Transesophageal Echocardiogram Before Cardioversion in Atrial Fibrillation Patients

Transesophageal echocardiography (TEE) offers an invaluable, non-invasive avenue for diagnosing and managing various cardiac conditions, including atrial fibrillation (AF). As the most common cardiac arrhythmia, AF affects millions and can lead to severe complications. Cardioversion, a procedure to restore the heart's normal rhythm, is frequently conducted on AF patients resistant to medication. Due to inconclusive data, TEE's utility prior to cardioversion in AF patients remains ambiguous. Understanding TEE's potential benefits and limitations in this population could significantly influence clinical practice. This review aims to scrutinize the current literature on the use of TEE before cardioversion in AF patients. The principal objective is to understand TEE's potential benefits and limitations comprehensively. The study seeks to offer a clear understanding and practical recommendations for clinical practice, thereby improving the management of AF patients before cardioversion using TEE. A literature search of databases was conducted using the keywords "Atrial Fibrillation," "Cardioversion" and "Transesophageal echocardiography," resulting in 640 articles. These were narrowed to 103 following title and abstract reviews. After applying exclusion and inclusion criteria with a quality assessment, 20 papers were included: seven retrospective studies, 12 prospective observational studies, and one randomized controlled trial (RCT). Stroke risk associated with direct-current cardioversion (DCC) potentially results from post-cardioversion atrial stunning. Thromboembolic events occur post cardioversion, with or without prior atrial thrombus or cardioversion complications. Generally, cardiac thrombus localizes in the left atrial appendage (LAA), a clear contraindication to cardioversion. Atrial sludge without LAA thrombus in TEE is a relative contraindication. TEE before electrical cardioversion (ECV) in anticoagulated AF individuals is uncommon. In AF patients planned for cardioversion, contrast enhancement facilitates thrombus exclusion in TEE images, reducing embolic events. Left atrial thrombus (LAT) frequently occurs in AF patients, necessitating TEE examination. Despite the increased use of pre-cardioversion TEE, thromboembolic events persist. Notably, patients with post-DCC thromboembolic events had no LA thrombus or LAA sludge. The use of TEE-guided DCC has grown due to its ability to detect atrial thrombi pre-cardioversion, aiding risk stratification. Thrombus in the left atrium also signals an elevated risk of future thromboembolic events in AF patients. While atrial stunning post cardioversion detected by TEE is a significant risk factor for future thromboembolic events, further evidence is required. Therapeutic anticoagulation is essential during and post cardioversion, even if no atrial thrombus is detected. Current data recommends cardioversion guided by TEE, particularly in outpatient settings.


Introduction And Background
Transesophageal echocardiography (TEE) is a non-invasive diagnostic tool that allows for detailed visualization of the heart and its structures using ultrasound waves. Physicians utilize TEE the most when they try to find more details than a standard echocardiogram. It is a widely accepted and commonly used technique in diagnosing and managing various cardiac conditions, including atrial fibrillation (AF) [1]. According to the American Heart Association, AF is the most common cardiac arrhythmia, affecting an estimated 2.7-6.1 million individuals in the United States alone [2]. It is characterized by an irregular and often rapid heart rate, which can lead to severe complications such as stroke, heart failure, and other cardiac issues. Exclusion of the thrombus is extremely important with respect to the planned reversal of sinus rhythm [3].
Cardioversion is a procedure that aims to restore the normal rhythm of the heart and is often performed in AF patients who are resistant to medical management [4]. However, the use of TEE before cardioversion in AF patients still needs to be better understood. Currently, data on routine TEE before cardioversion is inconclusive [3]. The motivation for this review is to study the current literature on using TEE as a diagnostic tool before cardioversion in AF patients. The study aims to comprehensively understand TEE's potential benefits and limitations in this population and guide clinical practice.
Patients with AF and flutter routinely require TEE with cardioversion [5]. The focus of this review is the current literature on the use of TEE before cardioversion in AF patients, with the research question being the role of TEE in the management of AF patients before cardioversion. The paper has been structured by reviewing the current literature on the topic, analyzing the findings, and discussing the implications for clinical practice. This review provides a comprehensive understanding of the potential benefits and limitations of this diagnostic tool and also provides practical recommendations for clinical practice. The importance of this review lies in the growing use of TEE in the management of AF patients and the need for further research to understand its potential benefits and limitations in this population.

Review Methods
A thorough medical literature search of various databases was done using the keywords "Atrial Fibrillation," "Cardioversion", and "Transesophageal echocardiography." A total of 640 results were shortlisted. A review of the article's title and abstract was done, after which 103 articles were selected. Further inclusion and exclusion criteria were implemented to refine the search, and a quality assessment was done. Ultimately 20 papers were included in this review article. The inclusion criteria comprised original studies, observational studies, and clinical trials. The exclusion criteria included narrative reviews, editorials, brief communications, case reports, case series, review articles, articles not written in English, and articles for which the complete text was unavailable. Seven of the 20 studies included were retrospective observational studies, while 12 were prospective observational studies ( Figure 1). There was one randomized control trial (RCT) included

