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Introduction Ventricular arrhythmias are one of the main causes of morbidity and mortality in patients with repaired tetralogy of fallot (rTF). These life-threatening arrhythmias are related to specific isthmuses of viable tissue between areas of scar and/or valve rings of the right ventricle (RV) that have been already described in the literature. Late gadolinium-enhanced cardiac magnetic resonance (LGE-CMR) has proven useful in characterizing the arrhythmogenic substrate in several heart diseases. Nevertheless, LGE-CMR evidence in patients with rTF is scarce. Purpose To compare the characterization of the ventricular arrhythmogenic substrate by means of LGE-CMR and electroanatomic mapping (EAM) of the right ventricle (RV) in patients with rTF. Methods Unicentric and observational study of consecutive patients with rTF who underwent LGE-CMR performed with 1.5T equipment and RV high-density voltage map, performed with multipolar catheter and completed with contact force-sensing catheter. The LGE-CMR segmentation was performed with dedicated software. The extent (area and percentage) and location of the dense scar (defined as <0.5 mV in EAM and <40% of the maximum intensity pixel in LGE-CMR) were compared, as well as the location of the isthmuses of viable tissue. Results Eight patients were included (45.7±10.4 years; 50% male). The extent of the scar was 20.7±13.6 cm2 (15.1±9.3%) by EAM and 21.7±8.8 cm2 (11.8±7.6%) by LGE-CMR. There was an absolute correlation regarding the location of the dense scar and the distribution of the isthmuses of viable tissue. The quantification of the dense scar evidenced a positive linear correlation between both techniques (area correlation: ρ = 0.71, p=0.047; percentage correlation: ρ = 0.88; p=0.004). The average time spent for the segmentation of the LGE-CMR with the dedicated software was 19.9±3.0 minutes. Conclusions Characterization of the RV arrhythmogenic substrate in patients with rTF with LGE-CMR is feasible. An absolute association regarding the location of the dense scar and the distribution of the isthmuses of viable tissue was observed when compared to the RV high-density EAM. In the same way, a statistically significant linear correlation in the quantification of the dense scar between both techniques was documented. LGE-CMR and EAM of two patients with rTF Funding Acknowledgement Type of funding source: None

Introduction Patients with D- transposition of the great arteries (TGA) treated with Senning or Mustard surgeries have several atrial scars that predispose them to develop atrial tachycardias (AT). Identification of scar zones and possible arrhythmic isthmus in voltage mapping will help to guide the ablation. Aim To describe the feasibility of using a specific mapping catheter to identify possible arrhythmic isthmus in this set of patients. Methods Prospective observational study in patients with history of SVT and atrial switch surgery, that underwent electrophysiologic study (EP) and electroanatomic (EA) mapping with a new 8Fr deflectable, multipoint wavefront-activation-orientation independent Grid catheter, in a third level hospital since April 2018 until January 2020, with medium-term follow-up. Results A total of 9 EPs were performed in 8 patients (3 (37,5%) Female, median age 35.2 y.o. (IQI 29,2–37,6)). Figure 1A shows an example of an activation and substrate mapping. Figure 1B shows the localization and percentage of scar identified in both atria. A total of 7 tachycardias were induced. In this, an arrhythmogenic isthmus was identified and in all patients at least one non-arrhytmogenic isthmus was documented. Figure 1C shows anatomical and electrophysiological characteristics of the isthmus. Arrhythmogenic isthmus had slower conduction velocity than non-arrhytmogenic (mean 0,31m/s (IQI 0,14–0,63) vs 0,94 m/s (IQI 0,81–1,24) p=0.02) and fractionated potentials were detected more frequently (100% vs 55% p=0.05) Conclusion EA mapping with a new a multipoint, high-definition, Grid Cather allows the identification and electrophysiological characterization of arrhythmogenic and non-arrhytmogenic isthmus in patients with TGA treated with atrial switch surgery. Figure 1 Funding Acknowledgement Type of funding source: Public hospital(s). Main funding source(s): Hospital Universitari Vall d'Hebron. VHIR

