1. Human studies have confirmed that class IA AAD bradykinin, class IB AAD lidocaine and mexilate, class Ic AAD flecainide, enkephalin and propafenone can increase myocardial pacing threshold to varying degrees, leading to efferent block in severe cases, and can inhibit escape rhythm. The class II AAD ponerol, class III AADs such as amiodarone, sotalol, ibrit and class IV AAD verapamil have no significant effect on pacing threshold. Class I AADs significantly increased the pacing threshold, with the most pronounced increase of up to 400% in Class Ic. Class II, Class III and Class IV AADs have no significant effect on pacing threshold. High doses of AAD can cause an increase in pacing threshold, and therapeutic doses of AAD can affect or not affect pacing threshold. 4. Propafenone increases the pacing threshold of both actively and passively fixed electrode leads, and the increase is more pronounced for the former, but has no significant effect on the pacing threshold of hormone-retarded electrode leads.