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Funding Acknowledgements Type of funding sources: None. Introduction Ventricular overdrive pacing during tachycardia is one of the most common and useful maneuvers to assess de differential diagnosis of supraventricular tachycardia (SVT). Focal atrial tachycardia (FAT) usually presents long ventriculo-atrial (VA) interval, which is a passive interval since FAT is not an atrio-ventricular reentry. Therefore, during ventricular entrainment of a FAT, the stimulus-atrial (SA) interval will depend solely on the retrograde VA conduction time, if retrograde conduction exists. This retrograde conduction time is usually shorter than the VA Interval during tachycardia, thus being able to cause a negative SA-VA difference. This does not occur in other types of SVT, where the SA-VA difference helps to differential diagnosis, but positive values have been described. Purpose Our aim was to analyze whether the SA-VA value discriminates FAT from the other types of SVT, in patients with SVT and VA conduction when stimulating the ventricle during tachycardia. Methods Multicenter data of SVT entrainment were collected retrospectively, including FAT, atrioventricular nodal reentry tachycardia (AVNRT), and atrioventricular reciprocating tachycardia (AVRT). The numeric value of SA-VA difference was calculated for each case. The best SA-VA cut-off point for the diagnosis of TAF was determined, evaluating the sensitivity and specificity of this value for the diagnosis of TAF with respect to the gold standard (classical criteria). Results Continuous ventricular pacing during tachycardia succeeded in accelerating the atrium to the pacing rate in 80 cases out of the total studied cases: 32 (40%) AVNRT, 28 (35%) AVRT and 20 (25%) FAT. All FAT cases had a negative SA-VA value and all AVNRT and AVRT cases obtained positive SA-VA (Figure 1). SA-VA value lower than 0 ms was the best cut-off point (using ROC curve, Figure 2) with an area under the curve of 1. SA-VA difference lower than 0 ms (or negative SA-VA difference) showed 100% sensitivity and specificity for the diagnosis of FAT. Conclusions Negative SA-VA difference is a new and accurate criterion for the diagnosis of focal atrial tachycardia.

Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Instituto de Salud Carlos III BACKGROUND Cardiac regenerative therapy is a promising treatment for patients with myocardial infarction (MI) and heart failure. Nevertheless, previous ex-vivo studies have raised concern on the potential increased risk of arrhythmic events following certain cell therapies. Adipose graft transposition procedure (AGTP) is a cardiac reparative therapy consisting in transposing a vascularized adipose flap from the autologous pericardium and placing it over the epicardial scar area and has demonstrated to reduce infarct size and improve the left ventricular ejection fraction in preclinical and human studies. PURPOSE To assess the effect of the AGTP on the post-MI scar composition and image-based ventricular tachycardia (VT) corridors detection by means of late gadolinium enhanced cardiac magnetic resonance (LGE-CMR). METHODS A left circumflex artery (first marginal branch) MI was induced in 9 Landrace X Large White Pigs by delivering 1-3 coils. Two weeks post-MI, all subjects underwent a 3 Tesla LGE-CMR and randomized to the AGTP or sham group. LGE-CMR was repeated 30 days post-treatment (6 weeks post-MI). The arrhythmogenic substrate was characterized with an advanced image post-processing tool (ADAS 3D) and included quantification of dense scar and border zone (BZ) mass and detection of ventricular tachycardia (VT) corridors (including corridor scar mass). RESULTS The overall scar mass did not differ between scans in the overall population (7.6 ± 3.5 g vs 7.5 ± 2.2 g in the baseline and post-treatment scans, respectively; p = 0.9). Compared to the sham subjects, those receiving AGTP showed an absolute reduction of the total (-3.2 ± 1.4 g vs. +2.4 ± 1.7 g, p = 0.04) and dense scar (-0.9 ± 0.4 g vs. +0.7 ± 0.5 g, p = 0.03). BZ mass tended to decrease in the AGTP group (-2.2 vs 1.63 g; p = 0.06). The AGTP group showed a trend to reduce the number of VT corridors (-1 ± 0.7 vs. +0.4 ± 0.2, p = 0.078) and corridor scar mass (-0.3 ± 0.26 g vs. +0.1 ± 0.1 g, p = 0.11) (figure). CONCLUSIONS Cardiac reparative therapy of MI with AGTP reduced dense scar mass, compared to the increase observed in the sham group. The trend to reduce the BZ mass and the number/mass of VT corridors suggests a beneficial effect on the arrhythmic remodeling of the post-MI scar. Abstract Figure. Reduction in corridor"s number

Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Insituto de Salud Carlos III BACKGROUND Cardiac regenerative therapy is a promising treatment for patients with ischemic heart disease, but there are some concerns on the potential increased risk of arrhythmic events following specific cell therapies. Adipose graft transposition procedure (AGTP) is a cardiac reparative therapy consisting in transposing a vascularized adipose flap from the autologous pericardium and placing it over the epicardial scar area and has demonstrated to reduce infarct size and improve the left ventricular ejection fraction in preclinical and human studies. Specific electrophysiological properties of the scar, (i.e. slow conduction velocity (CV)) have been identified as key features of ventricular tachycardia (VT) isthmuses. PURPOSE To assess the effect of the AGTP on VT inducibility and the electrophysiological properties of the post-MI scar with ultra-high density (UHD) mapping. METHODS A left circumflex artery (first marginal branch) MI was induced in 10 Landrace X Large White pigs by delivering 1-3 coils. Two weeks post-MI, all subjects underwent baseline left ventricular endocardial UHD mapping during right ventricular pacing with 64-electrode basket mapping catheter, as well as electrophysiological study (EPS) to test for VT inducibility. Following the mapping, subjects were allocated 1:1 to AGTP or sham group. UHD mapping and EPS were repeated 30 days post-treatment (6 weeks after MI). Voltage and activation maps were analyzed off-line with self-customized Paraview-based software. Voltage cut-offs of 1.5 and 0.5mV (bipolar) defined normal tissue, border zone (BZ) and dense scar, respectively, and 6.7mV for unipolar. Conduction velocity (CV) was determined for every pair of contiguous points and areas of similar CV were quantified for every 0.2m/s steps (for up to 4 m/s). RESULTS There were no differences between groups with regard of dense scar, BZ an low unipolar voltage areas. The AGTP group had a significant reduction of the size of slow CV ( CONCLUSIONS Cardiac reparative therapy with AGTP of post-MI scar reduced the size of slow conduction areas and could provide a protective effect against arrhythmic events in ischemic heart disease. Abstract Figure.

Funding Acknowledgements Type of funding sources: None. BACKGROUND Left atrial fibrosis is a marker of atrial disease and it has an important role in the pathophysiology of atrial fibrillation (AF). Late gadolinium enhancement cardiac magnetic resonance (LGE-CMR) is an emerging tool to detect left atrial fibrosis. However, data on the correlation between LGE-CMR detected fibrosis and low voltage areas to define fibrotic tissue is scarce. PURPOSE To assess the correlation and degree of concordance between LGE-CMR and high-density bipolar voltage mapping for the identification of left atrial abnormal tissue. METHODS Seven patients scheduled for AF ablation (including first and redo procedures) underwent a preprocedural 1.5 Tesla LGE-CMR including left atrial 3D inversion-recovery steady-state free precession sequence (ECG and respiratory triggering) 20 minutes after the injection of 0.2 mmol/kg of gadobutrol. A high-density electroanatomical voltage mapping was acquired with a 16-electrode grid configuration mapping catheter during sinus rhythm. LGE-CMR studies were analyzed off-line with an advanced image post-processing tool (ADAS 3D). Atrial wall intensity was normalized to blood pool, obtaining an image intensity ratio (IIR) value for each CMR point of the 3D model. High-density bipolar voltage maps and LGE-CMR 3D left atrial reconstruction were merged (figure, panel A). Voltage