Mario F. Meza

Myocardial contrast echocardiography: reliable, safe, and efficacious myocardial perfusion assessment after intravenous injections of a new echocardiographic contrast agent.

Reliable and reproducible myocardial opacification after intravenous administration of echocardiographic contrast agents has remained elusive. This study was performed to determine whether a new agent, FS069, a suspension of perfluoropropane-filled albumin microspheres (3.6 microns average microbubble size, concentration 8 x 8(8)/ml), could achieve safe and successful myocardial opacification in open-chest dogs. Seventeen dogs (group 1, n = 7, group 2, n = 10) underwent two-dimensional echocardiography before, during, and after the administration of intravenous FS069. Safety was evaluated by measuring arterial and pulmonary artery pressures, heart rate, blood gases, systolic function, myocardial blood flow, and postmortem analysis of myocardial viability by triphenyl-tetrazolium chloride staining. Efficacy to detect changes in regional myocardial perfusion was assessed by injecting FS069 at baseline, after sequential coronary occlusions and reperfusion, and during intravenous vasodilators with and without coronary occlusions. Results were compared with radiolabeled microspheres. FS069 was found to be safe and effective. In the absence of coronary occlusions, uniform myocardial opacification was observed in all dogs. A perfusion defect was observed in all dogs during coronary occlusions. Background-subtracted peak contrast intensity in the myocardium correctly identified regional myocardial blood flow changes and showed a significant correlation with radiolabeled microspheres (r = 0.65, p = 0.0001).

Myocardial contrast echocardiography in human beings : Correlation of resting perfusion defects to sestamibi single photon emission computed tomography

The presence of myocardial perfusion abnormalities is generally accepted to suggest underlying coronary artery disease. In previous animal studies, myocardial contrast echocardiography (MCE) has been shown to be useful in delineating areas at risk after coronary occlusions. We sought to compare the presence or absence, size, and location of perfusion defects detected in human beings by MCE and sestamibi single photon emission computed tomography (SPECT). Regional wall motion was qualitatively assessed in the parasternal and apical views of a resting two-dimensional echocardiogram. Coronary angiography was performed in all patients and myocardial contrast echocardiography performed with 2 ml of intracoronary sonicated meglumine (Nycomed). A cine loop of the digitized contrast echocardiograms was used to analyze perfusion defects. Gated SPECT resting images in standard views were obtained after technetium 99m sestamibi (20 mCi) was administered. Visually perceived perfusion defects were established at 30% of maximal counts at end diastole. Perfusion defects by both techniques were planimetered, assigned to one of three perfusion artery territories, and expressed as a percentage of the perfusion territory studied. Comparison was made by linear regression analysis. Forty-one patients were studied. Perfusion defects were observed in 12 (29%) patients by MCE, 19 (46%) patients by SPECT, and 11 (27%) patients by both techniques. No perfusion defects were detected by MCE in 29 (70%) patients, by SPECT in 22 (53%) patients, or by either technique in 21 (51%) patients. The two techniques agreed in 78% of the patients. In 67 matching orthogonal views suitable for comparison between the two techniques, an 82% concordance for the presence or absence of defects was observed. The location of the defects matched in 86% of the cases. A significant correlation (p < 0.001; r = 0.62) between these techniques was observed in assessing the size of perfusion defects. In conclusion, our results suggest that MCE and sestamibi SPECT are comparable techniques for detecting severely underperfused myocardium in human beings.

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.

Potential clinical implications of abnormal myocardial perfusion patterns immediately after reperfusion in a canine model: A myocardial contrast echocardiography study

During myocardial infarction, lack of myocardial opacification after reperfusion has been associated with poor or no recovery of function. We have previously documented the presence of perfusion abnormalities after brief coronary occlusions without infarction and the absence of perfusion abnormalities after prolonged occlusions with infarction. To characterize myocardial perfusion patterns immediately after reperfusion, we studied 53 animals in two groups in a coronary occlusion-reperfusion model. Temporary occlusions (group 1, 15 minutes; group 2, 30 to 360 minutes) were performed, followed by reperfusion with and without dobutamine. Myocardial contrast echocardiography was performed with aortic root injections of sonicated 5% serum human albumin (Albunex) during each intervention. Group 1 dogs showed no evidence of myocardial infarction. In group 2, 26 of 40 dogs had infarctions. After reperfusion, no perfusion abnormalities were seen in 13 of 26 group 2 dogs with infarctions; perfusion abnormalities were identified after reperfusion in 2 of 13 group 1 and in 8 of 14 group 2 dogs without infarctions. In animals subjected to prolonged ischemia, the absence of perfusion abnormalities after reperfusion did not rule out the presence of necrosis. Similarly, in animals without infarction subjected to ischemia, the presence of a perfusion defect after reperfusion did not represent the presence of necrosis but an abnormal microvascular reserve. These results suggest that early after reperfusion, assessment of perfusion by myocardial contrast echocardiography has significant limitations in the evaluation of myocardial viability and salvage.

Identification of Perfusion Abnormalities Using FSO69, a Novel Contrast Agent, in Conscious Dogs

Recent advances in the production of echocardiographic contrast agents has resulted in the ability to delineate areas of hypoperfusion after coronary occlusions and stenoses following their intravenous injection. Most of these studies though have been done in open chest animals. This study was done to determine if we could assess myocardial perfusion following the intravenous administration of FSO69, a suspension of perfluoropropane filled albumin microspheres (3.6 μm average microbubble size, concentration 8 × 108), in spontaneously breathing closed chest dogs. Twenty‐seven mongrel dogs were instrumented on day 1. The chest was then closed and the dogs were restudied 3–7 days later, while spontaneously breathing. Homogeneous perfusion was observed in most dogs by all three independent and blinded observers. Perfusion abnormalities were likewise identified in most instances by all blinded reviewers on interventions designed to decrease regional blood flow. A good correlation between perfusion defect size between investigators was observed. In summary, our data suggest that FSO69 can be used to assess regional myocardial perfusion in spontaneously breathing dogs. These results support its use in humans.