Why the study?
Does quinidine affect cardiac pacemaker activity differently depending on the level of adrenergic activity in dogs with complete heart block?
Does quinidine affect cardiac pacemaker activity differently depending on the level of adrenergic activity in dogs with complete heart block?
The cardiac effects of quinidine, particularly its depressant action on pacemakers, are unmasked or exacerbated when background adrenergic activity is reduced.
Quinidine's pacemaker depression may emerge with reduced sympathetic tone; leaves open relevance to human antiarrhythmic use in complete heart block.
Unanesthetized dogs with complete heart block were used to explore the relationship between adrenergic activity and quinidine action on the heart. After vagolysis, quinidine still increased both the atrial and ventricular rates. Following reduction in adrenergic activity by reserpine, hexamethonium, or surgical sympathectomy, the atrial and ventricular pacemakers were depressed. After sympathetic activity had been reduced by a combination of hexamethonium and reserpine, quinidine caused profound pacemaker depression and sometimes ventricular asystole. Quinidine produced coupling and occasionally runs of ventricular tachycardia independent of the level of sympathetic activity. There was no significant prolongation of the QRS time by quinidine in doses of 5 and 10 mg./Kg. Both the development of ectopic pacemakers and the depression of pacemaker activity of quinidine were dose dependent.
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Roberts et al. (1962) studied this question.
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