Esmolol is a very short acting, cardioselective β-adrenergic receptor antagonist.

i.v. administration is used for rapid beta-receptor blockade (often for treatment of atrial fibrillation with high ventricular following rates)

Antiarrhythmic effects are due mainly to β-adrenergic receptor blockade. Normally, sympathetic drive results in increased in Ca²⁺ , K⁺ and Cl^- currents.

Increased sympathetic tone also increases phase 4 depolarization (heart rate goes up), and increases DAD (delayed afterdepolarizations) and EAD (early afterdepolarization) mediated arrhythmias.

• These effects are blocked by β-adrenergic receptor blockers.

β-adrenergic receptor blockers

• Increase AV conduction time

• Increase AV nodal refractoriness, thereby helping to terminate nodal reentrant arrhythmias.