Areas of minimal generator impedance drop during the index atrial fibrillation ablation correlate with pulmonary vein reconnection sites despite adopting the CLOSE protocol

Funding Acknowledgements

Type of funding sources: None.

Background

Pulmonary vein (PV) isolation is the cornerstone of atrial fibrillation (AF) management. However, AF recurrence is extremely common after a single procedure. The CLOSE protocol, which is the standardisation of radiofrequency catheter ablation by delivering a point-by-point lesion set defined by ablation index (AI), has demonstrated 80% freedom of AF. Yet PV reconnection is still up to 38% in these patients (1). A small decrease in generator impedance (GI), which is not part of the AI algorithm, has been associated with recovery of PV conduction.

Purpose

The study aimed to identify whether lesions having a poor impedance drop (PID) after wide area circumferential ablation (WACA) are associated with PV reconnection, despite adopting to the CLOSE protocol.

Methods

120 consecutive patients who had both the index (i-AFA) and redo AF ablations (r-AFA) due to AF recurrence at our centre from Jan 2018 to Jun 2021 were screened. 18 patients who had WACA around PVs using high power (40 to 50W) with a minimum AI of 400, whilst adhering the CLOSE protocol during the i-AFA, and who had evidence of PV reconnection during r-AFA, were included in the study. Ones who had left atrial (LA) substrate or cryoablation were excluded. GI was measured between the skin patch and ablation catheter. CARTO® system was used to create LA electroanatomical maps (EAMs) and register ablation lesions.

Each WACA around PVs was divided into eight anatomical segments (Figure). PID was defined as an impedance change of <8Ω, based on previous studies (2). These lesions were identified and categorised to the relevant anatomical segment in the i-AFA. Locations of the discrete ablation lesions that re-isolated PVs during the r-AFA, were used as a surrogate to denote areas of PV reconnection. These were also spatially matched to the relevant anatomical segment. Each EAM was reviewed by two electrophysiologists.

Results

30 out of the 36 WACAs (83%) and on average, at least 2 segments per WACA (2.6; 95% confidence interval (CI): 2.2-3.1) had reconnected. 54% of the reconnected segments had at least one lesion with PID. Having a lesion with PID in a PV segment in the i-AFA was significantly associated with evidence of PV reconnection in the same segment in the r-AFA (odds ratio: 2.1 [95% CI: 1.3-3.6; p<0.01]). Right posterior/inferior (56%) and left anterior/superior (50%) PV segments were the most common areas to reconnect and these areas were also associated with a higher incidence of PID lesions in the i-AFA (94% and 67%, respectively). Conversely, 80% of segments with all lesions having an impedance drop of ≥8Ω had no PV reconnection.

Conclusion

Lesions with PID in the i-AFA could impact PV reconnection, despite lesion contiguity and an adequate AI. Identifying and targeting these areas of PID, in addition to the CLOSE protocol, could potentially reduce AF recurrence. Prospective studies are needed to validate this hypothesis and its safety.

A mixed-reality holographic viewing platform enabling interaction with 3D electroanatomical maps using the HoloLens

Introduction

Three dimensional (3D) electroanatomical maps (EAMs) created during electrophysiology procedures are traditionally displayed on 2D monitors connected to mapping systems. This has limitations, such as the lack of interaction with EAMs, the need for another user to control them, and the size of EAM displayed, which is limited by the resolution of these monitors. To overcome these, we created a novel technology to display EAMs on a mixed reality (MR) platform.

Methods

We used the Microsoft® HoloLens to create this MR platform. Studies from patients who had already undergone catheter ablation for atrial fibrillation, where EAMs of the left atria had been generated using different mapping systems (CARTO®, Rhythmia™ and EnSite Precision™) were utilised. These EAMs consisting of 3D coordinates and annotations (e.g. voltage & activation times) were exported from the mapping system. EAMs were then compiled and transferred to the HoloLens using custom-developed functions on Unity©, Microsoft® C# and VisualStudio. Subsequently, feedback was obtained from 3 independent electrophysiologists on this technology.

Results

We successfully exported the EAMs generated on CARTO®, Rhythmia™ and EnSite Precision™ mapping systems as holograms on to the HoloLens (Figure). Positive feedback included themes such as 1) the ability to use hand gestures and voice commands to interact with EAMs independent of another user unlike traditional cardiac mapping systems 2) offering an interactive 3D holographic experience whilst preserving the operators' physical interaction in the cardiac catheter lab 3) the capacity to better appreciate 3D geometry of EAMs in comparison to 2D monitors. The challenge of wearing a headset during long procedures was perceived as a disadvantage.

Conclusion

This technology, which can be used with any mapping system, is currently optimised for offline display. Our software will be made available as an opensource teaching and simulation tool. Users will be able to explore EAMs for research, planning complex cases and immersive learning. The future directions will include extending this toolkit for real-time cardiac mapping with catheter localisation, and could potentially be translated to other cardiac imaging modalities.

Funding Acknowledgement

Type of funding sources: Public hospital(s). Main funding source(s): Cardiovascular diseases charitable fund (CDCF) at Guy's and St Thomas' NHS Foundation Trust. Process of creating Holograms of EAMsVoltage map of left atrium as a Hologram