Effect of lidocaine on escape rate in patients with complete atrioventricular block. A. Distal his bundle block

Lidocaine was administered intravenously as a 1.5 mg/kg bolus injection followed by a 2 to 4 mg/min infusion to 18 patients with complete atrioventricular (A-V) block to determine its safety in this situation. As an electrophysiologic corollary, the in vivo effects of lidocaine on ventricular automaticity in man were also evaluated. In 13 of the 18 patients, the ventricular rate was either unchanged or slowed by 16 percent or less after administration of lidocaine. In the remaining five patients, the rate slowed abruptly in a manner suggesting 2:1 or 3:1 exit block. The site of block was located distal to the His bundle potential in these five patients and in eight others who did not exhibit exit block. It is concluded that (1) the pacemaker fibers responsible for the ventricular escape rhythm were insensitive to the effects of lidocaine, thereby suggesting that the spontaneous depolarization in those fibers may be slow channel-dependent; (2) lidocaine is nonetheless unsafe to use in patients with complete A-V block located distal to the His bundle potential without prior pacemaker insertion because of the risk of inducing high grade exit block; (3) the development of exit block depends more on a critical degree of His-Pur-kinje conduction abnormality than on the rate of lidocaine administration or the plasma drug level achieved; and (4) patients at risk for the development of exit block cannot be identified on the basis of clinical presentation.