Influence of glucose, insulin, and potassium on vulnerability to ventricular fibrillation in the canine heart.

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Abstract
The influence of glucose (G), insulin (I) and K+ on vulnerability to ventricular fibrillation (VF) of the nonischemic canine myocardium was studied. Vulnerability was assessed by determining VF and repetitive extrasystole (RE) thresholds with a single stimulus applied to the right ventricular endocardium during the vulnerable period. Electrical testing of the heart was performed before and after 1 and 2 h of infusing G (10 mg/kg per min) and I (0.025 U(units)/kg per min) with and without K+. Infusion of glucose, insulin and K+ (GIK) in 11 dogs significantly increased both VF (22%) and RE (33%) thresholds within the 1st h and only the VF threshold (64%) in the 2nd h. No significant changes in serum K+ concentration occurred. Spontaneous termination of VF was observed in 6 dogs during GIK infusion. Glucose and insulin infusion increased both VF and RE thresholds within the 1st (17% and 19%) and 2nd h (43% and 43%). This occurred despite substantial reductions in serum K+ concentration. Lowering serum K+ by hemodialysis in 6 dogs decreased both VF and RE thresholds within the 1st (33% and 32%) and 2nd h (35% and 14%). Restoration of the serum K+ concentration by KCl infusion while maintaining dialysis returned the thresholds to control values. In 6 dogs, insulin infusion during low K+ dialysis increased the VF and RE thresholds despite a further reduction in serum K+ concentration. Insulin exerts a protective effect against vulnerability to VF in the normal canine heart. This salutary action is most marked when the drug''s hypokalemic effect is prevented by concomitant K+ infusion.

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