title: Visualizing intramyocardial steam formation with a radiofrequency ablation catheter incorporating near-field ultrasound.
abstract: BACKGROUND
  Steam pops are a risk of irrigated RF ablation even when limiting power delivery. There is currently no way to predict gas formation during ablation. It would be useful to visualize intramyocardial gas formation prior to a steam pop occurring using near-field ultrasound integrated into a RF ablation catheter.
  
  
  RESULTS
  In an in vivo open-chest ovine model (n = 9), 86 lesions were delivered to the epicardial surface of the ventricles. Energy was delivered for 15-60 seconds, to achieve lesions with and without steam pops, based on modeling data. The ultrasound image was compared to a digital audio recording from within the pericardium by a blinded observer. Of 86 lesions, 28 resulted in an audible steam pop. For lesions that resulted in a steam pop compared to those that did not (n = 58), the mean power delivered was 8.0 ± 1.8 W versus 6.7 ± 2.0 W, P = 0.006. A change in US contrast due to gas formation in the tissue occurred in all lesions that resulted in a steam pop. In 4 ablations, a similar change in US contrast was observed in the tissue and RF delivery was stopped; in these cases, no pop occurred. The mean depth of gas formation was 0.9 ± 0.8 mm, which correlated with maximal temperature predicted by modeling. Changes in US contrast occurred 7.6 ± 7.2 seconds before the impedance rise and 7.9 ± 6.2 seconds (0.1-17.0) before an audible pop.
  
  
  CONCLUSIONS
  Integrated US in an RF ablation catheter is able to visualize gas formation intramyocardially several seconds prior to a steam pop occurring. This technology may help prevent complications arising from steam pops.
authors.affiliation: Kings College London BHF Centre, Cardiovascular Division, NIHR Biomedical Research Centre at Guy's and St. Thomas' NHS Foundation Trust, London, UK.
authors.forename: Matthew
authors.initials: M
authors.lastname: Wright
authors.forename: Erik
authors.initials: E
authors.lastname: Harks
authors.forename: Szabolcs
authors.initials: S
authors.lastname: Deladi
authors.forename: Steven
authors.initials: S
authors.lastname: Fokkenrood
authors.forename: Fei
authors.initials: F
authors.lastname: Zuo
authors.forename: Anneke
authors.initials: A
authors.lastname: Van Dusschoten
authors.forename: Alexander F
authors.initials: AF
authors.lastname: Kolen
authors.forename: Harm
authors.initials: H
authors.lastname: Belt
authors.forename: Frederic
authors.initials: F
authors.lastname: Sacher
authors.forename: Mélèze
authors.initials: M
authors.lastname: Hocini
authors.forename: Michel
authors.initials: M
authors.lastname: Haïssaguerre
authors.forename: Pierre
authors.initials: P
authors.lastname: Jaïs
mesh_terms: D000818:Animals; D062906:Cardiac Catheters; D017115:Catheter Ablation / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D003287:Contrast Media; D006352:Heart Ventricles / Q000000981:diagnostic imaging / Q000601:surgery*; D023421:Models, Animal; D012756:Sheep; D013227:Steam; D007507:Therapeutic Irrigation / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D013997:Time Factors; D018084:Ultrasonography, Interventional
chemical_list: D003287:Contrast Media; D013227:Steam
keywords: animal model; catheter ablation; pericardium; steam pops; ultrasound