Left Atrial Strain: Crucial Cardiac Navigator in Practice

Shantanu P Sengupta; Ashish Agarwal

doi:10.4103/jiae.jiae_16_23

REVIEW ARTICLE

Year : 2023 | Volume : 7 | Issue : 2 | Page : 174-177

Left Atrial Strain: Crucial Cardiac Navigator in Practice

Shantanu P Sengupta¹, Ashish Agarwal²
¹ Department of Cardiology, Sengupta Hospital and Research Institute, Nagpur, Maharashtra, India
² Korba Diabetic and Cardio Center, Korba, Chhattisgarh, India

Date of Submission	10-Apr-2023
Date of Acceptance	13-May-2023
Date of Web Publication	15-Jun-2023

Correspondence Address:
Dr. Shantanu P Sengupta
Sengupta Hospital and Research Institute, Nagpur, Maharashtra
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jiae.jiae_16_23

Abstract

Left ventricular (LV) diastolic pressure estimation is essential for characterization of heart failure. Despite extensive research and the availability of numerous metrics, the assessment of LV diastolic pressures both at rest and after exertion has been challenging. Left atrial strain assessment by echocardiography has recently shown promise in correlating with LV end-diastolic pressure. This review provides information about this novel technology.

Keywords: Left atrial reservoir strain, left atrial strain, peak atrial longitudinal strain

How to cite this article:
Sengupta SP, Agarwal A. Left Atrial Strain: Crucial Cardiac Navigator in Practice. J Indian Acad Echocardiogr Cardiovasc Imaging 2023;7:174-7

How to cite this URL:
Sengupta SP, Agarwal A. Left Atrial Strain: Crucial Cardiac Navigator in Practice. J Indian Acad Echocardiogr Cardiovasc Imaging [serial online] 2023 [cited 2023 Sep 27];7:174-7. Available from: https://jiaecho.org/text.asp?2023/7/2/174/378794

Introduction

Echocardiography is the main imaging modality to assess left ventricular (LV) diastolic function and plays a pivotal role in the diagnosis of heart failure with preserved ejection fraction (HFpEF).^[1] Echocardiographic assessment of left atrial pressure (LAP) involves a multiparametric algorithm according to the current guidelines of the American Society of Echocardiography (ASE) and European Association of Cardiovascular Imaging (EACVI).^[2] Despite significant improvements in its feasibility, as compared to previous recommendations, validation studies have demonstrated that the proposed approach shows moderate diagnostic value for resting LAP, which is further limited for identifying patients with excessive LAP elevation on exertion despite normal resting pressures.^[3] Left atrial (LA) function assessment by LA strain has emerged as a new parameter for the assessment of LV diastolic dysfunction.^[4],[5] LA strain is a quantitative measure of the deformation of the LA wall during the cardiac cycle.^[4] It has been shown that LA reservoir function is influenced by the LV performance and the intrinsic LA compliance and plays an important role in disease progression in various clinical states including heart failure (HF).^[6] In this context, quantitative LA deformation analysis using speckle-tracking echocardiography has evolved as a feasible and reproducible method for evaluating LA function.^[7] It has been demonstrated that LA strain is associated with mechanical changes and fibrosis even prior to LA geometrical remodeling, potentially enabling earlier diagnosis of elevated LAP.^[8],[9] This review aims to provide an overview of the importance of LA strain in clinical practice, its measurement methods, and its clinical applications and also highlights the potential limitations of using LA strain in different clinical settings.

How to Obtain Left Atrial Strain

LA strain can be measured using different imaging techniques, including two-dimensional (2D) echocardiography and cardiac magnetic resonance imaging. 2D speckle-tracking echocardiography is now the most widely used method for assessment of LA strain.^[8],[10] To perform this measurement, the patient lies in left lateral decubitus, and an echocardiogram is performed. A focused view is used to acquire images of the LA. Focused LA view can be obtained by moving the echocardiography probe one intercostal space higher than from where conventional apical four-chamber and apical two-chamber views are acquired. This makes the LV apex foreshortened but visualizes the left atrium in its long-axis. This maneuver is needed as the long-axes of left atrium and left ventricle are not in the same plane.

Apart from the imaging differences, the software used for LA strain measurement is also different. There are now software available which are specifically designed to measure LA strain.^[8],[10] It is not recommended to use the LV strain software to measure LA strain as the LA wall is much thinner compared to the LV myocardium.

