Describe the types of seconddegree atrioventricular block

  • Mobitz type I (Wenckebach): Involves progressive lengthening of the PR interval followed by a nonconducted P wave, followed by a conducted P wave with a shorter PR interval. When lengthening of the PR is difficult to identify, comparing the PR duration before and after the blocked P wave may confirm Wenckebach. The level of block is usually in the atrioventricular (AV) node with Mobitz I.
  • Mobitz type II: Far less common than Wenckebach. With Mobitz II block there is no progressive prolongation of the PR interval, which for the first conducted beat is the same as the PR interval before the nonconducted beat. The level of the AV block is generally below the AV node with Mobitz II, as suggested by a wide QRS complex. Permanent pacing is usually indicated in patients with Mobitz II block.
  • 2:1 AV block: A rhythm in which every other P wave is conducted. Because there is no opportunity to evaluate successive conducted beats, 2:1 AV block is neither Mobitz I nor Mobitz II.

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