ECG Case 090

Rate:

• Ventricular rate 42 bpm
• Atrial rate 84 bpm

Rhythm:

• Irregular atrial activity
• Short P-P (Green) followed by long P-P (Red) – see image below

• The shorter P-P interval occurs when a ventricular (QRS) complex occurs between the P waves whilst the longer P-P interval occurs when there is no ventricular (QRS) complex between the P waves
• This phenomenon is known as Ventriculophasic Arrhythmia
• 2:1 AV Block with ventricular (QRS) complexes only occurring after every second P wave

Axis:

• LAD

Intervals:

• QRS – Prolonged (160ms)

Segments:

• Subtle ST elevation leads II, III, aVL

Additional:

• RBBB Morphology

Interpretation:

• 2:1 2nd Degree AV Block
• Bifascicular block
  • RBBB + LAFB
• Ventriculophasic Sinus Arrhythmia
• Symptomatic Patient with syncope

The patient was referred to the cardiology team and had an uneventful PPM insertion.

Ventriculophasic Sinus Arrhythmia

This ECG is a nice example of ventriculophasic arrhythmia, this phenomenon can be seen in up 40% of case of complete AV block and, as in this case, can be seen with 2nd degree AV block also.
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 2011;3(1): e37 – e39

• ECG Library – Bifascicular Block
• ECG Library – AV block: 2nd degree, “fixed ratio” blocks
• Liu T, Shehata M, Wang X. Paradoxical ventriculophasic sinus arrhythmia during 2:1 atrioventricular block. Journal of Cardiology Cases 2011;3(1): e37 – e39