Wenckebach AV sequences can be interrupted and terminated by arrhythmic events. Once again, they frequently occur overnight with the times highlighted in blue.The most common interruption to Wenckebach AV sequences are non-conducted atrial ectopics.

Sinus rhythm (red arrows) with Wenckebach AV sequences (red highlight). A non-conducted atrial ectopic (yellow highlight, blue arrow) interrupts a sequence after the first complex.The non-conducted atrial ectopic frequently occurs after the dropped beat and therefore extends the pause.

Sinus rhythm (red arrows) with Wenckebach AV sequences (red highlight). A non-conducted atrial ectopic (yellow highlight, blue arrow) follows the dropped beat.Less commonly, the non-conducted atrial ectopic precedes the dropped beat and both combinations can be seen in the same patient.

Sinus rhythm (red arrows) with Wenckebach AV sequences (red highlight). In the above tracing, the non-conducted atrial ectopic follows the dropped beat (yellow highlight, blue arrow), whereas in the lower tracing, it precedes it.Concealed, non-conducted atrial ectopics interrupting Wenckebach AV sequences can result in bewildering ECG appearances.

Sinus rhythm (red arrows) with Wenckebach AV sequences (red highlight). Concealed, non-conducted atrial trigeminy marginally distort the T waves (blue arrows) and inhibit the dropped beat (red shadow arrow) thus interrupting the sequence. Below is a tracing at 12.5 mm/sec showing the repetitive pattern.An atrial triplet may also terminate a Wenckebach AV sequence.

Sinus rhythm (red arrows) with Wenckebach AV sequences (red highlight). An atrial triplet also with Wenckebach AV block (blue arrows) and aberration (yellow highlight) interrupts the sequence and the atrial ectopic provides the dropped beat.This was misdiagnosed as a ventricular couplet (green highlight).A short run of a non-conducting focal atrial tachycardia (yellow highlight) can also interrupt a Wenckebach AV sequence (red arrows, red highlight) again with the tachycardia providing the dropped beats.

When the Wenckebach AV sequence (red arrows, red highlight) is interrupted by a short run of a chaotic disorganized atrial rhythm (yellow highlight), then it is very likely that this will degenerate into paroxysmal atrial fibrillation (blue highlight).

Ventricular ectopy may also interrupt or terminate Wenckebach AV sequences.In each example, there is sinus rhythm (red arrows) with Wenckebach AV sequences (red highlight).

Ventricular ectopics (yellow highlight) have embedded concealed non-conducting sinus P waves (blue arrow). The next P wave (red stippled arrow) is also dropped. There is nocturnal sinus slowing.

A ventricular couplet (yellow highlight) with two concealed, non-conducting sinus P waves (blue arrows), which are the dropped beats of the sequence.

A ventricular triplet (yellow highlight) conceals two non-conducting sinus P waves (blue arrows) with the next beat (red stippled arrow) terminating the sequence.

Sinus rhythm (red arrows) with Wenckebach AV sequences (red highlight). A period of asystole (yellow highlight) interrupts the sequence without a dropped beat.Did you see the examples of ventriculophasic sinus arrhythmia?Harry Mond