Chapter 41

Supraventricular tachycardias (SVTs) include all tachyarrhythmias that either originate from or incorporate supraventricular tissue in a reentrant circuit. The ventricular rate may be the same or less than the atrial rate, depending on the atrioventricular (AV) nodal conduction. The term paroxysmal supraventricular tachycardia (PSVT) refers to a clinical syndrome characterized by a rapid, regular tachycardia with an abrupt onset and termination. Approximately two-thirds of cases of PSVT result from AV nodal reentrant tachycardia (AVNRT). Orthodromic AV reciprocating tachycardia (AVRT), which involves an accessory pathway (AP), is the second most common cause of PSVT, accounting for approximately one-third of cases. The term Wolff-Parkinson-White (WPW) syndrome designates a condition comprising both preexcitation and tachyarrhythmias. Atrial tachycardias, which arise exclusively from atrial tissue, account for approximately 5% of all cases of PSVT.1-3 The purpose of this chapter is to review the mechanism, clinical features, and approach to diagnosis and treatment of patients with AVNRT and AP-mediated tachycardias (including WPW syndrome). Particular attention is focused on reviewing management guidelines developed by the American Heart Association (AHA), American College of Cardiology (ACC), and Heart Rhythm Society (formerly known as the North American Society of Pacing and Electrophysiology).

AVNRT is an important arrhythmia for several reasons. First, AVNRT is extremely common. Studies report that AVNRT occurs in approximately 10% of the general population and accounts for up to two-thirds of all cases of PSVT.4 Although AVNRT can occur at any age, it is extremely uncommon before age 5 years. The usual age of onset is beyond the fourth decade of life and is later than the usual age of onset of AP-mediated tachycardias.4-10 Women are affected twice as often as men.6-10 A second reason for the importance of AVNRT is the fact that it can result in significant debility and decreased quality of life.11

### Pathophysiologic Basis of Atrioventricular Nodal Reentrant Tachycardia

#### Anatomic Considerations of the Atrioventricular Node

Early descriptions of the AV nodal tissue came from Albert Kent more than a century ago.12 The AV node is located epicardially just underlying the right atrial epicardium anterior to the nodal artery and between the coronary sinus (CS) and medial tricuspid valve leaflet. It comprises three different components: the transitional cell zone, the compact node, and the penetrating bundle of His (Fig. 41–1). The compact AV node refers to the most easily histologically distinguishable tissue located at the apex of the triangle of Koch (TOK). A zone of transitional cells is interposed between the compact node and the atrial myocardium. Transitional cells enter the TOK to join the compact node superiorly, inferiorly, posteriorly, and from the left. At its distal extent, the AV node is distinguished from the penetrating bundle, not so much by cellular characteristics as by the presence of a fibrous collar surrounding the specialized cells. Systematic anatomic investigation of the AV node in patients with AVNRT is lacking. No ...

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