The dominant side of the coronary system is determined by which artery?

• A. LAD
• B. RCA
• C. PDA
• D. LCx

Answer: (C)

Dominance in coronary circulation is defined by which artery gives rise to the posterior descending artery (PDA). The PDA runs in the posterior interventricular groove and supplies the inferior wall and posterior part of the interventricular septum. If the PDA originates from the right coronary artery, the heart is right-dominant; if it originates from the left circumflex artery, it is left-dominant. In some people, contributions from both arteries create a codominant pattern. The other arteries listed mainly supply different regions (the LAD the anterior wall and septum; the RCA/LCx contribute to their respective territories) and do not by themselves determine dominance. Therefore, the artery that defines dominance is the one that becomes the PDA.