MODERATED POSTER SESSION 12 - DON’T FORGET SVT ABLATION 689 Prediction of termination/conversion and subsequent second circuit of atrial tachycardia MT. Takigawa; ND. Derval; AF. Frontera; KV. Vlachos; TK. Kitamura; GC. Chenit; JD. Duchateau; CM. Martin; NK. Klotz; TP. Pambrun; AD. Denis; FS. Sacher; MH. Hocini; MH. Haissaguerre; PJ. Jais Hospital Haut Leveque, Bordeaux-Pessac, France Backgrounds: Ablation procedures, cardiac surgeries, and extensive fibrosis may create the substrate of complex ATs. In these ATs, to predict the impact of ablation and the subsequent circuit of the second tachycardia is sometimes difficult. We aimed to elucidate the simple algorithm to predict the behavior of AT during radiofrequency application from the primary activation map of high-density mapping system. Methods: A simple algorithm for predicting termination/conversion of AT and the sub- sequent second AT circuit, associated with the ablation site, was developed from 71 index AT-activation map (retrospective phase) using high-density mapping system. The algorithm showed the sensitivity of 98.3% and the specificity of 83.3% to predict the termination/change of AT during ablation and the subsequent second AT circuit. This algorithm was subsequently tested prospectively in 188 consecutive ATs in 135 patients () (Prospective phase). Result: 13 focal ATs, 20 ATs without complete activation map, and 5 undiagnosed ATs with complete activation map was excluded from the study. Among 150 ATs, 115 ATs were predicted to be terminated, among which 5/115 (4.3%) was converted to another AT. Thirty-five ATs were predicted to be converted to another AT, among which 1/35 (2.9%) was terminated. The sensitivity and the specificity to predict termi- nation/conversion of AT during ablation was 99.1% and 87.2% in total, 100% and 80.0% in macroreentrant AT, 100% and 90.9% in non-macroreentrant ATs, and 91.7% and 92.3% in deal-loop AT, respectively. Five ATs which were supposed to be terminated but to convert to the second ATs used the other atrral chamber or the epi- cardial structure in the second AT circuit. Conclusions: With the high-density mapping system, termination/conversion of the AT and the subsequent AT circuit was highly predictable from the index activation map. 690 High density to AVNRT, new insight C. Pandozi 1 ; M. Russo 1 ; M. Galeazzi 1 ; C. Lavalle 1 ; S. Ficili 1 ; F. Piccolo 2 ; M. Malacrida 2 ; F. Colivicchi 1 1 San Filippo Neri Hospital, Rome, Italy; 2 Boston Scientific Italia, Milan, Italy Background: Sinus impulse propagation and activation inside the Kock’s Triangle (KT) remains a controversial issue. The exact origin and significance of multicompo- nent potentials referred to as slow pathway (SP) potentials, are not perfectly known to date. Purpose: Clearly define the propagation of the sinus impulse in the KT and the con- duction path and the switch between the slow and the fast pathway during atrioven- tricular nodal reentrant tachycardia (AVNRT) in patients who underwent SP ablation. Methods: The 3-D KT geometry was created both during sinus rhythm and tachycar- dia from the basket mapping catheter IntellaMap OrionTM and the RHYTHMIATM Mapping System (Boston Scientific). The dual pathway physiology and the presence of collision between different wave-fronts inside the KT were confirmed through the propagation map. The collision points, joined by the line of collision (LOC), were tagged on the map. The basket catheter was then positioned at the site of LOC and the distribution and timing of all SP potentials in the KT were collected. Results: 5 consecutive successful SP ablation cases of AVNRT were included. The mean acquired points of RA were 58006600; 250650 of these were acquired inside the KT. The mean time of a complete RA mapping was 1762 minutes. The mean KT area was 30.662.9 mm2 and the mean slow pathway area was 9.461.5 mm2 result- ing in a relative percentage of 30.662.6%. In all the cases the wave-front descends from the fast pathway (from the anterior limbus in an anteroposterior -superior to infe- rior- direction) and it rises