God creates life  with  infinite variation .  The  heart gets  bulk of its blood supply from the left coronary  artery , which divides into two  after a short course.  Bifurcation is the rule . Left main becomes  left circumflex and LAD  in about in 85-90 %.

Note the left main divides into 3 equal caliber vessels.very lucky to have such a branching pattern !Distal left main is unloaded by three large ostia . This makes stasis of blood in left main very unlikely . LAO caudal view

 

 

Note : The OMs are small in these people. RAO caudal view

Few men and women are blessed with three branches from LCA . The anatomical and physiological importance of this  branching pattern  is not well analysed in the literature .There  could be  few advantages  of having a trifurcation instead of  bifurcation .

• Left main  impedence is less in trifurcation . This is due to the fact ,  left main empties into three distinct ostia rather than two.The combined  cross sectional area of these three ostia  confers a hydrodyamic advantage.
• The importance of  any proximal LAD lesion in these patients , is negated  by  33 % as two other vessels are there to take care the  rest of the heart.
• A large Ramus usually  supplies a vast area in the angle between LAD and LCX.  This   has a potential  to protect against ventricular  fibrillation during acute occlusion of LAD  by providing  electrical stability .

Disadvantage of trifurcation !

• It is also a fact , people with a large Ramus may have a trade off by having a diminutive diagonal or OM .
• A trifurcation with a small calibered  ramus  can often  be a disadvantage , as it is prone for atherosclerosis  since it  restricts  left main flow  by  venturi effect . (The first rule of atherosclerosis states its  prone at branching points)

* A related blog  elsewhere in my site . The explanations  offered above are based on personal observation .