Left Atrial Thrombus Prevalence in Atrial Fibrillation
- This meta-analysis set out to answer the prevalence of LA thrombus in patients with atrial fibrillation or flutter on guideline-directed anticoagulation. It further identified higher-risk populations in whom the diagnostic yield of a pre-procedure TEE would be beneficial.
- The overall prevalence of LA thrombus in patients with atrial fibrillation or flutter, receiving a minimum of 3 weeks of uninterrupted anticoagulation, was approximately 3%.
- The prevalence of LA thrombus was even higher in patients with nonparoxysmal atrial fibrillation or flutter (6.3%), CHA2DS2-VASc score ≥3 (4.81%), and those undergoing cardioversion (5.55%) as opposed to ablation.
How prevalent is left atrial (LA) thrombus in patients with atrial fibrillation (AF) or atrial flutter (AFL) on guideline-directed anticoagulation, and what risk factors could identify a higher-risk population in which the diagnostic yield of a transesophageal echocardiogram (TEE) may be greater?
A systematic review of MEDLINE, EMBASE, and CENTRAL was done of all studies from inception to July 2020 of patients with AF/AFL on continuous therapeutic oral anticoagulation with either direct oral anticoagulants (DOACs) or vitamin K antagonists (VKAs) for ≥3 weeks. Studies had to have ≥150 patients, and the imaging modality for LA thrombus detection had to be TEE, the gold standard. Studies had to include a CHADS2 or CHA2DS2-VASc score. Studies were excluded if there was valvular AF (presence of mitral stenosis or prior aortic or mitral valve replacement/repair), interruption of pre-procedural anticoagulation before TEE, bridging by intravenous anticoagulation, subtherapeutic international normalized ratio (mean time in therapeutic range <60%), documented DOAC noncompliance, or use of inappropriately low DOAC dosages. To identify higher-risk populations in which the diagnostic yield of TEE may be greater, subgroup analysis was done to evaluate the prevalence of LA thrombus by: 1) oral anticoagulation type; 2) AF pattern (paroxysmal vs. nonparoxysmal); 3) TEE indications (cardioversion vs. ablation); and 4) CHADS2 score (≤1 vs. ≥2) or CHA2DS2-VASc score (≤2 vs. ≥3).
A total of 3,755 unique studies were initially revealed, of which 35 were ultimately included for meta-analysis describing 14,753 patients. All studies were observational, 10 being prospective and 25 were retrospective. The mean-weighted prevalence of LA thrombus was 2.73% (95% confidence interval [CI], 1.95%-3.80%) with high interstudy heterogeneity (I2 = 91%). Prevalence of LA thrombus was similar for VKAs (2.80%; 95% CI, 1.86%-4.21%) versus DOAC-treated patients (3.12%; 95% CI, 1.92%-5.03%) (p = 0.674). Patients with nonparoxysmal AF/AFL had a four-fold higher prevalence of LA thrombus (4.81%; 95% CI, 3.35%-6.86%) versus paroxysmal patients (1.03%; 95% CI, 0.52%-2.03%) (p < 0.001). The prevalence of LA thrombus was also higher in patients undergoing cardioversion (5.55%; 95% CI, 3.15%-9.58%) versus ablation (1.65%; 95% CI, 1.07-2.53%) (p < 0.001). Patients with CHA2DS2-VASc score ≥3 had a higher prevalence of LA thrombus (6.31%; 95% CI, 3.72%-10.49%) versus score ≤2 (1.06%; 95% CI, 1.07%-2.53%) (p < 0.001).
In this meta-analysis, the overall prevalence of LA thrombus in patients with AF/AFL, receiving a minimum of 3 weeks of uninterrupted anticoagulation, was approximately 3%. The prevalence of LA thrombus was even higher in patients with nonparoxysmal AF/AFL (6.3%), CHA2DS2-VASc score ≥3 (4.81%), and those undergoing cardioversion (5.55%).
Current guidelines do not recommend TEE prior to cardioversions for AF/AFL when patients have been continuously anticoagulated. The necessity for TEE prior to a catheter ablation is less clear and not consistently guideline-directed. Large data sets describing the prevalence of LA thrombus in various at-risk populations have been lacking, especially over the past decade with the advent of DOACs. This meta-analysis offers the best and most recent estimate and finds an overall rate of approximately 3%, with greater prevalence in patients with higher CHA2DS2-VASc scores and higher arrhythmia burden (i.e., nonparoxysmal AF/AFL). A number of factors limit the immediate applicability of the results, including the high interstudy heterogeneity, the grouping of AF and AFL, and the failure to evaluate the impact of the ejection fraction on LA thrombus prevalence. Future studies should focus on examining AF and AFL separately, as well as preserved versus depressed ejection fractions.
Clinical Topics: Anticoagulation Management, Arrhythmias and Clinical EP, Noninvasive Imaging, Prevention, Anticoagulation Management and Atrial Fibrillation, Implantable Devices, EP Basic Science, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Echocardiography/Ultrasound
Keywords: Anticoagulants, Arrhythmias, Cardiac, Atrial Fibrillation, Atrial Flutter, Catheter Ablation, Diagnostic Imaging, Echocardiography, Echocardiography, Transesophageal, Electric Countershock, Risk Factors, Secondary Prevention, Thrombosis, Vitamin K
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