Rational medical therapy for stable angina pectoris

Treatment of Perioperative Myocardial Ischemia

Prevention and treatment of myocardial ischemia re mains a central focus of perioperative care. Myocardial ischemia is best understood in terms of myocardial oxygen supply and demand ratios. Conventional ther apy includes nitrates, β-blockers, and calcium channel blockers. In all 3 drug classes, ischemia is reduced by either improving supply, decreasing demand, or both. More recent investigation evaluates these medications either as prophylactic therapy or as a component of long-term risk reduction for cardiac morbid events. Newer therapies, including anticoagulation, pain ther apy, normothermia, central neuroaxial techniques, and other therapies, are reviewed.

Concomitant use of nitrates, calcium channel blockers, and beta blockers for optimal antianginal therapy

Despite the introduction of new mechanical techniques for revascularization, pharmacologic therapy continues to be the mainstay of antianginal therapy. The conventional antianginal medications, which include nitrates, beta blockers, and calcium channel blockers, act to correct the imbalance between myocardial supply and demand by increasing coronary blood flow, reducing myocardial oxygen requirements, or both. All three are appropriate for the management of angina caused by a fixed coronary obstruction, but nitrates and calcium channel blockers, which not only reduce demand but also increase supply, are preferred in cases of angina believed to involve a significant increase in vasomotor tone. Because of the different yet complementary mechanisms of action of the three classes of anti-ischemic drugs, use of these agents in combination is a rational approach to the treatment of angina unresponsive to monotherapy. Such combinations have been shown to enhance the therapeutic response achieved with single-agent therapy. In addition, the pharmacologic action of one of the components of the combination regimen may serve to offset side effects typically associated with the other.

Mechanisms of action of the organic nitrates in the treatment of myocardial ischemia

Nitroglycerin and the long-acting nitrates are widely used in all of the anginal syndromes and have proven effectiveness in relieving or preventing myocardial ischemia. Recent developments into nitrate mechanisms of action provide new insights as to the many anti-ischemic effects of these agents. Important concepts relating to coronary arterial endothelial function are germane to nitrate therapy. Endothelial-derived relaxing factor (EDRF) is presently believed to be nitric oxide (NO), which exerts vasodilatory and/or antiplatelet actions by increasing intracellular cyclic guanosine monophosphate as a result of activation of the enzyme guanylate cyclase. In the setting of coronary atherosclerosis, or even hyperlipidemia without histologic vascular disease, endothelial dysfunction may be present, promoting a vasoconstrictor/proplatelet aggregatory milieu. Nitroglycerin and the organic nitrates are NO donors; NO is the final product of nitrate metabolism, and in the vascular smooth muscle NO induces relaxation, resulting in vasodilation of arteries and veins. In the presence of inadequate EDRF production and/or release, it appears that nitroglycerin may partially replenish EDRF-like activity. Nitrates have long been known to have major peripheral circulatory actions resulting in a marked decrease in cardiac work. Venodilation and arterial relaxation result in a decrease in intracardiac chamber size and pressures, with a resultant decrease in myocardial oxygen consumption. In addition, a variety of direct coronary circulatory actions of the nitrates have been documented. These include not only epicardial coronary artery dilation, but the prevention of coronary vasoconstriction, enhanced collateral flow, and coronary stenosis enlargement. Recent work suggests that the nitrates may also act by preventing distal coronary artery or collateral vasoconstriction, which can reduce blood flow downstream from a total coronary obstruction. Thus, there are many anti-ischemic mechanisms of action by which nitroglycerin and the organic nitrates may be beneficial in both acute and chronic ischemic heart disease syndromes. The unique salutory effects of the nitrates in subjects with left ventricular dysfunction or congestive heart failure make these drugs particularly attractive for patients with abnormal systolic function and intermittent myocardial ischemia. Finally, the emergent role of intravenous nitroglycerin in acute myocardial infarction offers new prospects that nitrate therapy may prove to be beneficial in acute myocardial infarction as well as postmyocardial infarction for the reduction of left ventricular remodeling.

