LEARNING ECG
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NSR WITH FIRST DEGREE AV BLOCK
SECOND DEGREE AV BLOCK TYPE I
Second degree AV
Block Type I (Wenckebach or Mobitz Type I) results from a cylcical progressive
conduction delay through the AV junction. The ECG presents with a cyclical
lengthening of the PR interval followed by a dropped QRS-a P wave not partnered
with a QRS . the QRS complexes yield and irreguler rhytm. Second degree AV
block type I may be caused by enchanced vagal tone, myocardial ischemia or the
effects of effects of drugs such as calcium-channel blockers, digitalis and
beta-blockers.
SECOND DEGREE AV BLOCK TYPE II
Second Degree AV
Block type II is tipically caused by an intermittent block (interrupted
supraventricular impulse) bellow the AV node. One or more QRS complexes are
dropped with PR intervals that do not change (fixed PR interval). This
irreguler rhytm requires close monitoring: 1) low cardiac output is likely when
multiple dropped QRS complexes occur; and 2) this rhytm can progress to
complete heart block (third degree AVB).
SECOND DEGREE AV BLOCK WITH 2:1 CONDUCTION
Second degree AV
Block with 2:1 Conduction is a special case of second degree AV block with each
alternative P wave NOT paired with a QRS complex. The PR interval remains
constant. This rhytm requires close monitoring due to risk of: 1) low cardiac
output associated with a slow heart rate; and 2) the potential to progress to
third degree AV blok.
THIRD DEGREE AV BLOCK
Third degree AV Block
(complete heart block) is often an ominous rhytm requiring close monitoring for
hemodynamic compromise, progression to ventricular standstill or asystole and
other lethal dysrjytmias. Significant characteristics of this rhytm are: 1)
Lonely P waves- P wave without an accompanied QRS complex; and 2) chaotic PR
intervals. A narrow QRS denotes a higher juntional block while a wide QRS
points more towards a sub nodal block high in the bundle branches.








