Biomedical subjects
Publications and source records attributed to Anthony N DeMaria.
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OBJECTIVES: We examined whether delayed post-injection imaging of a new ultrasound contrast agent (BR-14) could produce prolonged opacification and hyperenhancement of myocardium subjected to coronary occlusion/reperfusion. BACKGROUND: We hypothesized that ultrasound exposure destroyed BR-14 and eliminated visualization of sustained myocardial opacification from retained microbubbles. METHODS: We studied eight open-chest dogs with 3 h of left anterior descending coronary artery (LAD) occlusion followed by 3 h of reperfusion. Myocardial contrast echocardiography (MCE) was performed before occlusion and 120 min after the onset of both occlusion and reperfusion. Ultrasound imaging was initiated 15 min after injection. Myocardial blood flow (MBF) was assessed by microspheres. RESULTS: Pre-occlusion images revealed uniform opacification of left ventricular myocardium greater than that of the cavity, with a mean intensity of the LAD bed of 8.66 +/- 1.38 dB. During occlusion, MCE resulted in the appearance of a perfusion defect in the LAD risk area (intensity 2.08 +/- 1.10 dB). After 120 min of reperfusion, the LAD risk-area myocardium manifested dense opacification of a higher intensity ("hot spot") than baseline (13.7 vs. 8.7 dB), but with reduced MBF consistent with accumulation of a high concentration of microbubbles. Increased MCE intensity was associated with a greater myeloperoxidase score. CONCLUSIONS: These data establish that contrast opacification by BR-14 may be selectively retained within the perfusion bed of a coronary artery subjected to occlusion/reperfusion. Such opacification exhibits defects with occlusion, manifests hyperenhanced intensity (hot spot) with reperfusion, is associated with the level of myeloperoxidase activity, and conforms to the area of myocardium subjected to altered flow.
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OBJECTIVES: The purpose of this study was to examine the ability of myocardial contrast echocardiography (MCE) to assess right ventricular (RV) perfusion. BACKGROUND: Although MCE can readily assess left ventricular perfusion abnormalities, there are no data regarding the ability to assess RV perfusion abnormalities. METHODS: The right coronary artery (RCA) was occluded in 10 open-chest dogs. Myocardial contrast echocardiography was performed with 0.27 g/min Levovist infusion by harmonic power Doppler with electrocardiographically gated intermittent triggered imaging at pulsing intervals ranging from 1:1 to 1:20 at baseline and 90 min after RCA occlusion. Video-intensity of the RV wall was plotted against pulsing intervals and was fitted to an exponential function: y = A(1-exp(-bt)), where A is the plateau video-intensity and b is the rate of video-intensity rise. Myocardial contrast echocardiography and microsphere-derived myocardial blood flow (MBF) measurements were performed at baseline and 90 min after RCA occlusion. RESULTS: Because the severity of RV perfusion abnormalities assessed by MBF varied during RCA occlusion, diverse grades of patchy opacification defects were observed by MCE. The RV wall thickness decreased, and the RV dimension increased, after RCA occlusion in each dog. The correlation of occlusion to baseline MBF ratios in the RV wall was closer to the ratio of b (r = 0.897, p = 0.0004) than A (r = 0.767, p = 0.0097) and was the closest to the ratio of Axb (r = 0.935, p < 0.0001). CONCLUSIONS: The RCA occlusion is manifested by RV wall thinning and dilation as well as by perfusion abnormalities consisting of patchy opacification defects by MCE. Myocardial contrast echocardiography-derived refilling parameters can be applied to assess RV perfusion abnormalities produced by RCA occlusion.
