Dipole Density Mapping of Atrial Fibrillation

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1 CardioPulse 5 The next step is to offer stroke prevention to AF patients with 1 stroke risk factors. At this second step, a practical stroke score is meant to be reductionist, so that it does not matter whether the CHA 2 DS 2 -VASc score is 2 or 9 points, or whether 1 or 10 biomarkers are added that AF patient needs stroke prevention, which is OAC. For the latter, decision making between a VKA or NOAC can be helped by using the SAMe-TT 2 R 2 score, where patients with a score 0 2 are likely to do well on VKA with a good time in therapeutic range (TTR), whilst those with a score >2 are less likely to achieve a good TTR and additional measures such as regular followup (with INR checks) and counselling, or a NOAC could be considered. 19,20 Persistence and adherence with OAC are additional considerations, with some evidence for better compliance with NOACs compared to VKA. 21 Bleeding risk assessment has also been subject to much misinformation and bleeding risk scores have been misused by the ill-informed. 22 Bleeding risk factors are often modifiable, and the appropriate (and responsible) use of a bleeding risk score is to flag up the patient potentially at risk of bleeding for more regular review and follow-up, and most importantly, to identify the reversible bleeding risk factors. 22,23 Recent guidelines have focused on highlighting the reversible bleeding risk factors, as well as the non-reversible bleeding risk factors and biomarkers associated with increased bleeding (with the same biomarkers often associated with increased stroke, cardiovascular events, and mortality too). Many of the potentially reversible bleeding risk factors are contained within the HAS-BLED score 22,23 which is a simple and well validated score that has been tested in AF and non-af patients, and is also predictive of bleeding risks in a patient not on antithrombotic therapy, aspirin and on anticoagulation (whether with a VKA or a non-vka anticoagulant); thus, the HAS-BLED score is applicable throughout the patient pathway. A high HAS-BLED score (3) is not an excuse to withhold OAC, and has been shown to be predictive of intracranial haemorrhage, the most feared complication of OAC 1. Recent studies show how other new bleeding risk scores would significantly underperform in VKA treated patients, by not considering the quality of anticoagulation control (e.g. TTR), which is a parameter within the HAS-BLED score (the L or labile INR criterion). 24,25 In summary, simplicity is best, such that, the decision-making process for busy clinicians is helped by keeping concepts simple and practical. The Birmingham 3-step management pathway to streamline decision-making for stroke prevention in patients with AF is shown in the figure. AF is so common, and the default should be to offer stroke prevention to all AF patients unless deemed to be at low risk. Risk stratification is also not a one off assessment but a dynamic process, reflecting the elderly AF population with a high rate of hospitalisations, comorbidities, and polypharmacy. Gregory Y. H. Lip University of Birmingham, Institute of Cardiovascular Sciences, City Hospital, Birmingham B18 7QH, United Kingdom; Thrombosis Research Unit, Department of Clinical Medicine, Aalborg University, Aalborg, Denmark g.y.h.lip@bham.ac.uk Conflict of interest: GYHL has served as a consultant for Bayer/ Janssen, BMS/Pfizer, Biotronik, Medtronic, Boehringer Ingelheim, Microlife, and Daiichi-Sankyo. Speaker for Bayer, BMS/Pfizer, Medtronic, Boehringer Ingelheim, Microlife, Roche, and Daiichi- Sankyo. References References are available as supplementary material at European Heart Journal online. doi: /eurheartj/ehw585 Dipole Density Mapping of Atrial Fibrillation An ElectroFunctional Procedure breaks down the Complexity Non-contact, voltage-based surface electrograms underpin the electrocardiogram and when planning treatment strategies in complex arrhythmias, electrophysiologists rely on 2D and 3D displays of voltage-based, intracardiac electrograms. Whether derived through contact or non-contact, voltage-based signal analysis is fundamental to cardiology practice. At the physiological level, voltage is the measure of an electric field that includes both the local activation source and the sum of the surrounding activation sources. Accordingly, voltage-based mapping systems record the broad-and-smooth nature of voltage with the electrogram displaying a blended view of cardiac activity that may obscure the details of complex rhythm patterns. Dipole density mapping, as an alternative, represents only the local charge-sources on the interior surface of the chamber, resulting in a sharp-and-narrow delineation of cardiac activity (Figure 1).

