Heart Blocks

on 5.12.08 with 0 comments

First degree AV block

  • mechanism: disorder of impulse conduction (block or delay)

  • characterized by delay > 200 ms from onset of P wave to onset of QRS complex (i.e., PR > 200 ms)

  • in this example, the delay is 260 ms

  • if the delay exceeds 300 ms, they can get AV dissociation, leading to suboptimal filling. this manifests as shortness of breath, for example

Second degree AV block

  • this means there is an occasional dropped beat—every so often, a P wave won’t go to the ventricle

  • Mobitz type I (Wenckebach) block

    • gradually prolonging PR interval

    • then, the heart drops the beat and nothing gets to the ventricles

    • location of block is typically within AV node

    • does not usually progress to complete heart block, so generally don’t have to treat

  • Mobitz type II

    • mechanism: disorder of impulse conduction: conduction block

    • fixed PR interval and intermittent dropped beats

    • the location of the block is below AV node

    • presents greater risk of progressing suddenly to complete heart block

    • evaluate pt for placement of permanent pacemaker, else sudden death may occur

Complete (third degree) heart block

  • complete disruption of conduction between atria and ventricles, which are activated independently at different, fixed rates

  • symptoms: decreased CO

    • fatigue

    • dyspnea

    • SOB

    • syncope

  • risk for sudden death; require rx with pacemaker

Category: Pathology Notes



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