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Imaging
dysfunction. Global indices of contractile dysfunction such as ejection 1.7%; p=0.0002) despite similar mean ejection fraction (31.8 versus
fraction
9,11
and wall motion score
10,34–36
have been linked to thrombus. LV 31.7%; p=0.88) in the two groups, with increased prevalence of thrombus
aneurysms
37
and dyskinetic regions
5,38
have also been reported to be paralleled by increased prevalence of infarcted myocardium in patients
more common in patients with thrombus. These associations likely with ischemic cardiomyopathy. The association between infarct size and
reflect a link between contractile dysfunction and blood stasis, with thrombus has also been demonstrated in research that has employed
stasis producing a thrombogenic mileu within the LV cavity. echo to measure LV geometry and contractility. In our subsequent study
of echo and MRI,
4
thrombus was again associated with infarct size by
Infarct Size
Clinical studies have also reported that prevalence of thrombus is
increased in patients with large myocardial infarctions. Enzymatic infarct
size
9,36,38
and absence of vessel patency
39
have been associated with
Contrast-enhanced echo markedly
increased prevalence of thrombus. LV thrombus has also been reported
improves anatomical detection of
to be more prevalent following anterior MI,
11,12,39
suggesting that infarct
distribution modifies risk for thrombus. However, all of these studies
left vetricular thrombus versus
used indirect markers of infarct size and location, such as enzyme levels
non-contrast echo.
or angiographic indices, and employed a separate test (typically echo) to
assess contractile function. Thus, while an association between infarct
size and thrombus was demonstrated, the mechanism had commonly
been assumed to be more extensive systolic dysfunction and/or DE-MRI even after controlling for LVEF and aneurysmal dilation as
remodeling, and not necessarily the presence of infarction. measured by either echo or cine-MRI. These results demonstrate that
infarct size is an independent structural marker for thrombus irrespective
MRI provides highly accurate assessment of infarct size, contractility, of the modality used to assess contractile function.
and thrombus within a single imaging examination. Cine-MRI enables
highly reproducible assessment of LV contractile function with excellent The association between thrombus and infarct size is supported by
endocardial cavity definition.
40,41
DE-MRI provides non-invasive infarct pathology studies. Using a canine infarct model with post mortem
imaging with near exact replication of pathology-evidenced infarct size histopathological verification of scar, Jugdutt et al. reported that
and morphology.
42,43
Cine- and DE-MRI are typically performed during the thrombus prevalence was increased among dogs with Q-wave
same imaging session. This has facilitated study of the relative roles of compared with those with non-Q-wave MI (64 versus 0%; p<0.005).
44
LV geometry, contractile function, and infarct size as structural Infarct size was larger and LV remodeling more advanced in the Q-wave
predictors of thrombus. group, paralleling increased prevalence of thrombus. Clinical studies in
the post-MI setting have found thrombus to be associated with larger
Recent MRI studies have demonstrated that infarct size is linked to risk infarcts.
9,39
While the mechanism relating scar to thrombus is unknown,
for thrombus. In a study of 57 patients with acute MI or established CAD, this may be secondary to pro-thrombotic endocardial alterations or
Mollet et al. reported that patients with DE-MRI-evidenced thrombus had subtle differences in LV contraction between regions of infarction and
larger infarct size, lower ejection fraction, and more frequent LV those of dysfunctional but viable myocardium.
aneurysms.
1
However, the independent predictive value of infarct size
(after controlling for contractile dysfunction or aneurysmal dilation) was Screening Approaches
not assessed in this study. Data from our group have demonstrated that Consensus guidelines recommend that contrast-enhanced echo be
used to confirm or exclude the diagnosis of thrombus when non-
enhanced images are sub-optimal for definitive diagnosis.
21
However, as
Consensus guidelines recommend that
detailed above, emerging data suggest that contrast-enhanced imaging
may have broader utility as thrombus can be missed by non-contrast
contrast-enhanced echo be used to
echo even when image quality is judged to be optimal.
4
One alternative
confirm or exclude the diagnosis of
approach to thrombus screening concerns stratification based on risk
factors such as infarct size or contractile function, with an up-front
thrombus when non-enhanced images
strategy of contrast-enhanced tissue characterization imaging used for
are sub-optimal for definitive diagnosis.
patients at high pre-test risk for thrombus. In research settings, such a
strategy has yielded over a two-fold increase in thrombus detection
versus non-contrast echo. Future studies are necessary to assess the
risk for thrombus is independently linked to infarct size, contractile clinical implications and costs associated with a primary strategy of
dysfunction, and aneurysmal remodeling, with each parameter providing contrast-enhanced thrombus imaging based on clinical profiles rather
additive predictive value. In our initial comparative study of DE- and cine- than echo image quality.
MRI among heart failure patients,
3
LV thrombus was independently
associated with infarct size even after controlling for age, CAD, and Conclusions
ejection fraction. Thrombus prevalence was five-fold greater in patients Contrast-enhanced echo markedly improves anatomical detection of LV
with ischemic compared with non-ischemic cardiomyopathy (9.2 versus thrombus versus non-contrast echo and the diagnostic benefits of
32 US CARDIOLOGY