Mobitz II 2* AV Block

Mobitz II 2* AV block produces intermittent dropped beats without progressive lengthening of the PR interval. This means that the PR interval of the conducted beats is constant and the P-P interval is also constant. The R-R intervals are constant except the dropped beats (so not technically constant). The PR interval may be normal during conducted beats.

There may be multiple dropped beats in a row. There may be no pattern to the conduction blockade. If the patient has 2:1 AV conduction, it is impossible to differentiate between Mobitz I and Mobitz II.

The level of failure is at the His-Purkinje system, so these are almost never responsive to atropine. Mobitz II is usually (though not always) due to structural damage of the conduction system (ischemia, fibrosis) as opposed to functional suppression seen in that of Mobitz I (drugs). Because of this and the significantly higher likelihood of progression to 3* AV block, this is not considered a benign rhythm. Progression or hemodynamic compromise can be quite sudden, so one should have pads on the patient and be prepared for a sudden and unexpected decompensation.

Examples:

Further Reading:

https://litfl.com/av-block-2nd-degree-mobitz-ii-hay-block/

http://hqmeded-ecg.blogspot.com/search/label/2nd%20degree%20AV%20block%20Mobitz%20II

https://www.mayoclinicproceedings.org/article/S0025-6196(11)62080-6/fulltext