2 6 CardioPulse Description of imaging and mapping system The AcQMap imaging and mapping system rapidly creates highly accurate ultrasound-based heart chamber reconstructions combined with high resolution maps of electrical conduction using dipole density instead of voltage.1,2. This novel technology utilizes non-contact sensors that enable a continuous global view of the conduction of each heartbeat and permits mapping of any cardiac arrhythmia. The diagnostic recording AcQMap catheter is deployed by the user into a spheroid-shape comprising six splines each populated with eight ultrasound transducers and eight engineered electrodes (Figure 2A). Figure 1 The voltage signal represents the electrical field that includes both the local charge source plus the sum of the surrounding sources. The dipole density signal represents only the local charge sources. Ultrasound samples at a rate of up to surface points per minute from the endocardial surface with the 3D surface then algorithmically reconstructed from the ultrasound point-set being composed of more than 3600 vertices (Figure 2B). Intracardiac unipolar voltage is sampled times each second to map cardiac activity. Inverse and forward algorithms are then applied to the intracardiac voltage to derive and display electrical activation. The calculated data are applied to the final processed surface anatomy as a dipole density propagation history map in which the red colour band represents the leading edge of the activation wave front with the trailing colour bands representing earlier locations. The propagation history map identifies and locates the discrete and coupled mechanisms responsible for initiating and maintaining the arrhythmia (Figure 2C). AcQMap case study A 56-year-old male with a 16-year history of persistent AF, numerous cardioversions and two prior pulmonary vein isolation procedures experienced recurrence in April 2016 after discontinuation of amiodarone in January The patient was fully informed and consented for AF ablation to re-establish pulmonary vein isolation (PVI), followed by AcQMap guided ablation of non-pulmonary vein drivers and maintainers. The pulmonary veins were assessed and isolation confirmed. The AcQMap catheter was deployed in the left atrium and ultrasound was activated to collect points and reconstruct chamber anatomy. The final post-processed anatomy was used for navigation, mapping, and placement of ablation markers (Figure 3). The propagation history map showed two confined zones of localized rotational activation (LRA) located respectively inferior to the left inferior pulmonary vein (LIPV) antrum and on the anterior aspect of the roof. LRA refers to >360 rotation around a confined zone (or point) (Figure 4). A progressive ablation strategy was Figure 2 The AcQMap Catheter (A) with ultrasonic chamber reconstruction (B) and propagation history map showing localized rotational activation (C).

3 CardioPulse 7 Figure 3 Final anatomy used for navigation, mapping, and ablation marker placement. Figure 4 Initial propagation history map. Both zone 1 inferior to the LIPV (PA View) and zone 2 on the anterior aspect of the roof showed LRA. (AP view). designed to target the identified mechanisms followed by immediate remapping to assess therapy effect. Zone 1 was ablated first and anchored to the PVI line. Post-ablation remapping revealed a significant conduction modification of zone 1, including block along the lesionline. A new LRA (zone 3) emerged at the posterior junction of the Figure 5 Post-ablation map showed a new LRA (zone 3-PA view). Complex conduction at zone 2 had ceased and a second new LRA had emerged (zone 4-PA view). right superior pulmonary vein (RSPV) antrum. Complex conduction at zone 2 had ceased and a second new LRA (zone 4) had emerged at the anterior aspect of the right pulmonary veins (Figure 5). Based on the proximity of the newly identified zones 3 and 4 to the right pulmonary veins, a reinforcing RSPV/right inferior pulmonary vein (RIPV) isolation-line was next placed that captured both sites within the line. Nearing completion of the wider encirclement, AF terminated with conversion to typical atrial flutter at which point the AcQMap catheter was moved to the right atrium, ultrasound was activated to collect points and reconstruct that chamber (Figure 6). The chamber was mapped demonstrating a counterclockwise rotation around the crista terminalis with delayed conduction through the isthmus and within Koch s Triangle (Figure 7). A standard cavo-tricuspid isthmus line (CTI) ablation-line was performed with flutter terminating during ablation. The patient left the laboratory in sinus rhythm, maintained still in October 2016 and without the need for any drugs (Figure 8).