Effects of benazepril and metoprolol OROS alone and in combination on myocardial ischemia in patients with chronic stable angina

The efficacy of benazepril, metoprolol OROS and their combination was evaluated in 29 patients (42 to 74 years of age) with chronic stable angina and documented coronary artery disease in a placebo-controlled, double-blind, crossover trial using serial quantitated exercise testing and ambulatory electrocardiographic (ECG) monitoring. The mean (+/- SEM) exercise time was 8.5 +/- 0.7 min with placebo, 8.3 +/- 0.6 min (95% confidence interval [CI]-1.06 to 0.54) with benazepril, 9.4 +/- 0.5 min (95% CI -0.32 to 2.14) with metoprolol OROS and 9.6 +/- 0.5 min (95% CI -0.25 to 2.47) with the combination of benazepril and metoprolol OROS. The mean exercise time to the development of 1 mm ST segment depression was prolonged from 6.0 +/- 0.6 min with placebo to 6.3 +/- 0.6 min (95% CI -0.93 to 1.45) with benazepril, 7.9 +/- 0.5 min (95% CI 0.83 to 3.0) with metoprolol OROS and 8.1 +/- 0.6 min (95% CI 0.88 to 3.29) with the combination of benazepril and metoprolol OROS. Benazepril did not alter the rest or maximal heart rate, whereas metoprolol OROS alone and in combination significantly lowered the heart rate at rest and during maximal exercise. Systolic blood pressure at rest was nonsignificantly reduced, whereas diastolic blood pressure was lowered significantly by all treatments in comparison with placebo. At maximal exercise, only metoprolol OROS, whether given alone or in combination with benazepril, was able to blunt significantly systolic blood pressure and rate-pressure product.(ABSTRACT TRUNCATED AT 250 WORDS)

Beneficial effects of high-dose diltiazem in patients with persistent effort angina on beta-blockers and nitrates: a randomized, double-blind, placebo-controlled cross-over study

The effects of orally administered diltiazem combined with maximally tolerated doses of beta-blockers and nitrates were assessed in 12 patients, who during stress testing exhibited persistent effort angina and continued objective evidence for inducible myocardial ischemia. Patients performed multistage semisupine exercise on a bicycle ergometer during equilibrium-gated radionuclide angiography after consecutive 2 week treatment periods of placebo or diltiazem 90 mg qid (mean dose 340 mg/day) combined with maximally tolerated propranolol (mean dose 178 mg/day) and isosorbide dinitrate (mean dose 137 mg/day). All medications (including diltiazem or placebo) were administered four times daily for the duration of the study. Diltiazem or placebo was administered according to a double-blind design, with randomized cross-over at the end of each 2 week treatment period. The average number of angina attacks decreased during the double-blind cross-over phase of the trial (7 +/- 7 episodes/week at baseline vs 4 +/- 3 on placebo vs 2 +/- 2 on diltiazem; p = .08). Angina pectoris was abolished during peak exercise in eight of 12 patients on diltiazem (p less than .05 vs placebo). Diltiazem increased total exercise duration from 276 +/- 92 to 310 +/- 78 sec (p less than .005 vs baseline). Diltiazem likewise increased the time to onset of angina from 231 +/- 84 sec at baseline to 305 +/- 77 sec (p less than .005), as well as the time to the onset of 1 mm ischemic ST segment depression (p = .01). Diltiazem decreased heart rate at rest, during submaximal workload, and at peak exercise (p less than .05), and decreased systolic blood pressure at peak exercise only (p less than .05). A significant decline in rate-pressure product at submaximal and peak exercise was noted (p less than .05). At any given workload there was significantly less ST segment depression during submaximal (p = .05) and peak exercise (p less than .025).(ABSTRACT TRUNCATED AT 250 WORDS)