Discussion
From this study, we tested the diagnostic value of 2D, 3D strain and 3D volumetric analysis in detecting early changes of left ventricular function in breast cancer patients who was undergoing anthracycline chemotherapy. In particular, we further assessed and compared the global and segmental longitudinal strains about the left ventricle derived from 2D strain and 3D strain.
The findings of the study indicated that: 1) on standard 2D echocardiographic examination, with the cumulative doses of anthracycline increased 2D derived EF decreased gradually and the E/e’ ratio representing left ventricular diastolic function increased significantly; 2) on RT-3DE examination, the 3D volumetric parameters, especially 3D derived EF can detect changes that cannot be seen by two-dimensional echocardiography in time; 3) on 2D and 3D STE examination, The subclinical changes of LV longitudinal function can be found in the early stage of the course of the disease, whether it is the GLS parameters derived from 2D strain or the GLS parameters derived from the 3D strain. The difference is that 3D-derived GLS earlier, besides, 3D derived STE all the strain components decreased obviously with the cumulative doses of anthracycline increased. 4) After anthracycline chemotherapy, although the decrease degree of peak systolic strain in each myocardial segment was different, the apical segments were found to be the most vulnerable.
According to the time of occurrence, the myocardial damage caused by anthracyclines can be listed as three categories: acute, chronic, delayed cardiotoxicity. In most patients, cardiotoxicity can occur quickly after anthracycline administration, and the damage is obvious with the extension of time. The chronic and delayed cardiotoxicity of anthracyclines were positively correlated with their cumulative dose[22, 23]. Echocardiography and CMR have the advantage of obtaining information on cardiac structure and function, and both can avoid radiation exposure. More convenient and cheaper echocardiography is the first choice for most patients during monitoring. Monitoring the changes of LVEF is still the basis for the identification of cardiotoxicity. From this study, we could find both 2D derived EF, and 3D derived EF decreased with the increased doses of anthracycline[24]. And studies have proved that 3D derived EF and CMR have similar accuracy[25]. However, compared with STE, it is not sensitive to detect early myocardial damage, because a detectable decrease in EF occurs only after a large amount of myocardial tissue is lost, and this is consistent with recent research[26].
Anthracycline-based cardiac toxicity induced by drugs is characterized by myocardial cell death and irreversible cardiac injury. Because the affinity of the anthracycline with myocardial tissue is significantly higher than that of other tissues, so myocardial tissue is more likely to be damaged. The early cardiotoxicity is characterized by cardiomyocyte edema and degeneration, followed by cardiomyocytes myolysis, sarcoplasmic reticulum distortion, replaced by fibrous tissue, and even cardiomyocyte necrosis, resulting in heart failure. The basic structure of myocardium is made up of circumferential fibres in the mid-wall layer, the endocardial layers and epicardial layers are composed of longitudinal and oblique muscle fibres[27]. In an analysis by Crosby et al., researchers found that the absolute values of the peak strain of ventricular septum contraction in each segment after myocardial injury were different, and our results also confirmed this[28]. According to the latest recommended by the American college of cardiology section 17 section method, the left ventricular segmental 17 bull ’s-eye map blood supply distribution, the left anterior item first-just branch (left anterior descending, LAD) supply basal anterior(BA),basal anteroseptal(BAS), mid anterior(MA) , mid anteroseptal(MAS), apical anterior(AA), apical septal(AS) , apex section, right coronary (right coronary artery, RCA) supply basal inferoseptal(BIS), basal lateral(BL), mid inferoseptal(MIS), mid lateral(ML), apical inferior(AI) segment, and the left circumflex branch (left circumflex artery, LCX) supply basal inferolateral(BIL), basal anterolateral(BAL), mid inferolateral(MIL), mid anterolateral(MAL), apical lateral(AL) segment[29]. From the findings of this study, most of the descending segments belong to the blood supply region of the left anterior descending branch, and the trend of the apical segments were the most obvious. And 3D GLS was detected earlier than 2D GLS, which is more meaningful for early detection. 3D-STE the motion of echo spots from three-dimensional space by collecting real-time three-dimensional images of the heart, so it can evaluate the motion of the heart more accurately than 2D-STE.