A-V Blocks

Atrioventricular Blocks


Incomplete–1st degree, 2nd degree
Complete — 3rd degree

First degree
Characterized pr interval greater than 0.20 sec.  Junctional tissue delays impulse longer than normal.

Second degree
Every atrial impulse no conducted through to the ventricles — PR interval may be normal, shortened, or prolonged, but there are more P waves than QRS’s.

Two forms
(1) Mobitz – I–progressive prolongation of PR interval till a beat is dropped.

(2) Mobitz II–PR interval remains constant but there are occasional to frequently blocked beats.

Third degree
Complete heart block–no atrial impulses reach ventricles–cause mechanical atrial-ventricular dissociation–P waves and QRS’s do no correlate. Slow ventricular rate.

Nodal and Ventricular Escape Rhythms

  • Safety mechanism of heart to provide more heart beats when it becomes too slow.
  • Nodal escape–if SA node fails, AV node nest most likely pacemaker.  NO P waves, just normal QRS’s.
  • Ventricular escape–rhythm of ventricular complexes when higher pacemakers fail.
  • Escape  beats–occur when brady occurs (ventricular).