[Calcium antagonists in ischemic heart disease].

Recently, there has been some controversy concerning calcium antagonists, suggesting the need for further debate on this heterogeneous class of drugs. Three chemical families, dihydropyridines (DHP), phenylalkylamines (verapamil) and benzothiazepines (diltiazem) bind to the type L receptors of the calcium channels with different binding, modulation and tissue selectivity characteristics. DHP are selective for type L receptors and block the extracellular portion of the channel leading to vigorous vasodilatation and little or no cardiodepressive effect. Diltiazem and verapamil also interfere with type T channel receptors. These drugs have a cardiodepressive and a bradycardia effect. Verapamil blocks the intracellular portion of the calcium channel at the site where part of the catecholamine effect occurs, leading to less reflex sympathetic activation than with other calcium antagonists (namely DHP). Deleterious sympathetic stimulation is proportional to the intensity and degree of rapid onset of arterial vasodilatation and is attenuated with slow-release formulations. Calcium antagonists in general have an anti-angina effect but high-dose short-acting DHP can cause excessive vasodilatator leading to subsequent ischemia. In chronic stable angina, slow-release verapamil has been shown to have a preventive clinical effect comparable to that of beta blockers. Slow-release nifedipine is effective and safe but must be associated with betablockers. In unstable angina, only those calcium antagonists with a bradycardia effect appear to have an effect similar to beta blockers. Beta blockers are nevertheless to be preferred in these patients (excepting Prinzmetal angina) until results of convincing clinical studies are available. After the initial phase of myocardial infarction, again only calcium antagonists with a bradycardia effect have been shown to have a beneficial effect, in patients without cardiac failure: diltiazem in infarction without Q-wave and verapamil in all infarctions, in case of residual ischemia to reduce the risk of recurrence.