Dawn...

We often think of Mobitz I blocks with Wenckebach conduction as being benign conditions that usually require no treatment at all and Mobitz II blocks as conditions requiring immediate pacemaker insertion. It is NOT the TYPE of block that makes it benign or dangerous - it is the LOCATION of the block that determines how serious it is. A Mobitz I block is usually considered benign because it is usually located in the AV node. THAT is what makes it benign. A Mobitz I block located in the infra-Hisian conduction system has the SAME PROGNOSIS as Mobitz II block.

There is also an old adage that you don't see Mobitz I block and Mobitz II block in the same tracing. This is because Mobitz I blocks usually occur in the AV node and will typically have a narrow QRS complex and Mobitz II blocks are infra-Hisian and typically have a widened QRS. I suppose the extra delay in the AV node would would allow refractoriness in the Purkinje system to resolve and avoid the Mobitz II block. I've never seen any controlled studies that either proved or disproved that adage (or even addressed it, for that matter). This would appear to disprove it. The non-conducted P waves appear to end the same R-P interval whether they are preceded by a long or short R-R interval. As a general (but NOT absolute) rule, Mobitz I blocks are usually accompanied by a 1st degree AV block.

I'm currently teaching an Advanced ECG Interpretation Boot Camp in Budapest, Hungary so I don't have any means to print out the strip and make any measurements.

Keep up the good work - and thanks for including the reference!

Dawn...

After reviewing this rhythm strip while not under the influence of jet lag, I think the most plausible explanation would be a Mobitz I block with one episode of 3:2 block and the rest 2:1 block. To make any other diagnosis would really require a longer rhythm strip and a 12-lead ECG.

Thanks for maintaining a great website.