The effects of
nifedipine against
ischemia- and reperfusion-induced arrhythmias were investigated using anesthetized rats with transient coronary artery occlusion.
Nifedipine (5 micrograms/kg i.v.) administered 10 min prior to occlusion significantly decreased the incidence of arrhythmias occurring during 20-min
coronary occlusion. The incidence and duration of reperfusion-induced
ventricular fibrillation and subsequent mortality following 5-min
coronary occlusion were also significantly reduced by this intervention. However, administration of
nifedipine 1 min prior to reperfusion afforded no protection against reperfusion arrhythmias. To investigate whether
nifedipine possesses a true antiarrhythmic action or merely extends the ischemic duration prior to reperfusion resulting in maximal rhythm disturbances, reperfusion was initiated after 3, 5, 7, 10, 20, and 30 min of
ischemia.
Nifedipine reduced the incidence of reperfusion-induced
ventricular fibrillation after all ischemic intervals, with no change in the time of peak vulnerability to reperfusion arrhythmias. Measurements of coronary flow with 153Gadolinium
microspheres indicated that flow within ischemic tissue relative to that in normal tissue was significantly increased by
nifedipine. Thus, administration of
nifedipine prior to occlusion affords a protective effect against
ischemia- and reperfusion-induced arrhythmias, and this action is not due to extension of the ischemic duration prior to reperfusion resulting in maximal rhythm disturbances.