Class IV antiarrhythmics

Class IV antiarrhythmics

Class IV antiarrhythmics are composed of calcium channel blockers. The calcium channel blockers verapamil and diltiazem are used to treat supraventricular arrhythmias with a rapid ventricular response (rapid heart rate in which the rhythm originates above the ventricles).

For a thorough discussion of calcium channel blockers and how they work, 

Adenosine

Adenosine is an injectable antiarrhythmic indicated for acute treatment of PSVT.

 

Pharmacokinetics

After I.V. administration, adenosine is probably distributed rapidly throughout the body. It’s metabolized inside RBCs as well as in vascular endothelial cells.

 

Pharmacodynamics

Adenosine depresses the pacemaker activity of the SA node, reducing the heart rate and the ability of the AV node to conduct impulses from the atria to the ventricles.

 

Pharmacotherapeutics

Adenosine is especially effective against reentry tachycardias (when an impulse depolarizes an area of heart muscle, then returns and repolarizes it) that involve the AV node.

No slouch

Adenosine also effectively resolves PSVT in 90% of cases. It’s typically used to treat arrhythmias associated with accessory bypass tracts, as in Wolff-Parkinson-White syndrome (brief periods of rapid heart rate in which the rhythm originates above the ventricle).

Drug interactions

• Methylxanthines antagonize the effects of adenosine, so larger doses of adenosine may be necessary.
• Dipyridamole and carbamazepine potentiate the effects of adenosine, so smaller doses of adenosine may be necessary.
  P.134
  
  
• When adenosine is administered with carbamazepine, there’s an increased risk of heart block.