Right Ventricular Strain: Clinical Application

Satish Chandra Govind

doi:10.4103/jiae.jiae_48_23

REVIEW ARTICLE

Year : 2023 | Volume : 7 | Issue : 2 | Page : 168-173

Right Ventricular Strain: Clinical Application

Satish Chandra Govind
Department of Noninvasive Cardiology, Narayana Institute of Cardiac Sciences, NH Health City, Bengaluru, Karnataka, India

Date of Submission	12-Aug-2023
Date of Acceptance	19-Aug-2023
Date of Web Publication	30-Aug-2023

Correspondence Address:
Satish Chandra Govind
Department of Noninvasive Cardiology, Narayana Institute of Cardiac Sciences, NH Health City, 258/A, Bommasandra, Hosur Road, Bengaluru - 560 099, Karnataka
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jiae.jiae_48_23

Abstract

For many decades assessment of right ventricular function has been a challenge, with several parameters available for use but none being reliable and accurate. The oldest and still the most widely used is tricuspid annular plane systolic excursion (TAPSE), which has its own technical limitations. Later, the arrival of tissue Doppler imaging provided an additional parameter, with its measurement of peak systolic velocity of the lateral annulus of the tricuspid annulus, but this being angle-dependent also showed limited utility, like TAPSE. The advent of speckle-tracking echocardiography over the last decade, which is not angle-dependent and less load dependent, heralded a new way of looking at the RV function landscape. Despite some technical challenges, it has shown itself to be acceptable and has increasingly been used as a reliable parameter in clinical settings over the last few years. It has been recommended as a parameter with high feasibility and reproducibility.

Keywords: Deformation imaging, echocardiography, right ventricle, right ventricle function, speckle tracking echo, strain echo

How to cite this article:
Govind SC. Right Ventricular Strain: Clinical Application. J Indian Acad Echocardiogr Cardiovasc Imaging 2023;7:168-73

How to cite this URL:
Govind SC. Right Ventricular Strain: Clinical Application. J Indian Acad Echocardiogr Cardiovasc Imaging [serial online] 2023 [cited 2023 Sep 27];7:168-73. Available from: https://jiaecho.org/text.asp?2023/7/2/168/384776

Introduction

For many decades assessment of right ventricular (RV) function has been a challenge, with several parameters available for use but none being reliable and accurate. The oldest and still the most widely used is tricuspid annular plane systolic excursion (TAPSE), which has its own technical limitations. Later, the arrival of tissue Doppler imaging (TDI) provided an additional parameter, with its measurement of peak systolic velocity of the lateral annulus of the tricuspid annulus, but this being angle-dependent also showed limited utility, like TAPSE. The advent of speckle-tracking echocardiography (STE) over the last decade, which is not angle-dependent and less load dependent, heralded a new way of looking at the RV function landscape. Despite some technical challenges, it has shown itself to be acceptable and has increasingly been used as a reliable parameter in clinical settings over the last few years. It has been recommended as a parameter with high feasibility and reproducibility.^[1] Two-dimensional RV strain correlates well with RV ejection fraction, stroke volume and right atrial (RA) pressure. This article focuses on RV mechanics, strain techniques and clinical application.

Mechanics of the Right Ventricle

RV has an unusual shape (crescentic) with a highly compliant cavity and is characterised by a low-pressure chamber. It is very distensible and can accommodate large volumes but has a limited ability to withstand increased pressures. The adaptability of RV to changes in pressure (hypertrophy), volume (dilatation) and increased contractility determine its functionality and outcome. RV is characterised by smaller cardiomyocytes, hence a thinner wall (<5 mm), three walls (anterior, inferior, and lateral, also called free wall), and an inlet, apex, and outlet.^[2] In a normal person, the outlet or infundibulum can hold about 20–25 mL of end-diastolic volume and is an important part of the cavity.

