3.6 Repeatability test of 3D strain parameters
The intra-observer and inter-observer parameters showed that the intra-group repeatability test intraclass correlation coefficient (ICC ) of the left ventricular Tor and MCI were 0.868 and 0.899, respectively, and the inter-group repeatability test ICCs were 0.878 and 0.894, respectively; this indicated that the reliability and repeatability of the above parameters were relatively high (Figure 6).
Figure 6: 3D strain Parameters: Left ventricular Tor and MCI repeatability test (Bland–Altman diagram)
Discussion
As an autoimmune disease with the ability to impart chronic damage to multiple organs, SLE is characterized by remission and deterioration. Moreover, cardiovascular damage is an important cause of death and is becoming increasingly serious [5]. However, heart damage is often hidden in the early stage and can be easily ignored; if it can be detected earlier, prevention will be of great significance to the prognosis of the disease [6]. At the point when heart damage in SLE can be detected by two-dimensional ultrasound, the myocardium is seriously damaged, and the possibility of recovery is low. The 3D-STI technique eliminates the plane limitation of two-dimensional ultrasound and allows for comprehensive analysis of left ventricular wall motion such that the actual situation of the left ventricle is accurately reflected [7].
Compared with the control group, this study showed that LVEF and LVEDV in the mild-to-moderate and the severe groups decreased significantly, LV EDmass, and LV ESmass increased significantly. There was no statistically significant difference in terms of LVESV in the three studied groups. Moreover, although SPI reflected left ventricular geometry, there was no significant difference in the three studied groups, indicating that the early left ventricular systolic function may be locally impaired in SLE; however, the decline in function is not obvious, and the overall function is still within the normal range [8]. At the same time, there was a statistically significantly decrease in GLS, GCS and LVtw in the mild-to-moderate and severe groups compared to the control group, indicating that the left ventricular systolic function is damaged in the early stage. This may be due to fact that SLE can lead to the deposition of immune complexes in the cardiovascular system or inflammatory changes after complement activation that result in the degeneration of collagen fibers in the myocardial interstitium. Ultimately, this leads to damage to myocardial systolic function, which is consistent with the findings of Huang et al[9].
The results also showed that the sensitivity, specificity, and AUC of Tor were higher than those of GLS and GCS, indicating that LVtw may be a better index to reflect the changes in left ventricular systolic function than the three-dimensional strain GLS and GCS, whereas GLS is more sensitive in the three-dimensional strain[10]. This may be due to the high sensitivity of subendocardial myocardium to ischemia, so coronary artery lesions, endocarditis and myocardial metabolic disorders occur in patients with SLE. These lesions are the first to cause longitudinal myocardial injury, which lead to a decrease in systolic motor function along the long axis of the myocardium. Therefore, we conclude that the overall longitudinal strain of the left ventricle should be more sensitive to changes in ventricular systolic function than the circumference. Left ventricular torsion is also affected by the degree of myocardial contraction, the arrangement of endomyocardial muscle fibers, and the contraction balance. This is because the outer myocardial torque is larger and the contraction torque is greater. The left ventricular torsion direction is consistent with the outer myocardial rotation direction. SLE leads to a decrease in left ventricular myocardial elastic deformation ability, torsion abnormality, and amplitude, thus reflecting a decrease in left ventricular systolic function more accurately [11].
However, during collection, we found that the lack of clear anatomical reference in the apical part of the left ventricle led to differences in the location of LVtw in different patients, resulting in measurement errors. Therefore, the left ventricular Tor, which avoids this error, can be introduced as another index to evaluate left ventricular systolic function [12]. It was found that there was a statistically significantly decrease in Tor in the mild-to-moderate and severe groups compared to the control group, indicating that Tor can be used as an effective index to reflect the myocardial damage caused by SLE in the early stage. The ROC curve also showed that the sensitivity, specificity, and AUC of Tor were higher than those of LVtw, indicating that left ventricular Tor may reflect changes in left ventricular systolic function better than LVtw, with higher repeatability. At the same time, we found that myocardial deformation in the three-dimensional space is caused by myocardial strain and torsional motion. Thus, the new parameter MCI, which is composed of GLS and LVtw, may be used to evaluate left ventricular systolic function more comprehensively. The results showed that there was a statistically significantly decrease in MCI in the mild-to-moderate and severe groups compared to the control group, and the repeatability was high. The ROC curve showed the highest area and sensitivity under the left ventricular MCI curve, which was consistent with the results of Mornos et al, indicating that no single form of exercise can fully reflect the movement of the left ventricular myocardium [13]. At the same time, correlation analysis showed that there was a good correlation between MCI and hs-TropT [14]. Therefore, MCI can be used as a new sensitive index for the early detection of SLE heart injury and provide a basis for clinical intervention, timely adjustment, or change of drugs to avoid aggravation of myocardial damage, resulting in irreversible myocardial injury.
PSD is the standard deviation of the peak time of the longitudinal strain in 17 segments of the left ventricle. There was a statistically significantly increase in PSD in the mild-to-moderate and severe groups compared to the control group, indicating that the dispersion of myocardial mechanical motion is increased, that is, myocardial systolic synchronization is worse [15]. It has been suggested that the deposition of SLE-associated immune complexes in the cardiovascular system may lead to degeneration of cardiomyocytes and myocardial sympathetic nerves, which directly leads to the damage of the normal function of cardiomyocytes and the dysfunction of nerve fibers in the myocardial layer; this, in turn, has a serious impact on myocardial synchronous movement.
Limitations
The limitations of this study are as follows: (1) the image must be clear and of high quality; (2) the inspection operation and image post-processing greatly depend on the accuracy of human operation; (3) the sample size is small; (4) there are individual differences.
Conclusion
SLE can cause left ventricular systolic function damage in the early stage, and 3D-STI can be used to monitor myocardial subclinical injury at the early stage. The new parameters, including MCI and Tor, are particularly relevant as they can provide an objective imaging basis for early clinical diagnosis of left ventricular myocardial involvement and guide prognosis in patients with SLE.
Conflict of interest disclosure statement
The authors declare that they have no conflict of interest.