicated and native endocardial definition is inadequate.

Clinical Context¶

Interpret the study with attention to:

Indication
Rhythm and heart rate
Blood pressure
Body size
Preload and afterload
Mechanical ventilation
Vasoactive medications
Study quality
Use of an ultrasound-enhancing agent
Prior echocardiograms or other cardiac imaging

Loading conditions may substantially alter ventricular function, valve severity, pressure estimates, and Doppler measurements.

Reporting¶

A complete report should document:

Indication
Technical quality and limitations
Rhythm and relevant hemodynamics
Chamber size and function
Valve anatomy and function
Doppler hemodynamics
Pericardium, IVC, and visualized aorta
Comparison with prior imaging
Prioritized conclusion

Suggested opening:

INDICATION:
[Clinical indication]

TECHNICAL QUALITY:
Acoustic windows were [adequate/technically difficult/limited].
[An ultrasound-enhancing agent was administered.]

RHYTHM AND HEMODYNAMICS:
The patient was in [rhythm] at approximately [heart rate] bpm.
Blood pressure was [value] mm Hg.

COMPARISON:
[No prior study was available for comparison.]
[Compared with the study dated _____.]

Pitfalls¶

Apical foreshortening
Off-axis measurements
Excessive or inadequate gain
Doppler misalignment
Incorrect sample-volume placement
Tracing incomplete Doppler envelopes
Using a single parameter to grade disease
Ignoring rhythm and loading conditions
Comparing serial measurements obtained by different methods
Reporting precise measurements despite inadequate image quality

Key Points¶

Higher frequency improves resolution but reduces penetration.
Reflection forms anatomic images; scattering underlies Doppler.
Reduce depth and sector width to improve frame rate.
Doppler should be aligned parallel to flow.
Confirm abnormalities in multiple views.
Interpret measurements in the context of rhythm, blood pressure, loading conditions, and image quality.