Just like the LV strain, a good-quality electrocardiogram (ECG) is essential for LA strain measurement also.

Measurement Technique

Once the echocardiographic images have been obtained, LA strain can be measured using a specialized software. Although either four-chamber or two-chamber view may be used, in practice, the four-chamber view is used mostly. The analysis process involves the following steps:

Tracing: The first step involves tracing the LA wall. The endocardium is traced either manually or automatically by the software to generate a region of interest. Care should be taken to ensure that the region of interest covers only the LA wall and not the adjacent pericardium. A thickness of roughly 3 mm for the region of interest is generally recommended. The border tracing should not extend into the pulmonary veins or the LA appendage
Speckle-tracking: The software then uses speckle-tracking technology to track the movement of acoustic speckles in the LA wall. The quality of tracking should be visually checked. The region of interest should be seen moving in sync with LA wall movement and should follow both ends of the mitral annulus
Strain calculation: After confirming satisfactory tracking, the speckle-tracking software generates LA strain curves. The shape of the curves depends on whether the P-wave is used as the reference or the QRS [Figure 1].^[11] The QRS method is most widely used and the recommended method. In this method, all the waveforms are above the baseline and are positive, while in the P-wave method, there is a negative wave first, followed by a positive wave.

Figure 1: Left atrial (LA) strain waveforms according to P-P gating (left) and R-R gating (right)

Click here to view

From the LA strain curves thus obtained, several different measurements can be obtained [Figure 1] and [Figure 2].^{[8],[10],[11]} If the QRS method is used, the first positive wave represents the LA reservoir strain or the peak atrial longitudinal strain (PALS). This is the most important LA strain parameter. The second positive wave coinciding with the atrial contraction (i.e., the P wave in ECG) represents the LA contractile function or the booster function. This is also known as peak atrial contraction strain (PACS). PACS is calculated as the difference between the LA strain at end-diastole (i.e., zero) minus the LA strain at the onset of LA contraction. It always has a negative value. The difference between the PALS and PACS represents the conduit function, and it also has a negative value. These waveforms are seen only in the presence of sinus rhythm. If the patient is in AF, only one positive wave is seen which represents the LA reservoir strain.

Figure 2: Phases of left atrial strain. PACS: Peak atrial contraction strain, PALC: Peak atrial longitudinal strain

Click here to view

In the P-wave gated method, the initial negative wave represents the LA contractile function whereas the subsequent positive wave represents the conduit function. The sum total of the two is equal to the LA reservoir strain [Figure 1].

Normal Values of Left Atrial Strain

Several different studies have provided normal reference ranges of LA strain. Morris et al. performed a multicentric study involving 329 healthy adult subjects and 377 patients with LV diastolic dysfunction serving as the validation group. The lower limit of normal LA reservoir strain was found to be 23.1%.^[12] A similar cutoff value was reported in the Copenhagen City Heart Study also which included 1641 healthy participants.^[13] The median PALS in the entire cohort was 39.4% with the interquartile range being 23.0%–67.6%. Pathan et al. conducted a meta-analysis of forty studies with a total of 2,542 healthy subjects.^[11] The normal reference range for reservoir strain was 39% (95% confidence interval [CI]: 38%–41%), for conduit strain 23% (95% CI: 21%–25%), and for contractile strain 17% (95% CI: 16%–19%). Thus, this study also reported the same average LA reservoir strain, but the lower limit of normal was much higher than the aforementioned studies. In clinical practice, a PALS value <25% is generally considered abnormal.

Clinical Utility of Left Atrial Reservoir Strain

Left atrium plays a vital role in the cardiac cycle, and its function has important implications for cardiovascular health.^[7] It receives blood from the pulmonary veins and pumps the same into the left ventricle. The left atrium is a highly dynamic structure, and its function is influenced by a variety of factors, including atrial size, compliance, and contractility.^[14] LA strain is a quantitative measure of the deformation of the LA wall and provides information about its reservoir, conduit, and contractile phase. According to Appleton et al., for LV diastolic function evaluation, assessment of LA volume and function are very important.^[15] HFpEF and atrial fibrillation (AF) are two important conditions which are associated with significant LA and LV remodeling and LA strain can provide a plethora of information in these conditions.^[16],[17]

