Pharmacology of EKG

Pharmacology of EKG 

Class IA

e.g. procainamide, quinidine

block Na channels and K channels

drug interactions

• diuretics, steroids, amphotericin B = K loss
• low K interferes with phase 3 K efflux (K channels require bound K to function normally.
• other drugs
• tricyclic antidepressants

Class IB

e.g., lidocaine

• works on cells with long action potentials = ventricles, not atria
• little or no effect on QRS or AP  (nl EKG)

drug interactions

Hyperkalemia - lidocaine  increases chance of toxicity  

Class IC
e.g., flenainide

• effects on EKG similar but smaller than IA.
• works on both atria and ventricles