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 (LGL) is characterized by:
A short PR, less than 0.12 seconds.
The beam is the beam pathological James (originating in the atria and ends at the tail of the atrioventricular node or the beginning of the bundle of His. Therefore, sinus stimulation can quickly this way anomalous to the Bundle of His, atrioventricular node jumping and avoiding physiological conduction delay at this level.
No delta wave (because the excitation reaches the ventricles through the physiological pathways of intraventricular conduction, the Bundle of His and its branches).
QRS complex of normal appearance.
Pre-excitation syndrome Mahaim type: characterized by:
The beam is a beam Mahaim disease that originates in the low or AB node Bundle of His and usually ends in the interventricular septum.
A normal-length PR.
Presence of delta in the initial phase of the QRS complex (because the stimulus comes from the new sinus enters the AV node where physiological suffers delay and then depolarized to the ventricles via the bundle of Mahaim.
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