4 8 CardioPulse Summary Atrial fibrillation (AF) is a complex, patient-specific arrhythmia. For those with persistent AF current standard of care is no different than for patients with paroxysmal AF, yet outcomes are considerably inferior. The AcQMap System has been developed to provide a diagnostic tool that can locate the cardiac tissue responsible for an arrhythmia and precisely target areas for treatment whilst minimizing delivery of redundant therapy. Early clinical results demonstrate accurate left atrial reconstruction when compared to pre-procedural CT/MRI with dipole density mapping offering a >4-fold higher resolution than voltage-based mapping. The system has successfully mapped stable and unstable atrial arrhythmias without additional patient risk. The ability to quickly remap reveals new targets and Figure 6 Reconstruction of the right atrium. visualization of activation pattern changes without any prolongation of procedure time. Progressive AcQMap ElectroFunctional strategies (map, ablate, remap) break down the complexity of AF often resulting in arrhythmia termination and sinus rhythm. The advanced performance of AcQMap is likely to represent a significant advance in Figure 8 Post-ablation sinus rhythm activation. The red dots indicate placement of the CTI line. Figure 7 Right atrial flutter with counterclockwise rotation around the crista terminalis with delayed conduction in the isthmus and within Koch s Triangle. Note: The transparent grey rectangle to the left of the yellow cursor represents the duration of propagation history.

5 CardioPulse 9 treating persistent AF when compared to voltage-based 3D mapping systems that also require tissue-contact. The prospective, single-arm, multi-centre, multi-national, nonrandomized, post-market UNCOVER-AF clinical study(nct ) is now underway to assess the technology. The objective of this carefully designed study is to address procedural and long-term outcomes in 125 persistent AF patients treated with AcQMap guided ablation therapy. The first enrolled patient was treated at Papworth Hospital in Cambridge on 24 October Andrew Grace PhD FRCP FACC Papworth Hospital, Cambridge University Health Partners, Cambridge CB23 3RE, United Kingdom aag1000@cam.ac.uk Atul Verma MD FRCPC FHRS Southlake Regional Health Center, Newmarket, Ontario, Canada doi: /eurheartj/ehw586 Christina Fanola MD MSc Conflict of interest: Andrew Grace is a member of the Scientific Advisory Board of Acutus Medical, receives research support for relevant studies, has no personal financial interest and receives no compensation from the company. Atul Verma has received research funding from Bayer, Biosense, & Medtronic. Stefan Willems is a member of the Advisory Board of Bayer & Boehringer Ingelheim. He has received lecture fees/honoraria from: Bayer, Biosense Webster, Boehringer lngelheim, Boston Scientific, Bristol Myers, Daiichi Sankyo, St. Jude Medical. References References are available as supplementary material at European Heart Journal online. Recipient of the Young Investigator Award at ESC Congress 2016 and now first author for A Novel Risk Prediction Score in Atrial Fibrillation in this EHJ issue Dr Fanola is a practicing vascular cardiologist and current clinical trials Research Fellow with the TIMI Study Group, an academic research organization affiliated with Brigham and Women s Hospital and Harvard Medical School in Boston, Massachusetts, U.S.A. Prior to initiating work with the TIMI Group, Christina completed clinical and research training in both vascular medicine and cardiology at Boston University, and received a Young Leadership Award from the American College of Physicians. Her research training was supported by an NIH/NHLBI sponsored K12 vascular career development program, where she focused her research efforts on antithrombotic therapy, with a specific interest in outcomes for patients on warfarin therapy under the mentorship of Dr Elaine Hylek. She has published several articles on thrombosis, and has co-authored two chapters on arterial and venous diseases in aforthcomingbook. Dr Fanola received a Master of Science (MSc) in epidemiology, with a concentration in biostatistics and clinical trial design at the Boston University School of Public Health before starting the clinical Stephan Willems MD University Heart Center, University Hospital, Hamburg-Eppendorf, Hamburg, Germany trials Fellowship at Brigham and Women s Hospital. At present, with the TIMI group and under the senior mentorship of Dr Eugene Braunwald and Dr Marc Sabatine, Christina has an active role in the design, execution, and analysis of several clinical trials, including a large phase 3 clinical trial studying the cardiovascular effects of a weight-modification drug, and of a phase 2a trial of a novel lipidmodifying agent. In addition, she has a leading role in several ongoing sub-group analyses from the ENGAGE-AF TIMI 48 trial of edoxaban, and has recently won the Young Investigator Award from the European Society of Cardiology 2016 Congress in thrombosis research for a novel risk score in atrial fibrillation which can predict a differential therapeutic benefit of non-vitamin K oral anticoagulants. Dr Fanola is an independent peer reviewer for several top cardiology and vascular journals, including Circulation, Stroke, and Thrombosis Haemostasis, and has served as an abstract reviewer in vascular diseases for both the Frontiers in Cardiovascular Biology and the American College of Cardiology Scientific Sessions. When not involved in research or clinical work, Christina spends much of her leisure time as captain of a Sabre 30 or C&C 34 sailboat, either in races around the Boston Harbour or going along the New