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.