Second Degree AV Block Type 1 

2nd Degree AV Block Type 1


MOBITZ I ( WENCKEBACH OR SECOND DEGREE HEART BLOCK, TYPE I). A PROGRESSIVE BLOCK WHO’S IMPULSE IS FROM THE ATRIA AND IS INTERRUPTED AT THE AV JUNCTION. THE INTERRUPTION BECOMES LONGER WITH EACH IMPULSE DELAYING DEPOLARIZATION OF THE VENTRICLES UNTIL A COMPLETE INTERRUPTION BLOCKS THE IMPULSE. THE CYCLE OF PROGRESSIVELY DELAYED CONDUCTION IS THEN REPEATED. THE P-R INTERVAL BECOMES LONGER WITH EACH QRS UNTIL A DROPPED QRS OCCURS. THE P WAVE IS SEEN WITHOUT A QRS COMPLEX. A QRS FOLLOWS EACH P WAVE UNTIL A QRS IS DROPPED. THE OVERALL RHYTHM IS IRREGULAR AND THE RATE MAY VARY. IT IS NOT A LETHAL DYSRHYTHMIA ALTHOUGH THE PATIENT MAY BECOME MEDICALLY UNSTABLE. MAY BE SERIOUS WHEN IT INDICATES A RECENT CHANGE IN THE CONDUCTION SYSTEM FOLLOWING INJURY TO THE CARDIAC MUSCLE. MAY BE CAUSED BY INFECTION, M.I. OR DRUG TOXICITY

 

Characteristics

Rate Atrial rate is greater than ventricular rate

Rhythm Atrial regular (P waves plot on time. Ventricular irregular

P-Waves Normal in shape and size; Some P waves are not followed by QRS complex (More P’s than QRS)

PR Interval Lengthens with each cycle until a P wave appears without a QRS complex.

QRS Duration 0.11 seconds (almost 2 full boxes) but is periodically blocked


MEDS

Atropine 0.5-1mg SIVP over 1-2 min


Treatment

Monitor Diagnostic 12 lead
Usually requires none, but if Bradycardia is present, treat Bradycardia.


Non-Symptomatic Brady

No Treatment


Symptomatic Brady

Monitor Diagnostic 12 lead
Oxygen 15 LPM NR Mask
IV 18g
Atropine 0.5-1mg SIVP over 1-2 min (Repeat every 3-5 min. 3.0mg max)


Noticeable by: 

The Progressive lengthening of the PR interval followed by a P wave With NO QRS Complex. 

© Matt Dillard 2012