Which statement is true about Type 2 antiarrhythmics?

Which statement is true about Type 2 antiarrhythmics?

• A. They are Na+ channel blockers
• B. They are Beta blockers
• C. They block K+ channels
• D. They block Ca2+ channels

Answer: (B)

Beta-adrenergic blockade reduces sympathetic influence on the heart, especially at the SA node and AV node. By blocking beta-1 receptors, these drugs lower cAMP levels, decrease calcium influx in nodal tissue, and slow the slope of phase 4 and AV conduction. The result is a slower heart rate and a slower ventricular response, which helps control supraventricular tachyarrhythmias. This mechanism distinguishes them from drugs that block specific ion channels: Na+ channel blockers affect conduction in other ways (Class I), K+ channel blockers affect repolarization (Class III), and Ca2+ channel blockers (Class IV) act directly on calcium influx. Clinically, they are used to blunt sympathetic stimulation and control rate in tachyarrhythmias, with examples like propranolol, metoprolol, and esmolol.

Beta-adrenergic blockade reduces sympathetic influence on the heart, especially at the SA node and AV node. By blocking beta-1 receptors, these drugs lower cAMP levels, decrease calcium influx in nodal tissue, and slow the slope of phase 4 and AV conduction. The result is a slower heart rate and a slower ventricular response, which helps control supraventricular tachyarrhythmias. This mechanism distinguishes them from drugs that block specific ion channels: Na+ channel blockers affect conduction in other ways (Class I), K+ channel blockers affect repolarization (Class III), and Ca2+ channel blockers (Class IV) act directly on calcium influx. Clinically, they are used to blunt sympathetic stimulation and control rate in tachyarrhythmias, with examples like propranolol, metoprolol, and esmolol.