Baseline clinical characteristics
As shown in table 1, both groups had similar age ranges (58.7±14.2 vs. 55.2±7.0, p=0.067) and sex distributions (male: 76.8% vs. 60.0%, p=0.054). In our study cohort, 46 (56.1%) RV dysfunctional patients were concomitant with diabetes mellitus and/or hypertension. There were also no differences in clinical characteristics of all RV dysfunctional patients with and without performing CMR (table 2).
Conventional echocardiographic parameters
The table 3 listed all the values of conventional echocardiographic parameters. Compared to the controls, the patients with RV dysfunction had significantly lower TAPSE, RV-FAC and RV s’ (all p<0.001). By contrast, the MPI were higher in RV dysfunction patients (p<0.001). Among the patients with RV dysfunction, the differences of parameters, as the TAPSE and RV-FAC, were still significant between the subgroups with and without PH (all p<0.05). However, there was no statistical differences in the parameters of RV s’ or MPI between these two subgroups (all p>0.05).
Strain parameters
Comparison of strain parameters between each two groups were summarized in Table 4. As seen in the table, the values of 3DE-derived RV-fwLS and sLS in the normal subjects were -26.7±4.7% and -15.5±4.3 %, respectively. The longitudinal strain of interventricular septum, using both 2DE and 3DE methods, were consistently lower than the corresponding values in free wall of RV for all the subjects (all p<0.001). As expected, the longitudinal strain values were severely reduced in patients with RV dysfunction than control group (all p<0.001), take 3DE-derived RV-fwLS (-14.0±4.1 vs. -26.7±4.7%; p<0.001) for instance. The RV dysfunction patients with PH had greater impairments of RV function assessed by 2DE and 3DE-derived RV-fwLS than patients without PH (all p<0.05). Among the patients with RV dysfunction, we found that there existed no difference between subgroups with ischemia and nonischemic cardiomyopathy in the deformation parameters of 2DE- and 3DE-derived RV-fwLS (-16.1±6.0 vs. -15.2±6.9%, -14.4±4.3 vs. -13.6±3.7%, all p>0.05). For the overall study population, we found that the values of 3DE-derived deformation parameters of RV showed relatively lower in magnitude than the corresponding 2DE-derived deformation parameters: RV-fwLS (-18.2±7.3 vs. -19.4±7.9%, p=0.016), sLS (-10.0±5.3 vs. -10.3±6.4%, p=0.377).
The figure 2 showed the ROC analyses of 2DE and 3DE- derived RV-fwLS to predict the patients with RV dysfunction. We detected that both 2DE and 3DE-derived RV-fwLS had good diagnostic accuracies for detection of patients with impaired RV dysfunction, while 3DE-derived RV-fwLS (AUC=0.975) showed higher predictive power than 2DE-derived RV-fwLS (0.930) (p<0.05). With a cutoff value of >-21.1% for 3DE-derived RV-fwLS presented optimal sensitivity of 90% and specificity of 85% to identify patients who are at a greater risk of RV dysfunction. On ROC analysis, we also discovered that 3DE-derived RV-fwLS had a good predictive ability to detect RV dysfunctional patients with PH (AUC=0.638), a cutoff value of >-14.13% showed the best combination of sensitivity of 70% and specificity of 52%. Moreover, 2DE-derived RV-fwLS (AUC=0.648) showed a relatively higher predictive performance than 3DE-derived RV-fwLS, and the difference came to no significance (p=0.882).
Correlation analysis
The correlations of all the echocardiographic parameters to CMR-derived RVEF were presented in figure 3. We could know from the figure that all functional parameters were correlated significantly to CMR-derived RVEF (p<0.001). Among the parameters of RV contraction, only 3DE-derived RV-fwLS showed a good correlation to CMR-derived RVEF (r=-0.747, p<0.001). The correlation coefficient between 3DE-derived sLS and CMR-derived RVEF was moderate (r=-0.458, p=0.008), weaker than 3DE-derived RV-fwLS. It was also found that 3DE-derived RV-fwLS presented higher correlations to CMR-derived RVEF than any of the following 2DE-derived deformation parameters: RV-fwLS (r=-527, p=0.002), sLS (r=-0.366, p=0.039). Meanwhile, we discovered that the conventional echocardiographic parameters (as TAPSE, RV-FAC, RV s’ or MPI) showed lower correlations to CMR-derived RVEF than either the 2DE or 3DE-derived deformation parameters of RV. As expected, 3DE-derived RVEF had strong correlation with CMR-derived RVEF (r=0.855, p<0.001).
Significant univariate and multivariate correlates of 3DE-derived RV-fwLS in all the study subjects were shown in Table 5. The presence of diabetes, hypertension, hyperlipidemia, diminished LV end-diastolic volume (EDV), and lower TAPSE were all significant univariate associates of 3DE-derived RV-fwLS. Multivariate regression analysis using a stepwise forward algorithm demonstrated that combining with diabetes, hypertension, lower LVEDV and TAPSE were the independent determinants of 3DE-derived RV-fwLS.
Observer reproducibility
Figure 4 exhibited the intraobserver and interobserver variability of measurements of 3DE-derived RV deformation parameters by Bland-Altman graphs. As presented in the figure, intra- and interobserver reproducibility was excellent for both 3DE-derived deformation parameters of RV (ICC>0.9). Intraobserver reproducibility for echocardiographic parameters of 3DE-derived RV-fwLS and sLS was 0.92 and 0.93 as assessed by ICC, and interobserver reproducibility for 3DE-derived RV-fwLS and sLS was 0.92 and 0.90, respectively. Intraobserver reproducibility for 2DE-derived RV-fwLS and sLS was 0.91 and 0.89, and interobserver reproducibility for 2DE-derived RV-fwLS and sLS was 0.92 and 0.91, respectively.