I did a quilt with trapunto once. I had hearts that I wanted to have stand out. I put a batting behind the heart, stitched around the heart with soluble thread, the cut away the extra batting. Then I added the "real" batting behind the entire quilt. When I machined quilted it, I made sure that I stitched up close to the soluable thread in order to keep the shape of the heart. Then washed it.