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\begin{document}

\title{Transition from Transesophageal Echocardiography to Cardiac Computed
Tomography for the Evaluation of Left Atrial Appendage Thrombus Prior to
Atrial Fibrillation Ablation and Incidence of Cerebrovascular Events
During the COVID-19 Pandemic}



\author[1]{Tauseef Akhtar}%
\author[2]{Ryan Wallace}%
\author[2]{Usama Daimee}%
\author[2]{Erica Hart}%
\author[2]{Armin Arbab-Zadeh}%
\author[3]{Joseph Marine}%
\author[3]{Ronald Berger}%
\author[3]{Hugh Calkins}%
\author[3]{David Spragg}%
\affil[1]{Johns Hopkins School of Medicine}%
\affil[2]{Johns Hopkins University School of Medicine}%
\affil[3]{Johns Hopkins Hospital}%


\vspace{-1em}



  
  \date{May 15, 2024}


\begingroup
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\selectlanguage{english}
\begin{abstract}
Background Transesophageal echocardiography (TEE) is variably performed
before atrial fibrillation (AF) ablation to evaluate left atrial
appendage (LAA) thrombus. We describe our experience with transitioning
to the pre-ablation cardiac computed tomography (CT) approach for the
assessment of LAA thrombus during the COVID-19 pandemic. Methods We
studied consecutive patients undergoing AF ablation at our center. The
study cohort was divided into pre- vs. post-COVID groups. The pre-COVID
cohort included ablations performed during 1 year before the COVID-19
pandemic; pre-ablation TEE was used routinely to evaluate LAA thrombus
in high-risk patients. Post-COVID cohort included ablations performed
during the 1 year after the COVID-19 pandemic; pre-ablation CT was
performed in all patients, with TEE performed only in patients with LAA
thrombus by CT imaging. The demographics, clinical history, imaging, and
ablation characteristics, and peri-procedural cerebrovascular events
(CVE) were recorded. Results A total of 637 patients (pre-COVID n=424,
post-COVID n=213) were studied. The mean age was 65.6 ? 10.1 years in
the total cohort, and the majority were men. There was a significant
increase in pre-ablation CT imaging from pre to post-COVID cohort (74.8
vs. 93.9\%, p=\textless{}0.01), with a significant reduction in TEEs
(34.6 vs. 3.7\%, p=\textless{}0.01). One patient in the post-COVID
cohort developed CVE following negative pre-ablation CT. However, the
incidence of peri-procedural CVE between both cohorts remained
statistically unchanged (0 vs. 0.4\%, p=0.33). Conclusion Implementation
of pre ablation CT-only imaging strategy with selective use of TEE for
LAA thrombus evaluation is not associated with increased CVE risk during
the COVID- 19 pandemic.%
\end{abstract}%



\sloppy


\textbf{Transition from Transesophageal Echocardiography to Cardiac
Computed Tomography for the Evaluation of Left Atrial Appendage Thrombus
Prior to Atrial Fibrillation Ablation and Incidence of Cerebrovascular
Events During the COVID-19 Pandemic}

\textbf{Short Title:} Utility of pre-ablation CT only approach to LAA
thrombus evaluation before AF ablation during COVId-19 pandemic

Tauseef Akhtar MD\textbf{,} Ryan Wallace MD\textbf{,} Usama A Daimee MD,
Erica Hart MSc, Armin Arbab-Zadeh MD, MPH, PhD, Joseph E Marine MD,
Ronald Berger MD, PhD, Hugh Calkins MD, David Spragg MD

Division of Cardiology, Johns Hopkins University School of Medicine,
Baltimore, MD, 21287 USA.

\textbf{Funding:} (None)

\textbf{Conflict of Interest}

Dr. Arbab-Zadeh discloses research grant support from Canon Medical
Systems. All other authors have reported that they have no relationships
relevant to the contents of this paper to disclose.

\textbf{Data Availability Statement}

The data that support the findings of this study are available from the
corresponding author upon reasonable request.

\textbf{Word count: 2729}

\textbf{For correspondence:}

Tauseef Akhtar MD

Johns Hopkins Hospital

600 N. Wolfe St., Baltimore MD 21287

Phone: 2814646952

tausif.akhtar@gmail.com

\textbf{Abstract}

\textbf{Background}

Transesophageal echocardiography (TEE) is variably performed before
atrial fibrillation (AF) ablation to evaluate left atrial appendage
(LAA) thrombus. We describe our experience with transitioning to the
pre-ablation cardiac computed tomography (CT) approach for the
assessment of LAA thrombus during the COVID-19 pandemic.

