MRX 115, an echocardiographic contrast agent, produces myocardial opacification after intravenous injection in primates: studies before and after occlusion of left anterior descending coronary artery

A minimally-invasive closed chest myocardial occlusion-reperfusion model in rhesus monkeys (Macaca mulatta): monitoring by contrast-enhanced ultrasound imaging

Myocardial infarction is frequently developed in canine and porcine models but exceptionally in non-human primates. The aim of this study was to develop a minimally invasive myocardial ischemic/reperfusion model in the monkey intended to be combined with imaging techniques, in particular myocardial contrast echocardiography (MCE). A balloon-tipped catheter was advanced via the femoral artery into the left anterior descending artery (LAD) under fluoroscopic guidance in ten anaesthetized male rhesus monkeys (Macaca mulatta). The balloon was inflated to completely occlude the vessel. Coronary angiography (CA) was performed to control the reality of the LAD occlusion/reperfusion. The ischemia period was followed by 3-6 h of reperfusion. Myocardial perfusion was evaluated during ischemia and at reperfusion by MCE using a novel ultrasound contrast agent (BR38). Occlusion was successfully induced during 18-50 min in nine out of the ten evaluated monkeys. ST segment elevation indicated myocardial ischemia. MCE showed complete transmural arrest of myocardial blood flow during the ischemia period and no persistent microvascular perfusion defects during reperfusion. A minimally invasive closed-chest model was successfully developed for creating myocardial ischemia in the rhesus monkey (Macaca mulatta). This technique could have an important role in mimicking acute coronary syndrome under physiologically and ethically-acceptable conditions. MCE provides non-invasively information on myocardial perfusion status, information not available from CA.

Hemodynamic instability after receiving intravenous Perflutren for contrast echocardiography in an elderly female

Myocardial contrast echocardiography (MCE) has been used with increasing frequency and is considered a safe way to improve left ventricular border opacification. Studies have consistently documented that MCE can improve the ability to assess both global and regional left ventricular function by echocardiography. We report the case of an 83-year-old female who developed immediate and sustained hemodynamic instability after the injection of Perflutren for a contrast echocardiogram. We reviewed the literature and found no such previous reactions with Perflutren. Based on the temporal sequence of hypotension following Perflutren injection along with other clinical data, we concluded that our patient's hemodynamic instability was most likely secondary to an anaphylactic reaction.

Rapid quantitative assessment of myocardial perfusion: spectral analysis of myocardial contrast echocardiographic images

We described a novel rapid spectral analysis technique performed on raw digital in-phase quadrature (IQ) data that quantitatively differentiated perfused from nonperfused myocardium based on the simultaneous comparison of local fundamental and harmonic frequency band intensity levels. In open-chest pigs after ligation of the left anterior descending coronary artery (LAD) and continuous venous contrast infusion, the fundamental-to-harmonic intensity ratio (FHIR) for samples placed within the left ventricular (LV) cavity (10.8 +/- 1.7 dB) and perfused myocardium (13.7 +/- 1.6 dB) were significantly (P <.001) lower than for nonperfused myocardium (27.1 +/- 2.9 dB). In attenuated images, the FHIR for the LV cavity and perfused myocardium were also significantly (P <.05) lower than for the nonperfused myocardium (21.4 +/- 3.0 dB, 34.4 +/- 3.2 dB, and 40.2 +/- 4.4 dB, respectively). Spectral properties of contrast microbubbles, as characterized by the FHIR, allow for rapid quantitative assessment of myocardial perfusion from data contained in a single-image frame, without requiring background image subtraction and image averaging.

Grey-scale contrast enhancement in rabbit liver with DMP115 at different acoustic power levels

The contrast enhancement effect of ultrasound (US) contrast agent DMP-115 (YM454, Definity) in rabbit liver at two acoustic transmit power levels was studied. A total of 12 rabbits with healthy livers and 7 rabbits with VX-2 tumors were used. Grey-scale ultrasonograms in both fundamental (3.75 MHz) and harmonic (2.5/5.0 MHz) imaging modes were performed at a frame rate of 26 Hz under baseline acoustic power (MI = 0.6) or lower acoustic power (MI = 0.2). The contrast enhancement depended on the contrast agent dose and the acoustic power. The video intensity change was higher in the portal vein under the baseline acoustic power and higher in the liver parenchyma under the lower acoustic power. The contrast-enhanced US observation of the VX-2 tumor in the arterial phase correlated well with the angiographic and histopathological appearance of the tumor. In the parenchymal phase, the borderline of the tumor could be clearly delineated from the surrounding liver parenchyma. Continuous fundamental and harmonic grey-scale imaging with DMP115 has the capability of making peripheral circulation images of liver parenchyma and tumors.

