ESSENTIALS OF DIAGNOSIS
Two classic features of Wolff-Parkinson-White (WPW) pattern on ECG are short PR interval and wide, slurred QRS complex due to manifest preexcitation (delta wave).
Most patients with WPW pattern do not have clinical history of arrhythmia but have a higher risk of sudden cardiac death due to rapidly conducted atrial fibrillation through the accessory pathway. Risk factors include age younger than 20, history of tachycardia, and rapid conduction properties at electrophysiologic testing.
Accessory pathways or bypass tracts between the atrium and the ventricle bypass the compact AV node and can predispose to reentrant arrhythmias, such as AVRT and atrial fibrillation. These may be wholly or partly within the node (eg, Mahaim fibers), yielding a short PR interval and normal QRS morphology (eFigure 10–76). More commonly, they make direct connections between the atrium and ventricle through Kent bundles (eFigure 10–77). When direct AV connections conduct antegrade (manifest preexcitation) they produce a classic WPW pattern on the baseline ECG consisting of a short PR interval and a wide, slurred QRS complex (delta wave) owing to early ventricular depolarization of the region adjacent to the pathway. Although the morphology and polarity of the delta wave can suggest the location of the pathway, mapping by intracardiac recordings is required for precise anatomic localization.
Short PR interval due to intra-atrioventricular (AV) nodal, atrionodal, or atrio-His bypass tracts or to an anatomically short AV node. Since the ventricles are depolarized via the normal His-Purkinje system, the QRS complexes are normal. (Reproduced, with permission, from Goldschlager N, Goldman MJ. Principles of Clinical Electrocardiography, 13th ed. Originally published by Appleton & Lange. Copyright © 1989 by The McGraw-Hill Companies, Inc.)
Ventricular preexcitation (Wolff-Parkinson-White conduction) (A) reverting to normal (B). A: WPW conduction. The PR interval = 0.1 s. A positive delta wave is present in I, aVL, and V4-5, and a negative delta wave is seen in II, II, and aVF. The negative delta wave should not be confused with the Q wave of myocardial infarction. B: A fter treatment with quinidine, which has caused conduction delay in the accessory atrioventricular (AV) pathway to exceed that in the AV node, conduction of the sinus impulses is occurring normally via the AV node–His-Purkinje system. The PR interval is normal, and the QRS complexes do not show delta waves. (Reproduced, with permission, from Goldschlager N, Goldman MJ. Principles of Clinical Electrocardiography, 13th ed. Originally published by Appleton & Lange. Copyright © 1989 by The McGraw-Hill Companies, Inc.)
Accessory pathways occur in 0.1–0.3% of the population and facilitate reentrant arrhythmias owing to the disparity in refractory periods of the AV node ...