Interesting tracing! I will highlight some additional comments:

i) The atrial rate is actually not completely regular when measured with calipers (at least not in the earlier part of the tracing). It is common with 2nd or 3rd degree AV block to encounter some irregularity of the atrial rate — called “ventriculophasic sinus arrhythmia”. Typically, the somewhat longer P-P intervals occur away from QRS complexes (thought to be the result of reduced perfusion, because these beats are not near QRS complexes) — and that is what we see here.

ii) Although the QTc does appear to be long — I calculate it at less than 549 msec., especially when corrected for the exceedingly slow ventricular rate. That said, clear distinction of both the P-P interval (beginning and end of P waves) — separation from U waves that may be present — and, distinction of ECG waveforms from artifact (which is prominent in several leads) — are all difficult to assess on this tracing. The presence of both bundle branch block and bradycardia make determination of the significance of the long QT that we see challenging. My suspicion is that improvement of the ventricular rate is likely for the most part to resolve the problem with the QT here — but additional monitoring and follow-up would be needed to know this with any certainty.

iii) I would describe the AV conduction disorder a bit differently. There clearly is 2nd-Degree AV Block — since sinus P waves that should conduct do not. I would further qualify this AV conduction disturbance as “High-Grade AV Block” — since consecutive P waves are not conducted (there is 3:1 AV conduction — with only one out of every 3 P waves being conducted). But we can not with certainty distinguish between Mobitz I vs Mobitz II on the basis of this single tracing — because we never see 2 consecutively conducted P waves in a row. Therefore, we cannot tell if the PR interval would increase if given a chance to do so … Although Mobitz I usually does not manifest with consecutively nonconducted P waves — it can do so on occasion. And it is also possible for Mobitz I to be associated with underlying RBBB. Failure to appreciate the need for at least some consecutively conducted QRS complexes on a tracing to define the rhythm as Mobitz II predisposes to misclassification of this conduction defect.

iv) Statistically, Mobitz I is far more common than Mobitz II 2nd-Degree AV Block. Although I’ve never seen statistics on this — in my experience, well over 90-95% of all 2nd-Degree AV Blocks are of the Mobitz I variety. The reason it is so important to recognize the minority that are true Mobitz II blocks, is the disturbing tendency of Mobitz II to sometimes very suddenly progress to ventricular standstill — which is why pacing of Mobitz II is essential.

v) Practically speaking — it does not matter in this case whether the conduction disturbance is Mobitz I or Mobitz II — since regardless, there is high-grade AV Block with marked bradycardia in an elderly woman with syncope. Assuming there is no readily correctable cause — pacing will almost certainly be needed.

vi) As per Dawn — QRS morphology is consistent with complete RBBB. Assessment of ST-T wave changes does not suggest acute or recent MI — although deeper-than-usual lateral Q waves are seen in leads I and aVL, and this could reflect a prior event.

It is a shame we do not have additional tracings and follow-up on this patient …

===============

NOTE: For those interested in review of the AV Blocks — Please check out my hour-long ECG Video on this topic — www.avblockecg.com — If you click on SHOW MORE at this link (under the video), you’ll see a detailed linked Contents to all in the video.