Ultrasound Strain Imaging of Altered Myocardial Stiffness

Abstract

Background— In this study we evaluate the diastolic deformation of ischemic/reperfused myocardium and relate this deformation to tissue elastic properties. Methods and Results— Farm pigs were subjected to left anterior descending coronary artery occlusion followed by reperfusion to create either stunning (n=12) or transmural myocardial infarction (n=12). Ultrasound-derived radial strain rates (SR) and strain were measured in the ischemic and remote walls. Myocardial stiffness was estimated from diastolic pressure–wall thickness relationship obtained from preload alterations. At reperfusion, end-systolic strain (ε sys ) was significantly reduced in both stunned and infarcted walls compared with their remote walls (3±3% versus 26±2% and 1±0% versus 33±5%, respectively; P <0.0001) or baseline values. Diastolic passive deformation (ε A ) and rates of deformation during early (E SR ) and late (A SR ) diastole were comparable between stunned and remote walls (ε A : 7.3±1.6% versus 7.9±1.9%; E SR : −2.7±0.4 s −1 versus −2.6±0.5 s −1 ; A SR : −1.8±0.2 s −1 versus −1.9±0.3 s −1 ; P =NS for all) but were of significantly lower magnitude in infarcted walls versus remote walls (ε A : 1.1±0.2% versus 11.4±1.9%; E SR : −0.3±0.1 s −1 versus −2.4±0.4 s −1 ; A SR : −0.3±0.1 s −1 versus −2.5±0.4 s −1 ; P <0.0001 for all). Stiffness coefficient of exponential diastolic pressure–wall thickness relation was higher for infarcted ( P <0.05) but not for stunned walls ( P =NS) compared with their remote walls. Conclusions— Early after postischemic reperfusion and in the presence of severely reduced systolic deformation, diastolic passive deformation (and rates of deformation) can distinguish stiff, noncompliant, transmurally infarcted myocardial walls from those more compliant walls containing viable but stunned myocardium.