The unfinished issue of ischaemic stroke and embolic events during catheter ablation of atrial fibrillation

We have read with interest the paper by Liu et al.,1 who report a very low incidence of ischaemic stroke (0.36%; 7 patients) in 1946 consecutive procedures of catheter ablation of atrial fibrillation (AF). Although these findings are noteworthy, we would like to comment on two aspects of the study that deserve reflection. Firstly, the authors have not provided details pertaining to the anticoagulation regimes used in their cohort, or assessed its impact on cerebrovascular events. Interruption of oral anticoagulation has previously been shown to be a major predictor of embolic events.2 As such, inclusion of anticoagulation regime in logistic regression analysis would have provided a useful insight into the effect of oral anticoagulation on stroke in their cohort. Secondly, the authors suggest that previous ischaemic stroke, mechanical valve replacement, and CHA2DS2-VASc score ≥3 are independent predictors of cerebrovascular complications during catheter ablation of AF. Such conclusions may be considered intuitively reasonable, albeit premature for the following reasons: (i) although the authors present data from almost two thousand procedures, the study may be underpowered due to the low event rate; (ii) most centres are currently performing AF ablation using uninterrupted anticoagulation,3 contrary to that presented in this study. Indeed, uninterrupted anticoagulation has shown to be associated with a lower rate of bleeding and embolic peri-procedural complications,2 and therefore we do not know if these single-centre data can be extrapolated to a wider population; (iii) in our single-centre experience of anticoagulation with heparin bridging (protocol and timing of anticoagulation interruption have been previously described4) in 1483 consecutive procedures from September 2010 to August 2013, we have also observed a low incidence of ischaemic stroke (0.40%; n = 6). Assessment for predictors of ischaemic events in our sample does not reproduce the data from Liu et al., as high CHA2DS2-VASc (one patient had a score of 3 and the remaining had 1 or 2), previous stroke (not present in any of our patients), and mechanical valve replacement (one patient had a previous mitral valve repair procedure) were not predictors of ischaemic cerebral events. On the other hand, CHADS2 and female gender were shown to be independent predictors in a previous randomized controlled trial including 1584 patients.2 Therefore, it is our belief that a collaboration between high-volume centres, with pooling of data from at least 10 000 procedures, may be necessary to provide a more definite answer to the unsolved matter of peri-procedural stroke and associated risk factors during AF ablation. Previous evidence has suggested that these events may also occur as a result of technical issues.5 Procedural aspects like air embolism, late administration of intravenous heparin, suboptimal ACT control, long-radiofrequency application, or warming up of the catheter tip with clot formation have been implicated in procedure-related stroke. However, as the latter may be under-reported or unaccounted for in large registries, the occurrence of ischaemic events during catheter ablation of AF and the causative factors may be challenging to elucidate. In the interim, and according to the last Expert Consensus, a carefully planned and highly meticulous ablation procedure in highly experienced centres using non-interrupted anticoagulation and pre-procedural imaging may be the best way of minimizing the risk of ischaemic and embolic phenomena. Conflict of interest: R.P. has received training grant from Boston Scientific, and Sorin Group and a Research Grant from Medtronic; S.B. has received consulting fees from Medtronic, Boston Scientific, and Sorin Group. J.-P.A. has received consultant fees from St. Jude Medical and Biosense Webster.