Relationship of Left Atrial Global Peak Systolic Strain with Left Ventricular Diastolic Dysfunction and Brain Natriuretic Peptide Level in Patients Presenting with Non-ST Elevation Myocardial Infarction

Background

Left atrial (LA) function has been associated with adverse outcomes in patients after myocardial infarction (MI). MI results in left ventricular (LV) systolic and diastolic dysfunction. During the early phases of MI, 38% of patients have impaired relaxation and 24% of patients have restrictive LV filling pattern [1]. The important consequence of diastolic dysfunction is elevated filling pressures [2,3]. LV diastolic dysfunction was related to morbidity and death independently from systolic function in MI [4,5]. Therefore, assessment of diastolic function and LV filling pressures after non-ST segment elevation myocardial infarction (NSTEMI) has important prognostic implications. Diastolic function can be evaluated with several noninvasive and invasive techniques. Tissue Doppler imaging (TDI)-derived indices, including systolic velocity (S), early (Em), and late (Am) diastolic velocities of mitral annulus and early mitral inflow peak velocity (E)/Em ratio, are sensitive and widely used parameters to estimate LV filling pressures [6]. Increased B-type natriuretic peptide (BNP) levels also provide reliable estimation of LV filling pressures, particularly for left ventricular end diastolic pressure (LVEDP) and pulmonary capillary wedge pressure (PCWP) [7–9]. LA function and morphology is affected by increased LV filling pressures. Compared with Doppler and 2-D echocardiography, 2-dimensional speckle tracking imaging (2D-STI) has the advantage of angle independence, and is also less affected by reverberations, side lobes, or drop-out artifacts. While this novel echocardiographic method has been frequently used to assess LV function, it has more recently been used to evaluate atrial function in normal subjects and in conditions with atrial dysfunction. Assessment of LA strain using 2-D STI is a recently introduced and accurate method for evaluating LA functions. Current studies have shown the clinical importance of LA strain in atrial fibrillation and cardiomyopathy [10]. Moreover, decreased LA peak strain during LV systole (LAGLSs) was related to increased LVEDP, [11]. In the setting of NSTEMI treated with percutaneous coronary intervention (PCI) and medical treatment, we aimed to investigate the effects of diastolic dysfunction detected by echocardiography and BNP on LA deformational parameters evaluated with 2-D STI. We also measured phasic LA volumes and assessed their relation to diastolic dysfunction and LA strain.

Material and Methods

STUDY POPULATION:

The study group consisted of 74 (65 male, 9 female) consecutive NSTEMI patients who were treated with PCI in our institution (Group 1) and the control group (Group 2) consisted of 58 healthy subjects (48 male, 10 female) with no known history of cardiovascular disease, hypertension, or diabetes mellitus, and with normal treadmill exercise stress echocardiography. Patients with critical stenosis in coronary angiography were included in the study. We excluded patients with atrial fibrillation or moderate-to-severe valvular stenosis or regurgitation, as well as patients whose LA had an insufficient imaging quality.

STUDY DESIGN:

There were 2 groups: Group 1 consisted of 74 patients with NSTEMI and Group 2 consisted of 58 healthy control subjects. NSTEMI patients had an echocardiographic examination 48 h after the PCI procedure and venous blood samples were drawn simultaneously.

CONVENTIONAL ECHOCARDIOGRAPHIC EVALUATION:

All patients underwent an echocardiographic evaluation in the left lateral position, using the GE Vivid 7 system (GE Vingmed Ultrasound AS, Horten, Norway) with a 3.5-MHz transducer. Heart rate and blood pressure were continually monitored during the transthoracic evaluation. All data were transferred to a workstation for offline analyses (EchoPac PC). The Group 1 patients had echocardiographic evaluation 48 h after PCI. Transmitral early (E) and atrial contraction (A) flow wave velocities were attained by pulsed-wave Doppler echocardiography in the apical 4-chamber image. The ratio of E/A and E wave deceleration time were evaluated. For tissue Doppler imaging, the same echocardiography was used to achieve tissue Doppler imaging data at high frame rates. The myocardial systolic (Sm), early diastolic (Em), and late diastolic (Am) wave velocities were attained at the septal and lateral mitral annulus. The E/Em for septal and lateral annulus, as well as E/A ratios, were calculated. LA dimensions and LV end-systolic (LVESD) and end-diastolic diameters (LVEDD) were evaluated. LV ejection fraction (LVEF) was anticipated by Simpson’s biplane method using apical 4-chamber and 2-chamber images. LA volumes were evaluated using the biplane “area-length” method from apical 4- and 2-chamber images and their averages were calculated. LA maximum volume (LAVmax) was measured when the mitral valve was completely opened, LA minimum volume (LAVmin) was measured when the mitral valve was completely closed, and following parameters were calculated using these measurements:

Cardiac dimensions were measured in accordance with recommendations of the American Society of Echocardiography [12].

