• Arrhythmias (or abnormal heart rhythm-- that is, any rhythm that is not normal sinus rhythm) arise from 4 main mechanisms:
Block: any delay or disruption along the conduction pathway
Ectopy (or enhanced automaticity): an erratic firing of an automaticity focus or multiple foci
Reentry: a continuously conducting circuit
Afterdepolarization (or triggered activity): a triggered beat during the repolarization phase of action potential
• Arrhythmias can be classified, based on heart rate, into brady- and tachy- arrhythmias. Both of these forms, if left untreated, can progress to cardiac arrest.
Bradyarrhythmia: slow heart rate, < 60 bpm, often caused by a block as in the case of SA and AV node dysfunction
Tachyarrhythmia: fast heart rate, > 100 bpm, caused by either ectopy, reentry, or afterdepolarization.
• Arrhythmias can also be classified based on the regions within the heart they arise from, which is essentially anywhere, including the sinus node, AV node, atria, ventricles, and in some cases, an accessory pathway connecting the atria and ventricles.
• Inherited arrhythmias arise from either:
Cardiac ion channel dysfunctions (such as Na, K, and Ca channels), these disorders are collectively referred to as channelopathy, which is often associated with an increased risk of life-threatening ventricular arrhythmias, including sustained monomorphic ventricular tachycardia, polymorphic ventricular tachycardia, and ventricular fibrillation
Presence of an accessory pathway that allows anterograde or retrograde conduction of abnormal rhythm between the atria to ventricles (recall that impulses can only travel from the atria to the ventricles via the AV node)