Present strain measurements interestingly focus only on the lateral wall and ventricular septum, which means a major part of RV (anterior and inferior walls along with the outlet) is excluded from its measurement. RV has two types of myocardial fibres: an outer epicardium (20%–25%) that is geometrically more circumferential and extends across into the left ventricle (LV), and the other is the inner endocardium (75%–80%) consisting of longitudinal fibres. RV contraction is predominantly longitudinal shortening in its long axis combined with radial motion due to circumferential shortening in its minor axis, and there is also the circumferential shortening of the outflow tract. The ventricular septal motion is closely intertwined with the LV because of the almost helical nature of the myocardial fibres within the septum; hence one would say that the septum is a shared structure between the two ventricles.

Right Ventricular Strain

Image acquisition

Proper image acquisition is the key to accurate strain measurement, and it is important to have a correct echocardiographic view for obtaining accurate 2D RV strain values. An ideal image acquisition should be:

From an RV-focused view [Figure 1]
An ideal RV-focused apical-4 chamber view should completely visualise the RV free wall, RV apex and tricuspid valve/annulus within the imaging sector during both systole and diastole. No structure should disappear out of the imaging sector at any part of the cardiac cycle
With an appropriate depth (intermediate depth), avoid an excessive anterior tilt (left ventricular outflow tract should not be seen) and avoid a posterior tilt (coronary sinus should not be seen)
Sector width should be optimised (limit the sector width as much as possible – keep it narrow) with a view to getting a good frame rate (between 50 and 80 fps)
Gain should be optimised, especially avoid under gain
Avoid imaging artifacts of any kind
A video loop with a steady image, with an electrocardiogram (ECG) gating, well-defined tall positive ECG complexes, and in sinus rhythm, with 3 beats and preferably with breath-hold, is acquired.

Figure 1: Right ventricular (RV) focused apical 4-chamber view showing how RV longitudinal strain is done. (a) RV focused view. (b) RV tracking by the software. (c) RV free wall segmental strain. (d) Waveforms of the three segments

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After image acquisition, STE is done per the vendor-specific semi-automatic software. All strain measurements are automatically provided by the software with colour coding. The image is assessed for the quality of tracking. If required, manual corrections are made:

Every segment region of interest (ROI) should be carefully observed for proper placement along the RV-free wall and ventricular septum. ROI thickness can be set at 5 mm in a nonhypertrophied RV-free wall and can be increased in a hypertrophied RV. Too thin an ROI (mainly on the endocardium) will result in spuriously high values
To avoid spuriously low values, ROI should not be too much into the cavity nor outside the cavity. For the outer contour, pericardial tracking should ideally be avoided completely or, at best, minimised to the lowest extent possible. The inner contour should be along the endocardial border, excluding trabeculations and papillary muscle
Ensure that the tracking stops at the tricuspid annulus and is not into the RA, nor should it be too much into the RV and away from the tricuspid annulus.

By observing the cine-loop of the image, correct tracking is confirmed of the RV free wall, RV apex and ventricular septum and is to the satisfaction of the user [Figure 2]. The measurements are then approved and analysed. Users must note that vendors may have different algorithms: Some measure strain at the endocardium, and some measure the full wall, which may result in different normal ranges. But despite this, inter-vendor variability is acceptable for RV FWS and RV GLS but not for regional strain due to its wide variation.

Figure 2: Right ventricular (RV) focused apical 4-chamber view showing normal RV longitudinal strain. RV-free wall strain is 33% and RV global longitudinal strain termed as RV 4-chamber strain is 25%. Regional strain values of basal, mid and apical segments are also seen. The waveforms of these segments are shown in the lower image. RV4CSL: Right ventricular 4-chamber strain longitudinal, RVFWSL: Right ventricular free wall strain longitudinal

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Analysis

Typically, two measurements are routinely sought:

RV global longitudinal strain (RV GLS): Includes the RV-free wall and the ventricular septum
RV-free wall strain (RV FWS): Excludes the ventricular septum.

