Dogs at high or low risk of ventricular fibrillation. An experimental study of acute myocardial ischaemia

In the last 15 years, measurement of the ventricular fibrillation threshold (VFT) after ligation of the coronary artery in anaesthetised dogs has become our standard method for the evaluation of the stabilizing effect of antifibrillation drugs. Analysis of a group of 143 dogs revealed that in 75 animals the VFT 8 minutes after the ligation of the coronary artery dropped to less than 1 mA (high risk group), while in the remaining 68 dogs the decrease was smaller and not below 1 mA (low risk animals). The difference between the groups could be seen already before the ligation of the coronary artery. The high risk animals had a lower VFT and a higher heart rate. The groups also differed in the response to drugs administered 15 minutes after the ligation of the coronary artery. Metipranolol, a liposoluble beta blocker of the beta 1 and 2 cardiac receptors (Trimepranol Spofa 0.3 mg.kg-1 b.w.), increased greatly the VFT in both groups already 8 minutes after the injection of the drug and eliminated the difference between the groups. Flunitrazepam (Rohypnol Hoffmann-La Roche 0.25 mg.kg-1 b.w.) increased the VFT less than metipranolol and the difference between the groups disappeared only 30 minutes after its injection. Celiprolol (Selectol Linz Chemie 3.0 mg.kg-1 b.w.) blocking beta 1 and stimulating beta 2 receptors as well as trimecaine (sodium channel blocker, Mesocain Spofa 3.0 mg.kg-1 b.w.) led only to a small insignificant increase in the VFT and the difference between the groups of dogs remained.(ABSTRACT TRUNCATED AT 250 WORDS)