Bundle Branch Blocks

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    61 year old female with heart palpitations.

    61 year old female with heart palpitations.

    Questions

    Question 1: Why are the QRS complexes after the PACs wider than the others?

    Question 2: How do you know that the last 3 beats are not due to sinus tachycardia?

    Question 3: Why do the P waves often look different in the Lead II rhythm strip?

    Key Findings

    - Sinus rhythm

    - Premature atrial contractions

    - Intermittent Left bundle branch block

    Coding for the Boards

    - Sinus rhythm

    - Premature atrial contractions

    - Atrial tachycardia

    - Left bundle branch block

    Answers

    Question 1: The prematurity of the PACs results in the left bundle branch being activated during phase 3, causing aberration.

    Question 2: The abrupt change in heart rate suggests the last 3 beats are PACs, or a run of atrial tachycardia. Sinus tachycardia would result in a more gradual change in heart rate.

    Question 3: There may be several populations of PACs originating from different areas of the atrium.