Wednesday, 3 April 2013

ECG of the Week - 1st April 2013 - Interpretation

We didn't have any clinical information on this week's ECG, but that shouldn't stop us being able to review the ECG.




 


Click to enlarge

Rate:
  • Ventricular rate 48 bpm
  • Atrial rate 66 bpm
Rhythm:
  • 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)
Axis:
  • Normal (-50 deg)
Intervals:
  • PR - Progressive prolongation (~210 - 360 ms)
  • QRS - Normal (100ms)
  • QT - 480ms (QTc Bazette ~ 480 ms)
Segments:
  • Slight concave / flat ST elevation V2-4
  • No ST depression
Additional:
  • P Wave Inversion V1,V2, aVL
    • ? V2 inversion secondary to lead placement as other P wave morphology appears normal
Interpretation:

  • AV Block
    • 2nd Degree
    • Mobitz Type I
    • Wenckebach
Clinical Implication
  • 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
Something to think about ...
 
Click on the question link to read our follow-up post on 'The Wenckebach Counter-Intuition'
References / Further Reading 

Life in the Fast Lane
  • Wenckebach Phenomenon here
  • Wenckebach Squared ECG Case here
eMedicine
  • Second-Degree Atrioventricular Block here
Textbook
  • Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.