Key work previously published has demonstrated that myocyte loss is associated with loss of the microvasculatureand that contrast signal intensity correlated strongly with capillary density on biopsy samples obtained from corresponding segments.
Practical Point - Using MCE to assess myocardial viabilityRest contrast images are acquired as described previously in this chapter. However, when real-time imaging is used, it is important to acquire at least 15s post-flash for optimal assessment (it has been shown that both the presence of homogenous contrast uptake and, alternatively, the absence of contrast uptake are very accurate indicators of the presence or absence of myocardial viability, respectively). It is, however, important to exclude apical and basal artefacts before concluding that there is absent contrast uptake. High MI imaging should also include imaging up to 15s post-flash. The transmit focus should be moved towards the apex to confirm an apical perfusion defect when suspected. A thin and scarred (bright) myocardium of <5 mm in size indicates non-viable tissue and it is unnecessary to assess perfusion in these segments.
Therefore, MCE is able to detect presence or absence of viable myocardium by virtue of its ability to assess the integrity of the microcirculation.
In conclusion, Myocardial Contrast Echocardiography:
- accurately differentiates stunned and necrotic myocardium
- delineates the transmural extent of infarction
- predicts recovery of regional and global left ventricular systolic function
- identifies patients at high risk of left ventricular remodeling
- provides incremental viability data when performed in conjunction with low-dose dobutamine echocardiography
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