\textbf{Methods}

We studied consecutive patients undergoing AF ablation at our center.
The study cohort was divided into pre- vs. post-COVID groups. The
pre-COVID cohort included ablations performed during 1 year before the
COVID-19 pandemic; pre-ablation TEE was used routinely to evaluate LAA
thrombus in high-risk patients. Post-COVID cohort included ablations
performed during the 1 year after the COVID-19 pandemic; pre-ablation CT
was performed in all patients, with TEE performed only in patients with
LAA thrombus by CT imaging. The demographics, clinical history, imaging,
and ablation characteristics, and peri-procedural cerebrovascular events
(CVE) were recorded.

\textbf{Results}

A total of 637 patients (pre-COVID n=424, post-COVID n=213) were
studied. The mean age was 65.6 \selectlanguage{ngerman}± 10.1 years in the total cohort, and the
majority were men. There was a significant increase in pre-ablation CT
imaging from pre to post-COVID cohort (74.8 vs. 93.9\%,
p=\textless{}0.01), with a significant reduction in TEEs (34.6 vs.
3.7\%, p=\textless{}0.01). One patient in the post-COVID cohort
developed CVE following negative pre-ablation CT. However, the incidence
of peri-procedural CVE between both cohorts remained statistically
unchanged (0 vs. 0.4\%, p=0.33).

\textbf{Conclusion}

Implementation of pre ablation CT-only imaging strategy with selective
use of TEE for LAA thrombus evaluation is not associated with increased
CVE risk during the COVID- 19 pandemic.

\textbf{Keywords:}

Atrial fibrillation ablation, Left atrial appendage thrombus,
Peri-procedural cerebrovascular event, Cardiac computed tomography,
Transesophageal echocardiography

\textbf{Introduction}

The COVID 19 pandemic has significantly affected health care delivery
across cardiac specialties, including cardiac electrophysiology (EP).
Infection prevention efforts mandate reallocation of resources with the
postponement of the elective procedures and minimization of invasive
pre-procedural investigations\textsuperscript{1}. Catheter ablation of
atrial fibrillation (AF) is a commonly performed procedure in the EP lab
and carries a risk of peri-procedural thromboembolic cerebrovascular
events (CVEs)\textsuperscript{2}. Left atrial appendage (LAA) thrombus
is the most common source of embolism in such patients. To minimize the
peri-procedural risk of CVEs, current guidelines recommend at least 3
weeks of effective anticoagulation or pre-procedural transesophageal
echocardiographic (TEE) evaluation of LAA for patients who present for
their ablation procedure in AF\textsuperscript{2}. TEE is variably
employed in other populations of patients undergoing AF ablation based
on their stroke risk profile and physician preferences. Previous studies
have suggested the utility of pre-procedural cardiac computed tomography
(CT) in place of TEE for evaluation of LAA
thrombus\textsuperscript{3-9}. In the current study, we describe our
institutional experience of transitioning from pre-procedural TEE to
cardiac CT for evaluation of LAA thrombus during the COVID-19 pandemic
(part of an effort to reduce COVID transmission risks to healthcare
providers), and the risk of peri-procedural CVEs among patients
undergoing pulmonary vein isolation (PVI) with minimally interrupted
peri-procedural anticoagulation before and after this practice change.

\textbf{Methods}

\textbf{Study Cohort}

We conducted a single-center, retrospective cohort study comprising
patients derived from an IRB-approved, prospectively populated clinical
database of AF ablation patients. All patients underwent either first or
repeat AF ablation between February 2019 to March 2021 at the Johns
Hopkins Hospital. All patients underwent a preprocedural cardiac CT scan
or cardiac magnet resonance imaging (MRI) to assess the left atrium (LA)
and pulmonary vein (PV) anatomy in detail. The total patient cohort was
divided into pre-COVID and post-COVID cohorts based on the Spring 2020
peak of the COVID-19 pandemic (when ablation procedures were temporarily
halted in our hospital) and pre-procedural imaging for LAA thrombus
evaluation. The pre-COVID cohort consisted of ablations performed
between February 2019 to January 2020, and the post-COVID cohort
included ablations performed between April 2020 to March 2021. All
patients signed written informed consent at the time of the procedure.
Demographics, clinical history, imaging data, procedural data, and
complications were recorded for each procedure.

