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Atrial Structure and Function – Methodology of Atrial Strain

“If echocardiographers are to stand still, depend on standard 2D echo imaging using equipment produced a decade ago and not upgraded since, perform “ejectionfractionograms,” focus primarily on the left ventricle and simply ‘‘eyeball’’ the other chambers, and avoid new methods such as strain imaging and contrast echo because they are perceived as ‘‘a waste of time’’, then I fear that echocardiography will be passed by. As the dinosaurs illustrated, we need to adapt and continue to evolve, or face the consequences.”   –Alan Pearlman- JASE editor, 2010

My research experience focused on heart failure and atrial function. I conducted medical research on the derivation and validation of novel echocardiographic approaches to myocardial and atrial deformations. I have been heavily involved with all projects using strain echocardiography at Duke University (approximately 50 projects over the last 7 years). I have completed over 10,000 speckle tracking strain measurements analysis on different cardiac diseases and on different cardiac chambers.

Both left and right atrium function moderate ventricular function through three components:

  1. Atrial diastole (Reservoir phase) or expansion during ventricular systole. This function is dependent on ventricle longitudinal function, atrial wall elastance and venous return. Reservoir function may increase during physical activity in a normal healthy heart. Increase of this phase help to increase ventricular filling.
  2. Passive atrial systolic phase (Conduit function) during ventricle early diastole. This phase is dependent on the ventricle end-diastolic pressure. Conduit function does not affect by physical activity.
  3. Active atrial systolic phase (Active contraction) (when sinus rhythm is present) during ventricle late diastole. This phase is dependent on atrial wall contractile properties and ventricular end diastolic pressure. Active contraction function is affected by physical activity in a normal heart.

Traditionally atrial function was measured indirectly by using volumes. However, this is still not resembling the actual atrial deformation and mechanics. With a high feasibility and reproducibility of speckle tracking strain echocardiography, atrial function is ready to be a part of an echo report in a daily clinical practice.

Speckle tracking strain imaging has been around for quite a while and we celebrated the first decade 3 years ago, whereas the technique described in 2004 (Leitman M-JASE) and clinical applications appeared around 2005 (Notomi Y- JACC). Since then, the interest has risen dramatically and so far, we have > 5000 publications on this topic. Left ventricular (LV) ejection fraction (LVEF), the most widely used measure of cardiac function, has important limitations including low sensitivity for incident HF, technique-related variability and does not directly assess LV contractility. Global longitudinal strain (GLS) is the most studied among strain parameters and its prognostic value has been demonstrated in several clinical scenarios.

GLS inter-Vendor variety has dramatically dropped over a short period of time. However, still if we look at the same images with different software vendors, we may have different values. This difference is due to several factors: 1) Image quality and acquisition; 2) Software used; 3) Where to measure (endocardial, myocardial, median); 4) Post-processing of data; 5) Patients age, gender variabilities and loading conditions. With regard to regional (segmental) function, we now have, for the first time, the possibility to measure regional myocardial function. However, I think this is more challenging than GLS, and there is still progress to be made. The challenges become because we have only one segment to work with, and less data to average. Tracking quality becomes more important, regional artifacts matters more, definition of sample position more relevant, and more importantly, we cannot simply measure peak values anymore. For regional analysis, the strain curve shape (not peak values, because peak values can be the same), become critical.

atrial function and structure

Technical factors that may influence atrial strain values:

  • Optimization of images quality and frame rates are vital (ideally, no less than 40 fps).
  • Start tracing at the lateral valve annulus, along the endocardial border of the atrial lateral wall, atrial roof, atrial septal wall, and ending at the septal valve annulus.
  • Difficulties tracking atrial segments relate to the thin wall, insertion of blood vessels and atrial appendages.
  • Significant age-related reductions in strain have been reported. Similarly, sex-related differences have been described, with lower deformation noted in male patients than in female patients.
  • Atrial strain increases in response to early physiological heart rate increase in the setting of exercise in normal patients. However, decreased values are found in the setting of pathological heart rate increase.
  • Atrial strain also affected by loading condition. Reporting, BP, HR and heart rhythm, IVC diameter are crucial.
  • Atrial phases function (Reservoir, conduit and atrial) is also dependent on the ventricular function. Report both atrial and ventricular functions are important.
  • Atrial strain maybe useful as an early marker of DD.

In summary, I think GLS is ready for clinical practice. Its robust, reproducible and has been shown to add unique data that can guide diagnosis and management. I recommend GLS as a valuable complement to traditional function parameters. Further studies are needed to standardize vendors, recognizing specific strain patterns and to determine if there are age, gender variabilities or loading conditions difference.

