Beta blockers, also called beta-adrenergic receptor antagonists, are prescription medications used primarily in the treatment and prevention of cardiovascular disease, including heart attacks, high blood pressure and arrhythmia. Since cardiovascular disease is the No. 1 cause of death in adults, these medications are commonly prescribed.
There are two predominant types of beta-adrenergic receptors: beta-1 and beta-2. Beta-1 receptors are found primarily in the heart, while beta-2 receptors are found primarily in tissues other than the heart, such as the airway, muscle and blood vessels. Drugs that mostly target beta-1 receptors are called cardioselective beta blockers. Non-cardioselective beta blockers bind to both receptor types. Examples of cardioselective beta blockers commonly used in the United States are metoprolol and atenolol. Examples of the non-cardioselective type are propranolol and nadolol.
Cardioselective beta blockers slow heart rate, reduce electrical conduction speed in the heart and decrease the force of heart contraction. In principle, non-cardioselective beta blockers have less effect on the heart, but in “Brunwald’s Heart Disease,” Dr. Norman Kaplan suggests that non-cardioselective beta blockers have similar cardiovascular effects at doses commonly prescribed. Both types of beta blockers blunt the increase in heart rate in response to exercise and stress. The net effect is to reduce the heart’s workload and lower blood pressure.
According to Dr. Kaplan, non-cardioselective beta blockers are more likely to impair blood sugar regulation, especially in diabetic patients. The non-cardioselective agents are also more likely to cause airway constriction in asthmatic patients, since beta-2 receptors are found in the airway. Beta blockers in general may cause fatigue, sexual dysfunction and hypotension, a condition that occurs when blood pressure becomes too low.
Both types of beta blockers are used in the treatment of high blood pressure. According to the American Heart Association, certain cardioselective beta blockers are sometimes preferred in patients following a heart attack, heart failure or arrhythmia. Non-cardioselective beta blockers are used in the treatment of glaucoma. Other uses for beta blockers include the treatment of migraines, anxiety and tremor.
Both types of beta blockers can be dangerous in patients with airway disease or difficulty breathing. According to Dr. Kaplan, the non-cardioselective agents are used with caution in patients with diabetes and other metabolic disorders. Beta blockers are usually avoided in patients who already have a low heart rate or low blood pressure.