LA strain is a good marker of LV filling pressure, and in patients with unexplained dyspnea and preserved LV ejection fraction, LA reservoir strain provides incremental information above the 2016 ASE/EACVI algorithm for the estimation of LV filling pressure.^[2] Kurt et al. demonstrated that LA strain correlates with invasive LV end-diastolic pressure and N-terminal pro–B-type natriuretic peptide levels.^[4] Yoshida et al. studied LA function in relation to gender and age.^[18] In a study of 414 patients, they demonstrated a lower value of LA reservoir strain in women with AF.^[18] They also showed that LA function, and not LA size, had important relation with stroke risk.^[18] The prognostic value of LA strain has been demonstrated in a variety of clinical settings, including HF, hypertension, and AF. In patients with AF, LA reservoir strain has been shown to be a predictor of LA appendage thrombus formation, which is a risk factor for stroke. In patients with HF, improvement in LA strain is a predictor of improved outcomes. There has been a lot of interest about the role of LA reservoir strain in exercise intolerance seen in both HF with reduced ejection fraction (HFrEF) and HFpEF patients. In a recent study, our group showed that the patients with HFpEF had more profound deterioration of LA reservoir function with exercise which appeared to contribute to exercise intolerance.^[19] One study reported that there was a 60% chance of new-onset AF if LA reservoir strain was <18%.^[18] It also showed that the LA reservoir strain was an early sign of local structure changes like fibrosis, correlating with chamber dysfunction and remodeling.^[18]

Jia et al. in a meta-analysis described the normal range of PALS in the HF patients.^[20] The average PALS ranged from 8.8% to 36.2%, with a cutoff value of 12%–25% being predictive of adverse events. They also showed that HFrEF patients had a lower PALS cutoff in comparison to HFpEF patients. This was also shown in our work.^[19] The meta-analysis by Jia et al. asserted that PALS could be an independent and improved tool for predicting cardiac hospitalization and all-cause mortality.^[20]

PALS is also a good tool for differentiating HFpEF from mere LV diastolic dysfunction. In the study by Kurt et al., it was shown that LA strain was lower in HFpEF than in patients with LV diastolic dysfunction without HF.^[4] Cameli et al. in a study with a right heart catheterization, involving patients with HF with LV ejection fraction <35%, showed that the LA strain was the best measure for pulmonary capillary wedge pressure and had high sensitivity and specificity for diagnosing elevated LV filling pressure.^[16] In HFrEF patients, LA strain was found to be of lower value in idiopathic cardiomyopathies than in ischemic cardiomyopathy.^[7] LA strain was also reduced in hypertrophic cardiomyopathy.^[21] Morris et al. in two different papers inform that replacing the LA volume index with PALS can significantly improve the recognition of LV diastolic dysfunction in patients otherwise having indeterminate LV diastolic dysfunction as per the 2016 ASE/EACVI guidelines. Furthermore, such reclassification correlates with the HF risk during follow-up.^[22]

PALS plays an important role in diabetes also as diabetes patients have a higher incidence of LV diastolic dysfunction.^[23] Muranaka et al. showed that diabetes patient had a marked reduction in PALS.^[24] There was impairment of the conduit and LA reservoir strain, in the absence of hypertension or overt LV diastolic dysfunction.^[24] LA strain was also reduced in hypertension without any LA volumetric changes. Mondillo et al. showed that strain changes occurred before the structural change in left atrium in hypertension.^[25] LA strain was found to be a sensitive parameter for myocardial involvement in chronic kidney disease. This was demonstrated by Gan et al. in a study in which PALS was reduced in patients with chronic kidney disease.^[26] Maffeis et al. demonstrated that PALS was a better metric than the LA volume index in indeterminate cases.^[23]

Limitations

A major concern while acquiring LA strain is the anatomy of LA. The thickness of the LA wall is only 1–2 mm and, hence, may not have sufficient acoustic speckles for LA strain measurement.^[16] The distribution of these acoustic speckles is further compromised by the presence of LA appendage, fossa ovalis, and pulmonary veins creating problems in accurate speckle-tracking analysis.^[16] The LA measurement is also affected by several other technical factors such as the quality of the imaging (including proper orientation of the imaging planes to avoid LA foreshortening) and the operator variability in the measurement method and the interpretation of the strain curves. These factors further affect the reproducibility of the measurement. Another area of concern is the lack of uniform cutoff values and the changes in the LA strain due to age and other risk factors. However, continuous advancements are being made to overcome these limitations.

Conclusions

LA strain measurement is now an important component of echocardiographic examination and provides useful information about LV filling pressure. It has also been shown to have prognostic information in various disease processes. Its wider application and availability are needed for realizing its full potential in clinical practice.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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