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Selection of Critical Isthmus in Scar-Related Atrial Tachycardia Using a New Automated Ultrahigh Resolution Mapping System

Background— Accurate activation mapping of reentrant scar-related atrial tachycardias (AT) allows efficient radiofrequency ablation by targeting the critical isthmus (CI). We aimed to assess the electrophysiological properties of CI channels during mapping with the IntellaMap Orion basket and the Rhythmia system. Methods and Results— We prospectively studied 33 AT (post– atrial fibrillation ablation or surgical mitral valve repair). The noise of bipolar electrogram (EGM) was systematically measured at 10 prespecified sites, as well as on a standard catheter and on the surface ECG. Bipolar EGM of CI regions were analyzed for amplitude, duration, and conduction velocity. The isthmus region to be targeted was chosen based solely on propagation. For each AT, 25 684±14 276 EGMs were automatically annotated. Noise of the Orion EGM was 0.011±0.004 mV, lower than that of a standard catheter (0.016±0.019) and surface ECG (0.02±0.01; P<0.05). For reentrant AT, within the CI, bipolar EGM amplitude (0.08±0.11 mV) and conduction velocity (0.27±0.19 m/s) were lower than those orthodromically before (0.62±0.93 mV; 1±0.49 m/s) and after (0.80±1.59 mV; 1±0.73 m/s) the isthmus (P<0.001 for all). In 97% of AT, ablation at the CI resulted in AT termination. No complications occurred. Conclusions— This new automated ultrahigh resolution mapping system produces low noise and allows accurate diagnosis of AT circuits. CI on reentrant scar-related AT showed much lower EGM amplitude with a significantly slower conduction velocity than the surrounding parts of the circuit. Ablation of the areas of slow conduction resulted in a high acute success.