Myocardial ischaemic preconditioning in the pig has no effect on the ventricular fibrillation and defibrillation thresholds.
BACKGROUND
The effects of myocardial ischaemia preconditioning in pigs on the vulnerability to ventricular fibrillation during subsequent ischaemic events are controversial. This study examined the time course of changes in ventricular fibrillation (VFT) and defibrillation (DFT) thresholds during transient myocardial ischaemia after a 45 min preconditioning period.


RESULTS
In five open-chest pigs, VFT was measured after 3 min of regional myocardial ischaemia, at time 0, 2, 15, 30, 60 and 90 min (Control group). In seven other pigs (Test group), VFT was measured before (time 0) and 2, 15, 30, 60 and 90 min after ischaemic preconditioning by three consecutive 5 min periods of regional coronary occlusion, followed by 10 min of reperfusion. DFT was measured by increasing the stored energy systematically until successful defibrillation. Ischaemic preconditioning caused no significant change in the effective refractory period (ERP), VFT or DFT over the 90 min of the experiments. In the Control group, ERP remained stable for 30 min, though was significantly lower at 90 min (178 +/- 28 ms) than at baseline (204 +/- 32 ms, P = 0.007). VFT and DFT remained unchanged throughout the experiments, and no difference was observed in ERP, VFT and DFT between the two groups at any time during the experiment.


CONCLUSIONS
No changes were observed in the refractory duration, ventricular vulnerability or defibrillation energy requirements up to 90 min after ventricular ischaemic preconditioning in the pig.
Anastasiou-Nana
Maria I
MI
University of Athens School of Medicine, Department of Clinical Therapeutics, Alexandra Hospital, Makedonias 24, 104 33 Athens, Greece. jnanas@ath.forthnet.gr
Tsagalou
Eleftheria P
EP
Mavrikakis
Emmanuel M
EM
Siafakas
Kostantinos X
KX
Tsolakis
Elias J
EJ
Drakos
Stavros G
SG
Dalianis
Argirios
A
Karelas
John
J
Terrovitis
John V
JV
Nanas
John N
JN
D000818:Animals; D004554:Electric Countershock; D019157:Ischemic Preconditioning, Myocardial; D013552:Swine; D013997:Time Factors; D014693:Ventricular Fibrillation / Q000503:physiopathology* / Q000628:therapy