Function by 2D and 3D Echocardiography using STE

This section of the website is dedicated to the use of 3D echocardiography for functional assessment of the Right and Left Ventricle (RV and LV). We are using, in the NeoCardioLab, the Philips Epiq-7 machine with the X6-1 and X5-1 transducers (Pediatric and Adult xMatrix Array Transducers). We are also using the TomTec arena software in order to obtain LV and RV volumes. This website will not be discussing the use of 3D echocardiography for anatomical evaluation, valvular structural assessment or trans-esophageal evaluations.

Background overview

Speckle Tracking Echocardiography (STE) is an advanced echocardiographic technique that allows for the quantitative assessment of myocardial deformation, offering a more precise understanding of cardiac function than conventional methods.

1. Fundamentals of Cardiac Function

Cardiac function is a continuous process involving the filling of the ventricles and the ejection of blood into the outflow tracts. This complex process is dependent on several factors:

• The unique architecture of each ventricle.

• The afterload of the outflow tract(s), which represents the resistance the ventricles must overcome to eject blood.

• The cross-talk between the right ventricle (RV) and left ventricle (LV), which can be disturbed in abnormal cardiac architecture. This interaction is influenced by independent and shared muscle fibers, as well as a common multi-layer septum.

• Precise activation by the conducting system and fibers to ensure synchrony (coordinated contraction) versus dyssynchrony (uncoordinated contraction). The interventricular septum (IVS) activates first (left to right), and the ventricles activate from the endocardium to the epicardium.

The cardiac cycle is divided into two main phases: Systole (contraction and ejection) and Diastole (relaxation and filling). These phases include periods of isovolumetric contraction and relaxation where intracardiac volumes remain stable (unless there is valvular insufficiency).

Left Ventricular (LV) Contraction and Relaxation

The LV has a bullet shape, though this can be altered by congenital defects or loading conditions. Its contraction is primarily circumferential (towards the inside of the cavity, with the circumference of the circular cross-section reducing throughout systole) and involves torsion (a wringing movement), with a minor contribution from longitudinal contraction.

• Torsion/Twisting: The LV apex rotates counterclockwise, and the LV base rotates clockwise when viewed from the apex and at the subepicardial level (fibers goes in different directions at subendocardial level). This twisting motion aids contraction by supporting fiber direction in the subepicardium and enhancing circumferential shortening in the midwall.

• During relaxation, the base rotates counterclockwise and the apex clockwise. The rate of untwisting provides insight into diastolic function.

• Radial Contraction: When the LV muscle contracts, it also undergoes radial thickening, increasing its wall thickness. The subendocardial fibers are sheared towards the LV cavity, leading to LV wall thickening.

Right Ventricular (RV) Contraction and Relaxation

The RV has a distinct conformation compared to the LV, with fibrous discontinuity between its tricuspid and pulmonary valves (the pulmonary valve sits a "tube" of muscle, the conus). The RV contracts predominantly longitudinally with a peristaltic “bellows” motion, pushing blood from the inflow tract to the RV outflow tract (RVOT). This involves the IVS bulging into the RV cavity and the free wall moving towards the IVS. The peak speed at which the free wall expands offers insight into RV diastolic function. The movement of the tricuspid valve during systole (TAPSE) is an easily obtainable marker of RV function.

2. What is Speckle Tracking Echocardiography (STE)?

STE involves identifying and tracking "speckles" (echodensities or pixels) that form the ultrasound images. By tracking these speckles frame-by-frame, the software measures the magnitude or percentage of myocardial deformation. This allows for regional and global quantification of myocardial strain and strain rate, providing insights into myocardial function and synchrony.

2.1 Key Measurements in STE

• Strain: Represents the absolute percentage of deformation of each myocardial segment and the overall ventricle. It is defined as the distance modification between two points. Example: the perimeter outlined is 10 cm in diastole, and 8 cm in systole; the strain will be (10-8)/10=20%. It is negative because it is a "shortening" so -20%. 

  • Interpretation of Values:

    • Negative Values: Indicate shortening of the myocardial fibers, typically seen in longitudinal and circumferential contraction during systole.

    • Positive Values: Indicate lengthening (during diastolic relaxation) or thickening (during radial contraction in systole).

  • Types of Strain:

    • Longitudinal Strain: Measures shortening from base to apex.

    • Circumferential Strain: Measures shortening around the circumference of the ventricle.

    • Radial Strain: Measures thickening of the myocardial wall.

• Strain Rate: Measures the speed at which strain occurs (deformation per second; 1/sec unit). While some studies suggest strain rate is less sensitive to preload and afterload changes, there remains some debate.

