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.

Demonstrates:

• 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 .