 

References:

Myocardial Strain Measured by Speckle-Tracking Echocardiography: Patrick Collier, MD, PHD, Dermot Phelan, MD, PHD, Allan Klein, MD VOL. 69, NO. 8, 2017 – ISSN 0735-1097

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Right Ventricular Structure and Function

The effect of anticancer medication on the (LV) function and structure has been extensively investigated in comparison to the right ventricle (RV). In general, it’s known that deterioration of RV function is associated with significant morbidity and mortality. However, despite advancement in echocardiographic and other imaging techniques, the RV assessment remains challenging in comparison to the LV. In this short statement I will summarize some of the RV characteristics and distinguish

First: The right and left ventricles have distinct morphological difference. Embryologically, the RV is derived from the secondary heart field whereas the LV is derived from the primary heart field. The RV has crescentic non-ellipsoidal configuration and three anatomic divisions (an inlet region, trabeculae free wall/ apical region and an outflow tract). In addition, the RV mass and wall thickness is about 1/3 of the LV.1

Second: The RV has different cardiodynamics:

  1. The RV contraction is sequential and peristaltic: started by the RV inlet toward the trabecular free wall and end up with infundibulum. Rather than the LV contraction which is uniform, longitudinal and torsion. In case of RV volume or pressure overloads it’s become more uniform in contraction.
  2. The RV has 3 separate mechanisms of contraction:1
    1. Free wall inward movement “bellows – like effect) that is dependent on the moderator/ septomarginal band’s position and contractility.
    2. Contraction of longitudinal fibers (shortens long axis TV annulus toward apex)
    3. Traction of free wall from septal LV attachments.
  3. Shortening of RV is much greater longitudinally (75%) than radially (25%). The radius of the curvature and RV surface area do not change appreciably.
  4. The epicardial layer is mainly made with circumferential muscle and the endocardial is mainly made with longitudinal muscle loop. In comparison, the LV has helix that formed by ascending and descending obliquely oriented loops. Thus, twisting and rotational movements do NOT contribute significantly to RV ejection in compare to the LV.

Third: The RV surface/ volume ratio is high, therefore, a smaller free wall inward motion is required to eject the same amount of the LV stroke volume. Also, the RV isovolumetric contraction and relaxation are shooter than the LV, simply, because the pulmonary artery diastolic and RV filling pressure are low. In addition, about 30% of the RV systolic and stroke volume occur due to the interventricular septum (IVS) by the phenomena called “systolic ventricular interdependence.”1

Forth: Proper IVS position and contractile function are crucial for the RV function. The IVS function and curvature are modified in response to any pressure or volume overload. Under normal RV pressure, the IVS is concave toward the LV in both systole and diastole. However, in patient with pulmonary hypertension the IVS curvature become more convex shape which may help the RV to eject more blood against high pulmonary pressure.1,2

Fifth: RV failure occurs under almost two conditions, excessive RV afterload and IVS dysfunction. The most important determinant of the RV function is:1,2

  1. RV afterload (Vascular resistance and compliance)
  2. RV contractility (systolic function)
  3. The coupling of RV contractility to RV afterload
  4. Pericardial constraint/RV-LV diastole interactions

The RV function and structure assessment is challenging. An ideal index of contractility should be independent of afterload and preload, sensitive to change in inotropy, independent of heart size and mass, easy and safe to apply, and proven to be useful in the clinical setting.1,2 Invasively, the gold standard measure of RV function still the volume/ pressure relationship. The most clinically used measures of RV systolic function (RVEF, RV FAC, TAPSE, S’ tricuspid valve velocity, RV SV, strain and RVMPI) are load dependent. Just like the LV, we are slowly evolving into global longitudinal strain (GLS). Important to remember that LV GLS is a surrogate of LV ejection fraction (LVEF) and the dichotomy between the LVEF and GLS can be explained by global circumferential strain (GCS), (Figure 1).

Figure 1: Right ventricular structure and function

References:

  1. François Haddad, MD; Sharon A. Hunt, MD; David N. Rosenthal, MD; Daniel J. Murphy, MD Right Ventricular Function in Cardiovascular, Part I. Circulation 2008, 117:1436-1448
  2. François Haddad, Ramona Doyle, Daniel J. Murphy and Sharon A. Hunt. Right Ventricular Function in Cardiovascular Disease, Part II. Circulation 2008, 117:1717-1731

 

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Cardiac Longitudinal Function: GLS vs. MAPSE

Over the history of echocardiography, there have been a multitude of research studies on the feasibility, reproducibility and the prognostic values of different echocardiographic parameters in different disease groups. Fifty years later, no single echocardiographic parameter is unique for assessment of the cardiac structure and function. Even the most widely used measurement for left ventricle ejection fraction (LVEF) has important limitations, including low sensitivity for incident heart failure (HF), specifically HF with preserved ejection fraction (HFpEF). With the advent of speckle tracking echocardiography (STE), early detection of cardiac dysfunction before signs or symptoms of HF develop (stage A or B HF) has become a target of many researchers in the last 15 years. Although, there has been some success, there is still a long way to go. In this blog, I want to discuss the differences, advantages and the limitations of mitral annular plane systolic excursion (MAPSE) vs. global longitudinal strain (GLS).

