ELECTROPHYSIOLOGY
Original Article

https://doi.org/10.24207/jca.v33i1.3392

Use of Computed Tomography Scan toRule Out Phantom Thrombus in the Left
Atrial Appendage
Luis Arabia1,*, Sergio Lucino1, José Tibaldi1, Diego Li Gambi1, Romina García1, Maria Eugenia Pérez1,
Franco Bottello1

ORCID IDs
Arabia L

https://orcid.org/0000-0003-0673-0234

Lucino S

https://orcid.org/0000-0002-9041-1713

García R

https://orcid.org/0000-0001-6447-3059

Tibaldi J

https://orcid.org/0000-0003-1812-7985

Pérez ME

https://orcid.org/0000-0002-1274-4571

Bottello F

https://orcid.org/0000-0001-6449-8117

Li Gambi D

https://orcid.org/0000-0001-6724-9511

ABSTRACT
Objective: The aim of study was to evaluate the utility of CT scan with delayed acquisition protocol to exclude LAA thrombus.
The occurrence of left atrial appendage (LAA) thrombus is a frequent complication of atrial fibrillation (AF) and increases thethromboembolic risk. Transesophageal echocardiography (TEE) is considered the gold standard to ensure that this chamber isthrombus-free. Multidetector computed tomography (CT) scan has some advantages, such the possibility to get 3D reconstructionand explore other structures in relationship with the LAA. However, there is a lack of specificity in case of false positive images withfilling defects due to slow velocities in the LAA. Methods and Results: Thirty-four patients with suspected thrombus by a previous
CT scan or transesophageal echocardiogram were included in the study. In all of patients, complete LAA filling was observed, withsensitivity, specificity and negative predictive value of 100% to differentiate circulatory stasis from thrombus. Conclusion: Performinga CT scan with delayed acquisition protocol and in prone position are safe techniques to discard false thrombus.

KEYWORDS: Atrial fibrillation; Thrombus; Left atrial appendage; Computed tomography.

1.Instituto Oulton – Cordoba, Argentina.
*Correspondence author: luisarabi@hotmail.com
Received: 12 May 2020 | Accepted: 20 May 2020
40

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Use of Computed Tomography Scan to Rule Out Phantom Thrombus in the Left Atrial Appendage

INTRODUCTION
The occurrence of thrombus in the left atrial appendage (LAA) is a frequent complication of atrial fibrillation (AF),increases systemic and cerebral thromboembolic risk, and is a contraindication to perform percutaneous proceduresin the left atrium (LA), so it must be ruled out before performing them1.

The LAA is the source of clots in almost 90% in patients with AF2. Transesophageal echocardiography (TEE)is considered the gold standard to ensure that this chamber is thrombus-free, but it is a semiinvasive study, withdifferent degrees of discomfort, sometimes requiring anesthetic support and, in really few cases, perforation of theesophagus have been reported1,3–8.

By the other hand, multidetector computed tomography (CT) scan has some advantages, such as the possibility

to get 3D reconstruction and explore other structures in relationship with the LAA, but it has the risk of contrast
toxicity and radiation exposure, and lack of specificity, in case of false positive images, with filling defects due to slow

velocities in the LAA. Several protocols were used to increase positive and negative predictor value (PPV, NPV ),such as delayed acquisitions sequences, different position of the body (prone position), and use of Hounsfield unit(HU) density9–23.

PATIENTS AND METHODS
From May 2017 to January 2020, 34 patients were enrolled., of which 26 were male, between 41–84 years old(mean age = 68), referred for AF ablation and/or LAA occlusion (LAAO). All of them suspected to have a thrombus
by a previous CT scan or transesophageal echocardiogram.

ProcedureA 64-detector-row CT scanner (Toshiba Multislice Aquilion 64; Toshiba Medical Systems, Otawara, Japan)

was used from 2017 to May 2019 and, after that, an Aquilion Prime Cannon/Toshiba 80/160. Slices thickness weredone every 0.5 mm and 0.3 s. With Aquilion 64 system, the electrocardiogram (ECG) was simultaneously recorded

for retrospective gating, and a prospective volumetric iterative reconstruction was made with the Aquilion Prime.
80 – 100 kV, 80 – 150 ml of contrast, 4,5- 5 mSv for all the three sequences (about 1.5 each), depending of the BMI
with the last MDCT scan, instead 15 +/- 3 mSv with the first MDCT.