\textbf{Anticoagulation Protocol}

All patients in the pre-and post-COVID epochs were treated with a
minimally interrupted anticoagulation strategy. Patients treated with
warfarin continued uninterrupted therapy throughout the ablation period.
Patients treated with direct oral anticoagulants (DOACs) underwent
cessation of anticoagulation for 12--24 hours prior to the ablation
procedure, with resumption 4 hours post-procedure. Adherence to a
prescribed anticoagulation regimen was assessed by international
normalized ratio (INR) for warfarin-treated patients or by verbal
confirmation (for NOAC-treated patients) pre-and post-procedure. During
the ablation procedure itself, activated clotting time levels were
maintained above 350s with intravenous heparin during LA access.
Anticoagulation was continued for a minimum of 3 months following the
ablation procedure for all patients unless contraindicated.

\textbf{Pre-ablation imaging protocol for LAA thrombus evaluation}

In the pre-COVID cohort, pre-procedural TEE was performed routinely for
all the patients presenting in AF or atrial flutter (AFL) on the day of
ablation, and ablation was conducted after LAA thrombus was ruled out.
CT scans in the pre-COVID cohort were not analyzed for the presence or
absence of LAA thrombus but were used solely for assistance in
electroanatomical mapping during the ablation itself. In the post-COVID
cohort, we implemented a cardiac CT-based protocol for LAA thrombus
evaluation, with TEE used selectively only in patients with findings
suggestive of LAA thrombus on CT imaging. All patients underwent CT
imaging with first- and second-pass image acquisition to assess for LAA
thrombus. TEE imaging was triggered only in patients with positive CT
scan findings. If CT imaging was negative, or if triggered TEE imaging
was negative, patients underwent ablation as planned. If triggered TEE
was positive for LAA thrombus, the ablation procedure was canceled.

\textbf{Echocardiography}

LA size and left ventricular ejection fraction (LVEF) were assessed by
transthoracic echocardiography (TTE) when available prior to the
ablation. All TEEs were performed immediately before the planned
ablation procedure. LA size and LAA velocities were assessed, and the LA
and LAA were examined for the presence of thrombus or spontaneous echo
contrast (SEC). In addition, the presence of patent foramen ovale (PFO)
or atrial septal defect was assessed with color Doppler and/or injection
of agitated saline. TEEs were interpreted independently by experienced
cardiologists specializing in echocardiography.

\textbf{Cardiac Computed} \textbf{Tomography}

CT images were obtained on the day of ablation using a 320-detector
scanner (Aquilion ONE, Canon Medical Systems) and prospective scan
acquisition targeted at 40\% of the R-R cycle (end-systole) without
padding. Computed tomographic angiography (CTA) of the heart and great
vessels was performed with intravenous iodinated contrast, including 3D
iterative reconstruction of the cardiac chambers at 40\% of the R-R
interval. ~Prospective ECG-gating was performed to reduce the effective
radiation dose. ~ CTA was optimized for imaging the cardiac chambers and
great vessels but not to visualize the complete course of the coronary
arteries. A second acquisition was performed 30 seconds after the
primary acquisition to assess for adequate filling of the left atrial
appendage. A LA/LAA thrombus was defined as an intracavitary contrast
filling defect with attenuation values similar to non-enhanced tissue.
Intracavitary thrombi were differentiated from normal pectinate muscles
and from filling, motion, and acquisition artifacts.

\textbf{Outcomes}

Peri-procedural CVE was defined as the acute onset of a new neurological
deficit between the start of the procedure and up to 30 days after
ablation. Stroke was defined as an acute infarct on imaging with the
neurological deficit; transient ischemic attack (TIA) was defined as the
absence of an acute infarct on imaging with an acute neurological
deficit that resolved within 24 hours\textsuperscript{10}.

\textbf{Post-Procedure Follow-Up}

All patients were monitored overnight in the hospital and clinically
evaluated before discharge the following day. Patients in whom
neurological deficits were reported or observed underwent brain magnetic
resonance imaging for evaluation of CVA. Clinical follow-up was
performed routinely at 3 months, 6 months, and 1 year or earlier if the
patient reported any symptoms.

