ECG of the Week – 3rd February 2014 – Interpretation

By | 5 februari 2014

An ECG from the archives this week. Unfortunately no clinical information on this case but at a glance it looks like a nice ‘rhythmic riddle’.
Check out the comments from our original post here.


Click to enlarge

Numbered Rhythm Strip

Click to enlarge



  • Mean ventricular rate ~72 bpm
  • Regular atrial activity ~95 bpm


  • Repeating pattern of atrial / ventricular acitivty
  • Pattern of:
    • Premature junctional complex (# 3, 6, 9, 12)
    • Sinus complex with pr interval ~200ms (# 4, 7, 10)
    • Sinus complex with pr interval ~300ms (# 2, 5, 8, 11)
    • P wave without QRS complex


  • Normal / Inferior (+90 deg)


  • QRS – Normal (100ms)
  • QT – 380ms


  • Nil ST segment change
  • Slight prominence anterior T waves


  • Group beating
  • Progressive R-R shortening prior to dropped QRS


  •  Mobitz 1 / Wenckebach (4:3 Pattern)
  • Group beating starts with Premature Junctional Complex

Check out our previous case of Wenckebach and the reason behind the PR prolongation and RR shortening seen with Wenckebach below:

 Wenckeback Recap
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 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

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

References / Further Reading

Life in the Fast Lane

  • AV Block – Mobtiz I / Wenckebach here


  • Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.

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