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Influence of Contrast Agent Dose and Ultrasound Exposure on Cardiomyocyte Injury Induced by Myocardial Contrast Echocardiography in Rats¹

¹ From the Departments of Radiology (D.L.M., C.D.), Internal Medicine (Cardiology) (P.L., W.F.A.), Pathology (D.G.), and Cell and Developmental Biology (C.A.E.), University of Michigan Medical Center, 3315 Kresge III, 200 Zina Pitcher Pl, Ann Arbor, MI 48109-0553. From the 2004 RSNA Annual Meeting. Received August 25, 2004; revision requested October 29; revision received November 19; accepted December 20. Supported by U.S. Public Health Service grant EB00338, awarded by the National Institutes of Health, Department of Health and Human Services. Address correspondence to D.L.M. (e-mail: douglm{at}umich.edu).

PURPOSE: To detect specific cardiomyocyte injury induced by myocardial contrast material–enhanced echocardiography (ie, myocardial contrast echocardiography) in rats and to ascertain the influences of contrast material dose and ultrasound exposure on this injury.

MATERIALS AND METHODS: All animal procedures were approved by the university committee for the use and care of animals. Myocardial contrast echocardiography with 1:4 electrocardiographic (ECG) triggering was performed at 1.5 MHz in 61 anesthetized rats. Evans blue (EB) dye was injected as the vital stain for cardiomyocyte injury. At the start of myocardial contrast echocardiography, which lasted 10 minutes, perflutren lipid microsphere–based contrast material was infused through the tail vein for 5 minutes. Premature heartbeats were counted from the ECG record. The numbers of EB-stained cells counted on sections of heart specimens obtained 24 hours after myocardial contrast echocardiography and then either fresh frozen or embedded in paraffin were determined by using fluorescence microscopy. Results were compared statistically by using t tests and Mann-Whitney rank sum tests.

RESULTS: EB-stained cells were concentrated in the anterior region of the myocardium. In the paraffin-embedded specimens, EB-stained cells were often accompanied by but largely separate from areas of inflammatory cell infiltration. At end-systolic triggering with a 50 µL/kg dose of microsphere contrast material, the EB-stained cell count increased with increasing peak rarefactional pressure amplitude, with significantly increased cell counts at 1.6 MPa (P < .02) and 2.0 MPa (P < .005) relative to the cell counts at sham myocardial contrast echocardiography. Premature heartbeats had a similar exposure-response relationship; however, number of premature heartbeats and EB-stained cell count did not appear to be directly related (coefficient of determination r² = 0.03). The EB-stained cell counts at end-diastolic triggering were not significantly different from those at end-systolic triggering (P > .1). EB-stained cell counts increased with increasing contrast material dose, from 10 to 50 µL/kg, at 2.0 MPa.

CONCLUSION: Cardiomyocyte injury was induced by the interaction of ultrasound pulses with contrast agent microbubbles during myocardial contrast echocardiography in rats, and the numbers of injured cells increased with increasing contrast agent dose and ultrasound exposure.

© RSNA, 2005

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