Bradycardia-dependent A-V block during acute cardiac ischemia or injury is best explained by applying knowledge of basic cellular electrophysiology. Spontaneous diastolic depolarization during phase 4, plus a reduction in the magnitude of the transmembrane action potential are the pathophysiologic changes responsible for "phase-4 block".

Bradycardia↗

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Arrhythmias in the coronary-care unit. I. Physiologic bases of ectopic beats.

Ectopic beats appearing in the wake of an acute myocardial infarction are best explained with a fundamental knowledge of myocardial cellular electrophysiology. When the physician or nurse has knowledge of the electrical events of intracellular recordings then normal as well as abnormal states of automaticity and conductivity are better understood.

Action Potentials↗

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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.

Adult↗

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Arrhythmias in the coronary-care unit. IV. Physiologic bases of paroxysmal tachycardia-dependent bundle branch block.

Paroxysmal BBB may be either tachycardia-dependent which is referred to as "phase 3 block" or bradycardia-dependent, referred to as "phase 4 block." Tachycardia-dependent BBB is related to prolonged recovery. Bradycardia-dependent BBB is related to hypopolarization and SDD. These fundamental electrophysiological properties aid in understanding of transient BBB occurring during an acute MI.

Bundle-Branch Block↗

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Arrhythmias in the coronary-care unit. V. Physiologic bases of paroxysmal bradycardia-dependent bundle branch block.

Bradycardia-dependent bundle branch block can occur during acute cardiac ischemia or infarction. Basic cellular electrophysiology helps in understanding the mechanisms involved. A review of the previous four vignettes of this series will be helpful in studying this vignette.

Bradycardia↗