Detection Of Stunned Myocardium Using Speckle Tracking Echocardiography Combined With Low-dose Dobutamine Stress

Objective: To evaluate the difference of mechanical parameters indifferent conditions between stunned myocardium and adjacent normalmyocardium using low-dose dobutamine stress (DBS) combined withtwo-dimensional speckle tracking imaging (2D-STI), and to explore thepotential mechanisms.Methods: The acute myocardium ischemia/reperfusion (I/R) of anteriorwall of left ventricle was induced with60minutes occlusion of leftanterior descending coronary artery (LAD), and with reperfusion of120minutes in10open-chest beagle dogs. DBS was administeredcontinuously via vein with two different dose of5ug/kg/min and10ug/kg/min. At baseline, post reperfusion, after the first DBS and thesecond, standard gray-scale images of three standard left ventricular shortaxis at the levels of mitral annulus, papillary muscle and apex wereacquired. Speckle tracking workstation was used to analyze the systolicpeak of circumferential strain (CS), radial displacement (RD) of eighteensegments of subendocardium and subepicardium. left ventricularend-systolic dimension(LVIDS), left ventricular end-diastolic dimension(LVIDD), left ventricle eject fraction(LVEF), heart rate(HR), aortic valveforward flow velocity time integral(AV-VTI) were also measured. The difference and correlationships were analyzed between them.Results:①There was no statistical significance (P>0.05) under the conditions ofbaseline, post ischemia/reperfusion, the first DBS and the second forLVIDD、LVIDS、LVEF、HR and AV-VTI.②Compared with the value at baseline, the peak systolicsubendocardium CS, RD decreased significantly at the apex andmiddle of short-axis anterior wall of LV; The parameters of thefirst DB stress was significantly increased compared with the I/R（P<0.05）; There was no difference between the two DB stress（P>0.05）. The peak systolic subendocardium CS, RD at the bottomsegment of LV were not different under the four conditions.③The peak systolic subendocardium RD of anterolateral wall andanterior septum of LV at the level of papillary muscle anteriorseptum decreased to some degree like those at the anterior wall.However, it increased correspondingly. There was no change in thefour conditions for anterior septum and anterolateral wall.④The peak systolic subepicardium CS of anterior septum of LV at thelevel of papillary muscle was the same as the anterior wall, whichdecreased to some degree after I/R, and correspondingly increasedafter the first DB stress. There was no difference for anterior septumand anterior wall under the four conditions. Conclusions:⑴Low–dose dobutamine stress combined with two-dimensionalspeckle tracking imaging can detect stunned myocardiumprecisely.⑵After the occurrence stunning myocardium, the peak systolicsubendocardium RD decreased slightly, subepicardium RD wasnormal, the subendocardium CS of the surrounding myocardiumwas still normal, and the peak systolic subepicardium CS decreasedto some degree.