Electrophysiologic basis by which epinephrine facilitates defibrillation after prolonged episodes of ventricular fibrillation.

STUDY
OBJECTIVE: Even though epinephrine has been shown to decrease the electrical stability of the heart, it is used extensively in cardiac resuscitation. The objective of this study is to document electrophysiologic parameters of epinephrine, which would facilitate defibrillation.
METHODS: In 20 swine, electrically induced ventricular fibrillation was allowed to continue for 10 minutes. Animals were then randomly assigned to receive either intracardiac injection of 1 mg of epinephrine or 10 mL of normal saline solution. Synchronization and dispersion of the repolarization of fibrillatory waves and cycle length were measured.
RESULTS: As the ventricular fibrillation continued, cycle length was prolonged, and synchronization and dispersion deteriorated. With epinephrine, cycle length shortened from 416+/-21 to 204+/-23 ms (P<.005), synchronization improved from 114+/-13 to 61+/-10 ms (P<.05), and dispersion narrowed from 84+/-10 to 49+/-8 ms (P<.005). Normal saline solution had no effect. Successful resuscitation was achieved in all 10 animals administered epinephrine and only 1 animal in the saline solution group.
CONCLUSION: Epinephrine's effect on cycle length, synchronization, and dispersion of repolarization of fibrillatory waves may be the mechanism with which it facilitates defibrillation.