Like you remember, duration of PR interval reflects the time required to reach the stimulus from the sinus node to the ventricles, and typically lasts from 0.12 to 0.20 seconds, therefore, is not less than 0.12 seconds. In the pre-excitation syndromes time atrioventricular conduction is lower than under physiological conditions, because the stimulus travels through alternate routes, which avoid abnormal physiological delay in the atrioventricular node. It is three types of syndromes: Wolff-Parkinson-White (WPW) is characterized by: A short PR, less than 0.12 seconds. QRS complexes starting with a delta wave (initial slurring at the base of the QRS upline. This delta wave positive or negative is plotted according to the location of the beam pathological and electrocardiographic lead. The beam is the beam pathological Kent. There are three types of routes: on the back, right anterolateral or anterolateral left, which, speaking of WPW syndrome type A, type B or type C. Lown-Ganong-Levine ...