Both transcatheter mitral edge-to-edge repair (TEER) and left atrial appendage closure (LAAC) are among the fastest growing interventional cardiology procedures in Europe.1 Both interventions require periprocedural anticoagulation with unfractionated heparin (UFH, heparin) to reduce the risk of thrombotic complications. UFH is administered either before or immediately after transseptal puncture (TSP), targeting an activated clotting time (ACT) value between 250 and 300 seconds throughout the procedure. The timing of the anticoagulation initiation (before or after TSP) varies among centers and operators.2., 3., 4., 5., 6., 7., 8., 9. Some physicians are concerned that UFH administration prior to TSP may aggravate pericardial bleeding in case of complicated TSP.2,3 However, this complication is rare if TSP is performed under transesophageal echocardiography (TEE) guidance.3., 4., 5., 6., 7., 8., 9., 10., 11., 12., 13., 14., 15., 16, 17., 18., 19., 20. The results of retrospective studies performed in patients undergoing atrial fibrillation (AF) ablation showed that late UFH administration (i.e., after TSP) was associated with an approximately 10% incidence of new thrombus formation on the transseptal needle/sheath introduced into the left atrium.15., 16, 17. Moreover, in retrospective studies, earlier UFH administration (i.e., prior to the TSP) resulted in significant reduction of thrombus occurrence on the transseptal sheath.15,16 In the PRAGUE -17 trial, new periprocedural thrombus was identified in 1.1% of patients.18 According to the retrospective study the prevalence of new thrombus was as high as 9% during mitral TEER.20 There were also several case reports on this complication.20., 21., 22.

The overall prevalence of clinically overt periprocedural embolic complications is low.4,8,10,19 However, according to several studies utilizing brain magnetic resonance imaging (MRI), new ischemic lesions occur in approximately 33% or 80% of patients undergoing LAAC or mitral TEER, respectively.3,5., 6., 7. The clinical significance of the occurrence of new ischemic lesions detected by brain MRI is uncertain.3,5., 6., 7. However, in the recent study by Braemswig et al. that included serial MRI brain imaging, mild neurological deterioration occurred in 9 out of 54 patients (17%) treated with mitral TEER, with new ischemic lesions detected by brain MRI corresponding neuroanatomically to new neurological symptoms.5

Many factors other than thrombus are potentially responsible for systemic embolization and occurrence of new brain ischemic lesions during LAAC and mitral TEER procedures.3,5., 6., 7. Besides acute thrombus formation during and shortly after TSP, factors might include air bubbles embolization despite adequate flushing of the delivery catheters, tissue fragments originating from the torn interatrial septum or the mitral valve, or small particles from the implanted devices. Despite other causes are possible, we believe that thrombotic complications have a major role, hence our hypothesis.