Bridge passive - Any passive ability from a non-equipped weapon that synergizes between one attribute from equipped weapon A and one attribute from equipped weapon B.
Next, lets assume you wanted Pistols as one of your weapons in part because you want your playstyle to revolve around crits, hindering (snares/roots), and weaken (debuffs). Blood is there primarily for heals, but you know that various healing abilities from Blood are likely to also induce Impairment effects, Affliction effects, and to improve the likelyhood of Penetrating hits. So you want to look for ways to synergize your Pistols when such things happen as a result of your chosen Blood abilities.
The green boxes in the chart show you exactly where to look for bridge passives that can create this type of synergy between Blood and Pistols. The weapons containing such bridge passives in this case are Shotgun, Elemental Magic, Hammers, and Chaos Magic.
So, since crits and hindering are two key elements of the playstyle you're going for (i.e., a "crit-hindering build"), the chart above tells you that the best places to look for bridge passives that will suit your build are in Elemental Magic and Hammers. Elemental shows a bridge between Affliction and both Crit and Hindering. Hammer shows a bridge between Impair and Crit.
So we go poking around in the ability wheel cells for Elemental Magic, and what do we find as a cheap, easy to acquire passive bridge in one of the inner "basic" rings for Elemental Magic? Why, this little gem:
Mind over Matter (passive)
Your critical hits cause the target to be Afflicted with a damage over time effect which deals 7 magical damage every second for 5 seconds.
Even better, this passive ability is the very first ability in the cell, so you can buy it for practically nothing. Just a minor blip in your AP that you're mostly spending on Pistol and Blood abilities at first. So for a simple, cheap investment in one single ability from Elemental Magic, you now have a bridge passive that will apply an Affliction DOT every time you make a critical hit from your Pistols. And there are sure to be some Blood Actives and passives that will do many nice things when used on an Afflicted target.