Cardio: Class II Antiarrhythmics

Question 1

What does sympathetic innervation do to the SA node?

Answer 1

It increases the rate of the SA node automaticity.

Question 2

Sympathetic innervation causes the AV node ______________.

Answer 2

conduction velocity to increase

Question 3

What is the key role of beta-blockers in treating arrhythmias?

Answer 3

Slowing the SA node automaticity and the AV node conduction (Think of the two musical nodes on Beta Fitzgerald’s music sheet.)

Question 4

The beta blockers _____________ calcium current. Why is this important in their effects?

Answer 4

decrease (by decreasing cAMP); this slows the upstroke of the nodal action potentialRecall that the nodes have slowly leaking sodium channels that create the phase 4 gradual depolarization, and that the action potential in the nodes is triggered by VSCC.

Question 5

Beta blockers cause prolonged phase __________.

Answer 5

4 (thereby decreasing heart rate)

Question 6

Why are beta blockers better at treating supraventricular arrhythmias?

Answer 6

Because their strongest effect is in slowing AV node conduction (Think of the heart light whose bottom half is broken.)This effect can also cause heart block (think of the heart shield on Louis Heartstrong’s hat).

Question 7

Beta-blockers are great at treating __________.

Answer 7

atrial fibrillation –they slow the heart rate, the first goal of treating atrial fibrillation