preexcitation /prē′eksitā″shən/ [L, prae + excitare, to arouse] , activation of part of the ventricular myocardium earlier than would be expected if the activating impulses traveled only down the normal routes and had experienced a normal delay within the atrioventricular (AV) node. Preexcitation may be a result of either an AV accessory pathway (Wolff-Parkinson-White syndrome), which is reflected on the electrocardiogram by a short P-R interval and a broad QRS complex, or an excessively fast intranodal pathway (Lown-Ganong-Levine syndrome), which manifests with a short P-R interval and a normal QRS complex. The degree of preexcitation is determined by the speed at which the impulse traverses the atrial tissue and the accessory pathway or the AV node. See also accessory pathway.