• Displacement: This is the actual distance the tissue travelled. It can be measured in different planes: the longitudinal, the transverse planes for example. The base of the RV is displaced towards its apex during contract. We can evaluate the absolute displacement in mm of distance. 

  • Velocity: The velocity in this context is the speed of this displacement in mm/sec.

• Rotational Mechanics:

  • Rotation: Assesses the angular movement of the LV base (clockwise, negative values) and apex (counterclockwise, positive values).

  • Twist: Calculated as the difference between apical and basal rotation (Apical – Basal).

  • Torsion: Twist normalized by the length from base to apex (Twist / Length in degrees/cm). Normal values are typically 1.5-2°/cm.

• Time to Peak (TTP): The time it takes for each segment to reach its peak deformation. This is used to assess synchrony or dyssynchrony (differences in contraction timing) between different myocardial regions.

2.2 Advantages of STE

• Less Angle Dependent: STE is less affected by the angle of image acquisition.

• Detects Subclinical Disease: EF might be preserved despite abnormal regional deformation in subclinical disease or myocardial infarction (MI). STE can identify local areas of decreased contractility that might be "tethered" (pulled) by healthier surrounding myocardium, appearing to move normally on conventional imaging, as surrounding tissue may compensate. 

• Comprehensive Analysis: Allows for detailed segmental analysis, assessment of myocardial expansion rate during diastole, and circumferential, radial, and rotational evaluation of the LV.

• Quantifies Speed of Deformation: Beyond just the magnitude, STE also quantifies the speed (strain rate) at which deformation occurs.

3. 2D Speckle Tracking Echocardiography

2D STE captures myocardial motion within a single imaging plane.

3.1 Technical Requirements for 2D STE Acquisition

High-quality image acquisition is critical for accurate STE analysis:

• ECG Gating: Essential for timing cardiac events (e.g., end-systole and end-diastole). M-mode tracing can also be used if ECG gating is unavailable or for specific timing.

• High Frame Rate: A minimum of 30 to 70 frames per second (FPS) is required, with at least 70 FPS being a target for better time resolution and tracking.

• Raw Images: Raw, uncompressed image data is essential for STE quality. Typical PACS systems often compress images to 20-30 FPS, even if recorded at a higher rate, which can compromise STE quality if analysis is performed post-processing. Therefore, STE analysis is often performed directly on the echocardiography machine during acquisition or immediately after.

• Optimal Visualization: Requires excellent visualization of the endocardial border to ensure good contrast with the blood pool. Narrowing the imaging sector and zooming in on the structure of interest can help increase frame rate and image quality.

3.2 2D STE Analysis Process

The process for 2D STE analysis typically involves:

1. Selecting Appropriate Views: For the LV, apical 2-chamber (A2C), 3-chamber (A3C), and 4-chamber (A4C) views are used for longitudinal strain assessment. Parasternal short axis (PSA) views at the valvular, mid-papillary, and apical levels are used for circumferential, radial, rotation deformation. For the RV, a modified apical 4-chamber view is often used to focus on its predominant longitudinal contraction. LA and RA views are optained from the apical view typically for obtaining the atrial strain. 

2. Identifying Cardiac Cycles: Two consecutive cardiac cycles (beats) are typically selected for analysis, with the software averaging the data from these cycles.

3. Defining Cardiac Phases: The software identifies the R-wave from the ECG, and the user (or auto-tracking) defines the end-systole and end-diastole points.

4. Tracing Endocardial Borders: The user traces the endocardial border (and sometimes epicardial for radial strain) in one frame (e.g., end-diastole). The software then automatically tracks this border throughout the cardiac cycle.

5. Quality Control: The tracking quality is visually confirmed. If tracking is poor, manual adjustments can be made.

6. Data Output: The software generates global and segmental strain and strain rate values, typically displayed as curves over time. A "Bow's Eye" plot is a common topographic map showing strain values across 17 or 18 myocardial segments.

7. Interpretation: Values are assessed for magnitude, timing, and synchronicity.

3.3 Normal Reference Values (Adults)

Typical adult values reported in literature include:

• LV Longitudinal Strain (pGLSs): -15% to -20% (or -20% by VVI).

• LV Circumferential Strain: -20% to -25% (or -28% by VVI).

• LV Radial Strain: +30% to +40% (or +30% by VVI).

• LV Twist: Approximately 9.9°.

• Torsion: Approximately 1.5-2°/cm.

Note: Pediatric and age-specific normal values also exist. Vendor algorithms for strain derivation may vary, so using the same vendor's software for longitudinal follow-up is recommended for consistency.