Efficacy and safety of the novel ultrasound contrast agent perflutren (definity) in patients with suboptimal baseline left ventricular echocardiographic images

Suboptimal left ventricular (LV) cavity visualization and endocardial border delineation often compromise the clinical utility of echocardiography. This study examines the safety and efficacy of perflutren, a novel ultrasound contrast agent, for LV cavity opacification and endocardial border delineation in patients with suboptimal baseline echocardiograms. In a multicenter, randomized, placebo-controlled, double-blind trial, 211 patients with suspected cardiac disease and suboptimal baseline echocardiograms were enrolled at 17 sites. Two intravenous injections of either placebo (saline) or perflutren (5 or 10 microl/kg) were given approximately 30 minutes apart. Images of the apical 4- and 2-chamber views were acquired and scored. Perflutren opacified the LV cavity after both dosages (5 and 10 microl/kg dosages). Clinically useful contrast was observed in 89% of patients who received perflutren and in 0% of patients who received placebo (p < 0.01). Quantitative assessment of LV opacification with videodensitometry showed similar results. The mean duration of clinically useful contrast was 90 seconds. Improvement in endocardial border delineation was demonstrated in 91% of patients who received perflutren and in 12% of those who received placebo (p < 0.001). Following perflutren, an average of 4 more segments per patient were evaluable compared with baseline. Salvage of nondiagnostic baseline examinations by perflutren was demonstrated in 48% of eligible subjects. The safety profile of perflutren was similar to placebo. These data indicate that administration of perflutren to patients with suboptimal baseline images is well tolerated and provides substantial LV cavity opacification and improvement in endocardial border delineation.

Rapid Three-Dimensional Myocardial Contrast Echocardiography: Volumetric Quantitation of Nonperfused Myocardium After Intravenous Contrast Administration

Current acquisition methods for quantitative three-dimensional myocardial contrast echocardiography require long acquisition times and therefore require the invasive administration of deposit contrast agents administered intra-arterially or into the left atrium. This study addressed the feasibility of obtaining accurate and precise quantitative volumetric measurements of nonperfused myocardium after an intravenous bolus of echocardiographic contrast agent using a rapid three-dimensional myocardial contrast echocardiographic acquisition technique. An open-chest pig model of acute left anterior descending coronary artery (LAD) occlusion was used. After LAD ligature, an intravenous bolus of contrast agent was given and images were obtained over a 12-second period using a continuously rotating transducer placed at the apical position. There was no significant microbubble destruction during the rotational acquisition period as measured by differences in mean gray scale values of apical, mid, and basal myocardial regions between the first and last image frames of acquisition. Calculated volumes of nonperfused myocardium demonstrated significant agreement and correlation (mean difference +/- SD = -0.30 +/- 1.71 cm(3); r = 0.89; P < 0.01; y = 1.06x - 1.08) with anatomic specimens. When expressed as percent of total LV volume being nonperfused, the mean difference +/- SD was 2.1 +/- 3.6%, r = 0.94, P < 0.01, and y = 1.33x - 4.08. We conclude that accurate and precise measurements of nonperfused myocardium after an acute LAD coronary artery occlusion can be obtained after the intravenous bolus administration of a contrast material when a rapid 12-second acquisition with a continuously rotating transducer is used.

In vitro studies of a new thrombus-specific ultrasound contrast agent

Ultrasound is used as a primary diagnostic technique for the detection of deep venous thrombosis. The purpose of this study is to describe the development of a new thrombus-specific ultrasound contrast agent: The linear hexapeptide (lysine-glutamine-alanine-glycine-aspartate-valine) was synthesized and coupled to a lipid moiety. The targeted lipid was then incorporated into the lipid blend for the contrast agent Aerosomes (ImaRx, Tucson, AZ, USA). The lipid blend was used to entrap perfluorobutane microbubbles. The microbubbles were sized and studied in vitro for acoustic stability, binding to blood clot, and ultrasound enhancement in vitro of blood clot. The results showed the mean size of the specific ultrasound contrast agent (MRX-408) was about 2.0 microm. The microbubbles appeared as smooth spherical structures. Microscopy showed that the targeted bubbles bound to blood clot whereas control, nontargeted bubbles did not bind to blood clot. In vitro acoustic study showed similar stability of the microbubbles compared with control microbubbles. The targeted microbubbles enhanced blood clot in vitro whereas nontargeted microbubbles did not enhance clot. Thus this promising new thrombus-specific ultrasound contrast agent could potentially improve detection of thrombosis by ultrasound and might be useful for distinguishing between new and old thrombosis. In vivo studies are in progress.

Phase I clinical trials of MRX-115. A new ultrasound contrast agent

RATIONALE AND OBJECTIVES

Stabilized microbubbles are under development as contrast agents for medical ultrasound. The authors report the results of Phase I clinical trials of a new ultrasound contrast agent based on lipidencapsulated perfluorocarbon gas microbubbles.

METHODS

Lipids encapsulating perfluoropropane gas (Aerosomes MRX-115, ImaRx Pharmaceutical Corp., Tucson, AZ) were evaluated in Phase I clinical trials. Two separate studies were performed. The first was a single escalating-dose study (n = 30 subjects), and the second was a multiple-dose study (n = 18 subjects) with rechallenge in several subjects (n = 4) after 21 days. Echocardiographic examinations were performed before and after contrast agent for each test drug administration for both studies, with the exception of the rechallenge group. Doses tested in the single-dose study ranged from 0.005 mL/kg to 0.100 mL/kg body weight. In the multiple-dose study, five doses of 0.005 mL/ kg to 0.030 mL/kg (0.025-0.150 mL/kg total dose) were evaluated. Studies were single-masked, placebo-controlled, and safety assessment and adverse events were monitored.

RESULTS

All doses in both studies were well tolerated with no treatment-related changes in safety measures for either study. Left ventricular cavity and myocardial enhancement were seen with all doses of MRX-115.

CONCLUSIONS

MRX-115 is a promising new intravascular ultrasound contrast agent that was safe and well tolerated at the doses evaluated in these studies.