LONDON, UNITED KINGDOM. It is now common practice to perform transesophageal echocardiography (TEE) on patients scheduled to undergo catheter ablation with the intent of curing atrial fibrillation (AF). The purpose of the TEE is to check for thrombi (blood clots) in the left atrium and left atrial appendage (LAA) since such thrombi can migrate to the brain during or immediately after the ablation procedure resulting in an ischemic (cardioembolic) stroke. A group of researchers at the University College Hospital in London now report the results of a study aimed at determining whether it is necessary to do a TEE on all patients scheduled for ablation, or whether certain groups of patients can avoid this rather uncomfortable procedure.

The study involved 635 patients who underwent TEEs and AF ablation procedures over a 4-year period. About 50% of the patients had persistent afib with the remainder having the paroxysmal variety. All patients were treated with warfarin (INR of 2 to 3) for at least 4 weeks prior to their TEE. Despite this, 12 out of the 635 patients (1.9%) were found to have thrombus at the time of their TEE. Initial (univariate) analysis showed that a large left atrium diameter, persistent AF, hypertension, age over 75 years, and cardiomyopathy were all associated with an increased risk of thrombi (all found in the LAA). However, a multivariate analysis showed that only hypertension, cardiomyopathy and age greater than 75 years were associated with an increased risk of thrombi.

It is of interest to note that no thrombi were found in patients without CHADS2 risk factors for ischemic stroke (age > 75 years, hypertension, heart disease, diabetes and history of TIA or ischemic stroke). It is also important to note that an enlarged left atrium and the presence of persistent afib did not increase the risk of thrombi in the left atrium and LAA. Other research has shown that an enlarged left atrium does not increase the risk of stroke in AF patients.

Another study involving 732 patients observed a 1.6% incidence of thrombi and concluded that a CHADS2 score of 2 or more and a left atrial diameter greater than 4.5 cm are independent risk factors for thrombi in the left atrium or LAA. Based on their own and other�s findings, the authors conclude that TEE should be performed prior to ablation on all patients with risk factors for thrombi, but may not be needed in the case of anticoagulated patients (paroxysmal or persistent) with no clinical risk factors.

McCready, JW, et al. Incidence of left atrial thrombus prior to atrial fibrillation ablation: Is pre-procedural transesophageal echocardiography mandatory? Europace, Vol. 12, 2010, pp. 927-32
Verheugt, FWA, et al. Oral anticoagulants before and ablation for atrial fibrillation. Europace, Vol. 12, 2010, pp. 913-14

Editor�s comment: This study confirms that paroxysmal and persistent lone afibbers with no risk factors for stroke have a very low to non-existent risk of harbouring thrombi in the left atrium and LAA and thus can forego a pre-ablation TEE without increasing their risk of stroke associated with the procedure.