Calcium antagonists in acute myocardial infarction

[Drug treatment of patients with heart infarcts before and after the acute stage: results of the Heart Infarct Registry Augsburg]

To assess the changes in medications prescribed before and after acute myocardial infarction (AMI), all surviving patients aged 25-74 years registered from 1985-1988 in the Coronary Event Register Augsburg were evaluated by sex, medical history, and drug use before and after the event. For the 1546 hospitalized patients (1181 men, 365 women) utilization of all drug groups is higher for patients with reinfarction than for patients with first-ever AMI. Before AMI, but not on hospital discharge, women received significantly more medications than men and were more frequently treated with diuretics (30%; men 18%), antihypertensive drugs (15%, men 8%) and cardiac glycosides (20%; men 14%). The most frequently used drug groups are nitrates (before AMI: 30%; after AMI: 80%) and calcium antagonists (before AMI: 26%; after AMI 61%). The four years show a significant increase in patients with reinfarction who were treated with platelet aggregation inhibitors (1985: 9%; 1988: 32%), as well as an increase in AMI patients released from hospital with this medication (1985: 38%; 1988: 64%). A concomitant significant decrease in reinfarction rates for men is found in the course of the four years under study. The results indicate a rapid assimilation of the results of clinical trials in practice down to the substance level.

Use of intravenous diltiazem in patients with acute coronary artery disease

The use of calcium antagonists for the treatment of patients with unstable angina and acute myocardial infarction has been a promising area of both basic and clinical research. Despite consistently beneficial effects experimentally, the clinical extrapolation of these results has been less than ideal, especially in patients with evolving myocardial infarction. Calcium antagonists have in some instances failed to manifest benefit and at times have been shown to have negative effects. One reason for this could be the use of oral or sublingual preparations, which result in variable absorption, variable volumes of distribution, and variable clearance. For this reason, an intravenous preparation of one of the calcium antagonists, diltiazem, may be more beneficial. Such a preparation has been developed and its safety confirmed in patients without cardiovascular disease and in patients with acute infarction. Substantial benefit has been documented in patients with stable angina and during noncardiac surgery. Preliminary data in patients with unstable angina suggest that the drug is effective, although studies comparing intravenous diltiazem with other agents or with the oral preparation of diltiazem have not yet been reported. Experimental data in animals with acute infarction have demonstrated that administration of intravenous diltiazem after occlusion, but prior to reperfusion, elicits a marked increase in the degree of myocardial salvage induced by thrombolysis. This appears to be due to the inhibition of lipid peroxidation rather than alterations in coronary perfusion. Thus, it appears that the intravenous preparation may permit the more effective use of diltiazem in patients with acute coronary artery disease.

Does verapamil limit myocardial infarct size in a heart deficient in xanthine oxidase?

1. The delay of ischaemic myocardial necrosis by verapamil has been reported in the dog heart, which contains a high level of xanthine oxidase, a potential source of cytotoxic free radicals. To test whether the retardation of ischaemic myocyte death by verapamil is not an isolated phenomenon in the xanthine oxidase rich heart, we assessed the effect of verapamil in the rabbit heart, which lacks xanthine oxidase. 2. Verapamil (200 micrograms/kg, i.v. bolus plus 40 micrograms/kg per min) was administered in a group of rabbits (n = 5) to test the haemodynamic response to this agent. The heart rate, blood pressure and left ventricular dp/dt max were reduced by 11, 25 and 57%, respectively, and the plasma concentration of verapamil was maintained at 300-400 ng/mL during the infusion. 3. In other groups of rabbits, the effect of the same dosage of verapamil on the size of myocardial infarct after 20 or 30 min ischaemia and 72 h reperfusion was examined. The verapamil was administered for 45 min, starting 15 min prior to ischaemia. The percentage of area at risk infarcted (%I/AAR) was 15.2 +/- 3.9% in the 20 min ischaemia control group and 15.4 +/- 4.5% in the 20 min ischaemia verapamil group, 49.1 +/- 3.4% in the 30 min ischaemia control group and 41.2 +/- 3.3% in the 30 min ischaemia verapamil group. The %I/AAR was significantly smaller in the 20 min ischaemia control groups and 15.4 +/- 4.5% in the 20 min ischaemia there was no difference in %I/AAR between the control and verapamil treated animals in either the 20 or the 30 min ischaemia groups. 4. These results suggest that verapamil does not delay the transition from reversible to irreversible myocardial injury during coronary occlusion in the rabbit, which like the human, lacks myocardial xanthine oxidase.

Nifedipine and experimental cardioprotection

Experimental studies using animal models designed to mimic the effect of ischemia and postischemic reperfusion have provided data indicating that the calcium antagonists might be cardioprotective. The laboratory studies have indicated consistently, however, that the timing of such drug administration is of critical importance. In the case of nifedipine (a dihydropyridine-based calcium antagonist), the laboratory studies have shown that when used prophylactically it has a protective effect during short (as in the "stunned heart") and long episodes (greater than 30 minutes) of ischemia. This protection has been quantitated in a variety of ways, including preservation of left ventricular function. A complete understanding of whether and how calcium antagonists can be used to protect the myocardium requires further detailed knowledge of not only of the voltage-activated calcium channel and its binding sites, but also of the sequence of events triggered by ischemia and reperfusion. Recent data from our laboratories indicate that cardiac membranes contain specific binding sites for the novel, endothelial-derived vasoconstrictor peptide, ET, and that the density of these sites increases during ischemia. ET promotes Ca2+ influx through the voltage-sensitive channels by a mechanism that does not involve a direct interaction with the dihydropyridine (DHP)-sensitive binding sites. Nevertheless, the ET-induced Ca2+ influx is attenuated by the dihydropyridine-based calcium channel blockers.