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Imaging
Figure 1: Representative Patient Example of Concordance Between Anatomical Imaging (A—Contrast Echo,
Four-chamber Orientation) and Tissue Characterization Imaging (B—Delayed-enhancement Magnetic Resonance
Imaging, Two-chamber Orientation)
A. Contrast echocardiography
B. Delayed-enhancement MRI C. Pathology
Both imaging modalities show a large intracavitary thrombus (arrows) within the left ventricular (LV) apex. Note that thrombus appears as a discrete filling defect on contrast echo, whereas it is
homogeneously black on tailored delayed-enhancement magnetic resonance imaging (DE-MRI) (inversion time 600ms). Histopathology (C: hemotoxin and eosin [H&E] stain, low power), obtained
following surgical resection, demonstrated thrombus with organizing features such as fibroblast ingrowth (asterisk).
LV masses such as neoplasms can appear similar to thrombus and be Contrast-enhanced Imaging
difficult to discriminate based on anatomical appearance alone. Third, Intravenous contrast agents have expanded imaging capabilities for
thrombus may vary in size and shape and therefore be difficult to thrombus detection, yielding improvements in both anatomical and tissue
identify using a uniform anatomical criterion. For example, intracavitary characterization approaches. The benefits of contrast-enhanced imaging
thrombus typically appears as a distinct mass whereas mural thrombus for thrombus have been demonstrated for multiple cardiac
is contiguous with surrounding myocardium. However, like intracavitary imaging modalities, including echo, magnetic resonance imaging (MRI), and
thrombus, mural thrombus can affect clinical outcomes; in prior studies, computed tomography (CT).
2–4,15–17
up to 40% of embolic events have occurred in patients with non-
protuberant or immobile thrombus,
14
emphasizing the importance of Anatomical Imaging
thrombus detection irrespective of shape or mobility. Echo has typically used contrast to facilitate anatomically based
assessment of thrombus. For this purpose, sonographic contrast agents
Tissue Characterization Criteria (microspheres) are administered as a bolus or continuous intravenous
While thrombus can vary in shape or size, it is intrinsically characterized infusion. Thrombus detection is facilitated as a consequence of
by its avascular tissue properties. As thrombus is composed of improved LV endocardial border definition and LV cavity visualization,
coagulated blood, it has no inherent vascular supply. This fundamental with thrombus defined based on standard anatomic criteria (see
characteristic—avascularity—is a distinguishing feature that can be ‘Definition of Left Ventricular Thrombus—Anatomical Criteria’, above).
used to discriminate thrombus from both surrounding myocardium and Figure 2 provides a typical example of improved detection of thrombus
other cardiac masses that can mimic thrombus in anatomical provided by contrast-enhanced cavity opacification.
appearance. For example, while neoplasm and thrombus can be similar
in shape, the former is reliant upon vascular supply whereas the latter is Multiple studies have demonstrated that contrast echo markedly
not. Recent advances in cardiac imaging have enabled assessment of improves thrombus detection in patients with sub-optimal-quality non-
vascular supply, allowing thrombus to be identified by avascular tissue contrast echoes. This concept was demonstrated by Mansecal et al., who
characteristics resulting from absence of contrast uptake. Using this performed non-contrast and contrast echo in a cohort of 50 consecutive
criterion, thrombus has been defined as an LV mass with tissue patients who had sustained anterior MI.
18
Both tests were performed
characteristics consistent with avascular tissue, identifiable as a low- seven days following MI and read independently. Contrast echo
signal-intensity mass surrounded by high-signal-intensity structures significantly improved LV cavity assessment, enabling full apical
such as cavity blood and/or surrounding myocardium.
2–4
Figure 1 visualization in 100% of patients compared with 89% with non-contrast
provides a representative example of tissue characterization imaging for echo (p<0.0001). Improved cavity visualization facilitated thrombus
LV thrombus (B), with a side-by-side comparison with thrombus detection: contrast echo detected LV thrombus in 12% of patients (n=6),
assessment using anatomical imaging (A). only half of whom had thrombus detected by non-contrast echo. Similarly,
28 US CARDIOLOGY