title: Effects of transient myocardial ischemia on the ventricular defibrillation threshold.
abstract: BACKGROUND
  Acute myocardial ischemia and the mode of ventricular fibrillation (VF) induction influence the ventricular defibrillation threshold (DFT).
  
  
  OBJECTIVE
  The purpose of this study was to determine the effects of transient regional left ventricular (LV) ischemia on the DFT.
  
  
  METHODS
  Ventricular effective refractory period (ERP), ventricular fibrillation threshold (VFT), and DFT were measured under nonischemic conditions (control) in 26 pigs weighing 25-35 kg. Myocardial ischemia was then induced by occlusion of the mid left anterior descending coronary artery, and measurements of ERP and VFT were repeated after 2 minutes of occlusion. The coronary artery ligation was released immediately after the onset of VF and DFT was measured.
  
  
  RESULTS
  LV ERP was unchanged by ischemia (199 +/- 19 ms at control vs. 200 +/- 22 ms under ischemic conditions, P = 0.799), whereas VFT was significantly lower during coronary occlusion (10.7 +/- 5.4 mA vs. 37.7 +/- 13 mA, P = 0.000). Brief myocardial ischemia caused a significant increase in DFT (13.5 +/- 12.6 J after coronary occlusion vs. 6.8 +/- 6.8 J at control, P = 0.023). The duration of coronary occlusion was not correlated with the amounts of energy required to defibrillate (P = 0.526).
  
  
  CONCLUSIONS
  This experimental study shows that transient myocardial ischemia markedly increases the DFT, suggesting that specific defibrillation algorithms should be designed for recipients of implantable defibrillators at risk of myocardial ischemia.
authors.affiliation: Department of Clinical Therapeutics, University of Athens School of Medicine, Alexandra Hospital, Athens, Greece. jnanas@ath.forthnet.gr
authors.forename: Maria I
authors.initials: MI
authors.lastname: Anastasiou-Nana
authors.forename: Eleftheria P
authors.initials: EP
authors.lastname: Tsagalou
authors.forename: Christos
authors.initials: C
authors.lastname: Charitos
authors.forename: Kostantinos X
authors.initials: KX
authors.lastname: Siafakas
authors.forename: Stavros
authors.initials: S
authors.lastname: Drakos
authors.forename: John V
authors.initials: JV
authors.lastname: Terrovitis
authors.forename: Argirios
authors.initials: A
authors.lastname: Ntalianis
authors.forename: Antonios
authors.initials: A
authors.lastname: Doufas
authors.forename: John
authors.initials: J
authors.lastname: Mavrikakis
authors.forename: John N
authors.initials: JN
authors.lastname: Nanas
mesh_terms: D000818:Animals; D017147:Defibrillators, Implantable; D004554:Electric Countershock; D004562:Electrocardiography; D016014:Linear Models; D017202:Myocardial Ischemia / Q000150:complications / Q000503:physiopathology*; D013552:Swine; D014693:Ventricular Fibrillation / Q000209:etiology / Q000503:physiopathology* / Q000628:therapy*