Atrial Rhythms

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    73 year old female with a history of supraventricular tachycardia (SVT).

    31 year old male who is asymptomatic and has a history of cardiomyopathy.

    Questions

    Question 1: Why do the 2 PACs conduct with different PR intervals? 

    Question 2: What type of SVT does this patient likely have?

    Key Findings

    -Sinus rhythm with PACs

    Coding for Boards

    -Sinus rhythm

    -Premature atrial complexes

    -Left axis deviation

    Answers

    Question 1: Both P waves occur during the relative refractory period of the AV node. The second PAC is slightly later than the first and only has mild PR prolongation. The first PAC occurs earlier with more pronounced PR prolongation.

    Question 2: The profound PR prolongation after the first PAC suggests that this beat conducts using a slow AV nodal pathway. This suggests the presence of dual AV nodal physiology and makes AVNRT the most likely type of SVT for this patient.