Treatment of Chronic Myocardial Ischemia: Rationale and Treatment Options

A rational approach to the treatment of chronic myocardial ischemia requires an appreciation of the pathophysiology of coronary artery disease and the treatment options available. Any factor that causes an imbalance between myocardial oxygen supply and demand can provoke ischemia. Myocardial oxygen requirements rise with increases in heart rate, contractility, or left ventricular wall stress. Myocardial oxygen supply is determined by coronary artery flow and myocardial oxygen extraction. Anti-anginal medications are the mainstay of anti-ischemic management and act to correct the balance between myocardial supply and demand by increasing coronary blood flow, reducing myocardial oxygen requirements, or both. These medications include nitrates (which act principally by venous vasodilation, but also probably by coronary dilation), beta-blockers (which act mainly by reducing heart rate and cardiac contractility), and calcium channel blockers (which act principally by arterial and coronary vasodilation). The choice of therapy and its effectiveness depend on the underlying cause of ischemia. The complimentary mechanisms of action of these drug classes suggest that their use in combination may result in a greater reduction in myocardial oxygen demand than that achieved with monotherapy. In addition, the pharmacological actions of some of these drugs may serve to offset the undesirable side effects associated with others, for example, the reflex tachycardia produced by some calcium channel blockers may be offset by beta-blocker therapy. Finally, aspirin and lipid-lowering drugs and the potential role for anti-oxidants must also be considered in combination therapy. Invasive techniques for myocardial ischemic management, such as coronary artery bypass and coronary angioplasty, improve myocardial oxygen supply by relieving or circumventing the atherosclerotic obstruction responsible for ischemia. Surgery is the preferred technique in patients with certain medical condi tions, for example, those with triple-vessel disease, but is not recommended in patients with mild angina unless left main artery disease is present.