Cardiology In Critical Care

Arrhythmia Recognition

Third Degree (Complete) AV Block

Impulses originate in the SA node or in an atrial pacemaker but none of them is conducted through the AV junction to the ventricles.  P waves are positive in L2 and negative in AVR and occur regularly at a rate 60-100; rarely atrial activity is represented by inverted (ectopic) P waves, F waves of f waves.  Since all P waves are blocked, the ventricles are activated by impulses activated by impulses arising (through escape mechanism) in pacemaker cells below the bifurcation of the common bundle.  The resulting QRS complexes are wide, slurred, frequently of RBBB configuration and occur regularly at a rate 20-40 (the so-called idioventricular rhythm).  P waves occurring at a faster rate are completely unrelated to QRS complexes (AV dissociation).

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