There is still an ongoing debate about which parameter should be used, with RV FWS being shown to be superior to RV GLS as a better predictor of disease outcomes.

Less used parameters are:

The regional strain (base, mid and apical) of RV-free wall and ventricular septum
Ventricular septal strain.

Regional/segmental strain has been shown to have high variability; hence its measurements are viewed with caution, and its value in clinical application is very limited. The use of isolated ventricular septal strain has scant data about its utility and hardly any role in routine clinical assessment.

Normal values

Normal ranges for 2D RV strain:

RV GLS: 20%–25% (mean of 22%–23%)
RV FWS: 23%–33% (mean of 27%–28%).

The lower limit of normal has been reported at 14%–16% for RV GLS and 18% for RV FWS.

These values vary with different vendor software, and it is crucial that the user is aware of this and ensures that serial measurements are made on the same vendor software. Women have a higher strain, about 2%–6%. No significant differences have been found among different ethnic groups. With age there is a nonsignificant decrease in strain.

RV FWS can be further segmented as basal (normal value: 27%), mid (normal value: 28%) and apical (normal value: 25%)^[3]

Wide variations in various studies are reported: Some with the same values in all segments, some with increased basal strain, some with the highest in mid-segment, some with lowest in the basal segment and some with base to apex gradient

The ventricular septal strain has a mean of 19%–22% (lower limit of normal 12%) and is generally not used in clinical routine
In children, higher values of strain have been observed. RV GLS mean is 29%, with a wide normal range of 21%–34% in studies published so far.^[4]

Limited information is available on 3D RV strain, with available studies showing:

Normal mean values of RV GLS of 21% (lower limit of normal: 14%)
RV FWS of 26% (lower limit of normal: 16%)
Ventricular septal strain of 21% (lower limit of normal:14%).^[5]

3D RV strain shows promise in terms of its potential ability to assess the entire RV comprehensively (since data is obtained from 3 orthogonal planes in the same cardiac cycle). It has shown promise in the detection of subclinical RV dysfunction. But its lack of established normative ranges and its utility and reliability in a clinical routine yet to be proven, combined with technical problems of low spatial and temporal resolution, makes it an incomplete tool in its present state.

Limitations

RV being a thin-walled structure, wall tracking with a narrow ROI makes measurement of strain a big challenge and can be especially problematic in suboptimal echo window.^[6] Also, with the use of only one view (apical 4-chamber view) with quantitation of fibres in only one direction, the technique can be a challenge encountered in certain clinical situations [Figure 3].

Figure 3: Right ventricular (RV) focused apical 4-chamber view showing limitation of RV longitudinal strain. A grossly dilated RV is seen in cor-pulmonale. Note that the RV apex is out of the imaging sector, and it is not possible to do RV strain in such an image. RV4CSL: Right ventricular 4-chamber strain longitudinal, RVFWSL: Right ventricular free wall strain longitudinal

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The ventricular septum receives myocardial fibres from the LV and hence can be influenced by changes in the LV. Hence, changes in the ventricular septal strain and RV GLS may not truly reflect the RV abnormalities alone. RV is very sensitive to load, heart rate, and rhythm changes; strain values can vary accordingly. Also, the influence of RA, the truly forgotten chamber and its impact on RV mechanics and RV strain is still unknown.

Some of the earlier studies of RV strain were done using LV software, and some used a standard apical-4 chamber view. Also, the number of healthy subjects in the studies to date is limited, while normative data for the elderly and pediatric population is yet to be well established. It has been shown that women have higher values of RV strain. In view of the heterogeneity of available data of RV strain accumulated over the years and vendor variability, present reference ranges are a work in progress and are subject to change in the coming years.^[7]

Clinical Applications

RV abnormalities can be broadly categorised as:

Pressure overload
Volume overload
Cardiomyopathies.