TWO-DIMENSIONAL SPECKLE TRACKING IMAGING ANALYSIS OF THE LEFT ATRIUM:

Two-dimensional echocardiography views for the LA were attained from the apical 4-chamber image. All views were attained with patients holding their breath at end-expiration and the views were stored in a cineloop format from 3 sequential beats. The frame rate for views was set at 60–90 frames/second. After determining the endocardial border manually, the software system was automatically improved for each frame. If the automatically attained tracking segments were sufficient for analysis, the software system was allowed to read the data, and analytically insufficient tracking segments were either corrected manually or excluded from the analysis. The view-tracking algorithm automatically divided the LA wall into 6 segments. The typical LA strain graph was attained for each patient. Mean peak LA strain valuations during LV systole (LAGLSs) for 6 segments were evaluated (Figure 1).

BNP MEASUREMENT:

Blood samples were obtained from NSTEMI patients and control subjects during the echocardiographic study. The blood samples were immediately centrifuged at 1500 rpm for 5 minutes and plasma was stored at −80°C until the time of evaluation. The quantitative definition of BNP in plasma was performed using the immune fluorescence method.

REPRODUCIBILITY:

Measurements were performed by a single person. Intraobserver reproducibility for the LAGLSs was assessed. For intraobserver evaluation, views from 25 randomly selected patients were reassessed after 1 week. The Bland-Altman analyses and intraclass correlation coefficient (ICC) demonstrated good intraobserver compromise; for intraobserver compromise, the mean difference was 1.3 (−2.1, 3.2) and ICC 0.91. To assess the intraobserver variability, selected images were analyzed at a different time by an observer blinded to the results of the previous measurements [13].

STATISTICAL ANALYSIS:

Results are reported as the mean ±SD and statistical analysis of clinical data between the 2 groups consisted of unpaired t-tests for parametric data, Mann-Whitney U test analysis for nonparametric data, and analysis of variance for repeated measures for parametric data. To analyze correlation between variables, the Pearson correlation coefficient was used. Statistical analysis was performed using PASW 18 (SPSS/IBM, Chicago, IL, USA). The level of significance was established at 0.05 (2-sided).

Results

There was a male dominancy in both Group 1 (88.7%) and Group 2 (83%); the mean ages of subjects were 56.4±9.2 years in Group 1 and 54.7±8.4 years in Group 2. Demographic characteristics of Group 1 patients are shown in Table 1. Table 2 shows a comparison of some clinical and echocardiographic characteristics of Group 1 patients and Group 2 individuals. Average time spent for offline analysis of LAGLSs for each patient was 4 min and 94% of LA segments were tracked appropriately by the software and included in our analysis. BNP values were significantly higher in Group 1 patients compared to Group 2 (114 [12.0–1249.5] vs. 6.0 [3.0–23.1]; pg/ml p=0.001). The differences between the measurements of transmitral flow velocities (E, A), and E/Em and E/A ratios of the groups were also significant (Table 2). Maximum and minimum left atrial volumes were increased in Group 1 patients (Table 3). Mean LAGLSs in Group 2 was higher than Group 1 (30.2±5.4% vs. 21.0±6.4% p=0.001). LAGLSs had significant correlation with LVEF (r=0.51, p=0.001), also there was a significant inverse correlation between LAGLSs and BNP level (Figure 2) (r=−0.44, p=0.001), E/Em (r=−0.34, p=0.001), LAVmax (r=−0.43, p=0.001), LAVmin (r=−0.48, p=0.001), LAEF (r=0.36 p=0.001) and LVESV (r=−0.37, p=0.001).

Discussion

STUDY LIMITATION:

This study has several limitations. Strain and strain rate have been demonstrated to be affected by preload change, and assessment of LA function by 2-dimensional STI is relatively time consuming and difficult. To attain suitable LA views for strain analysis in patients with inadequate echocardiographic views is difficult and sometimes impossible. The most important limitation of our research was that instead of evaluating LVEDP invasively, it was anticipated using BNP and echocardiographic measurements. The patients were not followed to evaluate the prognostic influence of diminished LAGLSs after NSTEMI.

Conclusions

We demonstrated that 2-dimensional STI is a non-invasive, reproducible, and relatively simple technique for evaluating LA myocardial function in patients with NSTEMI. We observed that LAGLSs values decreased consistently with deteriorating systolic and diastolic function. Our results suggest that LAGLSs measurements may be helpful as a complimentary method to evaluate diastolic function when inconclusive results are obtained by conventional echocardiographic parameters.