Atypical Wenckebach interrupted by bigeminal PAC's

Is this Mobitz II?

Image 1 - Long lead II

The rhythm is sinus at a rate about 94 bpm with a long PRI or first degree AV block. The middle of the strip seemingly shows sudden onset of bradycardia. Remember that the most common cause of sudden onset of bradycardia in premature atrial complex (PAC). However, it cannot be seen in lead II.

Image 2 - Full disclosure

The full disclosure image revealed the PAC in V2 and not on the rest of the leads. There is no preferred lead to look these nibs. You have to train your eyes to spot those distortions.

The second point what this strip would teach us is the existence of atypical Wenckebach. The PRI was measure using an electronic caliper. The PRI remained prolonged (310 ms) then it increased to 320 ms then it was interrupted by a PAC's. The latter PRI are shorter then there is gradual increase in the PRI. Also remember that when the Wenckebach cycle is longer than 5:6, the PRI prolongation becomes unpredictable and does not behave your typical Wenckebach cycle where most student memorize the longer-longer drop. Atypical Wenckebach does not behave that way.

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