This question is asking what left dominant circulation means. I suppose it wants us to infer that the PDA is supplying the diaphragm surface and AV node.

It is confusing to me because normally the Right marginal artery supplies the diaphragmatic border (acute margin) of the heart. I'm not sure that it changes in left dominant circulation. Furthermore it would not branch off the PDA, although maybe parts of it are supplied by the PDA

Also the AV node is supplied by the Atrioventricular nodal artery, which can be a branch off of the LCA or the LCX but not really the PDA

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3537199/

so confusing question for me but the point is to know the course of left dominant circulation to the PDA

Left dominant circulation - posterior descending artery (PDA) which supplies AV node etc is coming from the *left circumflex. Prompt says it is blocked. To get to there, the correct anatomical pathway is Left coronary artery, circumflex artery, posterior interventricular (PDA).

This can be reasoned by process of elimination too. 1- Given the Left dominant circulation, we can eliminate pathways beginning at the right coronary. 2- To get blockage at posterior of heart, we will NOT use anterior interventricular artery, so you can eliminate the 2 options listing those. 3 - The circumflex artery gives rise to the PDA, but is not the final artery in our path to the blockage (so can eliminate another two). This should give you the correct answer.

Anterior (or sternocostal) – Right ventricle.

Posterior (or base) – Left atrium.

Inferior (or diaphragmatic) – Left and right ventricles.

Right pulmonary – Right atrium.

Left pulmonary – Left ventricle.

both left and right ventricles are on the diaphragmatic surface. AV node is also affected. PDA supplies posterior 2/3rd walls of both right and left ventricles and the AV nodes so we know that PDA is affected. now we need to figure out the order of cath passage. question states left dominant circulation. so itll be left coronary -> LCX -> PDA (aka posterior interventricular since PDA supplies post. 1/3 of interventricular septum)