The EKG in the patient treated with quinidine
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
- Direct effect is to reduce the automaticity, excitability and conductivity, but this is counterbalanced by the indirect vagolytic effect of the drug which tends to increase the rate.
- With higher toxic doses, the automaticity of the SA node may be depressed resulting in sinus bradycardia or sinus arrest. SA and AV conduction may be impaired and intraventricular conduction time markedly prolonged. The automaticity of ventricular tissue may be paradoxically increased with the appearance of ventricular arrhythmias.
- Decrease in the amplitude of the T wave or T wave inversion
- ST depression
- Prominent U waves (an early finding)
- Prolongation of the QTC
- Notching and widening of the P waves
EKG Findings with Toxic Effects
- Widening of the QRS
- Various degrees of AV block
- Ventricular arrhythmias, syncope and sudden death
- Marked sinus bradycardia, sinus arrest or SA block