Localization of the site of ventricular preexcitation with body surface maps in patients with Wolff-Parkinson-White syndrome.

Forty-nine patients with Wolff-Parkinson-White syndrome, ages 7 weeks to 51 years, were studied with isopotential body surface maps during normal sinus rhythm, atrial pacing or induced atrial fibrillation. The location of the accessory pathway was determined by multicather electrophysiologic study or surgical ablation of the accessory pathway. When fusion was minimized and ventricular activation primarily controlled by a single accessory pathway, the distribution of positive and negative potentials on the anterior and posterior torso during QRS (observed at 40 msec) and the ST segment were an excellent index of the location of the site of the accessory pathway. The relationship between a specific sequence of QRS-T wave body surface maps and a specific preexcitation site was similar from patient to patient in the presence of marked differences in age, size, and different cardiac status due to structural congenital cardiac defects. The localization of the site of the accessory pathway using distributions too early in QRS (before 40 msec) was unreliable because the early distributions varied from patient to patient for the same preexcitation site; however, the potential distributions during the ST segment were both stable and consistent from patient to patient for the same preexcitation site. The presence of significant fusion of ventricular activation initiated via a single accessory pathway and the normal conduction system or via multiple accessory pathways complicated the interpretation of body surface distributions. Thus, one can predict accurately at least seven preexcitation sites by the combined use of QRS and ST-segment body surface maps.