4. 3D Speckle Tracking Echocardiography

3D STE allows for the capture of entire ventricular volumes, providing a more holistic and often faster assessment of global cardiac function than 2D methods.

3D Acquisition Techniques

• Multi-beat Acquisition: Reconstructs a full 3D volume by stitching together information from several consecutive heartbeats. While offering high resolution, it carries a risk of "stitch artifacts" if the patient moves or has an irregular rhythm.

• Single-beat (High Volume Rate) Acquisition: Captures the entire 3D volume within a single heartbeat, minimizing stitch artifacts. This method requires specialized matrix-array transducers and high frame rates (e.g., >30 Hz).

• Simultaneous Multi-plane Imaging (xPlane): A technique that captures multiple orthogonal planes simultaneously, allowing for live capture of volumetric information.

Once a 3D volume is acquired with high temporal resolution, STE algorithms can be applied to track speckles in three dimensions. This allows for the derivation of various functional parameters, including:

• Ventricular Volumes: End-diastolic volume (EDV) and end-systolic volume (ESV), from which ejection fraction (EF) can be accurately calculated.

• Global Strain and Strain Rate: Longitudinal, circumferential, and radial strain can be assessed globally across the entire ventricle.

• Rotational Properties: More robust assessment of LV twist and torsion.

• Time to Peak: Volumetric data allows for comprehensive assessment of global and regional synchrony.

The main advantages of 3D STE include its ability to overcome the limitations of 2D views by providing a complete volumetric assessment and its potential for more rapid quantification of comprehensive cardiac function. It can also generate a detailed "cartography" or map of the heart's performance.

Cardiac Function - Right and Left Ventricles

Represents the continuous process from filling of the ventricle(s) to ejection in the respective outflow tract(s)

• • Dependent on architecture of each ventricles (or of the single ventricle)

  • Dependent on afterload of outflow tract (s)

  • Cross-talk between RV-LV (disturbed in abnormal architecture)

    • Independent and shared fibers / common multi-layer septum

  • Precise activation by conducting system and fibers (synchrony vs dyssynchrony)

  • This can be altered if there is fibrosis, inflammation, ischemia

  • Coronary perfusion is essential for adequate myocardial oxygenation, as well as meeting metabolic needs - one may see an arrhythmia as demanding a lot of oxygen and energy substrates. 

  • Coronary perfusion is also essential for the pathways transmitting the electric impulse. Adequate cardiac perfusion is also important for the relaxation. 

  • Fibrosis/scarring may impact the diastolic function (and relaxation). These anomalies may be diffuse or circumscribed - leading to some inhomogeneity in contraction or relaxation. 

  • Activation and relaxation may happen at different timepoints if there is inhomogeneity in activation or disturbed spread of electrical impuse. 

  • Electrical activation usually through the interventricular septum first (left part to right right part) (if there is a septum and if it is of normal configuration). This may be altered in certain congenital heart defects (example: ccTGA). Very good article here on cardiac conduction system in ccTGA.

  • Ventricles get activated from the endocardium to the epicardium

All this results in “2 classical phases” of cardiac cycle that we divide (traditionally) between systole (which results eventually in ejection) and diastole (which results in ventricular filling). There is a phase of isovolumetric relaxation and isovolumetric contraction. 

Below is a great depiction of the left ventricle in 3D by computational reconstruction. One can see the circumferential contraction, the radial thickening of the myocardium during the contraction, as well as the wringing effect (rotational properties) of the various layers of the LV. This is a YouTube video and the profile of Dr Rossi on ResearchGate can be accessed here.

By convention

• Positive values (+) when thickening, Negative values (-) when thinning

  • Example: Longitudinal systolic strain is negative, longitudinal diastolic strain is positive, radial systolic strain of the LV is positive, radial diastolic strain of the LV is negative. 

    • If shortening during systole (longitudinal and circumferential), strain and strain rate values are negative 

    • Lengthening (diastolic relaxation) or thickening (radial contraction) = positive.

• Rotational mechanics of the LV can be assessed in 3D and in 2D.

  • When assessed at the base, contraction is usually a clockwise rotation as viewed from the apex and expressed in negative values 

  • When assessed at the apex, it is usually counterclockwise as viewed from the apex and expressed in positive values 

  • Twist = Rotation at Apex – Rotation at the base 

  • One may also evaluate the untwisting rate during diastole 

• Electrocardiogram gating is necessary with the highest frame-rate. We usually aim in the lab to be at a minimum of 70 frame per second. Ideally, one should narrow the sector around the structure of interest and save the clips in raw data.  

  • Typical PACS will integrate ECHO images at a compressed 20-30 FPS despite recording at a higher Frame Rate. Need to ensure the setup of the machine. 

