title: Locally propagated activation immediately after internal defibrillation.
abstract: BACKGROUND
  Electrical mapping studies indicate an interval of 40 to 100 ms between a defibrillation shock and the earliest activation that propagates globally over the ventricles (globally propagated activation, GPA). This study determined whether activation occurs during this interval but propagates only locally before being blocked (locally propagated activation, LPA).
  
  
  RESULTS
  In five anesthetized pigs, the heart was exposed and a 504-electrode sock with 4-mm interelectrode spacing was pulled over the ventricles. Ten biphasic shocks of a strength near the defibrillation threshold (DFT) were delivered via intracardiac catheter electrodes, and epicardial activation sequences were mapped before and after attempted defibrillation. Local activation was defined as dV/dt < or =-0.5 V/s. Postshock activation times and wave-front interaction patterns were determined with an animated display of dV/dt at each electrode in a computer representation of the ventricular epicardium. LPAs were observed after 40 of the 50 shocks. A total of 173 LPA regions were observed, each of which involved 2+/-2 (mean+/-SD) electrodes. LPAs were observed after both successful and failed shocks but occurred earlier (P<.0001) after failed (35+/-8 ms) than successful (41+/-16 ms) shocks, although the times at which the GPA appeared were not significantly different. On reaching the LPA region, the GPA front either propagated through it (n=135) or was blocked (n=38). The time from the onset of the LPA until the GPA front propagated to reach the LPA region was shorter (P<.01) when the GPA front was blocked (32+/-12 ms) than when it propagated through the LPA region (63+/-20 ms).
  
  
  CONCLUSIONS
  LPAs exist after successful and failed shocks near the DFT. Thus, the time from the shock to the GPA is not totally electrically silent.
authors.affiliation: Department of Physiology and Biophysics, University of Alabama at Birmingham, USA.
authors.forename: N
authors.initials: N
authors.lastname: Chattipakorn
authors.forename: B H
authors.initials: BH
authors.lastname: KenKnight
authors.forename: J M
authors.initials: JM
authors.lastname: Rogers
authors.forename: R G
authors.initials: RG
authors.lastname: Walker
authors.forename: G P
authors.initials: GP
authors.lastname: Walcott
authors.forename: D L
authors.initials: DL
authors.lastname: Rollins
authors.forename: W M
authors.initials: WM
authors.lastname: Smith
authors.forename: R E
authors.initials: RE
authors.lastname: Ideker
mesh_terms: D000818:Animals; D006328:Cardiac Catheterization / Q000295:instrumentation; D004554:Electric Countershock; D004562:Electrocardiography; D010496:Pericardium / Q000502:physiology*; D013552:Swine; D016896:Treatment Outcome