\textbf{Ablation Strategy}

All ablation procedures were performed under general anesthesia. Femoral
site access was

obtained, and intravenous heparin was administered to maintain activated
clotting times \textgreater{}350 s.

\emph{Radiofrequency (RF) ablation} :

After performing a double transseptal puncture, a Lasso or Penta Ray
mapping catheter (Biosense-Webster, Diamond Bar, California) was
positioned in the left atrium. An electroanatomic map of the left atrium
was obtained using the CARTO system (Biosense-Webster) and superimposed
on a pre-acquired CT scan. A 4-mm open-tip irrigated RF catheter with a
contact force sensor (Thermocool SmartTouch, Biosense-Webster) was then
positioned in the left atrium: PVI was performed using a real-time
automated display of RF application points (Visitag, Biosense-Webster)
with predefined catheter stability settings. Starting energy delivery
parameters were 25 to 40 W on the posterior wall and 35 to 45 W at other
sites. Target contact force was between 5 and 20 g at all sites.
Esophageal temperature was monitored, and the RF delivery paused if the
esophageal temperature increased by 0.5°C.

\emph{Cryoballoon (CB) ablation:}

After a trans-septal puncture at the fossa ovalis, a long deflectable
sheath (FlexCath Advance sheath; Medtronic, Inc, Minneapolis, MN) was
introduced into the LA using intracardiac echocardiographic guidance.
Pulmonary venous angiograms were obtained for each of the four PVs to
serve as a fluoroscopic reference. An endocardial map of the LA was
created via a CARTO-Biosense (Carto {[}R{]} 3; Biosense Webster, Inc,
Diamond Bar, CA) or Ensite system (NavX, St. Jude Medical, Inc, St.
Paul, MN). Right-sided phrenic nerve (PN) pacing was performed during
the ablation of the right PVs. A second-generation CB catheter with a
23- or 28-mm balloon (Arctic Front Advance, Medtronic) and a PV mapping
catheter were passed into the LA via the long sheath. Cryo lesions were
targeted to the PVs after the demonstration of balloon occlusion with
contrast injection. Goal temperatures were between -35 to -55C. Freezes
were aborted if the esophageal temperature fell below
28\textsuperscript{°}C or if phrenic nerve pacing showed diminution of
diaphragmatic excursion during right-sided PV lesion delivery. Following
the delivery of at least two lesion sets per vein, electrical isolation
of each PV was reassessed, and additional applications of cryotherapy
were delivered with either a 23- or 28-mm second-generation CB as
necessary.

\textbf{Statistical Analysis}

Statistics were calculated using SPSS Statistics Software for Windows
version 23.0 (IBM Corporation, Armonk, New York). Normality was tested
with the Shapiro-Wilks test. Continuous data was analyzed using the
Student's t-test for normally distributed data and the Mann-Whitney test
for non-normally distributed data. Categorical data was analyzed using
the \selectlanguage{greek}χ\selectlanguage{english}2 test. Values are presented as mean \selectlanguage{ngerman}±standard deviation or median
and interquartile range (Q1-Q3) according to distribution for continuous
data and count and percentage for categorical data, unless otherwise
stated.

\textbf{Results}

Our study included a total of 637 patients undergoing AF ablation, of
which 136 (21.4\%) were undergoing repeat ablation. The pre-COVID cohort
included 424 patients, and the post-COVID cohort included 213 patients.
The mean age was 65.6 ± 10.1 years in the total population, and the
majority were male (Table 1). The median body mass index (BMI) was 29.1
(26.0 -- 34.1) kg/m\textsuperscript{2}, and the median CHA2DS2-VASc
score was 2 (1--3), with no significant difference between cohorts. A
higher proportion of patients with paroxysmal AF (PAF) (70.4 vs. 62.3
\%, p=0.04) were included in the post-COVID cohort. A higher proportion
of the patients included in the pre-COVID cohort had hyperlipidemia (29
vs. 17.4 \%, p=\textless{}0.01) and a history of smoking (31.6 vs. 1.9
\%, p=\textless{}0.01). Other comorbidities remained comparable between
the two groups. Pre-procedure anticoagulation was used in 604 (94.8\%)
patients, with either uninterrupted warfarin therapy (n=45; 7.1\%), or
minimally interrupted dabigatran (n=45; 7.1\%), rivaroxaban (n=175;
27.5\%), or apixaban (n=339; 53.2\%). The use of rivaroxaban was higher
in the pre-COVID cohort (30.7 vs. 21.1 \%, p=0.01), whereas apixaban was
more commonly prescribed in the post-COVID cohort (61 vs. 49.3 \%,
p=\textless{}0.01).

