Complex sentence: Open communion is generally practiced in churches where the elements are passed through the congregation (also called self-communication), but may be practiced by those that utilize a communion procession; such is the case in the Episcopal Church (USA).
Split into simpler sentences: Open communion is generally practiced in churches where the elements are passed through the congregation (also called self-communication). However, it is also practiced in some churches that have a communion procession, where the congregation comes forward to receive communion in front of the altar; such is the case in the Episcopal Church (USA).