Cardiology In Critical Care

Arrhythmia Recognition

Second Degree AV Block Type II (Mobitz)

Rhythmic impulses originating  in the SA node are intermittently blocked at the AV junction.  P waves are positive in L2 and negative in AVR and occur regularly at a rate 60-100.  Only every second (or rarely third, fourth, etc.) P wave is followed by a QRS complex resulting in the P:QRS ratio 2:1, 3:1, 4:1, etc. and the ventricular rate 20-60.  Rarely the AV conduction and the P:QRS ratio may be 3:2, 4:3, 5:2 or other and may vary in the same tracing.  The PR interval of the conducted beats is normal or prolonged and usually constant.  QRS complexes are frequently wide and have RBBB configuration because the lesion extends below the AV junction.

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