Novel “red‐bull sign” during cavotricuspid isthmus ablation: Indication of an ablation catheter stuck in the subeustachian pouch

BACKGROUND: A subeustachian pouch (SEP) often hinders the completion of a cavotricuspid isthmus (CTI) ablation of typical atrial flutter (AFL) and sometimes causes steam‐pops during a power‐controlled ablation. We hypothesized that real‐time bull's‐eye monitoring of the catheter surface temperature might be useful to locate the SEP where the temperature can rise rapidly, and a temperature‐controlled ablation might avoid steam pops. This study aimed to demonstrate this hypothesis. METHODS: A temperature‐controlled CTI ablation with a QDOT MICRO™ catheter (n = 10) and a conventional power‐controlled CTI ablation (n = 10) were performed with an output power of 35 W. During the RF application, the bull's eye monitor for monitoring the catheter surface temperatures was assessed. A “red‐bull sign” was defined as an entire red‐colored bull's‐eye monitor, indicating that the catheter‐tip temperature of all 6 thermocouples rose rapidly over 47°C. RESULTS: In a total of 115 lesions (12 ± 3 per patient), a “red‐bull sign” was observed in 39 (33.9%) lesions where the RF output was reduced to 26 ± 8 W. All 39 “red‐bull sign” lesions corresponded to the location of the SEP as delineated by ICE before the ablation. The red‐bull sign accurately indicated the presence of a SEP with a sensitivity of 84.7% and specificity of 100%. Bidirectional block of the CTI was completed in all patients in either catheter group without any steam‐pops. CONCLUSION: Real‐time surface temperature monitoring and a red‐bull sign might be useful to detect the SEP. A temperature‐controlled CTI ablation with the QDOT MICRO catheter might be safe for avoiding steam pops.