If you are fortunate enough to be dealing with a long ECG strip showing regular rhythm before the VT, followed by the VT, and another longer strip with regular rhythm after the VT, then you will be able to measure P to P-intervals. The distance between the first visible P wave after the tachycardia and the last visible P wave before the tachycardia will be a multiple of one P to P-interval. This makes a lot of sense, since the sinus node and the atria keep on going while the ventricles are busy with their VT. This criterion is a sure sign of a VT. For this purpose, the entire episode of tachycardia should be documented from beginning to end, and the patient must be in sinus rhythm. As you can imagine, however, we rarely have the luxury of this scenario in routine clinical practice, but it is still a useful concept in terms of understanding VTs. And then, of course, we have to consider the fact that if the distance does not fit to our little mathematical calculation, this does not necessarily mean that it is definitely an SVT, since the sinus node is also influenced by the sympathetic nervous system. The sinus node is therefore likely to be activated during a longer lasting VT, since this is not exactly a relaxing situation for our patient.