Anti-arrhythmic drugs are used to manipulate how the electrical impulses of the heart are generated and conducted, to restore cardiac rhythm to normal where needed, as well as to effect the cardiac cells’ action potential in changing their impulse initiation and conductivity. Unfortunately, most anti-arrhythmic drugs can aggravate or cause new arrhythmias.
The phrase cardiac action potential (AP) refers to the change in voltage across the cell membrane of cardiac cells caused by the movement of ions between the inside and the outside of the cell through ion channels. An action potential happens when different ions cross the neuron membrane.
There are 5 phases in a Cardiac Action Potential:
- Phase 4 – resting phase a.k.a. resting membrane potential (when the heart is into diastole)
- Phase 0 – opening of the fast sodium channels causing sodium to move into the cell
- Phase 1 – initial rapid repolarisation: when fast sodium channels close
- Phase 2 – plateau phase caused by calcium moving in and potassium moving out (ST segment in an ECG)
- Phase 3 – repolarisation: potassium channels stay open allowing potassium to move out and repolarise the cell; when membrane potential reaches certain level, potassium channels close (T-wave on ECG)
Anti-Arrhythmics, which are classified according to the Vaughn Williams classification, are organised into 4 major classes:
CLASS 1 AGENTS: Fast sodium channel blockers (affect the depolarisation phase)
CLASS 2 AGENTS: Beta-blockers (affect depolarisation)
CLASS 3 AGENTS: Potassium channel blockers (reduce potassium current during the repolarisation phase)
CLASS 4 AGENTS: Calcium Channel Blockers (cause cardiac cells conduction to slow down)
OTHER ANTI-ARRHYTHMICS: Digoxin, Adenosine and Magnesium Sulphate
Class 1 Agents are further sub-divided into 3 types of anti-arrhythmics:
1A Quindine, Procainamide, Disopyramide
1B Lidocaine, Mexiletine
1C Flecanide, Propafenone
Below you can find a collection of videos that can help provide a more visual approach to Anti-Arrhythmic Drugs.
Cardiac Action Potential Animation
Anti-Arrhythmic Drugs Animation
Anti-Arrhythmics
Special thanks to the creators of the featured videos on this post, specifically Youtube Channels Alila Medical Media, MedLecturesMadeEasy
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