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Original Research

Cardiology 2012;121:255–260 DOI: 10.1159/000337291

Can Left Atrial Strain and Strain Rate Imaging Be Used to Assess Left Atrial Appendage Function?

Sakir Arslan Ziya Simsek Fuat Gundogdu Enbiya Aksakal

Mehmet Emin Kalkan Yekta Gurlertop Mustafa Kemal Erol Sule Karakelleoglu

Department of Cardiology, Faculty of Medicine, Ataturk University, Erzurum , Turkey

Introduction

The left atrium (LA) and left atrial appendage (LAA) are structures that play an important role in evaluating cardiovascular performance. LAA develops as a residue originating from LA at 4 weeks of embryonic develop-ment. Although ultrastructural and physiologic charac-teristics of LAA develop independently from LA in this process, muscle cell structures and the myocardium of both structures are similar [1] . The highly dynamic LAA structure prevents stasis in healthy individuals, yet in case of its dysfunction, spontaneous echo contrast (SEC) and/or thrombus formation may develop associated with increased stasis [1, 2] . The most important risk factor that arises from this status is systemic embolism. The recent-ly used strain (S) and strain rate (SR) echocardiography methods derived from color Doppler myocardial imag-ing are important parameters that detect myocardial functions rapidly and correctly [3] . S and SR imaging techniques were shown to be sound and effective meth-ods in evaluating longitudinal myocardial LA and LAA functions [4, 5] . Transesophageal echocardiography (TEE) is the diagnostic test to evaluate LAA morphology and function. TEE is a semi-invasive imaging technique and it is distressing for patients due to its endoscopic pro-cedure. Moreover, it cannot be performed on all individ-uals and may lead to some serious complications, albeit rarely, due to absolute and relative contraindications [6] .

Key Words

Contractile functions � Left atrium � Left atrial appendage � Strain � Strain rate

Abstract

Background: The aim of this study was to evaluate the effi-ciency of left atrial strain (S) and strain rate (SR) imaging in assessing left atrial appendage (LAA) function. Methods: We studied 78 consecutive patients (35 females and 43 males; mean age 38 8 15 years) referred for transesophageal echo-cardiography (TEE). LAA late emptying velocity (LAA-EV) was calculated. Real-time color Doppler myocardial velocity imaging (MVI) data were recorded from the LAA by TEE and the lateral wall of the left atrium (LA) by transthoracic echo-cardiography. Longitudinal S and SR were measured in the mid portion of the lateral LA wall and lateral LAA wall during the contractile period. LAA late systolic velocity (LSV) and LA-LSV were obtained from Doppler analysis. Results: A sig-nificant positive correlation was detected between LAA-EV and MVI parameters (for LAA-S, r = 0.88, p ! 0.001; for LAA-SR, r = 0.84, p ! 0.001; for LAA-LSV, r = 0.83, p ! 0.001; for LA-S, r = 0.84, p ! 0.001; for LA-SR, r = 0.79, p ! 0.001, and for LA-LSV, r = 0.70, p ! 0.001). In addition, a significant positive correlation was detected between LAA-S and LA-S (r = 0.85, p ! 0.001). Conclusion: We suggest that LA-S and LA-SR im-aging is a beneficial method to evaluate LAA functions non-invasively. Copyright © 2012 S. Karger AG, Basel

Received: December 12, 2011 Accepted after revision: February 9, 2012 Published online: May 12, 2012

Dr. Ziya Şimşek Osman Gazi Mah Gökdemir Sitesi A Blok, Kat. 6, Daire No. 29 TR–25100 Erzurum (Turkey) Tel. +90 505 884 1595, E-Mail ziyamposta   @   hotmail.com

© 2012 S. Karger AG, Basel0008–6312/12/1214–0255$38.00/0

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Cardiology 2012;121:255–260256

Therefore, the desired approach in this matter is to evalu-ate LAA structure, morphology and function with trans-thoracic echocardiography (TTE). However, it is difficult to take an LAA image by TTE. The relationship between LA and LAA function was studied with different meth-ods and different interpretations were introduced in this scope [7, 8] .

We aimed to evaluate the relationship between LA and LAA contractile functions using S/SR methods which were proven to be effective in this field.

Patients and Methods

Patient Population The study included 78 subjects (35 males and 43 females; mean

age 38 8 15 years) with different types of cardiac disease who were in sinus rhythm and referred for TEE. Patients with atrial fibrillation were excluded from the study. TEE was performed for atrial septal defect in 30, mitral valve failure in 19, mechanical aortic valve dysfunction in 8, mechanical mitral valve dysfunc-tion in 5, for research of the source of embolism in 2, mitral ste-nosis in 5, infective endocarditis in 6 and aortic aneurism in 3. All subjects gave written informed consent to the study, and the study was approved by the local ethics committee of our university.

