The Busy ECG - CardioScan Australia
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The Busy ECG

By Assoc Prof Harry Mond
August 5, 2021

This ECG was given to a Cardiologist to report and immediately returned with the comment. “Can’t report it as the ECG is too busy!”.  I am sure we all want to say this sometimes.

How do we try and work out what is going on?

Divide it into its separate components.


  • Bifascicular block – left anterior fascicular and right bundle branch block
  • Prolonged QT interval

There is also  group beating. When the QRS complexes are all the same in group beating, think of Wenckebach AV block.

  • Marked first degree AV block with the shortest PR interval 500 ms.
  • Wenckebach AV block sequences: The PR interval is longest before the dropped beat and shortest following the dropped beat (blue vertical arrow).
  • There are two sequences; 4:3 (red highlight) and 5:4 (yellow highlight).

The features are consistent with high degree AV block.

There is another feature which is almost always overlooked.

The P-P interval with the embedded QRS is shorter (740-780 ms) than the P-P interval without a QRS (820-840 ms). This is a well known physiologic phenomenon called ventriculophasic sinus arrhythmia.


Features of ventriculophasic sinus arrhythmia

  • Seen in about 50% of cases of second degree or complete AV block.
  • P-P interval with the embedded QRS complex is shorter than the P-P interval, without the QRS complex.
  • Reflex mediated: intracardiac pressures and volumes similar to sinus. Often subtle, but more obvious with marked pauses.

So you want more examples?

Wenckebach AV block

2:1 AV block

Complete heart block

Complete heart block with long pauses

Physiology and timing.

Harry Mond .

About Assoc Prof Harry Mond

In 49+ years as a practicing cardiologist, Dr Harry Mond has published 260+ published manuscripts & books. A co-founder of CardioScan, he remains Medical Director and oversees 500K+ heart studies each year.

Download his full profile here.

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