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KMID : 0352519840210020047
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Korea Univercity Medical Journal
1984 Volume.21 No. 2 p.47 ~ p.58
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Effects of Calcium Channel Blockers on Ischemic Myocardium
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Epstein, Stephen E.
Patterson, Randolph E.
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Abstract
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It remains unknown whether the actions of verapamil to depress and nifedipine to enhance contractile function of ischemic myocardium influence the degree of myocardial ischemic injury. Thus, we measured intramyocardial pH (pHm) as an index of myocardial ischemic injury using fiber-optic pH probes in 43 anesthetized dogs pretreated with verapamil (n=9), verapamil plus pacing to maintain constant heart rate (n=7), nifedipine (n=9), or placebo (saline, n=11, nifedipine dilutent, n=7). The dose of each drug we employed was that which decreased mean aortic pressure by 10 to 15mm Hg.
Verapamil groups showed higher pH of ischemic myocardium than did the nifedipine or placebo groups, whether or not the animals were paced to prevent the negative chronotropic effect of verapamil(p<0. 05). Although verapamil and nifedipine increased myocardial blood flow (MBF) to the normal zone, they did not change collateral MBF. Myocardial contractile function. estimated by left ventricular dp/dt and left atrial pressure, was depressed by verapamil and enhanced by nifedipine.
These findings indicate that verapamil, but not nifedipine, improves acidosis of ischemic myocardium following acute coronary occlusion in doses that cause a modest(10~15mm Hg) decrease in aortic pressure. The contrasting effects of verapamil vs nifedipine on pHm of ischemic myocardium are not explained by differences in heart rate, aortic pressure or collateral MBF. Contractile function, however, was lower in the verapamil groups, compared to the nifedipine group. Thus, we conclude that in this model of fixed coronary occlusion verapamil exerts salutary actions on myocardial ischemic injury. This beneficial effect probably results from a direct negative inotropic effect on the ischemic tissue, which reduces myocardial´ metabolic demand and decreases ischemia, to improve intramyocardial pH.
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