through the slow pathway. A portion of the wave-front slides posteriorly to the coronary sinus and ascends around the tricuspid valve. Multicomponent potentials were identified inside KT in the majority of the patients and were invariably found on the line of collision between the wave-fronts activating the KT in opposite directions, specifically between the coronary sinus and the tricuspid valve. None of them were found outside the KT area. The mean distance of SP poten- tial from the first activation was 13.861.6mm. After a mean of 1.260.4 RF ablations we obtained the abolition of the SP. The successful ablation was confirmed during sinus rhythm by looking at the junctional beats during RF delivery and performing additional conventional pacing maneuvers at the end of ablation. Conclusions: Our findings could have practical implications for improving the tradi- tional anatomy-guided approach within the triangle of Koch. The use of a propagation map-guided ablation technique for AVNRT ablation may result in faster selection of ablation site, reduction of RF delivery and shorter fluoroscopy time. 691 Atrial tachycardia with activation duration longer than tachycardia cycle length. Mechanisms and prevalence P. Maury 1 ; MASATE Takigawa 2 ; STEFAN Capellino 3 ; ANNE Rollin 1 ; NICOLA Derval 2 ; PIERRE Mondoly 1 ; BENJAM Monteil 1 ; ARNAUD Denis 2 ; JEAN R Roux 3 ; FREDER Sacher 2 ; MICHEL Haissaguerre 2 ; MELEZE Hocini 2 ; PIERRE Jais 2 1 University Hospital of Toulouse - Rangueil Hospital, Toulouse, France; 2 Hospital Haut Leveque, Bordeaux-Pessac, France; 3 Boston Scientific, paris, France Background: Ultra high-density mapping allows very accurate characterization of cir- cuits/mechanisms in atrial tachycardia (AT). Some complex patterns may involved a duration of atrial activation (AD) which is longer than the AT cycle length (CL) and dif- ficult to understand using other 3D system. Prevalence and characteristics of such AT are unknown. Methods: consecutive patients (n¼96) undergoing ablation of 125 right (n¼22) or left (n¼103) AT using ultra-high density mapping with the Rhythmia TM system were retro- spectively included. Offline cautious calculation of the complete duration of LA or RA activation was compared to the AT cycle length. Results: Mean CL was 293665 ms and mean AD was 290673 ms. AT mechanisms were macro-reentry in 75 (60%), small reentry in 27 (22%) and focal AT in 20 (16%) (mixed type in 3). CL was equal to AD in 96 AT (77%). Fourteen AT (11%) had AD superior to CL (mean 70645 ms more) due to bystander areas with delayed activation (terminating after a new activation has begun in the circuit of at the focus). Fourteen had AD less than CL (11%) essentially in focal AT. There was no difference between right and left atrium for prevalence of AT having AD longer than TCL. Small reentry were more often present in AT with AD > CL (26%) compared to focal AT (20%) and macro reentry (5%) (p¼0.001). Conclusion: AT with AD longer than CL are not exceptional (around 10%) and are more related to small reentry of focal AT rather than macro reentry. Ultra high-density mapping allows detection of these complex patterns of activation. Abstract 691 Figure. exemple of AT with AD > CL 692 Focal atrial tachycardia arising from the crista terminals; detailed electrophysiology and long-term ablation outcomes GM. Morris 1 ; L. Segan 2 ; P. Heck 3 ; G. Wynn 2 ; G. Wong 2 ; A. Mcclellan 2 ; A. Nisbet 4 ; T. Walters 2 ; J. Ariyaratnam 1 ; P. Sparks 2 ; J. Morton 2 ; P. Kistler 5 ; JM. Kalman 2 1 University of Manchester, Manchester, United Kingdom; 2 Royal Melbourne Hospital, Melbourne, Australia; 3 Papworth Hospital NHS Trust, Cambridge, United Kingdom; 4 Bristol Heart Institute, Bristol, United Kingdom; 5 Baker IDI Heart and Diabetes Institute, Melbourne, Australia Europace Abstracts Supplement, 2018 doi:10.1093/europace/euy015 Published on behalf of the European Society of Cardiology. All rights reserved. V C The Author 2018. For permissions please email: Journals.permissions@oup.com. 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