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Funding Acknowledgements Type of funding sources: None. Background The assessment of the ventricular myocardial substrate critically depends on the size of mapping electrodes, their orientation with respect to wavefront propagation, and interelectrode distance. Objective we conducted a dual-center study to evaluate the impact of microelectrode mapping in patients undergoing catheter ablation (CA) of ventricular tachycardia (VT). Methods We included 21 consecutive patients (median age, 68 [12], 95% male) with structural heart disease undergoing CA for electrical storm (n=14) or recurrent VT (n=7) using the QDOT Micro catheter and a multipolar catheter (PentaRay, n=9). The associations of peak-to-peak maximum standard bipolar (BVc) and minibipolar (PentaRay, BVp) with microbipolar (BVμMax) voltages were respectively tested in sinus rhythm with mixed effect models. Furthermore, we compared the features of standard bipolar (BE) and microbipolar (μBE) electrograms in sinus rhythm at sites of termination with radiofrequency energy. Results BVμMax was moderately associated with both BVc (β=0.85, p Conclusions Microelectrode mapping is more sensitive than standard bipolar mapping in the identification of viable myocytes in SR, and may facilitate recognition of targets for catheter ablation.

Funding Acknowledgements Type of funding sources: None. Background Catheter ablation is an increasingly used treatment option for patients with recurrent ventricular tachycardia (VT) or electrical storm (ES). The QDOT Micro (QDOT) Catheter (Biosense Webster) is a novel radiofrequency ablation catheter that was found to allow rapid and effective pulmonary vein isolation among patients with atrial fibrillation. There is no published data on the safety and efficacy of catheter ablation for VT using the QDOT catheter, and few data allow a direct comparison of different technologies in this setting. Purpose to assess outcomes of CA for VT among patients with structural heart disease using the QDOT catheter, and compare them to those observed with the Thermocool Smarttouch (TC-ST, Biosense Webster) catheter. Methods we conducted a dual-center, observational, prospective study enrolling patients with structural heart disease and recurrent VT/ES undergoing catheter ablation with the QDOT catheter. For comparison, we performed a 1:1 propensity score matching to identify patients who underwent VT CA with the TC-ST catheter, using the nearest neighbor method. Propensity score was based on gender, age, etiology of structural heart disease, left ventricular ejection fraction, electrical storm, and number of previous CAs for VT. The primary efficacy outcome was freedom from recurrent VT, as assessed by implantable defibrillator (ICD) interrogation; the primary safety outcome was in-hospital complications. Results Forty propensity-matched patients were included in the analysis (QDOT, n=20; TC-ST, n=20); baseline clinical characteristics are resumed in Table. After a median follow-up of 7 months, survival free from any recurrent VT measured 74 (95% CI, 57-97)% and 69 (95% CI, 51-93)% in the QDOT and TC-ST groups, respectively (log-rank p=0.54, Figure A), while survival free from ICD shocks was 95 (95% CI, 86-100)% versus 84 (95% CI, 69-100)% (log-rank p=0.26, Figure B). There were no major complications in the QDOT group, while three patients (15%) in the TC-ST had a primary safety event (p=0.23; femoral pseudoaneurysm, n=1; cardiac tamponade, n=1; aortic cusp perforation, n=1). Conclusion In a cohort of patients with structural heart disease and recurrent VT or ES, the novel QDOT ablation catheter had similar efficacy and safety compared to the TC-ST catheter. Interestingly, no major procedural complications were observed with the QDOT catheter, suggesting that this device may be safe even in most challenging patients.

