Failure of idioventricular suppression in man by overdrive pacing as well as lidocaine: the role of abnormal automaticity.

Five patients with third-degree atrioventricular block and an idioventricular escape rhythm who showed unusual responses to overdrive ventricular pacing and lidocaine are presented. In four cases, the idioventricular rhythm was not suppressed by overdrive; in one, the recovery time of the escape rhythm was shorter than the escape cycle length. Lidocaine did not affect the cycle lengths and recovery times of the idioventricular rhythms. These responses are characteristic of abnormal automaticity. The role of abnormal automaticity in human idioventricular escape rhythms has not been previously supported by these characteristic responses to overdrive pacing and lidocaine.