Antiarrhythmics Class 4

Question 1

What are the two Class 4 antiarrhythmics we need to know?

How do they work?

Answer 1

Verapamil and Diltiazem
Block Ca channels

Smooth muscle
1) vascular smooth muscle relaxation (vasodilation)
2) decreased myocardial contractility.
Cardiac myocytes:
1) shorten phase 2 of AP
2) reduce force of contraction (less Ca binds troponin).
Nodal cells:
1) decreased HR
2) decreased conduction velocity (AV node)

Question 2

What congenital disease precludes the safe use of verapamil?

Answer 2

Wolf-Parkison-White

Question 3

Therapaeutic use for Verapamil vs Diltiazem?

Answer 3

Verapamil
Supraventricular tachycardia, atrial fibrillation and flutter (reduces ventricular rate, not convert back to sinus rhythm)
Diltiazem
Stable angina (increases coronary blood flow and decreases myocardial O2 consumption).
SVT, A-fib/A-flutter

Question 4

Adverse side effects of Verapamil vs Diltiazem?

Answer 4

Verapamil
-peripheral vasodilation

Diltiazem

• reflex sympathetic response (dilation of vessels)-> drop in BP to counteract inotropic, chronotropic and dromotropic effects of diltiazem.
• “Off-label” use to treat HTN (low-renin)

Question 5

Toxicity of Verampamil?

Answer 5

• large doses can induce AV block, or normal doses when used in patients with AV nodal disease.
• Constipation, lassitude, nervousness, peripheral edema

Question 6

Toxicity of Diltiazem?

Answer 6

bradycardia, constipation, flushing, edema, dizziness, heart failure, av block sinus node depression, torsades (dangerous if missed with beta-blockers)