First, a conventional gated CT was done; if a filling defect in the LAA was seen, a second sequence would start

three minutes later, with a second bolus of 40 cc of contrast and delayed acquisition with six cuts every three seconds,
with the ROI in ascendant aorta, and compared with LAA not only the visual impression but the HU, and a third

sequence (same protocol than the first one), with the patient in prone position was done, with a low Rx exposure andcontrast dose protocol.

RESULTS
Complete filling in the second and third sequence was observed in all of the patients, and AF ablation, LAA

closure or both were done without thromboembolic complications neither during the procedure nor at a follow-up of

3 to 28 months. This protocol allowed us to differentiate circulatory stasis from thrombus with a sensitivity, specificity
and negative predictive value of 100%.

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Arabia L, Lucino S, Tibaldi J, Gambi DL, García R, Pérez ME, Bottello F

Figure 1. Magnetic resonance image from a male patient with 43 years old, permanent atrial fibrillation and restrictive cardiomyopathy.
40 minutes of symptoms onset. Next images are from the same patient performed at the same day.

(a)

(b)

Figure 2. Transesophageal echocardiogram: (a) with Doppler velocity of left atrial appendage (LAA), (b) with “smoke”, spontaneouscontrast in the left atrium (LA) and LAA, and sparklier image inside LAA.

(a)

(b)

(c)

Figure 3. Computed tomography (CT): (a) first sequence with a filling defect in the LAA, (b) second delayed sequence showing
complete filling of the LAA, (c) third sequence in prone position, showing complete filling of the LAA.

42J. Cardiac Arrythmias, São Paulo, v33, 1, pp. 40-45, Jan-Mar, 2020

Use of Computed Tomography Scan to Rule Out Phantom Thrombus in the Left Atrial Appendage

DISCUSSION
Intracavitary LA/LAA filling defects can be seen due to thrombus presence or for inadequate mixing of bloodand contrast, giving a false positive image of a clot. Altered flow with reduced velocities are not infrequent in patientswith AF; moreover, if they have ventricular disfunction12,24,25.
A filling defect was defined as an area of low attenuation seen in the LA or LAA, different of pectinate muscles
or another structure. These defects were classified in low, moderate or high risk using the homoneity of the low
attenuation zone, border aspect and HU value, the highest risk being those homogeneous, less than 100 HU andwell-defined border; and the opposite, nonhomogeneous aspect, an indefinite border and more than 100 HU for thelow risk studies10,26.
While there are different protocols using delayed acquisitions (single vs double bolus, different times ranging
from 30 to 180 seconds), when they are used, the diagnostic accuracy clearly improved, reducing the number of false
positive CT10,13–18.
Studies in prone position were published to have similar PPV and NPV, such as delayed acquisition protocols 19,21.
This research only found one study combining both techniques22, but not in the same three steps that were used inthis work if a filling defect was seen in the first scan.
The two mayor concerns about CT are the use of iodinate contrast agent and the amount of ionizing radiation tothese patients are exposed, both can be reduced using new systems, adjusting dose and using prospective volumetricreconstruction, because the radiation source is active only in a short segment of R–R interval, saving a big amountof the dose27.

CONCLUSION
Left atrial appendage thrombus has a severe risk of thromboembolic complications and is a contraindication topercutaneous access to the left atrium. Performing a multidetector CT scan with a delayed acquisition protocol andin prone position are safe techniques to rule out false thrombus. More studies are needed to validate these findings.

ACKNOWLEDGMENTS
Our acknowledgment to all technical workers of CT scan Department for their continuous support.

REFERENCES
1.

Calkins H, Kuck KH, Cappato R, Brugada J, Camm AJ, Chen S-A, et al. 2012 HRS/EHRA/ECAS expert consensus statement on catheterand surgical ablation of atrial fibrillation: recommendations for patient selection, procedural techniques, patient management
and follow-up, definitions, endpoints, and research trial design. Heart Rhythm. 2012;9(4):632-96. https://doi.org/10.1016/j.
hrthm.2011.12.016

2.

Allbutt C, Rolleston HD. A system of medicine. London: MacMillan; 1909.

3.

Beigel R, Wunderlich NC, Ho SY, Arsanjani R, Siegel RJ. The left atrial appendage: anatomy, function, and noninvasive evaluation. JACCCardiovasc Imaging. 2014;7(12):1251-65. https://doi.org/10.1016/j.jcmg.2014.08.009

4.

