Significant damage of the conduction system during cardioplegic arrest is due to necrosis not apoptosis.
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.
Sayk
Friedhelm
F
Institute of Pathology, University of Luebeck, Luebeck, Germany. friedhelm.sayk@innere1.uni-luebeck.de
Krüger
Stefan
S
Bechtel
J F Matthias
JF
Feller
Alfred C
AC
Sievers
Hans H
HH
Bartels
Claus
C
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