Class V Drugs (Anti-Arrhythmias)

Question 1

Amiodarone for Rate Control

Answer 1

For Rate Control if BP too low

• Uses (continued):
  – Rate control of supraventricular arrhythmias in unstable patients
  – Also used for rhythm control, already discussed
• MOA (continued):
  – Has properties of all four VW classes (Na, Beta, Ca, K)
  – Beta blockade is responsible for rate control properties
  – Does not significantly lower BP when dosed by slow IV infusion

Question 2

Digoxin

Answer 2

For Rate Control if BP too low

• Uses:
  – Rate control of supraventricular arrhythmias in unstable patients
• MOA:
  1. Inhibits Na/K ATPase
  2. ↑ Intracellular calcium
  3. ↑ Contractility
  4. Baroreceptor reflex (↑ Parasympathetic output to heart)
• SAN: ↓ Firing rate
• AVN: ↓ Conduction velocity

Question 3

Adenosine

Answer 3

MOA:
Binds adenosine A1 receptors in the SAN & AVN
* Gi coupled –> ↓cAMP –> ↑K channels, ↓Ca channels –>
* SAN: ↓ Firing rate
* AVN: ↓↓↓↓ Conduction velocity
– (FYI: Binds A2 receptors in vascular smooth muscle)
* Gs coupled –> ↑cAMP –>–> vasodilation
– Rapidly eliminated from circulation by cellular uptake
* T1/2 = seconds

Uses:
– Acute treatment of PSVT
– (FYI: Also used diagnostically as a coronary vasodilator)
– IV only

Effects:
– When given as a fast IV bolus, halts AVN conduction (~5sec)

Question 4

Magnesium

Answer 4

Uses:
– Treatment of TdP

MOA:
– Unknown