Manning WJ, Weintraub RM, Waksmonski CA, Haering M, Rooney PS, Maslow AD, et al. Accuracy of transesophageal echocardiography
for identifying left atrial thrombi: a prospective, intraoperative study. Ann Intern Med. 1995;123(11):817-22. https://doi.
org/10.7326/0003-4819-123-11-199512010-00001

J. Cardiac Arrythmias, São Paulo, v33, 1, pp. 40-45, Jan-Mar, 2020

43Arabia L, Lucino S, Tibaldi J, Gambi DL, García R, Pérez ME, Bottello F

5.

Chan K-L, Cohen GI, Sochowski RA, Baird MG. Complications of transesophageal echocardiography in ambulatory adultpatients: analysis of 1500 consecutive examinations. J Am Soc Echocardiogr. 1991;4(6):577-82. https://doi.org/10.1016/S08947317(14)80216-2

6.

Daniel WG, Erbel R, Kasper W, Visser CA, Engberding R, Sutherland GR, et al. Safety of transesophageal echocardiography. A
multicenter survey of 10,419 examinations. Circulation. 1991;83(3):817-21 https://doi.org/10.1161/01.CIR.83.3.817

7.

Kallmeyer IJ, Collard CD, Fox JA, Body SC, Shernan SK. The safety of intraoperative transesophageal echocardiography: a case seriesof 7200 cardiac surgical patients. Anesth Analg. 2001;92(5):1126-30. https://doi.org/10.1097/00000539-200105000-00009

8.

Min JK, Spencer KT, Furlong KT, DeCara JM, Sugeng L, Ward RP, et al. Clinical features of complications from transesophageal
echocardiography: a single-center case series of 10,000 consecutive examinations. J Am Soc Echocardiogr. 2005;18(9):925-9.
https://doi.org/10.1016/j.echo.2005.01.034

9.

Bilchick KC, Mealor A, Gonzalez J, Norton P, Zhuo D, Mason P, et al. Effectiveness of integrating delayed computed tomography
angiography imaging for left atrial appendage thrombus exclusion into the care of patients undergoing ablation of atrial fibrillation.
Heart Rhythm. 2016;13(1):12-9. https://doi.org/10.1016/j.hrthm.2015.09.002

