Metoprolol and ventricular repolarisation and refractoriness: lack of chronic adaptational class III effects in rabbit.
OBJECTIVE
The aim was to examine the right ventricular electrophysiological changes during metoprolol treatment and in conditions of stress in the adult rabbit.


METHODS
Metoprolol (6 mg.kg-1) was given twice daily for four weeks. Stress was induced by constant infusion of adrenaline (15.2 micrograms.kg-1.h-1) via osmotic pumps implanted in the left femoral vein. Control rabbits were treated with saline. Electrophysiological recordings were made weekly in conscious animals using bipolar pacing electrodes implanted in the right ventricular apex.


METHODS
Adult male New Zealand white rabbits, 2.8-3.3 kg, were used (n = 7 adrenaline/metoprolol treated, n = 7 adrenaline/saline treated, n = 7 saline/metoprolol treated, and n = 7 saline/saline treated).


RESULTS
Recordings were made of the effective refractory period and of the stimulus-T interval of the paced evoked response. Stimulus-T is used as an index of ventricular repolarisation time. No significant electrophysiological changes in these variables were observed throughout the study.


CONCLUSIONS
These results indicate that chronic metoprolol therapy does not result in a class III antiarrhythmic effect in this in vivo rabbit model.
Barr
S M
SM
Department of Medical Cardiology, Glasgow Royal Infirmary, United Kingdom.
Manley
B S
BS
Cobbe
S M
SM
D000818:Animals; D004195:Disease Models, Animal; D004594:Electrophysiology; D004837:Epinephrine / Q000097:blood / Q000494:pharmacology; D006321:Heart / Q000187:drug effects* / Q000503:physiopathology; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008790:Metoprolol / Q000097:blood / Q000494:pharmacology*; D010138:Pacemaker, Artificial; D011817:Rabbits; D013312:Stress, Physiological / Q000503:physiopathology*
D008790:Metoprolol; D007545:Isoproterenol; D004837:Epinephrine