Transmural Heterogeneity In Integrated Backscatter Of Recovery In Infarcted Myocardium After PTCA

Objective: Ultrasonic backscatter of the heart is a new application of echocardiography to evaluate the structural and functional state of myocardium. This method provides quantitative indexes of the heart's physical properties and variations due to pathophysiological changes. The cyclic variation of integrated backscatter (CVTB) is an expression of regional intramural myocardial contractile performance and is related to contractility, but is not directly dependent on inotropic state changes. In normal conditions, myocardium has a transmural heterogeneity of contraction: contractility decreases from subendocardium to subepicardium. Available data on myocardial contractility heterogeneity during ischemia have been exclusively obtained in animal studies, because techeniques of evaluating the transmurality of ischemia are quite complicated and are often invasive. To investigate the clinical application of myocardial backscatter in studying the transmural heterogeneity of recovery in infarcted myocardium after reperfusion therapy, we evaluated the behavior of CVIB in patients with acute myocardial infarction in the different transmural layers, before and after reperfusion therapy.Methods: 'Commercially available echocardiographic equipment (HP Sonos 5500) with a S3 transducer was used in this study. IBS data were acquired and analyzed using an Acoustic-Densitornetry system. The infarcted myocardium of a group of patients with acute myocardial infarction were measured on the day before PTCA, and the third day, the 21st day, the third month after PTCA. And the CVIB in total layers, the layers of subendocardium and subepicardium and TGCV, TGI as well as the wall thickening (WT) were calculated. Another group of healthy volunteers were enrolled in this study as contrasts.Results: The normal myocardium has a trarismural heterogeneity, and the value of CVIB was greater in the subendocardium than in the subepicardium. TGCV=1.23± 0.53(dB), TGI=0.22±0.08 (P<0.01). In patients with AMI, the IBS parameters and WT were decreased before PICA, and CVIB in the subendocardium was similar to that in the subepicardium. After PICA, the recovery of CVIB in the subepicardium was quicker than in the subendocardium. The recovery of CVIB in the subendocardium behaves blunt in the early of reperfusion. WT increased more slowly than overall myocardial CVIB. TGCV and TGI decreased on the third day after PTCA, and recovered significantly since the 21st day. WT correlated closely with CVIB in the subepicardium, but not with that in the subepicardium (p<0.01).Conclusions:1. There is a transmural gradient in CVIB of normal myocardium. The value of CVIB is greater in the subendocardium than in the subepicardium. This proves that the transmural heterogeneity of myocardial contraction exists in the human heart.2. The transmural heterogeneity of infarcted myocardium decreases, and CVIB in the subendocardium is similar to,that in the subepicardium. The values of TGVC and TGI are descented.3. The transmural heterogeneity occurs during recovery of post-infarcted myocardium. The magnitude of CVIB rise more quickly in the subepicardium than in the subendocardium, with a 'subendocardial stunning' phenomenon. In addition there is a post-infarcted dissociation between CVIB and WT recovery time. This may be explained by the transmural heterogeneity.4. Integrated backscatter can detect the transmural heterogeneity of myocardium quantitatively, and could provide the information of the recovery in infarcted myocardium after reperfusion convenientely in time. This method has a widely prospect in studying the transmural heterogeneity.