title: Significant damage of the conduction system during cardioplegic arrest is due to necrosis not apoptosis.
abstract: OBJECTIVE
  Ventricular conduction disturbances following cardioplegic arrest remains a serious, yet unsolved problem. In the present study we examined whether myocardial conduction cells (MCC, Purkinje fibers) are more vulnerable to ischemia/reperfusion injury than working myocardial cells and whether the damage is due to necrosis or apoptosis.
  
  
  METHODS
  Mini-pigs were subjected to 60 min of crystalloid (St Thomas; n = 15 group I) or blood (Buckberg; n = 6 group II) cardioplegic arrest followed by 3 h of reperfusion. Animals not subjected to either procedures served as controls (n = 5). Ventricular myocardial specimens were investigated by hematoxylin and eosin (HE) and periodic acid Schiff (PAS) staining and immunohistochemical labeling of apoptosis-associated proteins (Bax, Bcl-2, Caspase-3). DNA-breaks were visualized by in situ end labeling (terminal deoxynucleotidyl transferase dUTP-biotin nick-end labeling, TUNEL). Electron microscopy confirmed apoptosis or necrosis.
  
  
  RESULTS
  MCC of control hearts intrinsically expressed Bax, Bcl-2, and Caspase-3 without signs of either apoptotic or necrotic damage. Subendocardial Purkinje fibers of groups I and II hearts exhibited focal damage, with reduced labeling of apoptosis-associated proteins, glycogen loss, karyopycnosis and increased eosinophilia (15/21 hearts). The majority of damaged MCC displayed nuclear TUNEL-positivity (2.8+/-2.5% of MCC), whereas the average TUNEL-rate of the adjacent working myocardium was low (<0.1%). Electron microscopy demonstrated ischemic changes in MCC consistent with cellular necrosis.
  
  
  CONCLUSIONS
  Ischemia/reperfusion injury due to cardioplegic arrest inflicts significant damage on subendocardial MCC, but not on working myocardium. Ultrastructural and light-microscopic findings are consistent with coagulation necrosis, rather than apoptosis.
authors.affiliation: Institute of Pathology, University of Luebeck, Luebeck, Germany. friedhelm.sayk@innere1.uni-luebeck.de
authors.forename: Friedhelm
authors.initials: F
authors.lastname: Sayk
authors.forename: Stefan
authors.initials: S
authors.lastname: Krüger
authors.forename: J F Matthias
authors.initials: JF
authors.lastname: Bechtel
authors.forename: Alfred C
authors.initials: AC
authors.lastname: Feller
authors.forename: Hans H
authors.initials: HH
authors.lastname: Sievers
authors.forename: Claus
authors.initials: C
authors.lastname: Bartels
mesh_terms: D000818:Animals; D017209:Apoptosis; D006324:Heart Arrest, Induced / Q000009:adverse effects*; D006329:Heart Conduction System / Q000473:pathology* / Q000648:ultrastructure; D008854:Microscopy, Electron; D015428:Myocardial Reperfusion Injury / Q000209:etiology / Q000473:pathology*; D009336:Necrosis; D011690:Purkinje Fibers / Q000473:pathology / Q000648:ultrastructure; D013552:Swine; D013556:Swine, Miniature