Beta Blockers Mechanisms and Clinical Uses

Summary

Beta blockers are medications with a variety of mechanisms and clinical uses.

They belong to the drug class of class 2 antiarrhythmics. By blocking beta receptors, these medications slow the heart rate, slow conduction through the A/V node, and weaken the heart’s ability to contract. This leads to a decrease in cardiac output, as well as a lower cardiac oxygen demand. Beta blockers decrease renin release in the kidneys, and some also cause vasodilation. Beta blockers are also known for their ability to decrease intraocular pressure.

As antiarrhythmics, beta blockers are used to treat atrial fibrillation. They may also be prescribed to treat glaucoma and migraines. Other common clinical uses include angina, myocardial infarction, hypertension, and chronic heart failure. You may also see them prescribed off-label for tremor and anxiety.

It’s important to teach patients taking beta blockers to not stop taking them abruptly.  Instead the dose should be gradually tapered down over several weeks.

Key Points

• Beta Blockers
  • Mechanisms
    • Class 2 Antiarrhythmic
      • Block beta-adrenergic receptors
    • Slow heart rate
      • Negative chronotropic effect
      • Achieved by blocking beta-1 receptors in the SA node,
    • Slow conduction through AV node
      • Negative dromotropic effect
      • Due to blocking beta-1 receptors in the AV node, which can help control ventricular rate
    • Weaken heart contractions (Decrease myocardial contractility)
      • Negative inotropic effect
      • Caused by blocking beta-1 receptors in the cardiac muscle
    • Decrease cardiac output
      • Decreased myocardial contractility and decreased heart rate both cause less blood volume to be pumped out of the heart
    • Decrease cardiac oxygen demand
      • Beta blockers decrease the workload of the heart, resulting in the heart requiring less oxygen
    • Reduce renin release
      • Decreases angiotensin II → vasodilation
      • Promotes excretion of sodium and water → lower blood pressure
    • Vasodilation
      • Certain beta blockers like carvedilol and labetalol are also alpha blockers and cause vasodilation
    • Decrease intraocular pressure (IOP)
      • Decreases the amount of aqueous humor produced
  • Clinical Uses
    • Treat Atrial fibrillation
      • An irregular, rapid heart rhythm
      • Beta blockers slow down the heart rate, which can help control the ventricular rate in atrial fibrillation and reduce symptoms
    • Treat Hypertension
      • Decreased cardiac output means less blood is being ejected into the arteries, decreasing the blood pressure
      • Vasodilation lowers the pressure inside the arteries, directly treating hypertension
    • Treat Chronic Heart Failure
      • By slowing the heart rate and decreasing cardiac oxygen demand, beta blockers reduce the strain on the heart and allow the heart to pump more effectively. This is important in heart failure when the heart is weak.
      • It’s important to note that beta blockers should only be used in chronic heart failure, since they can actually exacerbate acute heart failure.
    • Prevent Myocardial Infarction (MI)
      • By reducing cardiac oxygen demand and preventing arrhythmias, beta blockers can help prevent myocardial infarctions (heart attacks), especially in patients with underlying coronary artery disease
    • Prevent Migraines
      • Beta blockers can be taken regularly as migraine prophylaxis
    • Treat Angina
      • By reducing cardiac oxygen demand and increasing oxygen supply to the heart muscle, beta blockers can help prevent and treat angina (chest pain caused by inadequate oxygen supply to the heart)
    • Treat Anxiety
      • Off-label use for performance anxiety
        • Beta blockers can be taken shortly before an anxiety-provoking situation to relieve the physical effects of anxiety (fast heart beat, sweating, shaking, etc.)
        • By blocking the physiological effects of the sympathetic nervous system (the "fight or flight" response), beta blockers can help reduce the physical symptoms of anxiety
    • Treat Tremors
      • Also called akathisia
      • Can also be used to treat tremors from other causes such as thyroid storm and extrapyramidal symptoms (EPS)
    • Treat Glaucoma
      • Primarily used to treat primary open-angle glaucoma (POAG)
      • May be used to treat acute narrow-angle glaucoma in emergencies
  • Nursing Considerations
    • Do not stop abruptly
      • The drug should be discontinued slowly over 1-2 weeks, and the patient should not discontinue without consulting their provider
      • Abrupt discontinuation of beta blockers can lead to a rebound effect, where the body's compensatory mechanisms can cause a sudden increase in heart rate, blood pressure, and angina symptoms