title: Single capacitive discharge utilizing an auxiliary shock in the coronary venous system reduces the defibrillation threshold.
abstract: Auxiliary shocks (AS) from electrodes sutured to the left ventricle (LV) prior to primary biphasic shocks (PS) have been shown to reduce defibrillation thresholds (DFT). Two capacitors are required to generate these waveforms. We investigate delivery of AS from one capacitor using a novel waveform. The epicardial surface of the LV is accessed transvenously via the middle cardiac vein (MCV) avoiding a thoracotomy.
  
  
  METHODS
  A defibrillation electrode was placed in the right ventricle (RV) and superior vena cava (SVC) in 12 pigs (37+/-2 kg). A 50x1.8 mm electrode was inserted in the MCV through a guide catheter. A can was placed in the left pectoral region. A monophasic AS (100 microF, 1.5 J) was delivered along one pathway before switching to deliver a biphasic waveform (40% tilt, 2 ms phase 2) along another. DFTs (PS+AS) were assessed using a binary search. Two configurations not incorporating AS acted as controls. DFTs were compared using repeated measures analysis of variance.
  
  
  RESULTS
  DFTs of the four novel configurations (AS/PS) were: RV-->Can/MCV-->Can=14.9+/-3.7 J, MCV-->Can/RV-->Can=17.2+/-5.7 J, RV-->SVC+Can/MCV-->SVC+Can=13.4+/-4.6 J, MCV-->SVC+Can/RV-->SVC+Can=17.1+/-5.9 J. Delivering AS in the RV followed by PS in the MCV reduced the DFT (RV-->Can (19.9+/-7.3 J, P<0.01) and RV-->SVC+Can (19.2+/-6.0 J, P<0.05)).
  
  
  CONCLUSIONS
  Delivering AS prior to PS in the MCV reduces the DFT by up to a third compared to conventional configurations of RV-->Can and RV-->SVC+Can. This is possible using only a single capacitor and an entirely transvenous approach to the LV.
authors.affiliation: Wessex Cardiothoracic Center, Southampton General Hospital, United Kingdom. DoctorPRR@aol.com
authors.forename: P R
authors.initials: PR
authors.lastname: Roberts
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
authors.forename: S
authors.initials: S
authors.lastname: Zhuan
authors.forename: K A
authors.initials: KA
authors.lastname: Mowrey
authors.forename: D W
authors.initials: DW
authors.lastname: Wallick
authors.forename: D G
authors.initials: DG
authors.lastname: Hills
authors.forename: T R
authors.initials: TR
authors.lastname: Betts
authors.forename: S
authors.initials: S
authors.lastname: Allen
authors.forename: J
authors.initials: J
authors.lastname: Ewert
authors.forename: T N
authors.initials: TN
authors.lastname: Mazgalev
authors.forename: J M
authors.initials: JM
authors.lastname: Morgan
mesh_terms: D000818:Animals; D003331:Coronary Vessels / Q000502:physiology* / Q000601:surgery*; D017147:Defibrillators, Implantable; D004554:Electric Countershock / Q000295:instrumentation*; D017097:Electric Impedance; D004567:Electrodes, Implanted; D022062:Electrophysiologic Techniques, Cardiac / Q000295:instrumentation; D004867:Equipment Design; D006352:Heart Ventricles / Q000601:surgery; D023421:Models, Animal; D008955:Models, Cardiovascular; D012684:Sensory Thresholds / Q000502:physiology*; D013552:Swine; D016276:Ventricular Function