IRA localization for both LAD and RCA , LCX is a fascinating exercise for cardiologists.I suspect our understanding about this crucial issue is far from complete .While localizing level of lesion within LCA or RCA requires more precise data and erring is acceptable , it is not uncommon to call even the IRA wrong especially in multi -vessel disease.
Why current criteria of IRA localisation goes awry many times ?
The factors that operate are not few . . . it runs into a dozen at least !
- Dominance is never considered during IRA localization (A right dominate system can vastly influence the LAD localization algorithm PLV branches can protect LV postero- lateral segments in spite of proximal LAD lesions )
- The length of mid LAD IS controversial entity ( Traditionally it refers to the segment between first major diagonal to second major diagonal or septal leads to faulty coronary mensuration .It is not uncommon to have a mid LAD measuring few mm when full the full length of LAD is about 15-19cm
- Diagonal vs OM trade off occurs in every alternate patient which is ignored !
- Ramus is never considered worthy enough to be included in the IRA localization scheme (In spite its presence in 20 % )
- Type of LAD is not given allowance.
- Finally & most importantly these rules of IRA localization will not apply in the setting of multivessel CAD
- In the presence of Pre existing CTO
- STEMI following chronic stable angina
- Extensive collaterals
- Re Infarctions
- Post CABG etc
Final message
Decide for yourself . . . how good is the value of IRA localization after considering all the above variable. . It is not a great thing to predict correctly RCA from LCX in an inferoposterior MI with a 70 % accuracy . (It actually means 20 % accuracy ) statistically when there are only two options . . . we are blindly right 50% of times !
Dr.S.Venkatesan MD 