The Study Of Left Ventricular Apical Transmul Mechanics Myocardium In Vivo Using Quantitative Tissue Doppler Strain Imaging

Objective To assess left ventricular apical peak radial strain and time-to-peak strain of segment,subendo,mid and subepi at baseline (the control region), and after ischemia at ischemic region, stunned region, nonischemic region respectly using quantitative tissue Doppler strain imaging.To observe the mechanical patterns during acute myocardial ischemia. To demonstrate the mechanical patterns of different regioal myocardium after acute myocardial ischemia. For the assessment and better the understanding of the left ventricle remodeling mechanism and asynchronization.Methods Left anterior descending coronary artery (LAD) was ligated in experimental open-chest Beagle canine models (n=9) for acute ischemia.the two-dimensional apical short-axis views of left ventricle in three complete cardiac cycles were acquired and stored in TDI-Q workstation at baseline, and after ischemia at ischemic region, stunned region, nonischemic region respectively.Sampling volume was uesd to measure the systolic S and the T of segments and different layers (subendocardium,medium,subepicardium) consesquently on the derived M–mode tissue Dopperlar velocity images at the different segments and layers. Statistical analyzing was performed using student's T- test and pearson,s correlations.Results ischemic region: S decreased at subendocardium, medium, subepicardium (p <0.05); the difference between layers disappeared, and the T at different layers of myocardium is significantly postponed (p<0.05). stunned region:S decreased at stunned subendocardium (p<0.05), with no significant difference between those at baseline and at stunned the medium (p>0.05),the S increasd at stunned subepicardium (p<0.05), and the T at different layers of stunned myocardium is significantly postponed (p<0.05).nonischemic region: S increased at subendocardium, medium, subepicardium, and the T at different layers is mild postponed (p>0.05). There was a significant correlationship of peak radial strain between subendocardium and segment as well as between the medium and segment at baseline(rSsubendo vs Ssegment=0.617,p<0.01; rSmid vs Ssegment =0.556,p<0.01 ) .This correlationship disappeared at ischemic region, stunned region and nonischemic region after acute myocardial ischemia.Conclusions1.Transmural mechanical remodeling at stunned myocardium of left ventricular apex was the result of mechanical interactions between ischemic and nonischemic myocardium, which might be one of the triggers for the structural and fundational remodeling processes involving in the pathophysiological foundation of ischemic abnormal mechanics.2.The S decreased at subendocardium, medium, subepicardium at ischemia region, which reflected that the ischemia region was dysfunction.3.The S increased at subendocardium, medium, subepicardium at nonischemic region, which reflected that the nonischemia region was hyperkinesia.4.The ischemic region was dysfunction and the nonischemic region was hyperkinesia. This discoordination maybe induce left ventricular dyssynchrony, untill heart failure.