Good question! I think it depends on the timing and degree of reperfusion. Wellens type A has terminal T inversion, suggesting early reperfusion after an LAD occlusion that has partially resolved. Wellens type B is likely the evolution over time after reperfusion, as the T wave inversion becomes symmetrical and complete. Steve Smith has written a really nice blog on this - hqmeded-ecg.blogspot.com/2013/11/why-we-need-12-lead-st-segment.html?m=1