Echocardiography TTE. Echocardiographic parameters of all study patients were

assessed in the left lateral position using a Vingmed ultrasound system (Vingmed System 7; General Electric, Horten, Norway) and a 2.5-MHz transducer. Measurements were performed to-gether with continuous blood pressure and single-lead electrocar-diographic monitoring. M-mode was assessed according to the criteria of American Society of Echocardiography [9] . Left ven-tricular ejection fraction was determined using a modification of the Simpson technique.

TEE. All subjects underwent TEE by means of a multiplane 5-MHz transducer. TEE was performed after at least 4 h of fasting. A 10% lidocaine spray was applied to the posterior pharynx for anesthesia. No atropine or other sedation was administered. LAA was scanned at an average of 30–40°. Cigarette smoke-like ap-pearance with a swirling motion in the LA cavity and LAA was identified as SEC, and graded from 0 to +4 [10] . LAA late empty-ing velocity (LAA-EV) was measured with pulse wave Doppler in the LAA orifice; LAA-EV was calculated as the mean of three consecutive cardiac cycles ( fig.  1 ). Subjects with LAA-EV ! 0.5 cm/s were considered having LAA dysfunction [11] .

S/SR Imaging Real-time color Doppler myocardial velocity imaging (MVI)

was taken at the mid portion of the lateral wall of the LAA and at the mid segment of the lateral wall of the LA. MVI of the LA lat-eral wall was assessed in apical 4-chamber view. MVI function frame rate was taken as 1 160/s. Images containing only the LA lateral wall with the narrowest possible angle and maximum frame rate values were taken, with a distance between the two measured points of 10 mm. Images containing three consecutive

sinus pulses were recorded digitally. These color Doppler images of the myocardium were analyzed off-line by means of a software program (Workstation; General Electric). Longitudinal myocar-dial S/SR values of the LAA and LA lateral mid segment were de-termined during the contractile period ( fig. 2 , 3 ). LA and LAA late systolic velocities (LSV) were measured by tissue Doppler analysis [4, 5] . Patients with poor imaging quality were excluded from the study.

Interobserver Variation S/SR, tissue LSV and SEC grading measurements for LA and

LAA were taken by two independent cardiologists, with a differ-ence between observers ! 5% for all parameters assessed. These values are considered as within acceptable limits.

Statistical Analysis Statistical analysis was performed using SPSS 10.0. Numerical

values were expressed as means 8 SD, and categorical values as percent. Pearson’s correlation analysis was applied to evaluate as-sociations between LAA and LA regarding S/SR, LAA-EV and LSV. A value of p ! 0.05 was accepted as statistically significant.

Results

Baseline clinical and echocardiographic characteris-tics of all cases included in the study are shown in table 1 . SEC was detected in 21 (27%) cases. Of these, 13 had grade I, 3 had grade II, 3 had grade III and 2 had grade IV SEC. LAA-EV was ! 0.5 cm/s in all patients with grade II–IV SEC, and in 6 patients with grade I SEC. LAA dys-

Fig. 1. LAA-EV.

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Left Atrial Appendage Function Cardiology 2012;121:255–260 257

function was noted in a total of 14 (18%) cases. Mean LAA-EV, LAA-S, LAA-SR, LAA-LSV, LA-S, LA-SRand LA-LSV were 0.76 8 0.28 cm/s, –14.5 8 4.9%, –2.2 8 1.1 s –1 , 5.3 8 1.8 cm/s, –46.5 8 16.2%, –3.7 8 1.3 s –1 and 5.6 8 1.6 cm/s, respectively. Associations between LAA-EV and MVI parameters were investigated, and signifi-cant correlations were found between LAA-S and LAA-EV, r = 0.88, p ! 0.001 ( fig. 4 ); between LAA-SR and LAA-

EV, r = 0.84, p ! 0.001; between LAA-LSV and LAA-EV, r = 0.83, p ! 0.001; between LA-S and LAA-EV, r = 0.84, p ! 0.001 ( fig. 5 ); between LA-SR and LAA-EV, r = 0.79, p ! 0.001, and between LA-LSV and LAA-EV, r = 0.70,p ! 0.001. Moreover, a significant positive correlationwas also observed between LA-S and LAA-S (r = 0.85,p ! 0.001) ( fig. 6 ).

1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.90.6 0.7 0.8 0.9 1.0 1.1 1.2

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Fig. 2. S and SR imaging of the lateral LA wall.

Fig. 3. S and SR imaging of the lateral LAA wall. C

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Discussion

Our study showed a strong correlation between LA-S/SR and LAA-S/SR and LAA-EV.

