Background: Two-dimensional (2D) Strain is a new reproducible technique for assessing regional myocardial function; however, its application for evaluation of left atrium (LA) function is less studied.

Objectives: We sought to assess LA function in heart failure patients using velocity vector imaging (VVI).

Patients and Methods: Thirty five patients (mean age: 43.34 ± 18.1 years, 59.3% male) with systolic dysfunction [left ventricle ejection fraction (LVEF) < 35%] enrolled. Standard Doppler echocardiography and 2D strain were performed on all subjects. Strain measurements were obtained from apical views.

Results: A significant differences in LA volume index (LAVI) and strain were found in patients with systolic heart failure (SHF) versus normal subjects (23.8 ± 4.1 versus 57.8 ± 19.7 ml/m², P < 0.001 and 39.6 ± 10.6 versus 8.2 ± 5.3%, P < 0.001). Multivariate analysis of separate walls revealed significant inverse relationship between LA size and volume with total and regional (2-ch view) 2D strains of LA. Significant inverse relationship were also detected between pulmonary artery systolic pressure and both total LA strain (22 ± 8 versus 42 ± 10 mmHg, r = -0.4, P < 0.001) and LA strain in 2-chamber (r = -0.5, P < 0.001). A cutoff value of total average LA strain (≥ 23.28%) can differentiate normal and abnormal LA function with a sensitivity of 93% and specificity of 100% and a cutoff value of total LA strain (in average) of 17.2% can differentiate mild and moderate and severe diastolic dysfunction with a sensitivity of 100% and a specificity of 97%.

Conclusions: LA strain seems to be a better determinant for diagnosis of abnormal LA function and the degree of diastolic dysfunction in SHF.

Heart failure is a major and growing public health problem because of aging of the population and improved survival of patients. Systolic heart failure is known as impaired organ perfusion due to inefficient cardiovascular pump function. LA plays an important role in the overall cardiovascular performance (1). The enlargement of LA diameter is associated with left ventricle (LV) remodeling, diastolic dysfunction and is a risk factor for cardiovascular events and death. LA function reliably predicts exercise capacity in patients with ischemic or non-ischemic dilated cardiomyopathy (DCM) and differs in these groups of patients. Traditionally, LA function has been mainly evaluated using LA volumetric parameters, such as LA area, LA volume, and LA emptying fraction (EF) by two-dimensional echocardiography (2-8). An alternative method has been incorporated since several years ago using tissue Doppler-derived strain and strain rate measures to evaluate atrial myocardial deformation (9-15). Strain rate imaging allows the non-invasive functional quantification of the LA function analyzing the deformation properties independent of cardiac rotational motion and the tethering effect (16). However, there are several limitations of Doppler-derived strains, such as angle-dependency, suboptimal reproducibility, and inability to assess the curved atrial roof. 2D strain overcomes these limitations in the quantification of atrial function (17-19), 2D strain allows angle-independent assessment of regional and global strain and strain rate from 2D echocardiographic images and has been validated for the LV and right ventricle (20-22). However, only a few studies have applied 2D strain for the assessment of atrial mechanic.

The purpose of this study was to assess LA strain by velocity vector imaging in SHF patients, compare with control group and evaluate its relation to LA size and volume and diastolic parameters.

3.1. Patients’ Population

This single center case series randomly enrolled thirty five SHF patients with an LVEF less than 35 % and normal sinus rhythm referring to the heart failure clinic of our institution. For all the patients, a thorough history taking was followed by a complete physical examination. The exclusion criteria comprised congenital heart disease, significant valvular heart disease, atrial fibrillation, acute ischemia, pericardial diseases, hypertrophic and restrictive cardiomyopathy, arrhythmias, and pulmonary arterial hypertension. Twenty five controls were enrolled from the referrals for a routine check-up who had nonanginal chest pain and normal echocardiography [(LVEF > 55% and normal LV diastolic function with no valvular disease and normal pulmonary artery pressure (PAP)].

Baseline characteristics of the patient and control subjects as well as echocardiography data are shown in Table 1 and 2. Two third of patients (59.3%) were male and 75% of the patients were diagnosed to have DCM with a mean LVEF of 19 ± 6.5%. Mean LA diameter, area and volume index were significantly larger in patients than control group (P < 0.000). In addition, total LA strain was substantially lower in SHF patients in comparison with normal subjects (39.6 ± 10.6 versus 8.2 ± 5.3%, P < 0.000). Multivariate analysis of separate walls revealed significant inverse relationship between LA size, area and LAVI with total and regional (2-ch view) 2D strains of LA (Table 3). Analysis of the diastolic parameters and LA strain also showed significant relationship between total and regional (2-ch view) LA 2D strain with systolic PAP, A wave velocity and degree of diastolic dysfunction, but not with either mitral E and Ea velocities, and or E/Ea (Table 3). Using ROC curve analysis, we could be able to suggest cutoff values of LA size and function to distinguish abnormal atrial function in SHF patients. A cutoff value of total average LA strain (≥ 23.28%) can differentiate normal and abnormal LA function with a sensitivity of 93% and specificity of 100%. Additionally, our results showed a cutoff value of total LA strain (in average) of 17.2% can differentiate mild and moderate and severe diastolic dysfunction with a sensitivity of 100% and a specificity of 97% (Table 4). The estimated sensitivity and specificity of suggested LA dimension, area and volume along with total and regional LA strains for differentiation between mild and moderate and severe diastolic dysfunction were shown in Table 4.

