Antitachycardia Pacing

A 70 yo with h/o HTN, CAD and s/p AICD placement.

There are (fast) pacer spikes in the middle. Is this an AICD malfunction or just artifacts?

Image # 1

This is a regular monomorphic VT (RBBB + RAD) which was terminated by antitachycardia pacing or overdrive pacing (8 pacer artifacts highlighted in red box). Antitachycardia pacing (ATP) or overdrive pacing is the delivery of short burst of rapid ventricular pacing to terminate ventricular tachycardia (VT). It is usually programmed at a rate faster than the rate of the detected tachycardia.

Image # 2

In several studies, as many as 95% of the VT were terminated by ATP and is comparable to the efficacy of low-energy cardioversion.

Reference: 

Ganz L. General principles of the implantable cardioverter-defibrillator. In: UpToDate, Olshansky B (Ed), UpToDate, Waltham, MA (Accessed on July 28, 2015)