Diagnosis
A detailed assessment of LVT is crucial for patient management and
prognosis. Cardiac magnetic resonance (CMR) is now considered the
diagnostic standard for detection of LVT with cine-CMR and
contrast-enhanced CMR (CE-CMR) being the most useful modalities (Fig.1).
This is particularly true in patients with mural or small
LVT.12 The only study that included surgical or
pathological evidence of LVT for confirmation of LVT showed that CE-CMR
has a diagnostic sensitivity of 88% and specificity of
99%.13 No other study has subsequently shown that an
alternative modality is superior to CE-CMR imaging in LVT
detection.14
Cardiac magnetic resonance imaging has not only the strength to provide
better spatial resolution for morphological
definition15 but can characterize and differentiate
the avascular LVT from neighboring structures after contrast
administration. Moreover, CE-CMR can distinguish between acute versus
older thrombus (Fig.1). Newer CMR sequences (such as T2* to identify
ferrous products of hemoglobin breakdown and the use of long inversion
time imaging to selectively null the normal myocardium) may provide
further diagnostic advantages above and beyond CE-CMR
imaging.16, 17
Contrast-enhanced CMR proved that an imaging delay after acute MI of
more than 5 days was associated with significantly higher LVT detection
rates compared to imaging performed within 5 days. Of note, CE-CMR
performed between 9–14 days post-MI provided the highest detection
rate.18, 19
Despite its diagnostic superiority, CMR remains a time consuming and
expensive test, not available in all centers. Indeed, it is impractical
to perform and repeat CMR in all patients with high-risk MI. A more
practical approach may be to perform a transthoracic echocardiography
(TTE) as the first-line imaging modality to screen for LVT in all
patients with recent MI. Accordingly, current European Society of
Cardiology guidelines recommend routine TTE during hospital stay in all
patients to exclude LVT after MI (Class I, Level B).20Furthermore, considering that LVT could develop at various times after
MI, performing repeated TTE rather than a single CE-CMR could have an
even greater clinical impact in patients with satisfactory ultrasound
quality.
The diagnosis of LVT by TTE should be defined as a mass in the LV cavity
located adjacent to an area of LV wall dyssynergia and seen from at
least two views (usually apical and short axis, Fig.2). Care must be
taken to exclude the most common causes for an erroneous diagnosis of a
thrombus (false tendons, trabeculae, technical artifacts and
tangentially-cut LV wall).1, 12 Usually, LVT have a
homogeneous texture with a softer echo density than myocardium, which
suggests that the thrombus may be relatively recent and still “in a
growing phase”, whereas an older thrombus tends to have a smoother
surface and is typically more static.21
On the basis of available data it is possible to extrapolate that, in
comparison with CE-CMR, non-contrast TTE has a sensitivity of 24%-33%,
a specificity of 94%-95%, an accuracy of 82%, a positive predictive
value of 57% and a negative predictive value of
85%.14 A low sensitivity may be of concern because
TTE is the examination performed regularly in daily practice to search
for LVT. However, it is difficult to generalize these data to the
current “real life” since previous studies evaluating TTE used
multiple gold standards, or none at all, and were conditioned by
subjective image quality and the use of the off-axis
projections.14 Indeed, TTE is more operator-dependent
than CE-CMR. Varying gain setting and depth of field, as well as using
transducers with different frequencies in multiple positions and
orientations, are helpful approaches to minimize the false-positive
studies. This important notion is highlighted by the finding that TTE
performance varies highly according to the exam indication: if LVT
search is prespecified, sensitivity is multiplied by 2 (60% vs. 26%)
and positive predictive value by 3 (75% vs. 21%) as compared with
unfocused routine TTE.22 When the search for LVT is
prespecified in high-risk patients with recent anterior MI and low
ejection fraction, the accuracy of TTE as compared with DE-CMR is even
better (sensitivity and specificity 94.7% and 98.5%,
respectively).19 Thus, we believe that the attempt to
uncritically combine results from the literature to provide a summary
estimate of the diagnostic accuracy of TTE might have led to inaccurate
or misleading results, at least when considering Echo labs with high
standards of quality in TTE. Indeed, considering the importance of the
echogenicity, TTE ideally should be scored for diagnostic quality using
previously validated quantitative tools.12
In short, we must emphasize that TTE accuracy can be excellent if
performed specifically for LVT search with a standardized protocol and
that non-visualized LVT are usually mural and small (Table).