Safety and Risk-Benefit Profile of Microbubble Contrast Agents in Echocardiography

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Citation
Asia Pacific Cardiology - Volume 2 Issue 1;2008:2(1):47-49

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Ultrasound contrast agents capable of transpulmonary passage following intravenous injection have been commercially available since the 1990s. These agents are microbubbles, which are smaller than red blood cells and persist long enough (due to reduced rate of gas diffusion) to reach the left ventricle (LV).1–3 Ultrasound contrast agent applications included LV cavity opacification, enhancement of spectral Doppler signals and evaluation of myocardial perfusion at rest or post-stress.3 The commercially available second-generation ultrasound agents are approved by the US Food and Drug Administration (FDA) only for the enhancement of LV endocardial delineation in patients with baseline suboptimal examinations.3 There are currently two commercially available ultrasound contrast agents in the US: Optison™ (perflutren protein-type A microspheres, GE Healthcare, Buckinghamshire, UK) and Definity® (perflutren lipid microspheres, Lantheus Medical Imaging, North Bellirica).

Efficacy of Ultrasound Contrast Agents

Although tissue harmonic imaging has significantly enhanced the diagnostic quality of baseline transthoracic echocardiography,4 the increasing prevalence of obesity and lung disease has added an extra layer of challenge; at least 10–15% of echocardiograms are technically difficult or non-diagnostic despite the use of harmonic imaging. The proportion of non-diagnostic studies is significantly increased during stress echocardiography and in echocardiograms performed in the intensive care unit.3
In non-selected patients, contrast-enhanced echocardiography leads to more accurate assessment of LV volumes and ejection fraction compared with magnetic resonance imaging.5,6 Even with the use of harmonic imaging, ultrasound contrast enhances accuracy and reproducibility in calculation of LV systolic function.6 In selected patients with excellent echocardiographic windows and adequate endocardial visualisation of all segments with harmonic imaging, the utilisation of contrast echocardiography reduces inter- and intra-reader variability in the assessment of LVEF.7
In patients with abnormal LV systolic function undergoing evaluation for LV remodeling, the use of ultrasound contrast agents reduces reader variability and increases accuracy compared with harmonic imaging with computed tomography as a reference standard.8 In intensive care patients, the use of ultrasound contrast agents increases the diagnostic yield of both individual myocardial segment evaluation and overall LV function assessment, and should be considered in all patients with non-diagnostic studies.9

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References
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