  • Raw images are rarely sent via PACS but are essential for STE quality. 

  • If no ECG available, may use the M-Mode in order to time the various periods of the cardiac cycle.

• EF might be preserved despite abnormal regional deformation in subclinical disease

  • Myocardial infarction: local area of decreased contractility tethered by more healthy myocardium and move during systole, despite not actively participating to the efficient contraction 

• Auto-tracking gives you FAC and EF evaluation; as well as estimated LV volumes

• For analysis, requires:

  • ECG gating or M-Mode traced by the software to time End Systole and End Diastole. 

• For Peak global longitudinal SYSTOLIC strain and strain rate, needs:

  • Time from R wave to Aortic valve closure for LV

    • PW of LVOT in 3 chamber

  • Time from R wave to Pulmonary valve closure for RV

    • PW of RVOT either by anterior sweep in apical, or in PSA

• For Peak GLS (global longitudinal strain):

  • A2C, A3C and Apical 4 chambers with good view of LV – 2-3 beats

  • If only A4C: Peak Longitudinal Strain: lateral and septal wall. 

  • PSA: view at valvular level, mid-papillary (typical) and apex for LV

Summary:

The LV contracts in a wringing (in french, we say: "essorage") motion (the apex and the base will rotate in different directions; with a gradient from the endocardium to the epicardium) and with a contraction towards the inside of the cavity (circumferential). The longitudinal aspect of contraction is not as pronounced as the longitudinal contraction of the RV. 

The RV, which has fibrous discontinuity between the AV valve (usually a tricuspid) and the Outflow tract (usually a pulmonary valve), will contract in a bellow motion with the inflow going towards the outflow, the free wall going towards the septum and the septum going towards the free wall (assuming there is no increase RV afterload, there is adequate spread of electrical activation and the conformation is as expected - ie: no VSD, etc). 

When we look at the LV, we can look at the global circumferential strain (% deformation towards the inside of the cavity) and torsion (gradience of difference of degrees of rotation from Apex to base of LV). 

For the RV, we can look at the RV free wall and septal longitudinal strain. 

Global just means we take free wall and septal together. 

Knowing that the LV is bullet shape, we often talk about "peak global longitudinal strain" (pGLS) when assessing the deformation in the longitudinal planes of all the standard views in 2D (A2C, A3C, A4C) or in full 3D volume. 

We talk about "peak longitudinal strain"  (pLS) when we have only one plane (example: A4C). 

We talk about "peak" (pGLS, pGCS - circumferential, pGRS - radial, pEDSR - peak early diastolic strain rate, pGLSR - peak GLS rate) - when we assess the peak at the contraction or relaxation. 

We talk about "pGLSs" (systolic) when we match the curves with the aortic valve opening and closure. 

"Deformation analysis" encompasses the assessment of % (strain), speed (strain rate), displacement (distance of movement), degrees (torsional properties) of the deformational properties of the ventricles. These properties can be assessed for segments, for global ventricle, in systole and in diastole. 

Although theoretically STE is less influenced by preload status compared to other standard measure of functions using 2D ECHO, TDI, M-Mode, etc... all these measures are realistically influenced by preload for the RV or the LV.

This article is key at explaining the Twisting mechanics of the LV

2D examples

3D examples

These are 2 presentations in PDF that are publicly available on the website of the ASE. You can access them by clicking here and here. The presentations are from Dr Wendy Tsang, from the University of Toronto at Toronto General Hospital. They are among the best presentations available on the web teaching on the use of 3D echocardiography. Please make sure to visit the UofT website on Virtual TEE. You can find the ResearchGate profile of Dr Tsang here. I have put the linked PDF from the ASE website available here:

Segmentation of the left ventricle

Good resource to check here: https://www.thinking3d.ac.uk/Echocardiography/ 

Important article:

Dorobantu, Dan M., et al. "The role of speckle tracking echocardiography in predicting mortality and morbidity in patients with congenital heart disease: a systematic review and meta-analysis." Journal of the American Society of Echocardiography (2023).

Ferraro AM, Harrild DM, Powell AJ, Levy PT, Marx GR. Evolving Role of Three-Dimensional Echocardiography for Right Ventricular Volume Analysis in Pediatric Heart Disease: Literature Review and Clinical Applications. J Am Soc Echocardiogr. 2024 Jun;37(6):634-640. doi: 10.1016/j.echo.2024.03.001. Epub 2024 Mar 11. PMID: 38467312.

Speckle Tracking Echocardiography in French 

Echocardiographie par suvie de pixel en français

Presentation (PDF) on STE principles