Definition of success
Procedural success varies substantially depending on how success is defined. The first 90 days following ablation, termed the blanking period, are characterized by a high burden of atrial arrhythmias resulting from atrial inflammation which does not necessarily portend a reduction in long term success and is frequently not used clinically or in research studies to indicate treatment failure. While one 30 second episode of AF over the course of a year, excluding the blanking period, technically constitutes treatment failure to maintain sinus rhythm, this low burden of AF is arguably clinically irrelevant to the individual patient and does not increase stroke risk17. AF burden reduction18 and improvement in quality of life (QoL)7 may be more clinically relevant endpoints. Clinical trials such as CIRCA Dose used insertable cardiac monitors (ICMs) for AF monitoring post-ablation and showed a reduction in AF burden by 99% even though almost half had one or more AF recurrences at 12 months18. Using a real-world dataset of 665 patients with a cardiac implantable electronic device (CIED) having undergone an AF catheter ablation, we showed that AF free survival at 1 year post-blanking period for patients with paroxysmal AF varied from 28.2 to 72.1% for AF events >6 min and >24 hrs, respectively, despite a 99.6% reduction in AF burden, and AF free survival at 1 year for patients with persistent AF varied from 24.9 to 60% for AF events >6 min and > 7 days with >23hrs, respectively, despite a 99.3% reduction in AF burden (Figure 1)19. These findings were similar to those found in the LINQ AF study in which 419 patients that had an ICM implanted following AF catheter ablation had a success rate that varied from 46 to 79%, depending on what threshold was used to define success.
A rational approach to AF detection post-intervention should rest in part on the minimal duration of AF associated with major events, with stroke constituting the most feared consequence of the disease. While AF burden has been directly correlated with stroke risk20–23, the exact duration of AF that is required to increase the risk of stroke is still being debated. In a sample of 725 patients with implanted pacemakers, Capucci and colleagues showed that the risk of stroke was increased with AF episodes >24hrs24. The TRENDS study25, which subsequently enrolled 2486 patients with CIEDs, found that only AF episodes >5.5 hours over a 30-day rolling window were associated with an increased risk of thromboembolic events (HR 2.2). The initial analysis of the ASSERT trial, which enrolled 2580 patients with CIEDs, found that AF events >6 minutes in duration increased the risk of stroke or systemic embolization (HR 2.49)26. However, a subsequent analysis of the ASSERT data showed that only AF events > 24 hours were associated with an increased stroke risk (HR 3.24) and that patients with <24hrs of AF had the same stroke risk as those without AF27. What further complicates the issue is the observation that the association between AF duration and stroke may be dependent on the individuals underlying risk factors. A study of 21 768 non-anticoagulated patients with CIEDs demonstrated a clear interaction between AF duration and CHA2DS2-VASc score, such that patients with a CHA2DS2-VASc score of 2 required > 23.5hrs of AF but those with a CHA2DS2-VASc score of 4 required only >6min of AF to have a stroke risk >1%, the threshold some suggest is the “tipping point” for anticoagulation20.