Arrhythmias in the coronary-care unit. III. Physiologic bases of paroxysmal tachycardia-dependent A-V block.

This vignette illustrates the application of electrophysiological principles to the clinical problems of acute trifascicular A-V block occurring during an acute MI. Paroxysmal trifascicular A-V block that occurs transiently during an acute MI can be explained electrophysiologically as being due to tachycardia-dependent or bradycardia-dependent A-V block or both. Tachycardia-dependent A-V block also referred to as phase 3 A-V block is a term used when a premature beat occurring during repolarization of the preceeding beat causes conduction failure. Bradycardia-dependent A-V block or phase 4 block is used to explain the slowing of conduction or block after a longer diastolic interval. Physicians and nurses can improve their care of the critically ill cardiac patient through a better understanding of pathophysiology.