Funding Acknowledgements Type of funding sources: None. Background Progression or regression of the atrial substrate in atrial fibrillation (AF) has been demonstrated in animal models and human right atrial maps. Dynamic changes over time of the left atrial (LA) substrate in patients with AF have not been evaluated in detail yet. Purpose To evaluate changes of the LA substrate between first and redo AF ablation procedures. Methods In our prospective single center observational study, consecutive patients undergoing first and redo AF ablation during sinus rhythm were included. The LA was divided into anterior, septal, lateral and inferior regions. The veins and posterior segments were excluded from the analysis. In each segment median voltages and area % of spontaneous low voltage zone (LVZ) of the LA ( Results In the first procedure 34.055 (1.216 points/patient) and in the second 76.958 (2.748 points/patient) points were analyzed in 28 patients (age: 61.2±9.5 years, 39% female, 39% persistent AF). The time between first and second procedure was 1.2 (0.4-2.3) years. Eleven (39%) patients had spontaneous >5% LVZ at both first and second procedure (p=1). In 17 (60%) patients progression was identified; in 5 patients in all 4 segments, in 8 in 3 and in 4 in 2. In the Progression group the total mean LA voltage (1.28±1.30 vs. 0.76±0.71 mV, p Conclusions Our preliminary study is the first to report bidirectional dynamic properties of the LA substrate with concordant either progressive or regressive changes of atrial voltage in different atrial regions outside of the PVs following AF ablation. A better understanding of the dynamic changes of the LA substrate could help to differentiate between patients with reversible and despite ablation therapy progressive irreversible atrial structural remodeling.

Funding Acknowledgements Type of funding sources: None. Background Conduction system pacing is a growing field in bradycardia-treatment. Evidence for His bundle pacing (HBP) and left bundle branch area pacing (LBBAP) to prevent pacing induced cardiomyopathy is growing. Promising data is also emerging to use CSP as an additional tool in cardiac-resynchronisation therapy (CRT). (1-5). Very often patients requiring an ICD also have an indication for bradycardia or resynchronisation pacing. Adding CSP-treatment to these patients requires an additional pacing lead (HBP or LBBAP) and the use of a CRT-D device. As opposed to HBP, in LBBAP atrial oversensing cannot occur. Using an ICD-lead in this position could reduce the number of intracardiac leads needed while maintaining the possibility of sensing and treating ventricular arrhythmias. Purpose We evaluated the acute electrical parameters before and after delivering an ICD shock with an ICD-lead positioned in the left bundle branch area (LBBA). As this ICD-lead position has never been described before, no data is available on dislocation after shock-delivery. We looked at the electrical parameters of the successful LBBAP ICD-lead implants in our LBBAD (Left Bundle Branch Area Defibrillator) pilot-trial which is a proof-of-concept study for LBBA-ICD lead implantation. Methods In the LBBAD pilot trial, we implant an ICD lead in the LBBA to evaluate for feasibility of implantation and functionality of defibrillation. As this is a proof of concept trial, after testing the lead is re-implanted in a conventional ventricular position. In this abstract we report the evaluation of the electrical parameters of the first 3 successfully implanted LBBAD-leads (n=3). Results After LBBA implantation initial electrical parameters were measured. The pacing threshold was 0,8 +/- 0,6 V @ 0,4 ms, while the sensed R-wave and the impedance measured 7,0 +/- 2,7 mV and 512,3 +/- 38,8 Ohms respectively. The shock-coil impedance was 68,0 +/- 7,0 Ohms. All these parameters are in range with the parameters seen in conventional ICD-lead implantation. After performing the defibrillation threshold test (DFT) all electrical parameters were re-evaluated. Sensing, threshold and impedance were 7,6 +/- 2,2 mV, 0,8 +/- 0,7 V @ 0,4 ms, 516,3 +/- 47,8 Ohms and 71,7 +/- 8,2 Ohms respectively. These post-shock measurements remained stable within normal ICD-lead functioning range precluding acute dislocation. Conclusions Our LBBAD pilot trial is the first-in-human experience with ICD-leads implanted in the LBBA. This pilot trial evaluates for implant-feasibility and also looked at the pre- and post shock electrical parameters of the ICD-lead. As the parameters remained in normal working range, precluding acute shock-induced dislocation, these results open the possibility in patients with an LBBAP-indication as well as an ICD-indication, for a follow-up study to implant an LBBAD-lead and perform longer-term evaluation.

