Very High Power Very Short Duration Ablation for Atrial Fibrillation: with great power comes great responsibility
Short Title: Very high power short duration ablation
Key words: HPSD ablation, 90 watts ablation, QDot, QMode
Dhiraj Gupta1 MD
Peter Calvert1 MBChB
1 Liverpool Centre for Cardiovascular Science, University of Liverpool and Liverpool Heart & Chest Hospital Liverpool, UK
Correspondence:
Professor Dhiraj Gupta
Professor of Cardiac Electrophysiology / Consultant Cardiologist & Electrophysiologist
Department of Cardiology,
Liverpool Heart and Chest Hospital,
Liverpool, L14 3PE, U.K.
Tel: +44(0)1516001616
Email: dhiraj.gupta@lhch.nhs.uk
Word count: 1562
Funding: None
Conflicts of Interest: DG has received research funding from Biosense Webster, Boston Scientific and Medtronic.
For all the advances in electrophysiology, the need to create a focal ablation lesion using radiofrequency (RF) energy has remained remarkably constant. However, the recipe for the perfect RF lesion continues to elude us even after almost 40 years of research and clinical experience. As we continue our search for the holy grail of transmurality and durability with assured safety, there has been renewed interest in temperature controlled (TC) ablation. Accurate tip temperature feedback from catheters such as the QDot MicroTM catheter (Biosense Webster Inc, Irwindale, CA) have allowed for the first time the use of very high power, very short duration (vHPvSD) ablation that utilises 90W RF power for just 4 seconds of ablation per lesion, delivered in the TC mode. Ex-vivo experiments have demonstrated that vHPvSD ablation produces larger, shallower, and more homogeneous lesions as compared to standard power-controlled ablation (sRF); characteristics that should be ideal for the thin-walled left atrial tissue. vHPvSD also produces more transmural and contiguous linear lesions with fewer steam pops compared to sRF ablation, which would be particularly useful for ventricular tissue. If these extremely encouraging results could be replicated in the clinical arena, our search for perfect RF lesion creation may be finally over. Are these high hopes being realised?
The clinical feasibility of the vHPvSD approach was first demonstrated in the QDOT-FAST trial, in which 52 patients underwent successful pulmonary vein isolation (PVI) with impressively short mean procedural and ablation times of 105 min and 8 min respectively. However, new asymptomatic cerebral lesions (ACLs) were identified in 6 (14%) patients who underwent MRI scanning, with 4 of these occurring despite uninterrupted anticoagulation. While no patients suffered clinically significant neurological effects, and all but one of these ACLs resolved on repeat MRI performed at 1 month, it did throw a spotlight on an issue that needed redressal before this technology could supplant the other well-established RF ablation techniques.
In this edition of the Journal of Cardiovascular Electrophysiology, Mueller and colleagues present a single-centre experience of safety outcomes in 34 patients undergoing vHPvSD AF ablation. The principal findings of this study are: 1) modest acute efficacy, as seen by disappointing first pass isolation (FPI) rates of 18% of patients and 54% of PV pairs; 2) a concerning safety signal in the form of coagulum on the catheter tip in 10 (18%) patients and ACLs on post-procedure MRI in 26% patients. The same group had described a similarly high rate of catheter tip coagulum (11%) and ACLs (24%) in a previous cohort of patients after which several software amendments to the RF generator (nGEN) were made. However, it appears that the underlying issue persists. Whilst Mueller and colleagues deserve credit for sharing their findings, these will cause consternation amongst the electrophysiology community. After all, with vHPvSD we were hoping for an improvement in both procedural efficacy and safety, but the data from Mueller et al. suggest the polar opposite. This editorial piece will attempt to put these new findings in context with other published work in this area, and also with our own observations gleaned from using vHPvSD for the past 18 months.