ECG of the Week - 2nd December 2013 - Interpretation

This week's ECG is from a 68yr old female who presents complaining of palpitations intermittently over the last 4 days with a concurrent viral upper respiratory tract infection. She has a history of paroxysmal atrial fibrillation and mitral valve replacement (St Jude's) and medications include warfarin and sotalol.

You can check out the comments on our original post here.

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Given that this week's ECG is a bit of a rhythm puzzler I've included a numbered rhythm strip version to aid in peoples written descriptions (I finally remembered Ken)

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Rate:

• Atrial rate ~205 bpm
• Ventricular rate ~66 bpm

Rhythm:

• Regular atrial activity
• Irregular ventricular conduction

Axis:

• Normal (75 deg)

Intervals:

• QRS - Normal (100ms)
• QT - 320-340ms

Segments:

• ST Depression leads II, III, aVF, V4-6 

Additional:

• Atrial activity
• Positive P wave leads II, III, aVF, and V1
• Inverted P wave leads I & aVL
• Morphology - small, low voltage waves
• R-R Intervals vary without pattern

Interpretation:

• Atrial flutter with variable conduction
• Atypical micro-rentry left atrial focus
• DDx includes atrial tachycardia with variable conduction
• Distinct between flutter and atrial tachycardia principally of interest only if ablation and EP mapping required

EP Thoughts

One of our blog team electrophysiologist has looked at the ECG and made the following points.

• A two level block is a reasonable explanation but this ECG is a little atypical for that.
• 2:1 Blocks usually occur below the AV node rather than above
• Wenckeback conduction if present usually occurs at or above the AV node
• This facilitates conduction patterns such as 5:2 or 7:3
• Variable block is probably due to significant vagal changes on the AV node
• AV Node conduction is independent of atrial or ventricular activity and will vary conduction based on autonomics which vary beat to beat

What happened ?

The patient was admitted under the cardiology team. She underwent successful DC cardioversion after electrolyte replacement. Myocardial perfusion study revealed no reversible ischaemia or evidence of prior ischaemia. Recent echo revealed severe left atrial enlargement, mild right atrial enlargement, and stable appearance of the mitral valve replacement. She was discharge with ongoing cardiology follow-up.

References / Further Reading

Life in the Fast Lane

• Atrial flutter here
• Atrial tachycardia here

Textbook

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