R. Wayne Barbee

Combination of dobutamine and myocardial contrast echocardiography to differentiate postischemic from infarcted myocardium

OBJECTIVES This study tested whether the combination of dobutamine echocardiography (DE) and myocardial contrast echocardiography (MCE) was superior to either technique alone in identifying postischemic myocardium and in differentiating it from necrotic myocardium. BACKGROUND Wall motion abnormalities at rest occur in postischemic myocardium in the presence of infarction, stunning or hibernation, alone or in combination. Various investigators have suggested that either DE or MCE can be used to identify the presence of myocardial viability. METHODS We studied a total of 53 mongrel dogs in an open chest model of coronary occlusion of various durations followed by reperfusion and dobutamine administration (10 microg/kg body weight per min). MCE with aortic root injections of Albunex (area under the curve) and DE (percent thickening fraction) were performed at the different stages. Postmortem triphenyltetrazolium chloride (TTC) staining was used to identify myocardial necrosis. RESULTS Thirteen dogs underwent brief (15 min) occlusions and developed no necrosis (Group I). Of 40 dogs that underwent prolonged (30 to 360 min) occlusions, 14 had no infarction (Group II), whereas 26 did (Group III: 12 papillary muscle, 7 subendocardial, 7 transmural). MCE (expressed as percent change from baseline) demonstrated changes that paralleled the blood flow changes observed by radiolabeled microspheres at all interventions (r = 0.67, p < 0.0001). Regional ventricular function improved with dobutamine administration in the ischemic region in all three groups. The sensitivity (88%) for detecting myocardial viability was superior when the two techniques were combined; however, a poor specificity (61%) was observed. CONCLUSIONS Contractile reserve and perfusion data are complementary when assessing regional wall motion abnormalities in postischemic myocardium. DE alone cannot differentiate postischemic from infarcted myocardium; simultaneous data on myocardial perfusion are required. The combination of DE and MCE is superior to either technique alone for identifying the absence of myocardial necrosis.

733-3 Successful Transplantation of Myoblasts into Adult Porcine Myocardium: A Potential Method to Repair a Failing Heart

The profound shortage of organ donors continues to fuel the search for other methods to refurbish a failing heart. The use of transgenic cells transplanted (Tx) in syngeneic rodents has shown modest success, but allogeneic and xenogeneic transplants have not been uniformly successful. To assess the feasibility of xenogeneic and allogeneic myoblast transplantation, six adult swine underwent transplantation of murine atrial tumor cells (Xenogeneic) and neonatal porcine myocytes (Allogeneic) into the left ventricular wall. Following general anesthesia, isolated cells were injected along the anterior and posterior wall ofthe porcine left ventricle (six sites per animal). All the animals were immunosuppressed with cyclosporine and prednisone and were followed for 1 month post-injection and then sacrificed. Results are as follows: In all 36 injected sites, the Tx cells proliferated within the host myocardium with no significant rejection. CPK MB did not increase after the procedure indicating that there was no damage to the host myocardium from the injection of cells. Moreover, Tx cells formed close associations with host myocytes that resembled intercalated discs on electron microscopy, and were composed of PAN cadherin on immunofluorescent staining. These cells also contained myofibrils and other cell architecture that resembled normal AT-l or neonatal myocytes. Additionally, these cells produced angiogenic factors resulting in a proliferation of the surrounding microvasculature. In conclusion, these findings indicate successful xenogeneic and allogeneic myocyte cell transplantation in a large animal model. These experiments set the stage for future studies testing the ability of these cells to form a syncitium, contract, and thereby “repair” a damaged heart.