3 - Class IV & Unclassified Antiarrhythmics

What is the MOA of class IV antiarrhythmics?

blocks entry of Ca²⁺ into myocardial cells, slowing conduction in SA & AV node

What are the effects of class IV antiarrhythmics on action potential?

1. decreases SA node automaticity

2. slows AV nodal conduction velocity

3. increases AV node refractoriness

What is the class and ingredient of class IV antiarrhythmics?

non-dihydropyridines

• verapamil

• diltiazem

• etripamil

What is unique about etripamil?

new, self-administered nasal spray for PSVT

What are the adverse effects of class IV antiarrhythmics?

• bradycardia

• hypotension

• constipation

• worsening of heart failure

• etripamil - nasopharyngeal

What are the patient care considerations for class IV antiarrhythmics?

• used in supraventricular and ventricular arrhythmias

• do not use in heart failure

What are the ingredients of antiarrhythmic agents with no vaughan williams class?

• adenosine

• digoxin

• magnesium

What is the MOA of adenosine?

activates an acetylcholine-sensitive outward K+ current in the atria, SA node, and AV node

What is the effect of adenosine on the AV node?

slows conduction and increases refractoriness

What is the effect of adenosine on intracellular Ca²⁺?

reduces the current that occurs with sympathetic stimulation, increasing refractoriness

What are the specific drug properties of adenosine (indication, elimination, efficacy requirement)?

• drug of choice for in-hospital acute termination of reentrant supraventricular tachycardias

• eliminated by carrier-mediated uptake

• t_1/2 = <10 seconds

• efficacy requires IV bolus

What are the ADE of adenosine?

• short lived adverse effects

• transient asystole (lack of cardiac rhythm)

• flushing, chest fullness/tightness, dyspnea

What are the patient care considerations for adenosine?

• theophylline and caffeine block adenosine receptors and decrease efficacy

• start with 6mg IVB, can repeat with 12mg IVB

What is the MOA of digoxin?

1. antiarrhythmic effect - enhances parasympathetic tone (AV node), slowing conduction

2. inhibits Na/K ATPase, increasing intracellular Ca²⁺

What are the specific drug properties of digoxin?

• t_1/2 = 36 hours

• interacts with P-glycoprotein inhibitors, require close monitoring of digoxin serum concentration

• can be given IV or PO, slow distribution

What are the ADE of digoxin?

• narrow therapeutic index

• toxicity - nausea & vomiting, CNS cognitive dysfunction, visual changes, arrhythmia

• serious arrhythmia can be treated with Digifab

What are the patient care considerations of digoxin?

• only marginally effective in patients with high sympathetic tone

• correct electrolytes

What is the MOA of magnesium?

• stabilizes the membrane

• mechanism not well understood, but affects Na/K ATPase pump, Na channels, Ca channels, some K channels

• IV admin can be used in TDP, doesn’t result in shortened QT interval

• may also be used for arrhythmias related to digoxin toxicity