points were projected to the LGE-CMR left atrial 3D model, allowing point-by-point correlation analysis between voltage (log transformed due to non-normal distribution) with IIR. Left atrial fibrosis area and percentage were quantified using the standard cut-off values (bipolar voltage 1.2). We assessed the degree of concordance for normal and abnormal (fibrosis) tissue classification between the two techniques using different cut-off values (< 0.5mV and 0.9, >1, >1.1 and >1.2 for IIR). RESULTS The average fibrosis area detected with LGE-CMR was lower than that detected with high-density bipolar voltage, using standard cut-off values (18.6 ± 5.7 cm2 vs. 40.6 ± 12.5 cm2, p = 0.13 respectively). There was a poor global point-by-point correlation between log-transformed voltage and IIR was r=-0.093, p 1, with an agreement percentage of 54.6%. CONCLUSIONS Left atrial tissue characterization between LGE-CMR and high-density bipolar voltage mapping showed significant but poor point-by-point correlation. Although the highest concordance was obtained using standard cutoff values, the Kappa index was best when applying non-standard cutoffs (1mV for bipolar voltage and >1 for IIR). Abstract Figure.

INTRODUCTION Cardiac implantable electronic device (CIED) infection is a severe disease with an increasing incidence due to the rise in the number of CIEDs implanted world-wide. Complete hardware removal is the treatment of choice, but there is little clinical data about the best antimicrobial strategy, such as the best choice of antibiotics, treatment duration and when to switch to oral administration in cases of local CIED infections. PURPOSE In 2013, we designed a new protocol for CIED infection management, by which local infections were treated with complete hardware removal followed by empiric parenteral antibiotic during the first 72h, which was replaced to an oral agent (in case of negative blood cultures) and continued for 10 days. The oral antibiotic was selected according to the local cultures when positive, or to Clindamicin, Levofloxacin or Cotrimoxazole when no germ was identified. Our purpose is to describe our experience and results after the implementation of this strategy. METHODS We retrospectively reviewed all consecutive local CIED infection cases from the implementation of the protocol until September 2019, and evaluated the population characteristics, type of infection, rate of positive cultures and outcomes. RESULTS We identified 74 cases of CIED infection, of which 46 (62%) were local. The average age of this population was 75.3 ± 13.2 yo and 65% (30) were male. The predominant comorbidities were diabetes (41%), congestive heart failure (30%), and malignancies (22%). Eighteen patients (39%) had previous local infection treated medically without hardware removal. Mean number of previous procedures was 2.65 ± 1.8, and 34 (74%) of the devices were pacemakers (single and dual chamber), 5 (11%) ICDs, 6 (13%)CRT-P and 1 (2%) CRT-D. Blood cultures were negative in all cases, whereas local cultures (exudate or intraoperative tissue) were positive in 32 (70%). The most frequent microorganisms were Staphylococcus epidermidis in 18 (56%) and Staphylococcus aureus in 8 (25%), including 1 case of meticillin-resistance. Intravenous Vancomycin was administered in all cases during 72 h, followed by oral antibiotics for a mean duration of 8.8 ± 3.3 days. Hardware removal was intended in all cases, with complete or clinical success in 42 and 3 cases respectively (global success rate 97.8%), and in one case (2.2%) an epicardial lead was not removed. During a mean follow-up of 30 months, 1 infection-related death occurred (2%) due to a side effect of intravenous antibiotic therapy, and there was 1 infection relapse (2%) in the only patient without complete hardware removal, related to the remnant epicardial lead. CONCLUSIONS Oral antimicrobial treatment with good bioavailability agents, associated with complete hardware removal is an effective strategy for the management of local CIED infections, with a low recurrence rate, and avoiding long hospitalizations and potential side effects of intravenous antibiotic therapy.