Result
There's a risk of stroke associated with direct-current cardioversion (DCC), which might result from atrial stunning taking place post cardioversion. Thromboembolic events have been noted post cardioversion, irrespective of whether there was a prior thrombus in the atria or any complication during cardioversion. However, the cardiac thrombus, when present, was usually localized in the left atrial appendage (LAA) and is a well-recognized clear contra-indication to cardioversion. However, atrial sludge without LAA thrombus in TEE is a relative contra-indication to cardioversion. In anticoagulated individuals, TEE before electrical cardioversion (ECV) in AF is not commonly conducted [5]. In patients with AF planned for cardioversion, contrast enhancement is helpful since it makes excluding atrial thrombi by the TEE images easier and thus reduces the rate of embolic adverse events.
Left atrial thrombus (LAT) is not an uncommon finding in AF patients before cardioversion. Neither clinical nor routine two-dimensional (2D) echo examinations reliably identify LAT, so the current practice of TEE examination is needed. Over the past 20 years, the practice of TEE before cardioversion has undoubtedly increased, but the rate of thromboembolic events has not decreased to zero. The patients with thromboembolic events post-DCC had no evidence of LAT or LAA sludge.

Discussion
The hypothesis that AF must persist for more than two to three days before a LAT form has gained widespread acceptance, even though the mechanism of LAT formation and subsequent embolization is complex and little understood [19]. Still, later on, it was proved false as there were many cases of thrombus formation with AF in less than two days. According to the FibStroke study, 21% of the patients who developed an ischemic stroke or TIA after cardioversion had a CHA2DS2-VASc (congestive heart failure, hypertension, age ≥75 (doubled), diabetes, stroke (doubled), vascular disease, age 65 to 74 and sex category (female)) score < 2 [25]. AF is associated with an increased risk of heart failure, thromboembolism, and death [9]. DCC is an effective procedure to restore sinus rhythm. It is widely used in patients with persistent AF patients undergoing DCC in moderate to relatively high-risk categories based on the CHA2DS2-VASc scoring scheme [6,8]. Yarmohammadi et al. reported no clear trend in the incidence of LAA thrombus, stroke, or embolic events across patients with different CHA2DS2-VASc scores [6]. TEE allows accurate detection of LAT.
Moreover, recent studies using TEE have shown a state of atrial stunning immediately after cardioversion, a thrombogenic milieu in which new thrombus formation and increased or de novo appearance of LA spontaneous echocardiographic contrast (SEC) have been observed [25]. Over the past 10 years, trends display that the application of TEE-guided DCC has consistently grown and that more DCC procedures are done in the outpatient setting. Given TEE's high LAT or sludge detection rate, TEE-guided DCC remains an essential part of AF management [14]. In AF patients undergoing cardioversion, contrast-enhanced TEE images are more interpretable, help exclude atrial thrombi, and may result in a decreased rate of embolic adverse events [12]. TEE helps to detect LAA thrombus and defer the cardioversion in selected patients. TEE before cardioversion does not eliminate the risk of embolism after cardioversion because of atrial stasis and new thrombosis [8]. Cardioversion should be performed inadequately in anticoagulated patients even when TEE shows no LAT. Hence, TEE is not an alternative to anticoagulant therapy [16].
Cardioversion briefly impairs the left ventricle contraction and creates a stasis which can be a thrombogenic milieu; hence, full anticoagulant therapy should be administered before undergoing cardioversion [7]. Electrical cardioversion disrupts the function of the LAA and could increase the risk of thrombus formation [7,26]. In patients with unknown or prolonged duration AF who are not receiving long-term anticoagulation, atrial thrombi are detected by TEE in only a small minority of patients. It suggests that if TEE excludes the thrombi, early cardioversion can be performed safely without needing prolonged oral anticoagulation before the procedure [10]. It is possible to selectively screen patients to identify those at low risk for developing thrombi subsequent to negative results on initial TEE, especially if patients are in sinus rhythm [11]. Sludge within the LAA is independently associated with subsequent thromboembolic events in patients with AF [27]. Decreased LAA emptying flow velocity is related to recurrent AF even after successful cardioversion; hence, real-time measurement of emptying velocity by TEE can help decide treatment in patients with AF [15]. The presence of left ventricular dysfunction or mitral stenosis in patients with acute AF or left atrial enlargement in patients with chronic AF is not a reliable predictor of developing a LAT [19]. Improved and automated image interpretation will allow us to understand the LA and LAA anatomy better and possibly detect specific anatomical features and early signs correlated to LAT and SEC occurrence [24]. TEE-guided cardioversion provided a safe, effective, and noninvasive means of establishing atrioventricular synchrony and improving ventricular systolic function while concomitantly allowing surveillance of intracardiac thrombi [28]. Left atrial spontaneous echo contrast was the only independent positive predictor of subsequent thromboembolic events, including stroke, transient ischemic attack, and peripheral embolism [29]. Most post-cardioversion strokes occur in patients not using oral anticoagulation before cardioversion of acute AF [30]. In previous studies, the risk of stroke after cardioversion guided by TEE has been 0.8% [31,32].

Conclusions
There has been a significant increase in the utilization of TEE-guided DCC mainly because it allows for the detection of atrial thrombi before cardioversion, which is important for risk stratification, especially in outpatient settings. The detection of a thrombus in the left atrium is also correlated with an increased risk of future thromboembolic events in patients with AF. Furthermore, atrial stunning detected on TEE after cardioversion is a significant risk factor for future thromboembolic events; however, further evidence is required to support this claim. Additionally, therapeutic anticoagulation is needed during and after cardioversion even if no atrial thrombus is detected on TEE. Finally, based on currently available data, it is recommended that TEE-guided cardioversion be performed, especially in outpatient settings.

Conflicts of interest:
In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.