MAPSE measures LV longitudinal shortening and it has been around for over 50 years. Reduction in MAPSE was described as a marker of LV dysfunction (Figure 1). Nowadays, newer and more refined echocardiographic technologies, such as strain, are used more widely for assessment of LV function and deformation. STE imaging has been around for quite a while and we celebrated it’s first decade just 4 years ago, whereas the technique described in 2004 (Leitman M-JASE) and clinical applications appeared around 2005 (Notomi Y- JACC). Since then, the interest has risen dramatically and so far, we have around 6,000 publications on this topic. GLS is the most studied among strain parameters and its prognostic value has been demonstrated in several clinical scenarios.

Figure 1: GLS vs. MAPSE – Fawaz Alenezi -2019.

 

MAPSE (cm) GLS (%)

Technique

  • Real time or reconstructed M-mode
  • Measure mitral annular displacement
  • Speckle tracking
  • Measure myocardial deformation
Advantages
  • Less dependent on image quality and almost (> 95%) is feasible
  • Good correlation with LVEF
  • Simple and fast
  • Excellent reproducibility
  • High temporal resolution
  • More standardized
  • Better than LVEF in some cases
  • Vendor independent
  • Not gender or BSA dependent
 

  • Assess regional and global longitudinal/radial/circumferential function, rotation/torsion, and ventricular synchrony
  • Less angle dependent
  • Better than LVEF in some cases
  • Good correlation with LVEF

 

Disadvantages
  • Unable to detect regional abnormalities
  • Angle dependent
  • Age dependent
  • Pericardial effusion: The interpretation of MAPSE should be carefully applied in case of a mobile apex.
  • RV dysfunction: In patients with paradox septal motion, septal MAPSE is not only reflecting LV function but rather RV abnormalities
  • Mitral valve disease and ring calcification: Sometimes in patients with mitral valve disease, the mitral ring is extremely calcified. In these patients, the direct MAPSE measurement at the mitral ring is not possible and longitudinal functional assessment should be done slightly more above in the myocardium
  • Septal MI: Another limitation of this parameter is that small localized abnormalities (i.e. small areas of fibrosis) cannot be detected as it is only possible to assess longitudinal function of the complete wall
  • LVH: In patients with LVH due to HTN or AS will have different values
 

  • Vendor dependent
  • Although, assessment of regional function is the main advantages of strain, but studies still showing a large variability and is not ready to clinical use
  • Variable in region of interest definition
  • Highly dependent on image quality
  • Gender and BSA dependent
  • Need experience and time consuming
  • Pre and after load dependent
  • Rhythm and rate dependent
  • Frame rate dependent

Table 1: Advantages and limitations of GLS vs. MAPSE- Fawaz Alenezi – 2019

 

What is thought to be the main advantage of STE over MAPSE is the ability of global and regional function assessment. However, with regard to regional (segmental) function, I think this is more challenging and there is still progress to be made. The challenges exist because we have only one segment to work with and less data to average. Tracking quality becomes more important, regional artifacts matters more, definition of sample position more relevant, and more importantly, we cannot simply measure peak values anymore. For regional analysis, the strain curve shape (not peak values, because peak values can be the same) become critical. Regional strain measurements have much higher variability among vendors when compared with GLS. Recently, the HUNT study (Stoylen A et al. 2018 –Wiley echocardiography journal) showed that MAPSE and GLS measured both as MAPSEn (n= normalized for end diastolic length) and GLS have similar biological variability in adults without improvement by normalizing for length for both.

In summary, I think both GLS and MAPSE are measuring the same cardiac function. GLS is robust, reproducible and has been shown to add unique data that can guide diagnosis and management. However, it is vendor, image quality and hemodynamics dependent that need more standardization and experience. On the other hand, MAPSE is simple, easy, available in every echo machine and, more importantly, feasible even in a poor image quality. But it is not measuring the global function. Further studies are needed to standardize vendors, recognize specific strain patterns, determine if there is loading conditions difference and head-to-head comparison between both methods.