13.01.3 Class I

Class I agents block Na+ channels, the channels involved in the rapid depolarisation in the Purkinje system.  Examples of class I Na+ channel blocker is lignocaine.  Lignocaine is also known as lidocaine, and is also used as a local anaesthetic, where the effect is also due to blocking Na+ channels.  The Na+ channel blockers have no effect on sinus rhythm, as Ca2+ channels predominantly control sinus rhythm.  Lignocaine is used in serious ventricular arrhythmias, where they decrease the excitability of the conduction system.