CLASSIFICATION OF ANTIARRHYTHMIC DRUGS-
FOUR CLASSES.-
APD action potential, ERP-Effective refractory period.
Class I Antiarrhythmic are again subclassified in three groups.
| Electrophysiologic activity | I A | IB | IC |
|---|---|---|---|
| Phase O | Decreased | Slight effect | Marked decreased |
| depolarisation | prolonged | Slight effect | Slight effect |
| conduction | Decreased | Slight effect | Markedly slowed |
| ERP | Increased | Slight effect | Slight prolonged |
| APD | Increased | Decreased | Slight effect |
| ERP/APD RATIO | Increased | Decreased | Slight effect |
| QRS duration | Increased | No effect during sinud rhythm | Marked increase |
| Automaticity | Decreased | Decreased | Decreased |
| Prototype drugs | Quinidine Procainamide Disopyramide |
Lidocaine Mexiletine Tocainamide |
Propafenon, Flecainamide, mercizine |
| P-R Duration | NO Effect | No effect | Increases |
| QRS Duration | increases | No effect | Greatly increases |
| QT interval | Markedly increases | No effect | increases |
| EFFECT | CLASS I Membrane stabilisers |
CLASS II B-adrenergic Receptor antagonist |
CLASS III Drugs prolonging Repolarisation |
CLASS IV Calcium antagonist. |
|---|---|---|---|---|
| Pharmacologic action | On Fast Na channel-blocking | B-adrenergic blockade | Uncertain-possible interference with Na and Ca exchange. | Dcereased slow calcium channel conductance |
| Electrophysiologic effect | Decreased rate of Vmax | Decreased Vmax, Increased APD Increased ERP Increased ERP/APD ratio. |
Increased APD,ERP,ERP/APD ratio. |