Objective: To evaluate the feasibility and value of determining myocardial perfusion and regional systolic function by myocardial contrast stress echocardiography (MCSE) with computer-assisted technique in a rabbit model of ischemia/reperfusion injury.
Methods: Rabbits underwent 30-(Group I, n = 15) and 120-(Group II, n = 15) minute left ventricular branch of the left circumflex coronary artery occlusion foll owed by 60-minute reperfusion, dobutamine at increasing doses (5, 10, 15 and 20 microg.kg(-1).min(-1)) was then infused after reperfusion for 15 min. Bolus myocardial contrast agent was injected and MCSE performed at baseline, at the end of coronary occlusion and reperfusion, at the end of each dobutamine infusion. Images were analyzed by computer-assisted technique and myocardial calibrated contrast intensity (CI) of each segment was measured and a color-coded map was then obtained automatically (yellow: from 0 to -20 pix, blue:from -21 to -40 pix, green: from -41 to -70 pix, red: < -70 pix). The area at risk and infarct area obtained by red-coded map were compared with ex vivo results determined by fluorescent microsphere and triphenyl-tetrazolium chloride (TTC) staining. Percentage wall thickening (WT) of each risk segment at each stage were also measured.
Results: (1) During occlusion, WT in the areas at risk decreased to zero or negative and the calibrated CI values were significantly lower than those at baseline. Area at risk obtained by red-coded map correlated well with that obtained by fluorescent staining (r = 0.91, P < 0.01). (2) After reperfusion and 5 microg.kg(-1).min(-1) dobutamine administration, WT and calibrated CI in all rabbits remained depressed. Calibrated CI at -70 pix was an optimal cutoff point to identify infarcted segments (sensitivity 95%, specificity 87%). The correlation between the infarct size by red-coded image and TTC was 0.89 (P < 0.01). (3) Calibrated CI and WT significantly improved in Group I rabbits while these parameters remained unchanged in Group II rabbits after increasing doses of dobutamine post ischemia.
Conclusions: Myocardial contrast stress echocardiography in combination with computer-assisted analysis technique are valuable techniques to quantitatively assess myocardial perfusion and regional systolic function and exactly identify stunned myocardium and infarcted myocardium.