Each of these abnormalities affects the RV mechanics in different ways; it can be isolated or mixed in its presentation.^[8] Chronic pressure overload goes through phases of initial concentric hypertrophy and later eccentric hypertrophy and dilatation. In such a state, long-axis motion gradually declines with a compensatory increase of the circumferential fibres.

Pulmonary hypertension

In pulmonary hypertension (PH) patients, conventional markers of RV function (like TAPSE and fractional area change) can be normal even though the RV strain is abnormal; thus, the strain is able to detect RV dysfunction quite early in the disease. Strain is more sensitive than traditional markers of RV function with even small changes in PH.^[9] In Group 1 PH, the decline in RV FWS is associated with a higher degree of disease progression within 6 months. 2D RV strain strongly predicts survival in patients PH. It is also a predictor of morbidity and mortality after medical therapy is started for PH. RV GLS of <19% is associated with all-cause mortality in patients with PH of different aetiologies. In the pediatric and adult PH population, RV GLS of <15% is a powerful prognostic indicator; it indicates poor outcomes.

When on therapy, patients who showed an improvement in more than 5% strain had a 7-fold reduction in mortality. RV FWS correlates well with functional capacity and survival and is a better predictor than TAPSE and had a better correlation with RA pressure assessed by inferior vena cava. Interestingly despite the wide variations in regional strain, segmental strain has shown to be useful in scleroderma. A preserved RV FWS is seen in scleroderma but has segmental variations: A excessively high basal strain compensated for reduced strain in mid and apical segments. In these patients worsening RV strain (<17%) was attributed to combined pulmonary fibrosis and PH, but this remains to be confirmed with larger studies.

Heart failure

Strain is a strong predictor of major adverse events in patients with chronic heart failure and in the onset of heart failure (HF) in patients with left heart disease.^[10] It is a reliable monitoring tool in patient follow-up to observe the status of RV function. In patients with normal TAPSE but who have reduced strain (indicating subclinical dysfunction), [Figure 4] and [Figure 5] it is an early marker and predictor of mortality and hospitalisation. RV strain can be used effectively in HF with reduced ejection fraction (HFrEF) and HF with preserved ejection fraction (HFpEF), more so in HFrEF patients. In HFpEF patients, RV FWS progressively declines (ranging from 20% to 24%) with increasing severity of LV diastolic dysfunction (LVDD) and is a sensitive marker even in the early stages of LVDD. When conventional parameters are unable to detect RV dysfunction, strain is quite sensitive in identifying subtle dysfunction in HFpEF patients. In HFrEF and HFpEF patients, <15% of RV FWS predicts outcomes and adverse events. In patients admitted with acute decompensated HF, RV FWS is an independent predictor of mortality and hospitalisation, with a cut-off of 13%. Patients with a combined reduction of LV GLS of 9% and RV GLS of 12% have the worst prognosis.

Figure 4: Right ventricular (RV) focused apical 4-chamber view showing mixed values of RV longitudinal strain in hypertension. RV-free wall strain is preserved at 25%, and RV global longitudinal strain termed as RV 4-chamber strain is reduced at 18%. RV4CSL: Right ventricular 4-chamber strain longitudinal, RVFWSL: Right ventricular free wall strain longitudinal

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Figure 5: Right ventricular (RV) focused apical 4-chamber view showing significantly reduced RV longitudinal strain in a patient with heart failure with preserved ejection fraction. RV-free wall strain is reduced at 15%, and RV global longitudinal strain termed as RV 4-chamber strain is reduced at 14%. RV4CSL: Right ventricular 4-chamber strain longitudinal, RVFWSL: Right ventricular free wall strain longitudinal

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In patients being considered for LV assist devices, strain is a better parameter than conventional parameters to predict RV failure. In patients being considered for heart transplant, it is superior to TAPSE and TDI for evaluating RV function. 2D RV strain has been shown to be useful in immediate postheart transplant patients as a monitoring tool: it is reduced in the early period but gradually improves and takes about a year to normalise.

