Successful catheter ablation of scar-related atrial tachycardia depends on correct identification of the critical isthmus. Often, this is a represented by a small bundle of viable conducting tissue within a low-voltage area. It's identification depends on the magnitude of the signal/ noise ratio. Ultra-high density mapping, multipolar catheters with small (eventually unidirectional) and closely-spaced electrodes improves low-voltage electrogram detection. Background noise limitation is also of major importance for improving the signal/noise ratio. Electrophysiological properties of the critical isthmus and the characteristics of the local bipolar electrograms have been recently demonstrated as hallmarks of successful ablation sites in the setting of scar-related atrial tachycardia.

Background Whether cavotricuspid isthmus (CTI) is a region of conduction slowing during typical flutter has been discussed with conflicting results in the literature. We aimed to evaluate conduction velocity (CV) along the different portions of the typical flutter circuit with a recently proposed method by means of ultra‐high‐resolution (UHR) mapping. Methods Consecutive patients referred for typical atrial flutter (AFL) ablation underwent UHR mapping (Rhythmia, Boston Scientific). CVs were measured in the CTI as well as laterally and septally, respectively, from its lateral and septal borders. Results A total of 33 patients (mean age: 65 ± 13 years; right atrial volume: 134 ± 57 mL) were mapped either during ongoing counterclockwise (n = 25), or clockwise (n = 3) AFL (mean cycle length: 264 ± 38 ms), or during coronary sinus pacing at 400 ms (n = 1), 500 ms (n = 1), or 600 ms (n = 3). A total of 13 671 ± 7264 electrograms were acquired in 14 ± 9 min. CTI CV was significantly lower (0.56  ± 0.18 m/s) in comparison with the lateral CV (1.31 ± 0.29 m/s; P < .0001) and the septal border CV of the CTI (1.29 ± 0.31 m/s; P < .0001). Conclusion UHR mapping confirmed that CTI CV was systematically twice lower than atrial conduction velocities outside the CTI.

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Introduction: Literature supports the existence of drivers as maintainers of atrial fibrillation (AF). Whether ultrahigh density (UHD) contact mapping may detect them is unknown. Methods:We sequentially mapped the left atrial (LA) activation during spontaneous persistent AF and performed circumferential pulmonary vein isolation (CPVI), followed by remapping and ablation of potential drivers (rotational and focal propagation sites) with Rhythmia™ in 90 patients. The time reference was an LA appendage (LAA) electrogram (EGM). Regions with uniform color were defined as "organized." Only patients (51) with no previous ablation were considered for acute results and follow-up reporting.Results: LA maps (175 ± 28 ml, 43578 ± 18013 EGM) were acquired in 23 ± 7 min. In all post-CPVI maps potential drivers (7.3 ± 3.2/patient) were visualized: 85% with rotational propagation and continuous low voltage in the center; the remaining with focal propagation and an organized EGM at the site of earliest activation. The RF delivery time for extra-PV driver ablation was 12.2 ± 7.9 min. There was a progressive increase of AF organization: the LAA cycle length prolonged, the number of potential drivers decreased, and the organized LA surface in AF increased from 14 ± 6% to 28 ± 16% (p = .0007). Termination of AF without cardioversion was obtained in 67%. AF recurrence rate at 15 ± 7.3 months was 17.6% after the first procedure.Conclusions: Sequential UHD contact activation mapping of persistent AF allows visualization of potential drivers. A sequential strategy of CPVI followed by ablation of potential drivers with limited RF time resulted in an increasing organization of AF and good acute and long-term results.