Real-time visualization of pulmonary vein isolation: the sooner the better

This editorial refers to ‘Procedural characteristics of pulmonary vein isolation using the novel third-generation cryoballoon’ by A. Fürnkranz et al., on pages 1795–1800. Real-time (RT) recordings of the pulmonary vein (PV) electrograms can be obtained during ablation with a dedicated inner lumen mapping catheter (ILMC Achieve, Medtronic, USA) that is used in conjunction with the cryoballoon (CB; Arctic Front Advance™, Medtronic, USA). This tool provides information on time to PV isolation and consequently on the conduction properties of the left atrium-pulmonary vein (LA–PV) junction.1,2 Recently published data have convincingly demonstrated that shorter times to isolation are associated with sustained LA–PV disconnection.1,2 Conversely, longer times to isolation tend to reliably predict early recovery of PV conduction.2 Anatomically, the PV sleeves are often thicker and occupy more of the circumference at the atrial end, but they tend to become thinner as you progressively move more distally into the vein.3 Recent articles focusing on the second-generation CB have reported a 50–60% rate of RT recordings visualization during ablation.4,5 However, given the above-mentioned considerations, this percentage may appear deceiving. Although the current strategy usually commences by recording baseline electrical activity at the PV ostium level before attempting occlusion and subsequently ablation, time to PV isolation might not only be crucial in offering valuable information on LA–PV conduction, but it might also guide the operator in tailoring the dosing strategy of the freeze–thaw cycle. In fact, recent data indicate that shorter application times might offer similar clinical outcome if compared with the recommended ‘2 times 4 min’ strategy.6–8 However, although shortening the freeze duration has proved effective in achieving faster procedural times and lower fluoroscopy exposure, these findings need to be confirmed in large randomized trials. As mentioned above, the time to PV isolation has been reported as one of the most important predictors of lesion durability, and RT recordings provide valuable information about the risk of PV reconnection and freezing efficacy. Alternatively, in case of no RT recordings, the decision to perform an additional freeze should be based on the optimal occlusion of PV, temperature drop and the minimal temperature achieved.6 Recently, a novel third-generation ‘short-tip’ CB (CB-ST) has been launched on the market with technological modifications aiming at increasing the rate of RT recordings visualization. Compared with the former second-generation CB device, the CB-ST has been designed with a 40% shortened tip. The other technical features having led to an excellent clinical outcome with the second-generation CB have not been modified between both devices. Ideally, a shorter tip should permit an improved identification of PV electrical activity due to a more proximal positioning of the ILMC. In this issue of EP-Europace, Furnkanz et al.9 described their first experience with this novel device. In addition, the authors compared their findings with a series of previously treated patients with the second-generation device. In a large cohort of consecutive patients, the novel CB-ST offered a significantly higher rate of PV electrogram mapping if compared with its predecessor (89.5 vs. 82.6%). The authors should be commended for their excellent acute outcomes and for meticulous methodology with which the study has been carried out. The opportunity of visualizing electrical activity in virtually all veins may pave the way to future studies defining the ideal dosing strategy. Albeit this technology is very popular among electrophysiology laboratories worldwide due to its excellent clinical outcome, CB ablation can also be hampered by collateral effects such as oesophageal lesions or more typically phrenic nerve damage.10 Therefore, the ideal balance between ‘enough’ freezing in order to ensure permanent PV isolation, but not ‘too much’ in order to avoid the unwanted damage to extra-cardiac structures is warranted. Considering the amount of research that is being carried out at an astonishingly high pace in this field, an answer to this issue may well be foreseeable in the near future. As stated by the authors, the shortened distal tip of the CB-ST required adaptation of standard catheter manoeuvres to avoid balloon dislodgement. In their series, in up to 8% of patients, the ILMC had to be exchanged with a stiff guide wire to achieve a stable balloon position with a satisfactory occlusion. This may cause some eyebrows to be raised as it may render the reproducibly straightforward procedure somewhat more cumbersome. Conversely, a recent publication that closely mirrors the current study draws a more optimistic conclusion on this issue. In fact, Heeger et al.11 stated that no differences in terms of catheter manoeuvrability and catheter stability could be observed between both generations of CB. This difference in findings between these studies may lie in the small population numbers. Future studies conducted on significantly larger cohorts of patients undergoing third-generation CB ablation are needed to shed light on this issue. Finally, albeit a slightly warmer mean nadir temperature recorded with the CB-ST device, no differences in acute performance parameters such as time to isolation or single freeze PV isolation were observed. This promising finding will certainly lead to the excellent mid-term outcome that we have been used to in the setting of AF ablation with the second-generation device. Hopefully, the third-generation device will tell us with more certainty if isolating the PVs sooner during the freeze will lead to better clinical outcomes. Conflict of interest: C.A. receive compensation for teaching purposes and proctoring from AF solutions, Medtronic, member steering committee ETNA-AF-Europe Daiichi Sankyo Europe. G.-B.C. receive compensation for teaching purposes and proctoring from AF solutions, Medtronic and speakers fees from Biosense-Webster. C.A. receives research grants on behalf of the centre from Biotronik, Medtronic, St Jude Medical, Sorin, Boston Scientific.