Effects of adrenaline on electrophysiological parameters during short exposure to global ischemia. A ventricular fibrillation study in isolated heart.
BACKGROUND
The mechanisms by which adrenaline may enhance defibrillation success rate, is poorly understood.


OBJECTIVE
To study electrophysiological effects of adrenaline during short exposure to global ischemia.


METHODS
In isolated perfused feline hearts, coronary perfusion was eliminated repeatedly for 1 min with 10 min reperfusion intervals. Treatment included: (1) continuous perfusion alone-control, (2) global ischemia alone, (3) adrenaline (10(-7) M) during perfusion, (4) adrenaline (10(-7) M) during global ischemia (n = 10), in separate hearts, (5) control and higher adrenaline concentration (1 x 10(-6) M), (6) during perfusion, (7) during global ischemia (n = 9). Measurements during pacing included: (1) diastolic threshold of excitability; (2) refractoriness; (3) epicardial conduction time; and (4) all tissue resistivity to indirectly detect changes in passive properties of conduction. Measurements during 1 min (or 90 sec) of electrically induced ventricular fibrillation included-all tissue resistivity and, based on maximal entropy spectral analysis and normalized entropy, rate of arrhythmia and degree of arrhythmia organization.


RESULTS
Adrenaline (10(-7) M) during global ischemia vs control caused spontaneous arrhythmia termination, increased threshold significantly but reduced conduction time. Higher adrenaline concentration (1 x 10(-6) M) during global ischemia improved the passive properties of conduction and arrhythmia organization and reduced arrhythmia rate. Global ischemia alone increased conduction time but had a deleterious effect on passive properties. Adrenaline (10(-7) M) during perfusion improved conduction, but did so less than during global ischemia. Higher adrenaline concentration during perfusion (10(-6) M) improved arrhythmia organization and caused spontaneous arrhythmia termination but again less than during global ischemia.


CONCLUSIONS
During short periods of global ischemia adrenaline improved the passive properties of conduction and arrhythmia organization, reduced arrhythmia rate and increased its spontaneous termination. Such changes may be operative in improving defibrillation success.
Amitzur
Giora
G
Neufeld Cardiac Research Institute, Tel-Aviv University, Tel-Hashomer, Israel. ncri@sheba.health.gov.il
Shenkar
Nitza
N
Leor
Jonathan
J
Novikov
Ilia
I
Eldar
Michael
M
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000704:Analysis of Variance; D000818:Animals; D002415:Cats; D004305:Dose-Response Relationship, Drug; D022062:Electrophysiologic Techniques, Cardiac; D004837:Epinephrine / Q000494:pharmacology* / Q000502:physiology; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D017202:Myocardial Ischemia / Q000150:complications*; D013610:Tachycardia / Q000209:etiology / Q000503:physiopathology; D014693:Ventricular Fibrillation / Q000209:etiology / Q000503:physiopathology*
D000318:Adrenergic beta-Agonists; D004837:Epinephrine