\textbf{Pre ablation imaging modality and ablation characteristics}

A total of 517 (81.2\%) pre-procedural CT scans were performed (Table
2). Following the implementation of CT-only protocol for LAA thrombus
evaluation, we observed a significant increase in pre-procedural CT scan
from pre-COVID to post-COVID cohorts (74.8 vs. 93.9\%,
p=\textless{}0.01). In contrast, a significant reduction was observed in
the number of TEEs performed in the pre- to post-COVID groups (34.6 vs.
3.7\%, p=\textless{}0.01). LA diameter (4.4 ± 0.9 vs. 4.2 ± 0.6 mm,
p=\textless{}0.01) and LA volume index {[}90.9 (74.1-103.1) vs 74.2
(61.9\selectlanguage{english}-85.3) mL/m2, p=0.02 {]} were significantly higher in the pre-COVID
cohort. A total of 412 (64.7\%) patients presented in normal sinus
rhythm (NSR), 178 (21.9\%) patients presented in AF, and 39 (6.1\%)
patients presented in AFL on the day of ablation.

In the pre-COVID cohort, out of a total number of 147 TEEs, 120 were
performed for presentation in AF, and 24 were performed for presentation
In AFL (Figure 1). While 5 TEEs showed spontaneous echo contrast (SEC),
none of the TEEs showed LAA thrombus, and therefore all the ablations
were carried out as scheduled. In the post-COVID cohort, a total of 8
patients were found to have CT findings concerning for LAA thrombus and
underwent TEE on the same day (Figure 2). TEE excluded the LAA thrombus
in 6 of these patients, and ablation was performed as planned without
any peri-procedural CVE. In 2 patients, TEE confirmed LAA thrombus
leading to the cancellation of the ablation procedure (Figure 3). LAA
thrombus resolved after 8 to 12 weeks of continued anticoagulation in
both of these patients. Apixaban was replaced with warfarin in one
patient, and warfarin therapy was continued in the other patient. Both
patients underwent ablation subsequently.

\textbf{Peri-procedural CVE}

The incidence of peri-procedural CVE in the total cohort was 0.1\%
(1/637). While none of the patients in the pre-COVID cohort had CVE, 1
patient in the post-COVID cohort developed CVE. This patient presented
in AF at the time of ablation and pre-ablation CT was unremarkable;
therefore, TEE was not performed prior to ablation (Figure 4; clinical
and procedural details are provided in Table 3). He underwent CB
ablation for persistent AF, with minimally interrupted DOAC therapy
(single dose of apixaban held) and developed stroke on the day after
ablation. Brain MRI revealed an acute infarct in the posterior cerebral
arterial territory. The proportion of CVE between pre vs. post-COVID
cohort remained comparable (0 vs. 0.4\%, p=0.33) (Figure 5).

\textbf{Discussion}

Infection prevention strategies during the COVID-19 pandemic have
impacted the workflow significantly at high volume centers performing
catheter ablation of AF. Omission of routine pre-ablation TEE use in
appropriately selected patients is associated with improved workflow
efficiency in the EP laboratory and promotes cost-effective utilization
of health care resources. Additionally, it may reduce the risk of viral
transmission to health care providers. We investigated the safety of a
pre-ablation CT-only imaging protocol for the evaluation of LAA thrombus
at our center to minimize the use of pre-procedural TEE. The following
are the main findings of our study: 1) Implementation of pre ablation
CT-only imaging strategy with selective use of TEE for LAA thrombus
evaluation does not lead to significantly increased CVE risk; 2)
Incidence of peri-procedural CVE is low; 3) Patients with CT imaging
suggestive of LAA thrombus may have TEE imaging that is negative for
thrombus.

