ENSO does modulate the PNA, with La Niña winters tending to negative PNA and El Niño tending winters tending to positive PNA. However, the PNA does have high internal variability, which often dominates on shorter timescales. Michelle's post about the PNA explains this in greater detail, Tom talks about a winter where PNA variability dominated the overall impacts, and my post from last February illustrates just how large swings in the PNA can be, and how that impacts temperature and precipitation patterns.