‘Nontrivial’ Amount of LA Thrombus Found Before AF Procedures

Left atrial (LA) thrombus is not infrequently found in patients with atrial fibrillation (AF) or flutter who have been taking oral anticoagulation continuously for at least 3 weeks, a meta-analysis suggests.

The mean-weighted prevalence was 2.73%, though that number varied widely from 0 to 15.42% across 35 studies of patients undergoing transesophageal echocardiography (TEE) before cardioversion or catheter ablation, researchers report.

Senior author Jorge Wong, MD (Population Health Research Institute, Hamilton, Canada), told TCTMD that indicates a “nontrivial” amount of thrombus in this patient population. And the analysis shows that prevalence was higher in certain subsets, including those with nonparoxysmal atrial fibrillation/flutter and those with higher CHA₂DS₂-VASc and CHADS₂ stroke risk scores.

Wong said this information can be helpful to physicians who are making decisions about the use of TEE before cardioversion or ablation, which is widely variable out in practice, particularly before ablation.

“You start thinking about the number of transesophageal echos that get done, and because it’s an invasive imaging modality, they’re not completely risk-free. So part of the reason that we did this study was to see whether we could get by with maybe doing TEEs in less individuals undergoing ablation, for example,” Wong said. “And I think our data does give physicians some ability to risk-stratify some of their patients, and perhaps TEEs don’t have to be done in patients who have, for example, paroxysmal atrial fibrillation or have low CHA₂DS₂-VASc and CHADS₂ scores, for instance.

“On the other side of the coin,” he continued, “we typically don’t do any TEEs at all in patients undergoing cardioversion if they have been anticoagulated for at least 3 weeks, and perhaps if anticoagulation’s just taken place for a minimum of 3 weeks yet the patient’s stroke score . . . is quite high, then perhaps for certain individuals clinicians can decide whether to do a TEE . . . just to make sure that the risk of potential stroke after cardioversion is minimized.”

Wael Alqarawi, MD (University of Ottawa Heart Institute, Canada), commented that there is the potential to overestimate the prevalence of LA thrombus in this setting when examining studies that involve patients selected for TEE use rather than all-comers, as was done in this meta-analysis. That issue was confirmed in a similar analysis by Alqarawi’s group published last year in CJC Open.

That caveat aside, “I think the idea that there are probably subgroups that are at higher risk and might benefit from TEE is true,” Alqarawi said.

There’s not enough evidence yet to propose changing recommendations regarding use of TEE before cardioversion or catheter ablation in patients with atrial fibrillation/flutter, he added, but this meta-analysis “certainly suggests that we need to think about it more” and “highlights that there is a need to better study this in order to come up with guidance into when to use TEEs for these patients.”

The study, with lead author Antony Lurie, BMSc (Population Health Research Institute), was published online ahead of print in the Journal of the American College of Cardiology.

Higher-Risk Subgroups

The presence of LA thrombus is a contraindication to cardioversion and catheter ablation based on the idea that the procedures could dislodge the clot and precipitate a stroke. Atrial fibrillation guidelines from the United States and Europe recommend anticoagulation for at least 3 weeks before cardioversion to minimize this risk. Or if the procedure needs to be done sooner, a TEE can be performed to exclude thrombus.

“Given the widespread use of periprocedural anticoagulation in these settings, and the significant uptake of direct oral anticoagulants (DOACs) in recent years, the utility and necessity of TEE for the preprocedural detection of LA thrombus requires reevaluation,” the researchers write in their paper.

To that end, they pooled data from 10 prospective studies and 25 retrospective studies that included a total of 14,653 patients who underwent TEE following at least 3 weeks of continuous therapeutic anticoagulation—18 studies focused on patients undergoing ablation, seven on those undergoing cardioversion, five on a mixed population, and five on patients without a specified indication for the imaging.

The prevalence of LA thrombus was not significantly different between patients who were treated with a vitamin K antagonist rather than a DOAC (2.80% vs 3.12%; P = 0.674). Thrombus was more likely to be found in the setting of cardioversion versus ablation (5.55% vs 1.65%; P < 0.001), although the researchers say that likely had to do with the higher-risk patient population.

Subgroups more likely to have LA thrombus on a preprocedural TEE were those with nonparoxysmal atrial fibrillation/flutter (4.81% vs 1.03%), those with a CHA₂DS₂-VASc score of 3 or higher (6.31% vs 1.06%), and those with a CHADS₂ score of 2 or higher (4.24% vs 0.82%; P < 0.001 for all).

“Overall, these results suggest that TEE may be helpful in select patients with atrial fibrillation/flutter despite guideline-directed anticoagulation before cardioversion or catheter ablation,” the authors write.

Periprocedural Stroke Risk Already Low

In an accompanying editorial, Paulus Kirchhof, MD, and Christoph Sinning, MD (both from University Heart & Vascular Center Hamburg, Germany), point out that the prevalence of LA thrombus identified in the meta-analysis is “several-fold higher” than the rate of periprocedural stroke observed in other studies when ablation and cardioversion are performed on continued anticoagulation. They also note that even when LA thrombus is excluded before a procedure using TEE, some periprocedural strokes can occur.

“Fortunately, continued oral anticoagulation already yields low periprocedural stroke rates,” they write. “Based on this new analysis of existing data, a risk-based use of TEE imaging in anticoagulated patients could enable further improvement in the safe delivery of rhythm control interventions in patients with AF.”

Alqarawi also highlighted more-individualized use of TEE. “This group of patients is heterogeneous, and one needs to think about them and to have a tailored approach when considering performing TEEs,” he advised.

Additional research is required, the investigators say, “to define optimum antithrombotic therapy for patients with atrial fibrillation/flutter in whom left atrial thrombus is identified despite conventional oral anticoagulation to promote thrombus resolution and prevent clinical embolic events.”