Safety of vHPvSD Ablation
It is important to note that all published case series utilising vHPvSD are extremely small, with patients ranging from 28 to 90. Given the relative infrequency of serious complications such as clinical stroke and atrio-oesophageal complications with AF ablation, these studies are grossly underpowered to provide conclusive safety data. As such, we need to look for surrogate markers of complications, such as oesophageal lesions on endoscopy and asymptomatic cerebral lesions (ACLs) on cranial MRIs.
The incidence of post-procedure oesophageal injury is reassuringly low in the 3 studies that have evaluated this systematically with endoscopy (Table 2). In QDOT-FAST, a haemorrhaging ulcer was seen in just 1 of the 52 patients, and healed with medical therapy. The other two studies, comprising 134 patients, showed no evidence of oesophageal injury in any patient. This reassuring observation is in keeping with the findings of the bench studies; vHPvSD lesions tend to be wider but shallower thereby reducing the potential for extracardiac damage.
However, more worrying are the reports of coagulum formation on the catheter tip and high rates of ACLs which likely represent associated thromboembolic events from this charring (Table 2). Rates of post-procedure ACL in vHPvSD studies have varied from 11.8% to 26%, which are higher than seen with sRF. These have occurred in spite of appropriate intra-procedural anticoagulation, and even after recent software modifications to the nGEN RF generator. Whilst these ACLs were not associated with clinical stroke events, and most (but not all) resolved on follow-up MRI a few months later, recent prospective data suggest that even silent ACLs can be associated with cognitive decline over a relatively short timeframe. As such, it is clearly preferable to minimise – or prevent entirely – the risk of ACL occurrence. How can we do so?
One possible solution is suggested by Mueller et al. themselves. While they found catheter tip coagulum in almost a third of patients initially (6 out of the first 19 patients), this stopped happening entirely when the baseline circuit impedance was increased – via repositioning of the neutral electrode – from 90Ω to 110Ω. This interesting observation lends credence to the theory that coagulum formation results from excessively high current flow with lower impedance. Bourier et al. recently demonstrated the critical impact of circuit impedance on ablation, emphasising that it is current delivery, rather than power input, which determines lesion size, and that current delivery can vary widely due to fluctuations in impedance. This effect may be particularly magnified in vHPvSD due to the short duration of current delivery. More research is needed to find the optimal balance of current delivery by modulation of impedance and power, perhaps by development of a ‘constant current mode’ as suggested by Bourier et al. .
vHPvSD ablation represents a quantum leap from the RF settings that have traditionally been used in electrophysiology. If used to its full potential, it may improve procedural efficiency by reducing ablation and procedure times. However, with great power comes great responsibility; we need to ensure that we use it judiciously and safely (Figure 1). To that end, we are grateful to Mueller and colleagues for highlighting these issues for us to work on.