Beta-Blocking Drugs

BETA-BLOCKING DRUGS

Although they are not vasodilators (with the exception of carvedilol and nebivolol), β-blocking drugs  are extremely useful in the management of effort angina. The beneficial effects of β-blocking agents are related to their hemodynamic effects—decreased heart rate, blood pressure, and contractility—which decrease myocardial oxygen requirements at rest and during exer-cise. Lower heart rate is also associated with an increase in diastolic perfusion time that may increase coronary perfusion. However, reduction of heart rate and blood pressure, and consequently decreased myocardial oxygen consumption, appear to be the most important mechanisms for relief of angina and improved exercise tolerance. Beta blockers may also be valuable in treating silent or ambulatory ischemia. Because this condition causes no pain, it is usually detected by the appearance of typical electrocardiographic signs of ischemia. The total amount of “ischemic time” per day is reduced by long-term therapy with a β blocker. Beta-blocking agents decrease mortality of patients with recent myocardial infarc-tion and improve survival and prevent stroke in patients with hypertension. Randomized trials in patients with stable angina have shown better outcome and symptomatic improvement withblockers compared with calcium channel blockers.

Undesirable effects of β-blocking agents in angina include an increase in end-diastolic volume and an increase in ejection time, both of which tend to increase myocardial oxygen requirement. These deleterious effects of β-blocking agents can be balanced by the concomitant use of nitrates as described below.

Contraindications to the use of β blockers are asthma and other bronchospastic conditions, severe bradycardia, atrioventric-ular blockade, bradycardia-tachycardia syndrome, and severe unstable left ventricular failure. Potential complications include fatigue, impaired exercise tolerance, insomnia, unpleasant dreams, worsening of claudication, and erectile dysfunction.