Mobitz I interrupted by a PVC

 What is the interpretation?

Figure 1 - Lead II

 

Figure 2 - Full disclosure

P waves are difficult to appreciate in all the leads except in V1. The best P wave to use as reference is the P wave after the PVC. By then you can appreciate the PR interval. The clue to the diagnosis that this is second degree AV block type I is by comparing the PRI of the last conducted P wave and that of the first conducted P wave which happens to be after the PVC. The PRI is 0.28s vs 0.20 s. After the first conducted P wave, you can then see the prolongation of the PRI. The latter PRI's remained the same but prolonged. This is a behavior of the PRI you see in atypical Wenckebach.

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