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Cardiac Arrhythmias
The abnormalities of cardiac rhythm which may arise from:
a. Abnormality in automaticity
– Increased firing from pre-existing dormant pacemaker
– Emergence of an autonomous pacemaker
Due to
- Diseases, ischemia, myocarditis, stress
- Drugs (digitalis, atropine, sympathomimetics, catecholamines)
- Electrolyte imbalance leading to hypokalemia and hypocalcaemia, acidosis
b. Abnormality in conduction
– complete or partial AV block
– Re-entrant phenomenon
Abnormalities Of Impulse Propagation
Circus movement (Re-enterant Arrhythmias)
Damage to certain part of heart results in fibrosis. The refractory period of this part is prolonged. Once the normal impulse reaches, the refractory period is over and it re-enters, exciting fibers, as a result vicious cycle occurs, known as re-entrant phenomenon.
Treatment
- Decrease refractory period of damaged part
- Further prolong refractory period.
Classification (Vaughan Williams classification)
Class 1: sodium channel blockers (membrane stabilizing agents)
Class 1A (Cause Moderate Phase “0” Depression. Prolong Action Potential Duration)
Class 1B (Cause Minimal Phase “0” Depression, Shorten Action Potential Duration)
Class 1c (Cause Marked Phase “0” Depression, Little Effect on Action Potential Duration)
Encainide
Lorcainide
Propaphenone
Class. II Beta Adrenergic Blockers
Class III (Drugs That Prolong Repolarization)
Class IV Calcium Channel Blockers
Miscellaneous
Digoxin (supraventricular arrhythmias)
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Sodium channel blockers (Class 1 antiarrhythmics)
Beta Adrenergic Blockers (Class II antiarrhythmics)
Potassium channel blockers (Class III antiarrhythmics)
Calcium channel blockers (Class IV antiarrhythmics)
Miscellaneous antiarrhythmic drugs
