Tachycardias Associated with Accessory Pathways: Mechanisms and Catheter Ablation

Abstract

Accessory pathways (AP) of abnormal conduction are pathways between the ventricular and atrial myocardium that exist apart from the conduction system structures. Patients with AP of abnormal atrioventricular conduction may have ventricular tachycardia known as atrioventricular (AV) reciprocating tachycardia (AVRT). Orthodromic AVRT often occurs in the presence of AP. The pathological impulse passes antegrade via the normal AV conduction system, whereas retrograde conduction to the atria via AP. Rarely, conduction occurs in the opposite direction, resulting in antidromic AVRT. APs occur at all points of the AV ring and usually as isolated anomalies, although in some patients, congenital anomalies are observed. Most APs have non-decremental conduction properties and are conducted more rapidly than normal tissue with AV conduction. In many patients with AP, baseline ECG reveals clear preexcitation signs and special algorithms can be used to presume their localization. Electrophysiologic study in these patients is often performed with in the purpose of diagnosing, localizing, and determining AP’s functional characteristics. Drug therapy for AVRT prevention is useful for temporary control while waiting for drastic actions and, in some cases, for long-term treatment. Over the last few decades, a radical treatment option as catheter ablation has emerged in patient’s treatment with WPW syndrome.