Table 1. Baseline Characteristics in Normal and Patients Group

Table 2. Left Atrial Strain Values (%) in Different Sites as mean (SD) in Patients and Normal Control Group

Table 3. Correlations Between LA Size, Area, Volume and LV Diastolic Parameters, and LA Strain Values in Systolic Heart Failure Patients

Table 4. Sensitivity and Specificity of Suggested Cut Points According to ROC Curve to Differentiate Mild From Moderate to Severe LV Diastolic Dysfunction in Heart Failure Patients

The left atrium plays an important role in the overall cardiovascular performance. This is accomplished through its action as a contractile chamber during late ventricular diastole, as a reservoir distended by the inflow volume from pulmonary veins during ventricular contraction and isovolumic relaxation and a conduit during the early ventricular diastole and diastases (23). Through these varying mechanical functions, the LA modulates LV filling. In addition, the LA also acts as a volume sensor with the atrial wall releasing natriuretic peptides in response to stretch, generating natriuresis, vasodilatation, and inhibition of the sympathetic nervous system and renin-angiotensin-aldosterone system. LA enlargement is often asymmetrical and may occur in the medial-lateral as well as the superior-inferior axes because the enlargement in the antero-posterior axis may be limited by the thoracic cavity. Thus left atrial volume is superior to LA diameter as a measure of LA size (24). Kuppahally et al. (25) mentioned that the relationship between LA size and burden of cardiovascular disease and its outcome is stronger for LA volume than LA dimension. The prognostic implications of LA volume have been more extensively studied in high-risk subgroups. In patients with dilated cardiomyopathy, increased LA volume was associated with poorer survival incremental to LV end-systolic volume, diastolic dysfunction, and mitral regurgitation. It has been reported that an LAVI of >32 mL/m² is a powerful marker for increased all-cause mortality, independent of other measures of LV systolic and diastolic function (26). Recently, increased LA volume has been reported as a predictor of diminished exercise capacity in patients with heart failure (27). In patients with DCM, atrial enlargement may also be due to concomitant atrial muscle myopathy caused by a more widespread primary pathologic process (28). Heart failure is associated with the progressive conversion of the LA from a storage and contractile chamber to a more passive simple conduit chamber (29). It is likely that intrinsic alterations of LA myocardial contractility play an important role. However, it is not clear that these myopathic changes happen firstly or occur lately as a consequence of LA dilatation and myofibrils stretching. Few studies have evaluated atrial function using myocardial strain in SHF patients (30). Schneider and colleagues (16) measured tissue Doppler-based strain and strain rate (measures of the degree and rate of LA deformation), in patients with either persistent or paroxysmal atrial fibrillation (AF). Mustafa Kurt et al. (5) evaluated LA strain in diastolic heart failure patients and showed that LA systolic strain and strain rate were significantly lower than those in patients with just diastolic dysfunction. Christina Janet et al. evaluated LA strain by VVI in patients with type 2 diabetes mellitus and mild or moderate LV diastolic dysfunction, and showed that LA strain seems value in distinguishing normal from abnormal diastolic function in diabetic patients (31). But the relation between LA volume, diastolic parameters and the degree of diastolic dysfunction with total and regional LA strains has not been evaluated before. In our study, LA strain was significantly lower in patients with SHF compared to normal subjects (39.6 ± 10.6 versus 8.2 ± 5.3%, P < 0.000). Mi-Sung Shin et al. mentioned that the maximal LA volumes were negatively correlated with the posterior wall longitudinal peak systolic strain and strain rate and posterior wall tissue velocity is an important factor of LA contractility (32) but we couldn’t find any significant relationship between posterior LA wall strain and either LAVI and or diastolic parameters. In contrast, we found a significant negative relation between LAVI and LA regional strain in 2-ch view and total LA strain. Kuppahally et al. showed that reduction in atrial strain did not appear to be caused by elevation of filling pressure as assessed by E/Ea (7). In our study, multivariate analysis of diastolic parameters showed a significant inverse relationship between A velocity and systolic PAP with total and most regional LA strain. The relationship between LA strain, as a marker of atrial mechanics and A velocity could be expected but the relationship between LA strain and systolic PAP in SHF patients may be due to advanced LA contractile dysfunction and more prominent passive conduit function in these patients resulting in post capillary pulmonary hypertension. According to our study, we should rely on LA 2D strain in 2-ch view (anterior and inferior walls and specially LA roof) as a valuable marker of LA function. It seems that the above mentioned portions are less influenced by aorta, inter-atrial and inter-ventricular septum and even pericardium, so they are more reliable for evaluation of LA mechanics by 2D strain. Several limitations should be mentioned. Individuals with normal diastolic function were relatively younger than patients’ group. Because diastolic function changes with age, this point affects the results of this study. Mitral inflow profiles are affected by loading conditions. However, we used standards for the classification of LV diastolic dysfunction using Doppler echocardiography that are widely accepted and used in clinical practice. We excluded patients with significant MR but LA strain and diastolic parameters might have been affected because of some degree of MR in our patients. Left atrial 2D strain in control subjects are significantly higher than those with SHF. In patients with systolic heart failure, LA strain seems to be a better surrogate than LA size and volume for diagnosing abnormal LA function and diastolic dysfunction.

We would like to thank our colleagues in Rajaie Cardiovascular Medical and Research Center in particular Echocardiography and Heart Failure and Transplant departments.