**3. Pitfalls in interpreting the VAAV/VAV response**

In order to evaluate the atrial response after V pacing, it is important to confirm that the atrium was indeed advanced during ongoing tachycardia.

Iso-arrhythmic dissociation of the ventricle at the atrial tachycardia rate may mimic 1:1 VA conduction resulting in a misdiagnosis of a VAV interval on cessation of pacing.

The next common problem is to recognise the pseudo VAAV pattern. This could occur coincidentally post ATP delivered in the ventricle with VA dissociation during an episode of AT (figure 11).

A long VA interval during an SVT as is the case in atypical AVNRT or the so called "fast-slow" variant can also yield a pseudo "VAAV" response (figure 7).
