Yes, there is heart block here but is it DEFINITELY complete? Maybe, but I just wonder if it might possibly be high-grade AV block with occasional conducted beats. Two of the beats – 2 and 5 – have QRS complexes that are different in shape from the rest. They are predominantly negative in lead II, where the rest are equiphasic or slightly positive, and they have a QRS that is predominantly positive in V2 whereas the others have slight overall negativity.

These two beats are also distinguished by ending relatively short RR intervals – 1600 ms in each case rather than 1640 or 1680 ms. So, could beats 2 and 5 be conducted beats, and the rest junctional escapes? If so, why would these 2 beats conduct when the rest cannot? It could be down to the RP interval. Perhaps, if the RP interval is long enough, the AV node has had sufficient time to recover and permit conduction. The RP intervals of the 2 beats with a different morphology are 1340 and 1400 ms, and these intervals are much longer than any of the others on the ECG. However, if these 2 beats are conducted, wouldn’t they be expected to have the same PR interval? Here the PR intervals are 260 and 200 ms but this difference can be explained again by the RP interval – the longer the RP interval, the better the AV node is able to conduct and therefore the shorter is the PR interval of conducted beats. This phenomenon is known as RP/PR reciprocity. Here an RP of 1340 ms is followed by a PR of 260 ms and an RP of 1400 ms is followed by a PR of 200 ms.

Maybe I’ve got an overactive imagination and this really is just complete heart block,
with the slight irregularity in ventricular rate perhaps due to autonomically mediated variation in the junctional discharge rate, analogous to what is seen in sinus arrhythmia, although I’m not sure this explains the different QRS morphologies.

This is a fascinating arrhythmia case with teaching points for every level provider. For less experienced clinicians — I’d be happy if their interpretation was “bradycardia with a rate in the 40s, and either high-grade or complete AV block in a symptomatic 91-year old who will probably need a pacemaker.” After all — what is important, is to recognize the severity of this bradyarrhythmia, with awareness of optimal management concerns (ie, admission to the hospital to rule out recent or acute infarction, hypothyroidism, electrolyte disturbance and/or overuse of rate-slowing antiarrhythmic medications).

I’d add “extra credit” for providers recognizing the low voltage — incomplete RBBB with LAHB — and clearly abnormal ST-T waves showing diffuse ST segment flattening with slight depression, in association with ST elevation in lead aVR > V1. More advanced providers should recognize this pattern of ST flattening and depression in multiple (more than 6) leads with ST elevation in lead aVR (and sometimes in V1) — as indicative of diffuse subendocardial ischemia. Advanced providers should know that in addition to severe coronary disease — that other entities might also produce an ECG pattern consistent with diffuse subendocardial ischemia (ie, anemia, electrolyte disturbance, hypoxemia, “sick patient”, etc.) — but given the age of this patient and the severe conduction disturbance, the likelihood of severe underlying coronary disease (albeit not necessarily recent infarction) is high.

And then there is the fascinating cardiac rhythm! On this — I completely agree with David Richley that this rhythm almost certainly is NOT complete AV block. I say this with full awareness that it is impossible for Dave and myself to prove from this single rhythm strip, that today’s rhythm is some complicated form of 2nd-degree, but NOT complete AV block.

Why then am I so sure? My attached laddergram shows my proposed theory. I’ve taken Dave’s measurements, and developed what I believe can be a plausible mechanism. I have NO doubt that variations on my laddergram are possible — but the “theme” of my proposed mechanism suggests 2nd-degree AV block with significant bradycardia because we see an underlying regular atrial rate (RED arrows) with multiple P waves that should conduct, but fail to do so.

The reasons I am all but certain that this rhythm is not complete AV block are: i) That the R-R interval (as per Dave’s measurements) is not equal (as it most often is with complete AV block); — and — ii) That there are 2 different SHAPES of QRS complexes (as per Dave) — with the preceding R-R interval before one of these shapes (ie, before beats #2 and 5) being precisely equal ( = 1,600 msec.). This is highly unlikely to be due to chance! On the contrary — one of the BEST clues I have found over the years for distinguishing between conducted vs junctional escape beats — is that QRS morphology may differ slightly for junctional escape beats compared to QRS morphology for sinus beats (felt to be the result of the impulse not necessarily arising from the same point within the AV node for junctional escape beats, compared to the path of normal sinus-conducted beats.

