Holter Monitor: Endless Loop Tachycardia

Report:

AV sequential pacemaker rhythm 75/min 1

SVEB, blocked, inhibiting atrial pacemaker 2

Ventricular pacemaker rhythm with 1:1 retrograde conduction 2

Endless loop tachycardia 120/min 3

VEB terminating the endless loop tachycardia 1

AV sequential pacemaker rhythm, decelerating 104 to 92/min 1

Comment:

The atrial paced P waves are rather flat but can be just made out in the top strips. Once the SVEB inhibits the atrial pacemaker, retrograde conduction takes place from the following paced beats, evidenced by shallow notches between the end of QRS complex and the T wave. The SVEB is only visible as a sharp peak in the last T wave of the AV sequential rhythm.

The tachycardia is, typically, at the upper (programmed) rate limit, which is usually (and in this case) 120/min. It is perpetuated by retrograde VA conduction, with retrograde P waves sensed and triggering paced QRS complexes, like in Case 13.

In the lower panel, the endless loop tachycardia is interrupted by a VEB. The VEB also has retrograde conduction, but its retrograde P wave falls within the post-ventricular atrial refractory period (PVARP) and does not inhibit atrial pacemaker. The latter effects atrial capture and abolishes retrograde conduction of the ensuing AV sequential paced rhythm.

The unit was re-programmed to VVIR mode and paroxysms of endless loop tachycardia ceased.