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1. Class 1: Sodium channel blockers that slow electrical conduction in the heart.

2. 1a: Quinidine, procainamide, disopyramide-slow conduction velocity, prolongs action potential duration, and can prolong QT interval.

3. 1b: Lidocaine, tocainide, mexiletine, phenytoin-shorten action potential duration slightly with no significant QT prolongation.

4. 1c: Flecainide and propafenone-slow conduction veloc­ ity without effect on potential duration or QT interval.

5. Class II: Beta-blockers-decrease heart rate and blood pressure by blocking impulses that can cause irregular heart rhythm and decreasing hormonal effects (e.g., adrenaline) on the heart.

6. Class Ill: Amiodarone, sotalol, and the newer agents, dofetilide (oral Tikosyn®) and dronedarone (Multaq®}­ prolong the action potential by potassium channel blockade. These agents can cause QT prolongation. Note: See side effects on dronedarone below.

7. Class IV: Calcium channel blockers, especially vera­ pamil and diltiazem, slow inward current. They decrease heart rate and blood pressure like class II.


1. Wilkinson, I. (2017). Oxford handbook of clinical medicine. Oxford: Oxford University Press.
2. Hannaman, R. A., Bullock, L., Hatchell, C. A., & Yoffe, M. (2016). Internal medicine review core curriculum, 2017-2018. CO Springs, CO: MedStudy.
3. Image: no reference available.

Ⓒ A. Manickam 2018

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