Corresponding Author
Key words: anticoagulation, atrial fibrillation, contrast agent, echocardiography, imaging, inotropes, thrombosis, ultrasound
In atrial fibrillation (AF), the left atrial appendage (LAA) embodies Virchow's triad, where stasis, endothelial dysfunction, and hypercoagulability converge to create a highly thrombogenic chamber.1 LAA-derived thrombus not only increases the burden of anticoagulant therapy but also continues to challenge the rapidly expanding field of transcatheter therapies for structural heart disease.
The presence of LAA thrombus has traditionally been considered a contraindication to left atrial appendage closure (LAAC).2 However, distinguishing true thrombus from spontaneous echo contrast (SEC) remains challenging. In this issue of JACC: Case Reports, Sliem et al3 share valuable experience by introducing their practical and real-time intraprocedural approach: pharmacologic testing. Patients previously considered to have refractory thrombus may therefore gain additional therapeutic opportunities.
Key Points and Challenges in Diagnosing LAA Thrombus
A comprehensive approach is required for the screening of LAA thrombosis, integrating multimodality imaging, clinical risk assessment, and intraoperative guidance (Figure 1). Risk stratification is fundamental for anticipating LAA thrombus formation. Major predictors include a high CHA2DS2-VASc score, cauliflower-type LAA morphology, reduced left ventricular ejection fraction, increased left atrial volume index, and a low left ventricular ejection fraction to left atrial volume index ratio (<1-1.5), all reflecting conditions that promote blood stasis within the appendage.4 Transesophageal echocardiography remains the gold standard for definitive diagnosis. Typical findings include reduced LAA emptying velocity (<20 cm/s), an echogenic mass with motion discordant with the adjacent LAA wall, and confirmation across multiple imaging planes, all of which increase diagnostic confidence.5 Cardiac computed tomography may identify thrombus by demonstrating a persistent filling defect during the delayed contrast phase, helping differentiate thrombus from slow flow.6 Cardiac magnetic resonance can also detect thrombus as a nonenhancing intracardiac mass, although image quality may be limited in specific protocols.7
Figure 1.
Screen and Risk Prediction of LAA Thrombosis
A comprehensive approach is required for the screening of LAA thrombosis, integrating multimodality imaging, clinical risk assessment, and intraoperative guidance. CMR = cardiac magnetic resonance; CT = computed tomography; ICE = intracardiac echocardiography; LAA = left atrial appendage; LAVI = left atrial volume index; LVEF = left ventricular ejection fraction; SEC = spontaneous echo contrast; TEE = transesophageal echocardiography; UEA = ultrasound-enhancing agent.
During procedures, intracardiac echocardiography provides excellent LAA visualization and has a class IIb recommendation for procedural guidance.8 Fluoroscopy may occasionally suggest thrombus through a filling defect, although its diagnostic applicability is limited. Diagnostic performance may be further improved with ultrasound-enhancing agents, which are Class IIa recommended for differentiating SEC from true thrombus.9,10 Although ultrasound-enhancing agents are guideline-recommended tools for detecting intracardiac thrombus, their preparation, dosing, administration technique, and optimization of ultrasound imaging parameters involve numerous technical nuances. Inadequate attention to these details or limited operator experience may significantly affect diagnostic interpretation. Conversely, careful attention to these technical details can often improve what may appear to be inadequate contrast enhancement. In selected situations, inotropic agents may augment LAA flow and reduce SEC.11 However, the appropriate dose remains uncertain, and potential hemodynamic effects—including challenges in rate control in AF—should be considered. Despite reports of safe use, caution is warranted given the potential risk for thrombus mobilization.
Future Directions in Managing LAA Thrombus
When LAA thrombus is detected, LAAC is typically deferred, anticoagulation is initiated, and repeat imaging is performed to confirm thrombus resolution.2 However, thrombus resolution is not always achievable, and the persistent risk for embolization may remain.
Emerging evidence suggests that LAAC may still be feasible in carefully selected patients even in the presence of LAA thrombus, with clinical outcomes comparable with those without thrombus. In such high-risk scenarios, several procedural strategies have been proposed to enhance safety, including selecting cases with distal thrombus only, adopting a no-contrast and no-touch technique, using thrombus-trapping deployment, and performing the procedure under intracardiac echocardiography or transesophageal echocardiography guidance. Additional adjunctive measures such as vacuum aspiration thrombectomy and cerebral protection embolic devices may also be considered to further reduce embolic risk.12,13 Furthermore, with the growing adoption of 1-stop procedures combining AF ablation and LAAC, treatment strategies in the presence of thrombus may differ from conventional approaches. As Carl Sagan famously stated, “Extraordinary claims require extraordinary evidence.” In the era of rapidly evolving transcatheter therapies, innovation must continue to be matched by rigorous validation.
Funding Support and Author Disclosures
The authors have reported that they have no relationships relevant to the contents of this paper to disclose.
Footnotes
The authors attest they are in compliance with human studies committees and animal welfare regulations of the authors’ institutions and Food and Drug Administration guidelines, including patient consent where appropriate. For more information, visit the Author Center.
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