AV  BLOCKS

 

  1. Causes can be medications (dig, CCB, bB, quinidine), electrolyte abnormalities, Lyme, CAD, no cause.
     
  2. Classified as follows:

Iš  AVB

  1. Causes are as above. The block is at AV node.
  2. PR is > 0.2 sec (i.e. 1 big box or 5 small boxes)
  3. No treatment is needed.

IIš AVB

  1. Is further classified into:

a)  Mobitz I or Wenckebach

  1. Causes as above. The block is at AV node.
     
  2. PR interval prolongs progressively until it is not conducted, i.e. not followed by QRS and cycle repeats its self. QRS is narrow. The block can be 4:3 (or 3:2 or 2:1) meaning that only 3 out of 4 beats are conducted.
     
  3. Pt has "irregular" HR (EKG  has A. fib-like look) but generally asymptomatic.
     
  4. Treatment is indicated if arrhythmia causes symptoms. In that case Atropine 0.5 mg (q 5min prn) is given to total of  0.03-0.04  mg/kg. If this arrhythmia occurs during MI, unless pt is symptomatic, treatment is not indicated. Otherwise, temporary PM is indicated.

b)  Mobitz II

  1. Causes are structural damage to the bundles, MI.
     
  2. In this arrhythmia the block is below the AV node i.e. at His-Purkinje and thus  QRS complexes may appear wide. PR interval is constant until one atrial beat is not conducted.  Since the block is at this level  BBB can coexist.
     
  3. The arrhythmia presents a "drop beat" meaning that only one P wave is not conducted. The ratio is constant i.e. in a block of 4:1 every 4th P is not followed by QRS. If the block is 2:1 it is hard to distinguish between  type I and type II AVB.
     
  4. Treatment is provided with permanent PM (transcutaneous in ER)even if pt is asymptomatic (class II indication). Some authors suggest to use Atropine in case of emergency while others (including ACLS) warn  that it has to be used with caution. The reason behind avoiding Atropine is that the medication will increase atrial  and AV conduction against blocked H-P bundle and thus increase the frequency of nonconducted P waves.

IIIš AVB

  1. Causes are MI, CAD, Trauma, Myopathy, Congenital, Dig, Lyme, infiltrative disease
     
  2. Atria and Ventricle are not in synchrony. Atria are under control of  SA node and beats at normal pace while Ventricles are under control of an escape node and beat slower than atria (usually  less than 60 bpm). QRS complexes are at a constant rate as are the P waves but they do not have constant relation among each other i.e. PR intervals are always variable. Depending on the location of the escape node the QRS can be narrow (escape node is in AV node) or wide (escape node is below the AV node).
     
  3. On clinical exam, pts with IIIšAVB have canon A waves since the atria beat against closed valves. Pt may or may not experience symptoms (dizziness, Ŋ BP).
     
  4. Treatment depends on:
     
        1. If pt is asymptomatic, IIIš AVB is congenital , is 2ry to IWMI, due to Dig toxicity or narrow QRS IIIš AVB, generally treatment is not needed; (or  see below)
        2. If pt is hemodynamically unstable Atropine and / or PM (Temporary or Permanent) are employed.

          Same precautions as above apply for Atropine use especially if there is wide QRS IIIš AVB. In ER always use Transcutaneous PM.
           
        3. Pt with IIIš AVB complicating AWMI PM is always indicated.

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