Second Degree Heart Block Type I | Reference Guide
EKG FeaturesRate: The underlying rate
Rhythm: Irregular but with progressively longer PR interval lengthening
P Wave: Normal
PR Interval: Progressively longer until a QRS complex is missed, then cycle repeats
QRS: Normal (0.06-0.10 sec)
A prolonging P-R interval from one cardiac complex to the next, until it reaches a point where the QRS complex is non-conducted (blocked or more simply missing). Then the pattern starts over again.
Second degree Heart Block Type I Wenckebach is a condition where the atrioventricular node conducts each successive impulse earlier and earlier. The PQ interval prolongs from beat to beat up until a drop-out of one QRS complex. The following impulse will then be conducted normally and the cycle to begin again. Thus, the presence of second-degree AV block is diagnosed when one or more (but not all) of the atrial impulses fail to conduct to the ventricles.
External Source: http://www.uptodate.com/contents/second-degree-atrioventricular-block-mobitz-type-i-wenckebach-block
Authors and ReviewersAuthored by Thomas O'Brien
EKG tracings reviewed by Dr. Pedro Azevedo, MD, Cardiology
Medically reviewed by Dr. Jonathan Keroes, MD, Cardiology
Last Update: 11/8/2021