ECG of the Week: ECG of the Week - 14th January 2013

Another week of mystery.

This ECG is from a male, and that's all I've got.

Click to enlarge

Rate:

Ventricular Rate 60 bpm
Atrial rate 90 bpm

Rhythm:

Regular rhythm
Regular atrial activity
Pattern

P wave -> QRS -> P wave -> Pause -> Paced Complex + Buried P wave

Axis :

Sinus Complexes - LAD (-37 deg)
Paced Complexes - LAD (-80 deg)

Intervals - Sinus Complexes:

PR - Normal (~180ms)

QRS - Prolonged (120ms)

QT - 440ms

Intervals - Paced Complexes:

QRS - Prolonged (160ms)
QT - 520ms

Segments:

Appropriate ST segment & T wave discordant changes in both Sinus & Paced Complexes

Additional:

LBBB Morphology of Sinus Complexes

Right Ventricle Pacing

Paced Complexes have LBBB Morphology

Pacing Interval 60 bpm from Conducted QRS

If no QRS sensed 1000ms after last QRS PM will pace
Unknown if P wave following sinus QRS would have conducted with long PR or would have blocked

P waves hidden in ST segment of Paced Complexes

Unlikely to be retrograde conduction
Likely Atrial Rate is Isorhythmic to Pacing in 3:1 Pattern

Interpretation:

High Grade AV Block with Escape Ventricular Pacing
LBBB

This is an interesting ECG and I would encourage our readers to go back and read both Jason's & Christopher's comments on this ECG, they can be found here.

Question Time

VVI vs DDD ?

Christopher raised the question if you can tell whether this PPM is DDD or VVI from this ECG.
Dr Arieh Keren, has kindly come to the rescue. and gives us a brief explanation of pacing modes and their ECG morphology.
"The PM is VVI. A DDD pacemaker will be pacing the atrium if the sinus rate is below the lower rate limit only. Usually if the sinus rate is normal or above the lower rate, the way you know it's a DDD, is that you have every P wave followed by a paced QRS (A sense V pace) or a conducted QRS with a max set PR interval. (not common).

If there is a pattern to the P wave association with the QRS and it is not timing off a conducted beat like in this case, it must be dual chamber otherwise the PM can not coordinate an association."

Why is the PR Interval Normal for Sinus Complexes ?

We know we have significant conduction system disease present in this case, and yet the PR segment is normal for the conducted QRS complexes, why ?

There are essentially two non-conducted P waves preceding every conducted QRS, this allows time for AVN & HIS systems to recover

Many thanks to all our commenter's for sharing their thoughts and raising some interesting questions. Also thanks to Dr Arieh Keren, from our blogging team, for his thoughts and explanations on this ECG.

References / Further Reading

Life in the Fast Lane