"In 2010 Joseph Brugada et al. published a new criterion to differentiate VT from SVT in wide complex tachycardias: the R wave peak time in Lead II . They suggest measuring the duration of onset of the QRS to the first change in polarity (either nadir Q or peak R) in lead II. If the RWPT is ≥ 50ms the likelihood of a VT very high (positive likelihood ratio 34.8). This criterion was successful in their own population of 163 selected patients and is awaiting prospective testing in a larger trial. "
In other words, if the beginning of the QRS and the peak of the complex (or trough of a downward deflecting wave) in lead II is more than 0.05 seconds, the chances are very high that you are dealing with ventricular tachycardia. If you will recall, each small box on a strip equals 0.04 of a second, or 40 milliseconds.