Wagner_Marriot's Practical Electrocardiography, 12e

F I G U R E 7 . 9 . Milstein’s algorithm for accessory pathway localization. LBBB, left-bundle-branch block; LL, left lateral; Neg., negative; Pos., positive; PS, posteroseptal; RAS, right anteroseptal; RL, right lateral. (Modified from Milstein S, Sharma AD, Guiraudon GM, et al. An algorithm for the elec- trocardiographic localization of accessory pathways in the Wolff-Parkinson-White syndrome. Pacing Clin Electrophysiol. 1987;10:555–563, with permission.)

Other classification systems consider the direction only of the abnormal delta wave in attempting to better localize the pathway of ventricular preexcitation. Because curative surgical and catheter ablation techniques for eliminating it have become available, more precise localization of the accessory pathway is clinically important, 7 and many additional ECG criteria have therefore been proposed for achieving this. However, precise localiza- tion of an accessory AV pathway is made difficult by several factors, including minor degrees of preexcitation, the presence of more than one accessory pathway, distortions of the QRS complex caused by superimposed myocardial infarction, or ventricular hypertro- phy. Nevertheless, Milstein and associates 8 devised an algorithm that enabled them to cor- rectly identify the location of 90% of 140 accessory pathways (Fig. 7.9). For purposes of this schema (see Fig. 7.9), LBBB indicates a positive QRS complex in lead I with a duration of 0.09 second and rS complexes in leads V1 and V2.

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SECTION II: Abnormal Wave Morphology