AV Block

(Circ 2019;140:e382) Type Features

1°

• Prolonged PR (>200 ms), all atrial impulses conducted (1:1).

2° Mobitz I (Wenckebach)

• Progressive ↑ PR until impulse not conducted (→ “grouped beating”).
• AV node pathology:
  • ischemia (IMI),
  • inflammation (myocarditis, endocarditis, MV surgery),
  • high vagal tone (athletes),
  • drug induced.
• Classically (~50%), absolute ↑ in PR decreases over time (→ ↓ RR intervals, duration of pause <2× preceding RR interval); nl QRS.
• AVB usually
  • worsens w/ carotid sinus massage,
  • improves w/ atropine.
• Often paroxysmal/nocturnal/asx, no Rx required.

2° Mobitz II

• Blocked impulses w/ consistent PR interval, often prolonged QRS
• His-Purkinje pathology:
  • ischemia (AMI),
  • degeneration of conduction system, infiltrative disease, inflammation.
• AVB may improve w/ carotid sinus massage, may worsen w/ atropine.
• May progress to 3° AVB. Pacing pads; transven. pacing often required.

3° (complete)

• No AV conduction. Escape, if present, narrow (jxnal) or wide (vent.)
• Nb, if 2:1 block, cannot distinguish type I vs. II 2° AVB (no chance to observe PR prolongation); usually categorize based on other ECG & clinical data. High-grade AVB usually refers to block of ≥2 successive impulses