SEC that develops in association with local stasis in the LA and LAA circulation causes thrombus formation and thromboembolic events [10, 12] . Therefore, clinical deter-mination of LAA function is important. Parameters used in evaluating LAA function are LAA flow velocities, which can be used during thromboembolic risk stratifi-cation. Handke et al. [13] suggested that LAA flow ve-locities were strong predictors in SEC/thrombus develop-

ment in their TEE study on 500 patients who developed ischemic stroke. In our study, a total of 21 patients (27%) were found to have SEC, and determination of LAA-EV in these patients showed LAA dysfunction ( ! 0.5 cm/s) in 14 (18%). In other words, in 7 patients presenting with SEC, LAA-EV was within normal limits. LAA contrac-tions can be measured indirectly by LAA-EV. Since LAA-EV is affected by extrinsic factors and dependent on acute hemodynamic changes [14] , more effective and novel pa-rameters are needed in this respect.

The heart performs complex myocardial movements: contraction, rotation, shortening and extension, i.e. movements which occur under the tethering effect of ad-jacent segments [15] . In S/SR imaging, intrinsic myocar-

Table 1. B aseline clinical and echocardiographic characteristics of the study patients

Age, years 38815Females/males 35/43Heart rate, beats/min 84815Blood pressure, mm Hg

Systolic 115810Diastolic 7487

Ejection fraction, % 6485LA diameter, mm 4086Left ventricle, mm

Diastolic diameter 4484Systolic diameter 3184

SEC 19/78

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Fig. 4. Correlation between LAA-S and LAA-EV. Fig. 5. Correlation between LA-S and LAA-EV.

Fig. 6. Correlation between LA-S and LAA-S.

Left Atrial Appendage Function Cardiology 2012;121:255–260 259

dial contractility measurements are made independently of cardiac rotational movements and tethering effects [16] . Myocardial contractility cannot directly be mea-sured by S/SR imaging. S is affected by parameters such as preload and heart rate, and SR parallels the inotropic status and contractility regardless of S circumstances [17] . In their TEE study, Sevimli et al. [4] showed that LAA-EV exhibited a strong correlation with S/SR param-eters and that these imaging techniques were relatively sound and effective techniques in evaluating LAA sys-tolic functions. Sirbu et al. [5] , on the other hand, sug-gested that noninvasive, smooth LA-S/SR imaging was an effective method to demonstrate longitudinal myocardi-al LA deformations and that data recording may help to understand the pathophysiology of LA. Considering the similarity of the muscle cell structure and myocardium of LA and LAA, it seems reasonable to evaluate their functions using these imaging techniques and to estab-lish possible relationships.

Although disputable, LAA functions can be subject to speculation by evaluating LA functions. A positive cor-relation between LA and LAA functions has been report-ed in several studies [18, 19] , which suggested that LAA contraction velocities can be used instead of global LA functions. In contrast, Agmon et al. [8] compared LAA contraction velocities with LA variables (differences be-tween maximal and minimal LA volumes, mitral inflow A velocity, atrial ejection force, mitral annulus late dia-stolic A’ velocity and pulmonary vein atrial reversal ve-locity) in their TEE and TTE studies on 349 patients in sinus rhythm, and they found a poor correlation between LAA contraction velocities and global LA functions. Therefore, they concluded that LAA contraction veloci-

ties could not be used instead of global LA functions, but their TTE and TEE data were collected at different times. Moreover, LA is under the impact of large pulmonary veins, and parameters studied are associated with differ-ent hemodynamic circumstances. Different from these studies, we used S/SR imaging techniques along with LAA-EV.

It is known that atrial stunning develops in patients with atrial fibrillation following cardioversion, and im-provement in atrial function takes time. Kaya et al. [20] studied LA and LAA functions by S/SR imaging in 22 pa-tients with atrial fibrillation after cardioversion, and both a strong correlation between LA and LAA functions and an improvement in LAA function after a certain time in-terval were detected. They suggested that the anticoagu-lation time can be estimated based on the follow-up of LA-S/SR values [20] . Similarly, our study also noted a strong correlation between LA- and LAA-S/SR parame-ters in a larger study cohort (78 patients in total).

The use of TEE may be problematic due to its limited availability and the need for experience in its implemen-tation in addition to its semi-invasive procedure. Assess-ment of LA contractile functions using different mea-surement methods is not feasible in clinical practice due to the longer assessment time required. However, an ear-ly detected reduction in LA contractile function may alert the investigator to SEC and/or thrombus formation in the LAA.

In conclusion, LA-S/SR measurements provide nonin-vasive information on LAA functions. However, large scale studies are needed to determine LA-S/SR cutoff val-ues indicating LAA dysfunction.

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