ECG of the Week - 7th October 2013 - Intepretation

This is one of the older ECG's I've got in my collection and as such I've got very little clinical information on the case except it is from a 71 year old female.
Please check out the great comments from our readers  on this ECG at our original post here.

Click to enlarge

Rate:

• Mean ventricular rate 132 bpm across ECG

Rhythm:

• Initial sinus rhythm
• Second ventricular complex preceded by p wave
• Best seen in lead II
• Followed by premature atrial complex
• Notching of T wave best seen in lead II
• Remainder of the ECG shows a regular broad complex tachycardia
• Rate ~ 135 bpm

Axis:

• LAD (-45 deg)

Intervals:

• QRS - Prolonged (120ms)
• QT - 345 ms (QTc Bazette ~ 430 ms)

Segments:

• Discordant ST / T wave change

Additional:

• Concordant positive T wave in V6
• Isoelectric segments appear flat
• LBBB morphology
• Morphology of sinus complex is the same as tachycardic rhythm

Interpretation:

• Supraventricular tachycardia with pre-existing bundle branch block.

So what's the rhythm ?

Our blog team electrophysiologists have looked over this ECG and their consensus opinion is that this is likely a typical slow-fast AVNRT.

Potential other differentials include atrial flutter with 2:1 block, AVRT with concealed accessory pathway, or atrial tachycardia with long 1st degree AV block, although all are felt to be less likely.

What happened next ?

This did:

Click to enlarge

The patient is now in sinus rhythm with borderline 1st degree AV block. This ECG shares the same QRS morphology as the initial ECG, with ongoing concordant positive T wave in V6. 
I unfortunately don't know whether the reversion to sinus rhythm was secondary to medical intervention or occured spontaneously.

References / Further Reading

Life in the Fast Lane

• Left Bundle Branch Block here
• VT vs SVT here
• SVT here

Textbook

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