Bundle Branch Blocks


    61 year old female with palpitations.

    61 year old female with palpitations.


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

    Key Findings

    - Atrial fibrillation with rapid ventricular response

    - Intermittent left bundle branch block

    Coding for the Boards

    - Sinus bradycardia

    - Premature atrial contractions


    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.