ECG of the Week - 4th November 2013 - Interpretation

Unfortunately I've got no clinical information on this case but the ECG looks interesting.

Click to enlarge

A numbered version of this ECG can be found below.

Click to enlarge

Rate:

• Mean ventricular rate 72 bpm
• Sinus rate 100bpm
• Junctional rhythm rate 60 bpm

Rhythm:

• Two distinct rhythms
• Complexes # 1,2,6,7,8,12 = Junctional rhythm
• P wave does precede complex #8 but pr too short for sinus
• Complexes # 3, 4, 5, 9, 10, 11 = Sinus rhythm

Axis:

• Normal (55 deg)

Intervals:

• PR - Normal (~160ms)
• Complexes # 3, 4, 5, 9, 10, 11
• QRS - Normal (80ms)
• QT - 340-360ms

Segments:

• ST Elevation lead aVR
• ST Depression upsloping leads II, aVF, V3-6
• PR Depression leads aVF, V3-6
• PR Elevation lead aVR

Additional:

• P-P Interval ~600ms
• Pause between P waves preceding complex #5 to complex #8 is 3000ms
• Pause interval 5 x P-P interval

P-P Intervals labelled
Click to enlarge

• Notching following T wave leads V4-6 ? Atrial vs U wave
• Prominent T waves leads II, V2-5
• QRS Morphology almost identical between sinus and non-sinus beats.

Interpretation:

• Sinoatrial exit block
• ? 2nd degree type II SA exit block
• Fixed sinus P-P interval 
• Pause duration is a multiple of sinus P-P interval 
• Sinus pause less likely given duration length in relation to P-P interval

Given I don't have any clinical information on this case there are several potential causes for these ECG findings, including:

• High vagal tone
• Drug toxicity especially digoxin
• Ischaemia
• Myocarditis
• Sick sinus syndrome
• Electrolyte disturbance

References / Further Reading

Life in the Fast Lane

• Sinoatrial Exit Blocks here
• Junctional Rhythm here

Textbook

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