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

We studied the influence of glucose (G), insulin (I) and potassium (K) on vulnerability to ventricular fibrillation (VF) of the nonischemic canine myocardium. 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 hours of infusing G (10 mg/kg per min) and I (0.025 U/kg per min) with and without K. Infusion of glucose, insulin, and potassium (GIK) in 11 dogs significantly increased both VF (22%) and RE (33%) thresholds within the 1st hour and only the VF threshold (64%) in the 2nd hour. No significant changes in serum K concentration occurred. Spontaneous termination of VF was observed in six dogs during GIK infusion. Glucose and insulin infusion increased both VF and RE thresholds within the 1st (17% and 19%) and 2nd hours (43% and 43%). This occurred despite substantial reductions in serum K concentration. Lowering serum K by hemodialysis in six dogs decreased both VF and RE thresholds within the 1st (33% and 32%) and 2nd hours (35% and 14%). Restoration of the serum K concentration by KC1 infusion while maintaining dialysis returned the thresholds to control values. In six dogs, insulin infusion during low K dialysis increased the VF and RE thresholds despite a further reduction in serum K concentration. We concluded that 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.