Supraventricular Tachycardia: Mechanisms and Management

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Abstract
The phrase paroxysmal supraventricular tachycardia describes a group of arrhythmias with similar ECG features but different mechanisms that were clarified in recent years with specialized intracardiac recording and pacing techniques. Re-entry accounts for most cases and was localized to the A-V [atrioventricular] node and less frequently to the sinus node, the atria themselves and A-V nodal bypass tracts (Wolff-Parkinson-White syndrome). These forms of supraventricular tachycardia are initiated by premature beats that dissociate conduction between 2 pathways and permit the establishment of circulating electrical activity that spreads to atrial and ventricular myocardium. Paroxysms cease when the conducting properties of the re-entrant circuits are disturbed by changes in autonomic tone or the application of certain drugs, pacing or cardioversion. Supraventricular tachycardia may result from abnormal automaticity in atrial tissues. Such automatic atrial tachycardias are often associated with A-V block (paroxysmal atrial tachycardia with block) and may be due to digitalis intoxication. This arrhythmia is treated by digitalis withdrawal or administration of antiarrhythmic drugs that decrease automaticity.