Funding Acknowledgements Type of funding sources: None. Background The benefit of an anterior mitral line (AML) in patients with persistent atrial fibrillation (AF) and anterior atrial scar undergoing ablation has never been investigated. Objective to evaluate the outcomes of AML on top of standard treatment, compared to standard treatment alone (no-AML), in this subset of patients. Methods Patients with persistent AF and anterior low voltage zone (LVZ) treated with AML in three Centers were retrospectively enrolled. These patients were matched in a 1:1 fashion with patients with persistent AF and anterior LVZ, who underwent conventional ablation, in the same centers. Matching parameters were: age, LVZ burden, and repeated ablation. Primary endpoint was AF/atrial tachycardia (AT) recurrence. Results 186 patients (66±9 years, 34% women) were selected and included into two matched groups. Bidirectional conduction block was achieved in 95% of AML. After a median follow-up of 2 years, AF/AT recurrence occurred in 29% of the patients in the AML-group, vs. 48% in the No-AML-group (log-Rank p=0.024) (Figure 1). At Cox-regression multivariate­-analysis left atrial volume (HR 1.03, p=0.006) and AML (HR 0.46, p=0.003) were significantly associated with the primary endpoint. At univariate logistic-regression, lower BMI, older age, extensive anterior LVZ and the position of the left atrial activation breakthrough away from the AML (Figure 2), were associated with first-pass AML block. Conclusion In this retrospective matched analysis of patients with persistent AF and anterior scar, AML on top of standard treatment was associated with improved AF/AT-free survival compared with matched patients treated with standard treatment alone.

Funding Acknowledgements Type of funding sources: Private company. Main funding source(s): The study has been financially supported by an investigator-initiated research grant by Biosense Webster (Study ID – IIS-532) (MRM) Background Left atrial (LA) substrate may have mechanistic relevance for ablation of atrial fibrillation (AF). We sought to analyze the relationship between low-voltage zones (LVZ), transition-zones (TrZ) and AF recurrence in patients undergoing pulmonary vein isolation (PVI). Methods We conducted a prospective multicenter study on consecutive patients undergoing PVI-only approach. LVZ and TrZ (0.5-1mV) were analyzed offline on high-density electroanatomical maps collected prior to PVI. Results 262 patients (61±11 years, 31% female) with paroxysmal (130 pts) or persistent (132 pts) AF were included. After 28 months of follow-up, 73 (28%) patients experienced recurrence. An extension of more than 5% LVZ in paroxysmal AF and more than 15% in persistent AF were associated with recurrence (HR=4.4 [2.0-9.8], p Conclusions In patients undergoing first PVI, the impact of LVZ on outcomes occurs with lower burden in paroxysmal than persistent AF suggesting that not all LVZs have equal prognostic implications. A proportional area of moderately decreased voltages accompanies LVZ, suggesting a continuous fibrotic substrate instead of the dichotomous division of healthy or diseased tissue. LAVI generally correlates with LVZ but a small subgroup of patients may present with disproportionate atrial remodeling, despite normal LAVI.

Aims To develop quality indicators (QIs) that may be used to evaluate the quality of care and outcomes for adults with atrial fibrillation (AF). Methods and results We followed the ESC methodology for QI development. This methodology involved (i) the identification of the domains of AF care for the diagnosis and management of AF (by a group of experts including members of the ESC Clinical Practice Guidelines Task Force for AF); (ii) the construction of candidate QIs (including a systematic review of the literature); and (iii) the selection of the final set of QIs (using a modified Delphi method). Six domains of care for the diagnosis and management of AF were identified: (i) Patient assessment (baseline and follow-up), (ii) Anticoagulation therapy, (iii) Rate control strategy, (iv) Rhythm control strategy, (v) Risk factor management, and (vi) Outcomes measures, including patient-reported outcome measures (PROMs). In total, 17 main and 17 secondary QIs, which covered all six domains of care for the diagnosis and management of AF, were selected. The outcome domain included measures on the consequences and treatment of AF, as well as PROMs. Conclusion This document defines six domains of AF care (patient assessment, anticoagulation, rate control, rhythm control, risk factor management, and outcomes), and provides 17 main and 17 secondary QIs for the diagnosis and management of AF. It is anticipated that implementation of these QIs will improve the quality of AF care.