Demographic and echocardiographic characteristics of the high risk population according to left atrial volume index
A total of 770 subjects at cardiovascular high risk in the community underwent comprehensive transthoracic echocardiogram. 55 were excluded the current study including 22 with poor image quality (unable to obtain adequate tracking quality in more than two LA segments during offline strain analysis), 14 in atrial fibrillation, and 19 with moderate or more mitral regurgitation. Among the 4314 segments analyzed in the remaining 715 subjects, the software was able to correctly track 4055 (94%) segments.
In this cross-sectional study, the average age was 66.56±8.86 years and 354 (49.51%) of the subjects were male. The existed CVD and risk factors included coronary heart disease (9.09%), stroke (20.98%), peripheral vascular disease (8.67%), HT (80.28%), DM (30.21%), smoke (33.71%), obesity (20.42%) and dyslipidemia (49.51%). According to the abnormality thresholds and severity cutoffs of LAVI in ASE/EACVI recommendation in 2015, subjects were grouped into normal LA size (LAVI 16-34ml/m2), mild LA enlargement (LAVI 35-41 ml/m2), moderate LA enlargement (LAVI 42-48 ml/m2) and sever LA enlargement (LAVI >48 ml/m2) group. Table 1 and Table 2 present demographic and conventional echocardiographic characteristics of the four study groups. Among-group differences were found in age, heart rate, the prevalence of HT (most prevalent in mild LAE group), LVMI, LVEDD, diastolic indexes (E, E/A, E/E’, A’) and PASP. There were no differences in other risk factors and medication among groups.
LA phasic strain in different LA size group
The comparison of LA strain among the study groups is shown in Table 3. Reservoir (Stot) indexes are different among groups (P =0.003) with the trend of the larger LA size the lower strain values. While contractile (Sa) indexes are maintained in mild and moderate LAE comparing with normal LA size group, but decreased in severe LAE group (P<0.001). The conduit (Se) indexes are similar among different LA size groups.
LA phasic strain between HT and non-HT groups with normal LA size
Within normal LA size group, subjects were further divided into HT and non-HT subgroups. The HT group had higher prevalence of stroke (23.91% vs. 10.17%, p<0.001) and obesity (23.65% vs. 9.32%, p<0.001) comparing with non-HT group. Differences between HT and non-HT group were also found in age (66.56±8.82 vs. 64.00±9.78years, p=0.007), body mass index (25.91±3.30 vs. 24.44±3.00 kg/ m2, p<0.001), LVMI (84.94±20.10 vs. 78.11±19.10 g/m2, p=0.001), A velocity(96.85±18.35 vs. 85.81±19.65 cm/s, p<0.001), E’ (5.76±1.63 vs. 7.12±2.29 cm/s, p<0.001), E/A (0.80±0.21 vs. 0.94±0.31, p<0.001) and E/e’ (13.80±4.10 vs. 11.67±3.67, p<0.001). There were no differences in other clinical and echocardiographic parameters. The comparison of clinical data and LA strain is shown in Table 4. Reservior (Stot) and conduit (Se) indexes are worse in HT than non-HT subgroup, while contractile (Sa) index has no difference.
Clinical and echocardiographic correlates of LA phasic strain and LAVI: regression analysis
Univariate correlations of LA strain includes demographic parameters (age, gender, body mass index, body surface area, heart rate, SBP and DBP), CVD (myocardial infarction, stroke, peripheral arterial disease), risk factors (HT, HT duration, grade of HT DM, smoke, obesity and hyperlipidemia) and echocardiographic variables (LAVI, LVEDD, LVMI, LVEF and LVSlong, E/A, E/e’, E’, A’ and PASP). Stepwise multiple regression analysis showed that the independent determinants were: for Stot — age, DM, smoking, dyslipidemia, LVSlong and A’ ; for Se — HR, dyslipidemia, LVSlong and E’ ; and for Sa — age, gender, smoking，LAVI，LVSlong，E/A，E’ and A’ . (Table 5).
Repeatability and reproducibility
The intra-observer intraclass correlation coefficient (ICC) and absolute difference for 2D STE measurements were Stot 0.97(1.62±1.45%), Se 0.98(1.43±0.76%) and Sa 0.92(1.17±0.99 %). And inter observer ICC and absolute difference were Stot 0.93 (2.07±1.73%), Se 0.89 (2.50±2.35%) and Sa 0.88 (1.76±1.23%), respectively.