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We sought to propose a simplified method to measure flow velocity based on ultrasonic microbubble destruction, and investigated the effect of microbubble shell fragility on such measurement. Acoustic density (AD) from the second harmonic short axis image of flow was obtained at variable velocities (2 to 73 mm/s) in an in vitro model during long (1000 ms) and short (33 ms) interval ultrasound (US) pulsing, allowing complete and partial microbubble replenishment between pulses, respectively. Microbubbles with shell elastic modulus of 0.4 MPa and 16 MPa were tested. By shortening pulsing interval, AD diminished gradually, rather than abruptly, to a plateau level for both microbubbles. The extent of AD decay was greater for the fragile than the strong microbubbles. A linear relationship existed between the magnitude of AD decay and flow velocity only in the higher and lower velocity range for the fragile and the strong microbubbles, respectively. Thus, difference in contrast intensities during long and short pulsing intervals, respectively, allowing complete and partial replenishment may provide for velocity measurement, in which choice of optimal microbubble fragility for the range of velocity to measure may increase the accuracy.
Although the coxibs have demonstrated superior gastrointestinal safety compared to traditional non-selective NSAIDs, questions remain regarding their effects on the renal and cardiovascular systems. In terms of renal function, both Type 1 and Type 2 cyclooxygenase (COX-1 and COX-2) are expressed constitutively in the kidney. Prostaglandins do not play a major role in the maintenance of renal function in healthy individuals but they become profoundly important in certain clinical situations such as renal stress, or volume depletion. In such situations the effects of the coxibs and non-selective NSAIDs are likely to be similar. The incidence of renal side effects is low (1-5%) and the patients at risk of renal complications are well defined and can usually be identified prospectively and followed up as appropriate. From the cardiovascular point of view, questions have been raised as to whether the coxibs have a prothrombotic effect. Here we review the available evidence and consider various hypotheses for an apparent increase in cardiovascular events reported in one coxib study (the VIGOR trial). Because of a lack of anti-platelet activity, coxibs are not suited for the provision of cardiovascular prophylaxis, and in patients at risk of myocardial infarction the prophylactic use of aspirin should always be considered. Although evidence suggests that use of coxibs with low-dose aspirin is safer than the combination of traditional NSAIDs with aspirin, further studies are required to confirm that this is the case.
RATIONALE AND OBJECTIVES: In myocardial contrast echocardiography (MCE), power Doppler imaging is more sensitive to contrast agent (microbubble) than gray-scale B-mode imaging; however, no data exist regarding the optimal contrast dose in power Doppler imaging. This study examined the optimal dose of contrast agent for power Doppler in assessing coronary stenosis. METHODS: Three grades of coronary stenosis were produced in 6 open-chest dogs. MCE was performed with gray-scale and power Doppler during continuous infusion of 0.2 mL/min FS-069. Thereafter, MCE was repeated with power Doppler during continuous infusion of 0.1 mL/min FS-069. RESULTS: Although the videointensity in the stenosed bed with power Doppler (214 +/- 14) was greater than gray scale (35 +/- 17) during 0.2 mL/min FS-069 infusion (P < 0.0001), power Doppler failed to identify milder coronary stenoses because videointensity in stenosed bed was quickly saturated with contrast agent. The videointensity in the stenosed bed with power Doppler (127 +/- 49) during 0.1 mL/min FS-069 infusion was greater than gray scale (35 +/- 17) during 0.2 mL/min FS-069 infusion (P < 0.0001), and all levels of stenosis were identified with power Doppler, even though the dose of contrast agent was half of that of gray scale imaging. The correlation between videointensity and myocardial blood flow was better in the case of power Doppler at 0.1 mL/min FS-069 infusion (r = 0.77, P < 0.0001) than in the case of gray scale imaging at 0.2 mL/min FS-069 infusion (r = 0.66, P < 0.01). CONCLUSIONS: These data support the need for a lower dose of contrast agent for power Doppler than for gray scale to detect milder coronary stenosis and avoid saturation of imaging fields.
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Early contrast agents could not achieve left-sided cardiac opacification because these microbubbles could not traverse the pulmonary circulation and remain intact. The specific shell material and gas used determine the properties of individual microbubbles, including fragility, persistence, and resonance. Persistence, perhaps the most important property of a microbubble, has been achieved by second-generation agents through the use of shells or surfactants and by substituting high-density, high molecular weight gas for air. Today's agents readily achieve opacification, not only of the cardiac chambers but also of the myocardium. Refinements in contrast agents and in the instrumentation for their detection are primarily responsible for these improvements.