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Rate:
- Ventricular rate 48 bpm
- Atrial rate 66 bpm
- Sinus
- Regular atrial activity
- P-P interval relatively fixed
- R-R interval progressively shortens
- Progressive PR prolongation culminating in a non-conducted p wave
- 4:3 & 3:2 relationship (atrial:ventricular activity)
- Normal (-50 deg)
- PR - Progressive prolongation (~210 - 360 ms)
- QRS - Normal (100ms)
- QT - 480ms (QTc Bazette ~ 480 ms)
- Slight concave / flat ST elevation V2-4
- No ST depression
- P Wave Inversion V1,V2, aVL
- ? V2 inversion secondary to lead placement as other P wave morphology appears normal
- AV Block
- 2nd Degree
- Mobitz Type I
- Wenckebach
- I don't have any clinical information on this case, so I don't know the likely cause or outcome.
- Type I second-degree AV block
- Can occur during sleep in healthy people
- It is NOT normal during waking hours
- Can result in significant exercise limitation if occurs during waking hours
- Symptomatic patient may require atropine +/- chemical +/- electrical pacing.
- Cardiology referral should be made for patients found to have a Wenckebach conduction for specialist opinion on management, further investigation, and PPM consideration
Multiple causes, as Clare had pointed out in her comments, which include:
- Ischaemia / Infarction
- Drugs - anti-arrhythmic, lithium, alcohols
- Inflammatory - myocarditis, endocarditis, Lyme's disease
- Metabolic
- Infiltrative diseases - amyloid, sarcoid
- Obstructive Sleep Apnoea
- Athletic Heart
Features of Wenckebach
Thanks to Jason for highlighting the cardinal features of Wenckebach which are:
- Progressive PR lengthening resulting in non-conducted P wave
- Progressive R-R interval shortening
- R-R interval length of dropped beat less than twice shortest R-R cycle
- Grouped beating
Click on the question link to read our follow-up post on 'The Wenckebach Counter-Intuition'
Life in the Fast Lane
- Second-Degree Atrioventricular Block here
- Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.
The amount the PR interval prolongs becomes less with each beat, leading to the shortening R-R interval (presuming a fixed P-P).
ReplyDeleteI found it to be an abstract concept to wrap my head around at first!
If you think of the R-R in terms of the PRi, it is a bit easier. With a fixed PRi you have a fixed R-R (we'll assume a fixed P-P). If you simply have a longer PRi the R-R does not change, and the same goes for a shorter PRi.
The PRi dictates when the R's occur relative to the P's.
If you vary the PRi from beat-to-beat, then you'll change when the R's occur from beat-to-beat. If you change when the R's occur, you'll change the R-R.
Going back, constant PRi's do not affect the R-R. Thus the amount which varies from beat-to-beat is the change in the R-R.
In AV Wenckebach the amount of beat-to-beat prolongation which occurs lessens (or stays the same), with the largest delta-PRi occurring in the first beat (e.g. 200ms, 260ms, 290ms, 310ms, drop; deltas of 60, 30, and 20). So, if the amount we vary decreases with each beat, the R-R will decrease with each beat.
Put in math form, assuming k is our baseline PRi and we have a repeating series of PRi's:
PRi := { k, k60, k90, k110, k, k60, ... }
The n'th R-wave (we'll ignore drops, and P is the PP interval):
R_n := nP + PRi_n
With an R-R:
RR_n := R_n+1 - R_n
:= ((n+1)P + PRi_n+1) - (nP + PRi_n)
:= (n+1)P - nP + PRi_n+1 - PRi_n
:= P + (PRi_n+1 - PRi_n)
If you plug in the PRi's in order you'll find you get a decremental series:
RR := { P + 59k, P + 30k, P + 20k, ... }
I hope that helps others understand it, I had to draw it a lot when I first noticed the decreasing R-R's.
(apologies if the math formats oddly)