title: Acoustic signal emission monitoring as a novel method to predict steam pops during radiofrequency ablation: preliminary observations.
abstract: Steam pop is an explosive rupture of cardiac tissue caused by tissue overheating above 100 °C, resulting in steam formation, predisposing to serious complications associated with radiofrequency (RF) ablations. However, there are currently no reliable techniques to predict the occurrence of steam pops. We propose the utility of acoustic signals emitted during RF ablation as a novel method to predict steam pop formation and potentially prevent serious complications.
  
  
  METHODS
  Radiofrequency generator parameters (power, impedance, and temperature) were temporally recorded during ablations performed in an in vitro bovine myocardial model. The acoustic system consisted of HTI-96-min hydrophone, microphone preamplifier, and sound card connected to a laptop computer. The hydrophone has the frequency range of 2 Hz to 30 kHz and nominal sensitivity in the range -240 to -165 dB. The sound was sampled at 96 kHz with 24-bit resolution. Output signal from the hydrophone was fed into the camera audio input to synchronize the video stream. An automated system was developed for the detection and analysis of acoustic events.
  
  
  RESULTS
  Nine steam pops were observed. Three distinct sounds were identified as warning signals, each indicating rapid steam formation and its release from tissue. These sounds had a broad frequency range up to 6 kHz with several spectral peaks around 2-3 kHz. Subjectively, these warning signals were perceived as separate loud clicks, a quick succession of clicks, or continuous squeaking noise. Characteristic acoustic signals were identified preceding 80% of pops occurrence. Six cardiologists were able to identify 65% of acoustic signals accurately preceding the pop. An automated system identified the characteristic warning signals in 85% of cases. The mean time from the first acoustic signal to pop occurrence was 46 ± 20 seconds. The automated system had 72.7% sensitivity and 88.9% specificity for predicting pops.
  
  
  CONCLUSIONS
  Easily identifiable characteristic acoustic emissions predictably occur before imminent steam popping during RF ablations. Such acoustic emissions can be carefully monitored during an ablation and may be useful to prevent serious complications during RF delivery.
authors.affiliation: Cardiology Department, Westmead Hospital, Sydney, Australia.|Sydney Medical School, University of Sydney, Sydney, Australia.
authors.forename: William W B
authors.initials: WWB
authors.lastname: Chik
authors.affiliation: Cardiology Department, Westmead Hospital, Sydney, Australia.
authors.forename: Roman
authors.initials: R
authors.lastname: Kosobrodov
authors.affiliation: Cardiology Department, Westmead Hospital, Sydney, Australia.
authors.forename: Abhishek
authors.initials: A
authors.lastname: Bhaskaran
authors.affiliation: Cardiology Department, Westmead Hospital, Sydney, Australia.
authors.forename: Michael Anthony Tony
authors.initials: MAT
authors.lastname: Barry
authors.affiliation: Sydney Medical School, University of Sydney, Sydney, Australia.|School of Electrical and Information Engineering, University of Sydney, Sydney, Australia.
authors.forename: Doan Trang
authors.initials: DT
authors.lastname: Nguyen
authors.affiliation: Cardiology Department, Westmead Hospital, Sydney, Australia.|Sydney Medical School, University of Sydney, Sydney, Australia.
authors.forename: Jim
authors.initials: J
authors.lastname: Pouliopoulos
authors.affiliation: Cardiology Department, Westmead Hospital, Sydney, Australia.|Sydney Medical School, University of Sydney, Sydney, Australia.
authors.forename: Karen
authors.initials: K
authors.lastname: Byth
authors.affiliation: Cardiology Department, Westmead Hospital, Sydney, Australia.|Sydney Medical School, University of Sydney, Sydney, Australia.
authors.forename: Gopal
authors.initials: G
authors.lastname: Sivagangabalan
authors.affiliation: Cardiology Department, Westmead Hospital, Sydney, Australia.|Sydney Medical School, University of Sydney, Sydney, Australia.
authors.forename: Stuart P
authors.initials: SP
authors.lastname: Thomas
authors.affiliation: Cardiology Department, Westmead Hospital, Sydney, Australia.|Sydney Medical School, University of Sydney, Sydney, Australia.
authors.forename: David L
authors.initials: DL
authors.lastname: Ross
authors.affiliation: School of Electrical and Information Engineering, University of Sydney, Sydney, Australia.
authors.forename: Alistair
authors.initials: A
authors.lastname: McEwan
authors.affiliation: Cardiology Department, Westmead Hospital, Sydney, Australia.|Sydney Medical School, University of Sydney, Sydney, Australia.
authors.forename: Pramesh
authors.initials: P
authors.lastname: Kovoor
authors.affiliation: Cardiology Department, Westmead Hospital, Sydney, Australia.|Sydney Medical School, University of Sydney, Sydney, Australia.
authors.forename: Aravinda
authors.initials: A
authors.lastname: Thiagalingam
mesh_terms: D000162:Acoustics / Q000295:instrumentation; D000818:Animals; D062906:Cardiac Catheters; D017115:Catheter Ablation / Q000009:adverse effects* / Q000295:instrumentation; D002417:Cattle; D004867:Equipment Design; D006352:Heart Ventricles / Q000473:pathology / Q000601:surgery*; D009206:Myocardium / Q000473:pathology; D009622:Noise; D012815:Signal Processing, Computer-Assisted; D013018:Sound Spectrography; D013227:Steam / Q000009:adverse effects*; D013997:Time Factors; D014159:Transducers
chemical_list: D013227:Steam
keywords: acoustic emissions; biophysics of ablation; complications of radiofrequency ablation; heating efficiency; hydrophone; radiofrequency ablation