Fig. 4

IMA subtypes: (A) Type I: the LCA branches first, followed by the SA and SRA ; (B) Type II: IMA first divides into one branch, which is the common branch of LCA and SA, SRA is a single branch, and then the common branch is divided into rising LCA and falling SA; (C) Type III: the LCA, SA and SRA branch from the IMA simultaneously at a node; (D) Type IV: the LCA is absent ,and the IMA divides directly into the SA and SRA