Study Of Left Ventricular Transmural Radial Displacement During Acute Myocardial Ischemia And Left Ventricular Pacing In Vivo: A Canine Model By Tissue Doppler Imaging

Objective: To evaluate the change of myocardial segmental and the transmural peak radial displacement (RD) of left ventricular (LV) wall during acute myocardial ischemia and in different pacings patterns. To provide a reliable data base for the optimal mechanical evaluation of myocardial structure and function.Methods:Left anterior descending coronary artery (LAD) was ligated to induce acute myocardial ischemia in open-chest Beagle canine model (n=10). Two-dimensional gray-scale images with overlaid tissue Doppler velocity imaging in three standard LV short axis views (MV: mitral valve level, PW: papillary muscle level, AP: apical level) were acquired in a randomized sequence with acute myocardial ischemia and different pacing patterns in which conditions were sustained for five minutes in three complete cardiac cycles. Parameters including peak RD, peak RD time (RD-TC), the standard deviation of TC (RD-TSD) of 12 segments and their myocardial layers (subend:subendocardium, mid:midmyocardium, subepi:subepiocardium) were measured and analyzed using TDI-Q workstation for different electric-mechanical states.Result:â—‹1 Before acute myocardial ischemia three layers transmual myocardial peak RD showed subend>mid>subepi trend without significant difference(P>0.05); After acute myocardial ischemia, the segments and subend,mid,subepi RD of anterior wall of MV, PW and AP were decreased, other counterpart segments were increased without significant difference(P>0.05); There were no significant peak RD differences between three myocardial layers of LV wall in each different pacing patterns group; There were no significant difference of peak RD from segments and transmural layers in the different LV pacing patterns.â—‹2 Before acute myocardial ischemia the RD correlation between all global segment and its subend,mid,subepi existed; After acute myocardial ischemia, the existed RD co-relationship revealed between subend,mid,subepi and the global segment were changed(i.e.,the co-relation in AM at PW and AP levels were vanished). With acute myocardial ischemia the RD correlation of LV lateral pacing and LV border pacing were higher than that of the LV apical pacing pattern between global segment and its subend,mid,subepi.â—‹3 Before acute myocardial ischemia myocardial RD-TC at all 12 segments and subend, mid, subepi appeared before T wave; Corrected by the heart rate,myocardial RD-TC at all 12 segments and subend, mid, subepi after acute myocardial ischemia were longer than that normal separately. RD-TC of 12 LV segments and their subend, mid, subepi appeared after T wave and there were no significant differences of RD-TC among different LV pacing patterns.â—‹4 Before acute myocardial ischemia RD-TSD at the 12 segments,subend, mid, subepi showed well; RD-TSD at the 12 segments, subend, mid, subepi was significantly wider after acute myocardial ischemia than that normal(P<0.05); RD-TSD of the corresponding parts of segments during different pacing patterns were significant lower than those during acute myocardial ischemia(P<0.05).Conclusion: During acute myocardial ischemia the changes were the decreased RD, dis-connective spatial co-relationship of RD, delayed RD-Tc and wide RD-TSD; The existed RD correlation of LVA-P between subend, mid, subepi and the segment were lowest among the different ischemic LV pacing patterns; the synchronization of transmural RD could be recovered partly with different other pacing patterns. The echocardiographic study of LV transmural peak RD might be useful to reveal the segmental and the transmural myocardial mechanical states with acute myocardial ischemia in different LV pacing patterns.