ECG of the Week - 23rd October 2017 - Interpretation

The following ECG is from a 24 yr old male who presents to the Emergency Department following a sporting injury. An ECG was performed as the patient stated they had a prior cardiac history. He had undergone an EP study and ablation for pre-excitation.

Click to enlarge

Rate:

• Ventricular rate ~54 bpm
• Atrial rate ~96 bpm

Rhythm:

• Complete AV dissociation
• Variable rate ventricular rhythm
• Variable rate atrial rhythm

Axis:

• Left axis deviation

Intervals:

• QRS - Prolonged

Additional:

• RSr' pattern V2
• Slurred up-stroke QRS in leads I, aVL, V3-6
• Looks similar to a delta wave but rhythm origin is not sinus
• ? Affect of ablation or AP pathway involvement in escape rhythm
• Discordant ST depression in lateral and high lateral leads
• T wave inversion in high lateral leads
• Variable R-R interval showing ventriculophasic arrythmia

Interpretation:

• Post ablation complete heart block

The patient was well aware of his longstanding heart block and had declined a pacemaker insertion.

Post catheter ablation complications

The are a number of potential complications of RF catheter ablation including:

• Local bleeding / infection at insertion site
• Procedural failure
• Valvular injury
• Cardiac puncture +/- tamponade
• Pulmonary vein stenosis
• High grade AV block
• Additional arrhythmic focus
• VTE & CVA

Ventriculophasic Sinus Arrhythmia

Ventriculophasic arrhythmia can be seen in up 40% of case of complete AV block.
You get a shorter P-P interval when there is an associate QRS complex with a longer P-P when there is no QRS between the P waves. Several mechanisms have been proposed including  alterations in sinus node perfusion related to ventricular contraction and the mechanical effects of atrial stretch.
To make things more confusing there is a much rarer paradoxical phenomenon when the P-P is longer when a QRS is contained between them.
It is important to recognized as the P-P variability may be mistaken for other ECG features such as U waves for example.
You can read more about ventriculophasic sinus arrhythmia in this nice case report of the paradoxical version here:

• Liu T, Shehata M, Wang X. Paradoxical ventriculophasic sinus arrhythmia during 2:1 atrioventricular block. Journal of Cardiology Cases , Volume 3 , Issue 1 , e37 - e39

 References / Further Reading

Life in the Fast Lane

• Pre-excitation
• Complete AV block 

Textbook

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