Valvular heart disease

Patients undergoing surgical aortic valve replacement with <15% RV FWS are at risk of low-output cardiac syndrome within 1 month of surgery, indicating that RV strain can be used as a risk stratification tool. Low flow, low gradient aortic stenosis patients with <13% RV FWS have a lower 2-year survival rate and is an independent predictor of mortality.

Patients who undergo robotic mitral valve repair have smaller reductions in RV strain and better recovery than those who undergo routine surgical mitral repair. In patients who undergo surgical mitral repair, improvement of RV strain within 1 month predicted improvement in ventricular function with reduced risk of future hospitalisation for HF.

In functional tricuspid regurgitation (TR), RV FWS is inversely proportional to the severity of TR.^[11] RV FWS <17%–18% is an independent predictor for RV HF and 2-year all-cause mortality. In significant TR, a cut-off of <23% indicates RV dysfunction (conventional parameters show normal RV function), and these patients have higher mortality, increased postoperative mortality and hospitalisation. Conversely, those with reduced RV FWS are more likely to develop TR. RV strain has high predictive value in TR and should be used more often.

Cardiomyopathies

Cardiomyopathies frequently involve RV, and assessing RV function carefully in such patients is very important.^[12] [Figure 6] RV strain is incremental in providing information about adverse events. In arrhythmogenic cardiomyopathy, RV is affected very early in the disease, and RV FWS is especially useful in detecting asymptomatic carriers who are at risk of arrhythmias. A combined assessment of 6 segments of the free wall and the ventricular septum is useful for measuring mechanical dispersion, a marker for ventricular arrhythmias. In athletes, a reduced RV strain indicates myocardial fibrosis and identifies those at risk of ventricular arrhythmias.

Figure 6: Right ventricular (RV) focused apical 4-chamber view showing reduced RV longitudinal strain in hypertrophic cardiomyopathy. RV-free wall strain is mildly reduced at 22%, and RV global longitudinal strain termed as RV 4-chamber strain is significantly reduced at 16%, with segmental strain progressively reducing from base to apex. RV4CSL: Right ventricular 4-chamber strain, RVFWSL: Right ventricular free wall strain longitudinal

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Congenital heart disease

In TOF patients, RV strain can be a good predictor of patients at risk for developing dysfunction of RV. Varying load in different types of congenital heart disease makes RV function assessment particularly challenging. Those with systemic RV have decreased longitudinal motion with a compensatory increase in circumferential function as a response to the high afterload.

Coronary artery disease

It is a predictor of adverse outcomes in patients presenting with acute myocardial infarction undergoing primary coronary intervention. Strain is more sensitive in detecting acute RV infarction than traditional echo parameters [Figure 7].

Figure 7: Right ventricular (RV) focused apical 4-chamber view showing mixed RV longitudinal strain in coronary artery disease-anterior wall myocardial infarction. RV-free wall strain is normal at 25%, and RV global longitudinal strain termed as RV 4-chamber strain is reduced at 17%. RV4CSL: Right ventricular 4-chamber strain, RVFWSL: Right ventricular free wall strain longitudinal

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Conclusion

2D RV strain is a robust parameter to assess RV function and is recommended to be used in clinical routine. The prerequisite for an accurate strain value is a good image, proper image acquisition and ensuring proper tracking of the RV by the software. Two parameters that can be used are RV FWS and RV GLS, with RV FWS shown to be a better predictor of disease outcomes, while RV GLS is useful only in certain diseases. RV FWS is generally higher than RV GLS. A 2D strain of <20% is considered abnormal, while a value of <15% is indicative of significant RV dysfunction and adverse outcome. Clinical conditions for application in routine clinical practice are PH, heart failure, cardiomyopathies, TR, congenital heart disease and coronary artery disease. It is a sensitive tool to detect subclinical dysfunction. It is a good predictor of patient outcomes in various disease states.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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