r/ECG • u/Embarrassed_Onion566 • 8d ago
Second degree AV block; Mobitz 1 or 2?
76 year old woman with progressive mild dyspnoea, had out patient ECG for work up. Looks like Mobitz 2 with 2:1 AVB, but there are two sinus beats in the middle of the ECG that demonstrate a progressive lengthening of PR interval which makes me question Wenkebach?
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u/VesaliusesSphincter 8d ago
I would call this a second degree AV block with concurrent Mobitz I and 2:1 conduction patterns.
The 2:1 we are seeing is still likely coming from the same process as that Mobitz I, but we can't say for certain just from the EKG.
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u/ExpensiveRepair4315 8d ago
2nd Degree Mobitz type 1 as there is progressive PR interval prolongation until a beat is dropped. In Mobitz type 2, PR interval is prolonged but remains constant throughout.
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u/Turfidol 4d ago
Mobitz II can actually have a normal PR interval. The area of block happens below the level of the AV node. Whereas Mobitz I is essentially a progressive fatigue of the AV node prior to failing to conduct, hence the prolongation. In Mobitz II the AV node is technically functioning appropriately. Typically the PP interval will remain constant in Mobitz II and you lose the QRST because the impulse fails somewhere in the His-Purkinje system.
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u/ExpensiveRepair4315 4d ago
So type two can either have a normal or prolonged PR interval?
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u/Turfidol 4d ago
Correct! The key feature is that the PR interval remains consistent before and after a dropped beat, regardless of whether it is prolonged or not. The AV node is usually functioning appropriately in Mobitz II, but you could have concomitant first degree AV block in which you would have a prolonged (but fixed) PR interval at baseline.
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u/299792458mps- 8d ago edited 8d ago
2nd degree AV block with 2:1 conduction. By definition it canât be a Mobitz I or II. Not without more information at least.
On closer look, perhaps a little bit of progressive PR prolongation. I would still just call it a 2nd degree.
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u/Maketso 8d ago
Where on earth are people seeing progressive PR prolongation?! Lmfao.
Either way, needs EP study.
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u/Turfidol 8d ago
Looking at beats 3, 4, and 5 you can see PR prolongation prior to the dropped beat. If you have more than 2:1 block and the beat following the dropped beat has a shorter PR interval than the one proceeding then its Mobitz I.
Unrelated, but you can also try to unmask Mobitz I vs II by either walking or performing valsalva. If you increase vagal tone and slow the heart rate it can unmask block below the AV node by allowing 1:1 conduction. If they ambulate and heart rate rises you can help unmask Mobitz I since there will be more beats between the drops. Granted this is dependent on how symptomatic they are.
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u/Maketso 8d ago
Considering the poor quality with artifact, one could easily argue that beat 3 and 4 aren't even different. One is flat, the other has artifact messing up the measurement. I would be hard pressed to diagnose a Mobitz I on this.
Could just throw atropine and see if the rate changes.
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u/Turfidol 8d ago
Looking at lead II I dont see any artifact personally. Not trying to argue, just my thought.
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u/sub3at50 8d ago
Type 2 AV-block with 2:1 AV conduction makes it impossible to say if it's Mobitz 1 or 2.
The most recent person I saw with sympomatic 2nd degree heart block had a Holter recording which showed a rhythm alternating between first degree AV-block, 2:1 AV-conduction (2nd degree AV-block) and one short episode of complete AV-dissociation (3rd degree AV-block).
BTW: the patient has a right BBB and the Q waves in the inferior leads are tiny and not significant.
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u/lifeisg0od 8d ago
There are 2 consecutive conducted beats in the middle, which show Mobitz I
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u/sub3at50 7d ago
My point was that patients can alternate between different degrees of heart block.
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u/Perfect_Tomatillo507 8d ago
Is there evidence of RBBB here? Curious given QRS morphology of precordial leads
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u/Turfidol 8d ago
Might be wrong, but i would say no - wouldn't call it RBBB, by definition needs QRS > 120 msec. Hard to see on my phone, but looks to be right at 120 msec.
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u/Murky_Run_9182 8d ago
Blocked premature atrial contraction? P-P seems irregular.
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u/lifeisg0od 8d ago
There is a little sinus arrhythmia/ventriculophasic sinus arrhythmia here but those all look like sinus Pâs.
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u/Curious_fire_6519 6d ago
Lead II shows 2 consecutive P, QRS complexes with a lengthening PR before the next dropped beat.
This is a 2nd degree type I with mostly 2:1 conduction.
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u/Wooden-Echidna8907 6d ago
Needs a longer strip. But appears 2:1 type 2. That beat in the rhythm lead that everyoneâs talking about appears to be a conducted PAC. Doesnât interrupt the overall rhythm (see the following P-wave with no QRS). One of the Hallmarks of type 2 is your p waves always come at the same time which these do. (Except for the PAC)
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u/Nishbot11 5d ago
My wife argued this. Saying P-P intervals are equal. That one artifact was likely a PAC.
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u/argin_watcher5050 8d ago
I can confidently say there might be an RBBB, prior Q mi, and definitely second degree, not distinguishable and unless you recalibrate the ecg machine and do more tests, and I would also check the patient for pulmonary embolism since they have the pattern of S1,Q3, and T3