Which lead for Q-T interval measurements?

There are several Q-T interval measures (individual lead, mean Q-T interval or Q-T dispersion) from a 12-lead ECG. Which should be used? As the ECG provides twelve different measures of the heart's "true" Q-T interval, and as, "a priori", no one measure is any better or worse than any other measure at estimating the "true" Q-T interval, the best measure is the average of these twelve measures, i.e., the mean Q-T interval. The best single lead to measure the Q-T interval is the lead that relates most closely to the mean Q-T interval which in 49 subjects with cardiac diseases was lead V(3), then lead II. The longest lead Q-T interval relates poorly to the mean and to the individual lead Q-T intervals and therefore carried information different to and quite unique from these measures. This unique information is Q-T dispersion which relates well to the longest lead Q-T interval (r = 0.71, p < 0.001).