CDs observed on late-pCT
For many years, TEE was the first choice for the detection of thrombi in
the LAA; the technique shows a high sensitivity of 93.3-100% and
specificity of 99-100%.11,12 However, the performance
of TEE can prove difficult or may be impossible in some patients, such
as those who experience pain on
probe insertion even under anesthesia or those with anatomical
abnormalities. The overall TEE complication rate is 0.18-2.8%,
inclusive of a mortality value of 0.01-0.02%, laryngospasm rate of
0.14%, dysphagia rate of 1.8%, hoarseness rate of 12%, and dental
injury rate of 0.1%.13 In addition, patients who have
experienced difficulties in association with TEE may be unwilling to
undergo the procedure again. Moreover, TEE has been shown to be
associated with a heightened risk of severe acute respiratory syndrome
coronavirus 2 transmission during the ongoing novel coronavirus disease
pandemic. Therefore, there is a need for another detection tool with a
high accuracy. Cardiac CT performed in the delayed phase has been
established as a reliable alternative to TEE in the detection of
thrombi, with a sensitivity of 96% and specificity of
92%.6 In the absence of contraindications to the
contrast medium used, CT is non-invasive and associated with a lower
level of differences in the evaluation of results and rarely leaves a
bad impression on patients.
Although the detection of thrombi using contrast CT exhibits excellent
negative predictive values (99-100%), the positive predictive value is
still low, at 13-31%.14-16 This may be attributed
predominantly to difficulties in distinguishing real thrombi from
circulatory stasis in the LAA, particularly at a low blood velocity. The
discrimination between thrombi and circulatory stasis is more crucial in
patients with persistent or long-standing AF than in those with
paroxysmal AF; in the former population, 28% of patients showed CDs on
sCT in the early phase and as a reference of TEE or ICE, the positive
and negative predictive values were 40.7% and 100%,
respectively.17 On the other hand, in patients with
paroxysmal AF, the assessment of thrombi using either TEE or CT is not
difficult, owing to a high blood flow rate during the sinus rhythm and
lower degree of LAA dysfunction. Although delayed or late-phase CT
reportedly improves the accuracy of the detection of thrombi and
significantly increases the positive predictive value to up to 92% from
41%,8 the value is still <100%. Several
case reports have shown that a shift from the supine to the prone
position allows for successful thrombus
classification.18, 19 Notably, Kantarci et al.
reported that pCT was associated with a positive and negative predictive
value of 100%.4 Nevertheless, in the present study,
early-pCT did not exclude all thrombi, and in some persistent or
long-standing AF patients, a CD detected on early-pCT scan disappeared
on late-pCT. In three of our participants, only late-pCT showed CD
absence, unlike in the case of sCT or early-pCT, and thrombus absence
was confirmed by ICE. In minimizing or nullifying the false-positive
rate, the performance of late-pCT is the most ideal. Among patients with
a CD on late-pCT, we did not perform TEE simultaneously for thrombus
confirmation; therefore, we could not determine the presence of true
thrombi. Regarding the resolution of CDs on CT, Gottlieb et al suggested
that a patient with atrial fibrillation and newly stroke showed CDs on
CT and diagnosed as thrombi on TEE.20 After several
months with warfarin controlled with higher INR, CDs were disappeared on
CT and no thrombus was confirmed on TEE. Likewise, all the CDs in this
study disappeared or changed the shape of that following anticoagulant
type alterations or increases in doses, indicating that the CD was most
likely a thrombus. Notably, CDs detected by late-pCT were diagnosed as
thrombi in all 4 patients who could be performed TEE.
Kawaji et al. presented some data on the effectiveness of late-pCT in
thrombus detection.5 They performed late-pCT only in
patients with incomplete filling of the contrast medium in the LAA or a
filling defect, as observed on early sCT. It was necessary for the
radiographers to perform prompt screening to assess the need for
additional late-phase CT. Furthermore, additional CT was performed in
patients in both the supine and prone positions, pointing to substantial
exposure to radiation. However, in our study, we performed early and
late-phase contrast CT only in the prone position, which required as
much radiation exposure as the previous study of patients without a
detectable CD in the early phase, although there was no requirement for
stationed physicians for the quick determination of CD presence in the
LAA. Moreover, the protocol of pCT scanning was simpler and there was no
timing shift due to re-positioning.
In this study, ICE was used as a reference for the detection of thrombi
in patients without CDs on late-pCT. For these days, ICE has been proved
to be a valid tool for the diagnosis of intracardiac thrombi and
sometime been superior to the TEE. Anter et al showed that TEE and ICE
were performed simultaneously in 71 patients and 4 thrombi were
detected.21 Among them, all were visualized on ICE but
1 on TEE. The difference of visibility between TEE and ICE was also
argued by Sriram et al that clear definition and complete visualization
of the LAA were achieved in 99 and 100% using TEE and ICE in 122
patients with AF.22 ICE identified a thrombus in 7
patients with a previous negative TEE, and in 2 patients, TEE could not
rule out a thrombus within the LAA due to spontaneous echo contrast.
Which was subsequently shown to be pectinate muscles, not a thrombus, on
ICE. Furthermore, Ikegami et al exhibited that four of 97 patients with
persistent or long-standing persistent AF who did not exhibit thrombi on
TEE revealed a thrombus on ICE; following this, the CA procedure was
cancelled.17 From these points, the efficacy of ICE
was deemed as being superior to that of TEE in thrombus detection.
However, the LAA could be observed using ICE from the right atrium in
only 71% of the 970 patients.23 To achieve the clear
visualization of the LAA, it is a key to place the ICE probe close to
the LAA as possible. Although the utility of ICE from the PA was
reported compared to the RA or right ventricular outflow tract (RVOT),
it is sometimes difficult to advance the ICE prove to the RVOT and above
PA and a risk for pericardial effusion.24 Therefore,
we inserted the ICE probe into the LA closer to the LAA. In one patient,
the LAA could not be clearly described from the body of the LA and we
moved the ICE prove to the left superior pulmonary vein. As a result,
the LAA could be clearly described in all 300 of our patients.