Previous studies have investigated the sensitivity and specificity of
pre-ablation CT by comparing it with TEE and reported conflicting
findings\textsuperscript{3-6,8,11-13}. Our study design precluded
head-to-head comparison of pre-ablation CT with TEE for LAA thrombus
evaluation. Nevertheless, our study provides data for the utility of
pre-ablation CT-only approach to LAA thrombus assessment during the
COVID-19 pandemic and supports the findings of previous
reports\textsuperscript{7-9}published during the non-COVID era. Bilchick
et al\textsuperscript{7}, demonstrated the safety of the pre-ablation
CT-only approach to assessment of LAA thrombus in low-risk patients
undergoing AF ablation\textsuperscript{7}. However, unlike the current
study, they restricted the use of pre-ablation CT-only protocol for LAA
thrombus evaluation to patients with PAF, without a history of prior
CVE/LAA thrombus and CHA\textsubscript{2}DS\textsubscript{2}-VASc score
\textless{}4. In contrast to previous studies\textsuperscript{7-9},
which included patients with low to intermediate stroke risk based on a
younger age of the study cohort, lower
CHA\textsubscript{2}DS\textsubscript{2}-VASc score and lower burden of
comorbidities, our study included patients at a high stroke risk given a
higher burden of comorbidities, older age, and a higher
CHA\textsubscript{2}DS\textsubscript{2}-VASc score. Moreover, in our
study, the pre-ablation CT-only protocol for LAA thrombus evaluation was
offered to all the patients regardless of the previous history of
stroke/TIA, type of AF, and CHA\textsubscript{2}DS\textsubscript{2}-VASc
score. Additionally, we followed the current practice of minimally
interrupted peri-procedural anticoagulation protocol with DOAC.

Similar to the previously published reports, our results suggest that
the incidence of peri-procedural stroke following atrial fibrillation
ablation remains low\textsuperscript{8,14}. However, an interesting
finding of our study is the development of peri-procedural stroke in a
patient with unremarkable pre-ablation CT. Previous
investigations\textsuperscript{4,5,7-9,11}suggest that pre-ablation CT
has a high sensitivity for LAA thrombus detection. Nevertheless, it is
possible that our patient had a false-negative CT result, or that he had
an embolic event from a different source (air embolism from a
transseptal sheath; char at the catheter tip; non-LAA cardiac
thrombus)\textsuperscript{15,16}. Previously published reports suggest
an increased propensity for LAA thrombus formation in patients with
PsAF, and high CHA\textsubscript{2}DS\textsubscript{2}-VASc
scores\textsuperscript{3,13,17}. Whether patients with PsAF and high
CHA\textsubscript{2}DS\textsubscript{2}-VASc scores would benefit from
the routine use of pre-ablation TEE regardless of pre-ablation CT
findings is a topic worthy of further investigation.

The findings of our study should be interpreted with attention to the
associated limitations, including: 1) Those limitations inherent to a
single-center, retrospective, and observational study; 2)We could not
perform the adjusted predictor analysis for CVE given the low event
rates; 3) The anticoagulation protocol at our center may be different
from other centers, limiting the generalization of our findings; 4)
There may be an underestimation of subclinical CVE or silent cerebral
infarcts given the fact that not all the patients underwent
post-procedural cardiac magnetic resonance imaging evaluation.5) We
cannot exclude the possibility of a significant difference in a larger
patient cohort.

In conclusion, based on our experience, implementation of pre ablation
CT-only imaging strategy with selective use of TEE for LAA thrombus
evaluation does not lead to significantly increased CVE risk during the
COVID- 19 pandemic, has greater physician acceptance, and improved
workflow efficiency. Further prospective randomized studies are required
to identify the patients deriving the maximum benefit from pre-ablation
TEE.

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\verb`Table 1.docx`  available at \url{https://authorea.com/users/384507/articles/524649-transition-from-transesophageal-echocardiography-to-cardiac-computed-tomography-for-the-evaluation-of-left-atrial-appendage-thrombus-prior-to-atrial-fibrillation-ablation-and-incidence-of-cerebrovascular-events-during-the-covid-19-pandemic}

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\verb`Table 2.docx`  available at \url{https://authorea.com/users/384507/articles/524649-transition-from-transesophageal-echocardiography-to-cardiac-computed-tomography-for-the-evaluation-of-left-atrial-appendage-thrombus-prior-to-atrial-fibrillation-ablation-and-incidence-of-cerebrovascular-events-during-the-covid-19-pandemic}

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\verb`Table 3.docx`  available at \url{https://authorea.com/users/384507/articles/524649-transition-from-transesophageal-echocardiography-to-cardiac-computed-tomography-for-the-evaluation-of-left-atrial-appendage-thrombus-prior-to-atrial-fibrillation-ablation-and-incidence-of-cerebrovascular-events-during-the-covid-19-pandemic}

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