A total of 80 professional strength athletes participating in wrestling, boxing, judo, and weightlifting were randomly selected from the Henan heavy competitive sports management center. Of these, 45 were male and 35 were female (age range, 18–25 years). Inclusion criteria included the following: strength athletes with training experience of ≥5 years, those training for ≥30 h per week, and athletes who have never stopped training. A total of 60 young adults (30 males and 30 females) who were declared to be healthy after a physical examination, those matching in age, and athletes with similar body mass indexes (BMIs) were randomly selected as the control group. The exclusion criteria in both groups included cardiovascular disease, such as history of atrial arrhythmia, hypertrophic cardiomyopathy, and severe valvular disease, and poor image quality for myocardial speckle tracing analysis. The study was approved by the Ethics Committee of The First Affiliated Hospital of Zhengzhou University. All subjects signed the informed consent form.
Transthoracic echocardiographic examinations were performed at rest in the left lateral decubitus position with a high-quality echocardiograph (Vivid E95, GE Medical Systems, Horten, Norway) equipped with a 3.5-MHz M5S 2D and 1.5–4.0-MHz 4-V transducers. Heart rate (HR) was recorded continuously via a three-lead electrocardiogram.
Two-dimensional and Doppler assessments
Dynamic two-dimensional grayscale images were acquired in the apical four-chamber, apical two-chamber, and LV long-axis views. Images were imported into the EchoPAC software (Version 204, GE Healthcare, Milwaukee, WI, USA) and analyzed off-line. Left atrial diameter (LAD) measurements were made in the parasternal long-axis view (2D-Mode) at end systole. M-mode measurements were performed to determine the thickness of the end-diastolic interventricular septal thickness (IVSTd), LV posterior wall thickness in diastole (PWTd), LV diameter in diastole (LVEDd), and LVEF. Pulsed-wave Doppler echocardiography was used to measure early (E) and late (A) blood flow velocities through the mitral valve. The peak early diastolic velocity (e’) was measured on the septal corner of mitral annulus using tissue Doppler. The E/A, E/e’, and left ventricular mass (LVM) were calculated from LV linear dimensions using the American Society of Echocardiography recommended formula of (0.8 × 1.04[(LVIDd + PWTd + SWTd)3 −(LVIDd)3] + 0.6 g). The LVMI was determined by indexing LVM to the BSA, and relative wall thickness (RWT) was calculated as the ratio of the sum of the IVSTd and PWTd in end-diastole to the LVEDd.
4D volume and strain assessment
The 4D probe was used to collect the apical four-chamber full-volume dynamic images, where the volume frame rate was adjusted to be >40% of the subjects' heart rate, and the subjects were asked to hold their breath to obtain the dynamic images. After the images were imported into the workstation, the 4D Auto LAQ option was selected and the software automatically identified and wrapped the LA intima, which could be adjusted manually to reduce the error. The 4D LA images were then obtained by selecting “Result”. The following LA parameters were analyzed by the software: maximum atrial volume (LAVmax), minimal atrial volume (LAVmin), volume before atrial contraction (LAVpre-a), left atrial ejection fraction (LAEF), left atrial reservoir longitudinal strain (LASr), conduit longitudinal strain (LAScd), contraction longitudinal strain (LASct), reservoir circumferential strain (LASr-c), conduit circumferential strain (LAScd-c), and contraction circumferential strain (LASct-c). Left atrial active ejection fraction (LAaEF) and left atrial passive ejection fraction (LApEF) were calculated using the following respective formulas: LAaEF=(LAVpre-LAVmin)/LAVpre×100% and LApEF=(LAVmax-LAVpre)/LAVmax×100%. The 4D LAQ technique for the analysis of the 4D LA parameters in the study subjects is shown in Figure 1.
All of the above parameters were measured by the same experienced doctor, and the average values were taken for three consecutive measurements.
The analyses were performed using the statistical software, SPSS21.0 (IBM, NC, USA). Normality for the continuous variables was determined using the Kolmogorov-Smirnov test. Normally distributed continuous data with equal variance were compared between two groups using the independent samples t-test. Otherwise, the corrected t-test was used. The Mann-Whitney U test was used to compare the non-normally distributed variables in the two groups. Pearson correlation analysis was performed to assess the potential association between conventional echocardiographic indexes and 4D LA parameters. In addition, the receiver operating characteristic (ROC) curve was used to identify the optimal diagnostic indices for LA function changes. The absolute values for LAScd and LASct were used for Pearson correlation and ROC analyses.