What you are looking for is the and operator listed in the <<if>> macro's documentation.
Your example should look something like the following.
<<if $item1 gt 1 and $item2 gt 1 and item3 gt 1 and $item4 gt 1>>[[Unlocks this passage]]<</if>>
warning: the above example was written from memory and has not been tested, it may contain syntax errors.