• Tachyarrhythmia, or fast heart beat > 100 bpm, arises from 3 mechanisms:
Ectopy (or enhanced automaticity): a spontaneous firing of an erratic automaticity focus
Reentry: a continuously conducting circuit
Afterdepolarization (or triggered activity): a triggered beat during repolarization phase of action potential
• Tachyarrhythmia is generally classified based on the origin of electrical impulses, either from within the ventricles "ventricular" or above the ventricles "supraventricular" (i.e. SA node, atria, AV junction).
• Ventricular tachyarrhythmias include have widened QRS complexes (> 120 ms) because the electrical impulses originate from ventricular foci and spread across adjacent ventricular myocytes, not using the AV-His-Purkinje system. Examples include ventricular tachycardia and ventricular fibrillation,
• Supraventricular tachyarrhythmias (also referred to as supraventricular tachycardia or SVT) often have narrow QRS complexes because impulses are conducted down the AV-His Bundle-Purkinje system. Examples include sinus tachycardia, atrial tachycardia, atrial flutter, atrial fibrillation, junctional tachycardia, AVNRT, and AVRT. SVT can have widened QRS's when the native QRS's are inherently widened due to either a bundle branch block, intraventricular conduction delay, or preexcitation.
• The general approach to tachyarrhythmia is to first determine if it's a narrow or wide complex tachycardia:
Narrow complex tachycardia: SVT
Wide complex tachycardia: can be either
1) Ventricular tachycardia,
2) Supraventricular tachycardia with aberrancy (i.e. bundle branch block, intraventricular conduction delay) or preexcitation,
3) Ventricular paced rhythm,
4) Metabolic or electrolyte disturbances (e.g. hyperkalemia), or
5) Drug effects (e.g. antiarrhythmics)
• The most life-threatening forms of tachyarrhythmia are sustained ventricular tachycardia and ventricular fibrillation where there is such chaotic electrical activity and poor, uncoordinated ventricular contraction that can result to cardiac arrest and death.