10. Teunissen C, Habets J, Velthuis BK, Cramer MJ, Loh P. Double-contrast, single-phase computed tomography angiography forruling out left atrial appendage thrombus prior to atrial fibrillation ablation. Int J Cardiovasc Imaging. 2017;33(1):121-8. https://doi.
org/10.1007/s10554-016-0973-2
11. Dorenkamp M, Sohns C, Vollmann D, Lüthje L, Seegers J, Wachter R, et al. Detection of left atrial thrombus during routine diagnostic
work-up prior to pulmonary vein isolation for atrial fibrillation: Role of transesophageal echocardiography and multidetector
computed tomography. Int J Cardiol. 2013;163(1):26-33. https://doi.org/10.1016/j.ijcard.2011.06.124
12. Tang RB, Dong JZ, Zhang ZQ, Li ZA, Liu XP, Kang JP, et al. Comparison of contrast enhanced 64-slice computed tomography andtransesophageal echocardiography in detection of left atrial thrombus in patients with atrial fibrillation. J Interv Card Electrophysiol.
2008;22(3):199-203. https://doi.org/10.1007/s10840-008-9243-0
13. Hur J, Kim JY, Lee H-J, Nam JE, Ha J-W, Heo JH, et al. Dual-enhanced cardiac CT for detection of left atrial appendage thrombus inpatients with stroke: a prospective comparison study with transesophageal echocardiography. Stroke. 2011;42(9):2471-7. https://doi.org/10.1161/STROKEAHA.110.611293
14. Hur J, Kim YJ, Lee H-J, Nam JE, Hong YJ, Kim HY, et al. Cardioembolic stroke: dual-energy cardiac CT for differentiation of left atrial
appendage thrombus and circulatory stasis. Radiology. 2012;263(3):688-95. https://doi.org/10.1148/radiol.12111691
15. Hur J, Kim YJ, Lee H-J, Ha J-W, Heo JH, Choi, E-Y, et al. Cardiac computed tomographic angiography for detection of cardiac sourcesof embolism in stroke patients. Stroke. 2009;40(6):2073-8. https://doi.org/10.1161/STROKEAHA.108.537928
16. Hur J, Kim YJ, Lee H-J, Ha J-W, Heo JH, Choi E-Y, et al. Left atrial appendage thrombi in stroke patients: detection with two-phasecardiac CT angiography versus transesophageal echocardiography. Radiology. 2009;251(3):683-90. https://doi.org/10.1148/radiol.2513090794
17. Kim SC, Chun EJ, Choi SI, Lee S-J, Chang H-J, Han M-K, et al. Differentiation between spontaneous echocardiographic contrast andleft atrial appendage thrombus in patients with suspected embolic stroke using two-phase multidetector computed tomography.
Am J Cardiol. 2010;106(8):1174-81. https://doi.org/10.1016/j.amjcard.2010.06.033
18. Sawit ST, Garcia-Alvarez A, Suri B, Gaztanaga J, Fernandez-Friera L, Mirelis JG, et al. Usefulness of cardiac computed tomographic
delayed contrast enhancement of the left atrial appendage before pulmonary vein ablation. Am J Cardiol. 2012;109(5):677-84.
https://doi.org/10.1016/j.amjcard.2011.10.028
19. Hasegawa K, Miyazaki S, Ishida T, Tada H. Computed tomography in the prone position is a simple and useful technique to detect
left atrial thrombi in persistent atrial fibrillation. J Cardiovasc Electrophysiol. 2018;29(4):632-3. https://doi.org/10.1111/jce.13411
20. Muramoto H, Higuchi K, Iwai S, et al. 1) Hiratsuka-Kyosai Hospital, Department of Cardiology, Kanagawa, Japan. 2) Hiratsuka-Kyosai
Hospital, Department of Radiology. 3) Tokyo Medical and Dental University. Tokyo, Japan. HRS poster Session. May 2018.
21. Kantarci M, Ogul H, Sade R, Aksakal E, Colak A, Tanboga IH. Circulatory stasis or thrombus in left atrial appendage, an easy diagnosticsolution. J Comput Assist Tomogr. 2019;43(3):406-9. https://doi.org/10.1097/RCT.0000000000000853
22. Kawaji T, Numamoto H, Yamagami S, Mabuchi R, Kitamura T, Enoki N, et al. Real-time surveillance of left atrial appendage thrombus
during contrast computed tomography imaging for catheter ablation: THe Reliability of cOMputed tomography Beyond UltraSoundin THROMBUS detection (THROMBUS) study. J Thromb Thrombolysis. 2019;47(1):42-50. https://doi.org/10.1007/s11239-0181742-y44J. Cardiac Arrythmias, São Paulo, v33, 1, pp. 40-45, Jan-Mar, 2020

Use of Computed Tomography Scan to Rule Out Phantom Thrombus in the Left Atrial Appendage

23. Budoff MJ, Shittu A, Hacioglu Y, Gang E, Li D, Bhatia H, et al. Comparison of transesophageal echocardiography versus computedtomography for detection of left atrial appendage filling defect (Thrombus). Am J Cardiol. 2014;113(1):173-7. https://doi.
org/10.1016/j.amjcard.2013.09.037
24. Singh N, Nallamothu N, Zuck V, Issa Z. Left atrial appendage filling defects on 64-slice multidetector computed tomography inpatients undergoing pulmonary vein isolation: predictors and comparison to transesophageal echocardiography. J Comput AssistTomogr. 2009;33(6):946-51. https://doi.org/10.1097/RCT.0b013e31819cabc3
25. Wu X, Wang C, Zhang C, Zhang Y, Ding F, Yan J. Systematic review/Meta-analysis: Computed tomography for detecting left atrial
thrombus: a meta-analysis. Arch Med Sci. 2012;8(6):943-51. https://doi.org/10.5114/aoms.2012.32400
26. Kirchhof K, Welzel T, Mecke C, Zoubaa S, Sartor K. Differentiation of white, mixed, and red thrombi: value of CT in estimation of theprognosis of thrombolysis—phantom study. Radiology. 2003;228(1):126-30. https://doi.org/10.1148/radiol.2273020530
27. Bardo DME, Brown P. Cardiac multidetector computed tomography: basic physics of image acquisition and clinical applications.
Curr Cardiol Rev. 2008;4(3):231-43. https://doi.org/10.2174/157340308785160615

J. Cardiac Arrythmias, São Paulo, v33, 1, pp. 40-45, Jan-Mar, 202045