Bundle Branch Blocks

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    64 year old male who is asymptomatic.

    64 year old male who is asymptomatic.

    Questions

    Question 1: Why are the PR intervals of the PACs slightly longer than the rest of the PR intervals?

    Question 2: Why are the QRS complexes after the PACs wider than the others?

    Key Findings

    - Sinus bradycardia

    - Premature atrial contractions

    - Intermittent left bundle branch block

    Coding for the Boards

    - Sinus bradycardia

    - Premature atrial contractions

    - Rate related aberration

    Answers

    Question 1: The slight prematurity of the PACs occurs when the AV node is still slightly refractory, resulting in subtle prolongation of the PR interval.

    Question 2: The slight prematurity of the PACs results in the left bundle branch being activated during phase 3, causing aberration.