Introduction Patients with repaired tetralogy of Fallot (rTF) and severe pulmonary regurgitation frequently progress to dilation and dysfunction of the right ventricle (RV). It has been documented in the literature that there is a correlation between the duration of the QRS in the surface electrocardiogram and the hemodynamic parameters of the RV of these patients, suggesting the presence of a mechanical-electrical interaction. Purpose To determine if there is an association between the contraction delay in certain areas of the RV measured in M-mode echocardiography and the delay in electrical activation measured in the electroanatomic map (EAM) of RV in patients with rTF. Methods Unicentric and observational study of all patients with rTF undergoing EAM, echocardiography with study of RV asynchrony and cardiac magnetic resonance imaging (MRI). Activation delay in the antero-basal area and in the RV outflow tract (RVOT) in the EAM were both analysed (Figure 1A). The shortening delay in the same areas in M-mode echocardiography was also evaluated (Figure 1B, C). MRI data regarding volume and ejection fraction was also collected. Results 64 patients were included (36.7±10.6 years, 65% men). The mean total activation time of the RV (RV-TAT) was 127.3±42.4 ms. Activation mapping showed a recurrent pattern with beginning in the interventricular septum and ending in RV antero-basal region and/or RVOT. A linear positive correlation was observed between RV-TAT and the activation delay in both regions analysed (ρ=0.60 and ρ=0.52, respectively; p<0.001) and also between the electrical and mechanical delay in the anterior wall (ρ=0.41; p=0.001). On the other hand, it was observed a negative correlation between RV ejection fraction (RVEF), measured on MRI, and the RV-TAT (ρ=−0.41, p=0.002) and also between RVEF and the activation delay in the RV antero-basal region and in the RVOT (ρ=−0.32, p=0.016 and ρ=−0.36, p=0.007, respectively). Conclusions There is a mechanical-electrical interaction in the RV of patients with rTF, with a negative correlation between the activation delay and RVEF and between mechanical and electrical activation delay in specific anatomical regions (regional mechanical-electrical interaction). These results may guide future studies on resynchronization in this heart disease. Figure 1. EAM and echocardiographic measures Funding Acknowledgement Type of funding source: None

Background Few information exists about the additive value of implantable loop recorders (ILR) for the diagnosis of subclinical atrial fibrillation or flutter (AF) in patients (p) studied for syncope and its therapeutic and prognostic implications. Purpose To evaluate the burden of new onset AF diagnosed by ILR in patients studied for syncope and its therapeutic and prognostic implications. Methods We conducted an observational cohort study in a tertiary center. From April 2014 to January 2019, 355 ILR were implanted in patients with syncope according the ESC syncope guidelines. We excluded the ones with previous known AF and younger than 18 years old (yo), with a final cohort of 197 patients. All of them were therefore followed in outpatient clinic and treated according to current clinical guidelines. New AF diagnosis and consequent therapeutic changes and related clinical events were recorded. Results Of 197p, 38 had a first episode of AF (19.29%), with a mean AF burden of 4.19%, and a median of 0.15%. The incidence rate of AF detection was 10.67patients/year (p-y), with higher incidence among patients older than 65 yo (14.17p-y vs 5.27p-y, p<0.05). Only 1 patient out of 38 had a symptomatic episode that triggered consultation to the emergency room (2.63%). Oral anticoagulants (OAC) were started in 30 of 38 patients with new onset AF (78.94%). Only one stroke was reported secondary to new onset AF before OAC were started. 2 mayor bleedings were reported (1.01%), both of them related to OAC start for new AF diagnosis. 4 patients died (2.03%), all of them from non-cardiovascular causes. Kaplan Meier survival from AF Conclusions New onset AF is frequent in patients with ILR implanted for syncope, especially among those older of 65 yo, with the vast majority consisting in short paroxysms. Following AF detection, generally OAC are initiated.