CardioNerds ECG Challenge #2

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67 year-old man status post ablation for atrial fibrillation presents with this ECG​

  1. Is the 9th P wave premature?
  2. What accounts for the PR prolongation?


  1. No. The 9th P wave is not premature.​
  2. Concealed Conduction accounts for the PR prolongation.

As seen best in rhythm strip V1, all of the P waves on this tracing are equidistant and are sinus beats according to the P wave axis. The VPC that precedes the 9th P wave retrograde conducts across the AV node.  While it is not sufficient to block forward conduction of the next sinus beat, it does prolong the ensuing PR interval.​

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