Narrow complex tachycardias. Differential diagnosis and management.

Narrow complex tachycardias are a common clinical problem and can be divided into those in which the arrhythmic circuit is located exclusively in the atrium (pharmacologic treatment is oriented toward altering atrial electrophysiologic properties) and those that involve the AV node or an accessory pathway (pharmacologic therapy is directed toward slowing conduction or increasing refractoriness in these structures). The electrocardiographic diagnosis of the mechanism responsible for SVT includes the regularity of the RR interval; the AV conduction ratio; the presence of P waves, P wave morphology, and the relationship of the P waves to the QRS complexes; and the response of the arrhythmia and atrial activity to vagal maneuvers. Acute therapy includes cardioversion in hemodynamically unstable patients and vagal maneuvers and specific pharmacologic therapy for SVT based on the electrocardiographic diagnosis. There have been recent exciting advances in the nonpharmacologic treatments of SVT, most notably surgery and radiofrequency percutaneous catheter ablation for AV nodal reentry, AV reciprocating tachycardia, atrial flutter, and atrial tachycardias.