I illustrate my proposed mechanism with a laddergram. Regarding laddergrams — these can take some time to learn to draw — but they are EASY to understand (My ECG Blog #188 (https://tinyurl.com/KG-Blog-188 provides numerous detailed illustrations for those interested in understanding and/or learning to draw laddergrams).

That said — I found today’s arrhythmia especially challenging to draw because: i) There are no repetitive R-R intervals; ii) There appears to be dual-level AV block ( = a complex concept that I explain and illustrate in detail in my ECG Blog #347 = https://tinyurl.com/KG-Blog-347 ); and iii) While not all the same, R-R intervals are of comparable length, such that there are no “easy” answers regarding which beats are conducted by which P waves.

As a result of this challenge — I had to guess which beats might be conducting — and then try to work this out in a plausible fashion (ie, drawing this laddergram took me much longer than it usually does). I knew beats #2 and 5 were junctional escape beat (for the reasons I cite above) — and I knew that with dual level AV block, there is usually some form of Wenckebach conduction — but because of the ever-changing PR intervals, there was no “predictable” pattern.

BOTTOM LINE: As I stated earlier — there is something to learn from today’s case for every level provider. I’m happy if a complex and severe form of 2nd- or 3rd-degree AV block is recognized — with realization of the probable need for a pacemaker. And for those who love solving complex arrhythmias — this is a “fun” tracing to try your hand at. I welcome those who come up with alternative solutions to the one I propose in my laddergram.

It’s interesting that Ken and I agree that this is probably high-grade rather than complete AV block, and for the same reasons, yet the beats that I think are conducted, Ken thinks are escape beats and the beats that I think are escape beats, Ken thinks are conducted. Ken’s laddergram and explanation show very nicely that complex arrhythmias often have multiple plausible explanations and it may be difficult if not impossible, on the basis of a single ECG, to determine which is the correct one.

Whenever I see what looks like high-grade AV block with an irregular ventricular rate I always assume that the relatively early beats are conducted and the those that end longer RR intervals are escapes because this seems to make the most sense. In Ken’s explanation the 2 escape beats emerge after an interval of 1600 ms, but if this is the escape interval, why are there longer RR intervals that are not terminated by escape beats? For instance, looking at the laddergram, it seems to me that if Ken is correct that beat 2 is an escape beat, then there should be another one after a further 1600 ms rather than the conducted beat that occurs after an interval of 1680 ms.

So, I’m sticking with my explanation for now, but it’s entirely possible that there is a better, more plausible explanation still waiting to be revealed.

I thought that Drs. Richley and Grauer had pretty much exhausted the possibilities here, but while looking at Ken's laddergram, another thought came to me.

The two beats that Ken felt were PJCs may be more than that. What if Ken had only laddergrammed the PJCs that were manifest - but others were concealed? I did not create a separate laddergram, but just added a bit to Ken's. What do the three of you think of the possibility that there is a junctional parasystole and we are seeing only those beats that manage to conduct to the ventricles? It may take a bit of minor readjustment of the laddergram, but I think that is a possibility which could also explain the different QRS morphologies as well as the different R-R intervals.

Sorry - my additions did not transfer to the JPG. Let's try once more.

Trying one last time!

Another layer of complexity! I think Dr Jones’s suggestion is a theoretical possibility but its plausibility just can’t be assessed over such a short time period – we would need a MUCH longer rhythm strip. If beats 2 and 5 are indeed of junctional origin, as Ken also believes, then a parasystolic mechanism, with exit block, might explain the apparently contradictory non-appearance of junctional beats when they might otherwise be expected. And entrance block, protecting the parasytolic focus, might explain why beats 2 and 5 are early in relation to other beats. However, on the basis that high-grade AV block and a junctional parasystole feels like a statistically unlikely combination, I’m sticking with my simpler explanation!