Learning ECG NSR WITH FIRST DEGREE AV BLOCK, SECOND DEGREE AV BLOCK TYPE I & II, THIRD DEGREE AV BLOCK

LEARNING ECG

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NSR WITH FIRST DEGREE AV BLOCK

First degree AV Block result from a prolonged transmission of the electricals impulse through the AV junction (AV Node and the Bundle of His). The significant finding of this rhytm is a prolonged PR interval of more than 0.20 second. The underlying rhytm should be identified and named prior to claiming a first degree AV block. For example, this rhytm is a normal sinus rhytm with a 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.

Literature: SkillStat Learning Inc, 2005.