ECG of the Week - 25th May 2015 - Interpretation

I don't have any clinical information on this case unfortunately. I think at first glance it's not a very interesting ECG but on closer inspection is a bit more interesting.
Check out the comments on our original post here.

Click to enlarge

Rate:

• 102 bpm

Rhythm:

• Regular
• Sinus Rhythm
• Alternating QRS Morphologies
• See annotated ECG below

Annotated ECG showing two distinct QRS morphologies in an alternating pattern
Click to enlarge

Axis:

• Normal
• All complexes

Intervals - QRS Complexes Labelled in Red

• PR - Short at ~110ms
• QRS - Normal at 100ms
• QT - 340ms

Intervals - QRS Complexes Labelled in Green

• PR - Normal at ~140ms
• QRS - Normal at 80ms
• QT - 320ms

Additional:

• Alternating variation in QRS voltages
• Alternating variation in T wave voltages in right precordial leads
• Subtle delta waves seen in the complexes labelled red in the right precordial and inferior leads

Interpretation:

• Alternating pre-excitation / accessory pathway conduction with sinus conduction

The EP members of our team agree this is likely a weak left sided pathway with classical intermittent pre-excitation which usually confers a benign prognosis in the setting of atrial fibrillation.

For a great overview article on pre-excitation and paroxysmal SVT check out:

Almendrala J, Castellanosa E, Ortiza M. Paroxysmal Supraventricular Tachycardias and Preexcitation Syndromes. Rev Esp Cardiol. 2012;65:456-69. Full text here.

Thanks to Dr S Razak for recommending this article.


References / Further Reading

Life in the Fast Lane

• Pre-excitation Syndromes

Textbook

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