NSTEMI constitutes an important sub group of ACS. In fact it forms the major group. Real world data would indicate it UA/NSTEMI could form up to 75% of all admissions for ACS in any cardiac emergency units. Risk stratification of NSTEMI is important and is available. It is one primarily with clinical features , ECG and troponin positivity. Classifying NSTEMI with reference to underlying patho anatomy is not available.
Classifying NSTEMI based on the following is is suggested .
A.Based on the extent of infarct.( For example there is no entity called extensive NSTEMI unlike STEMI)
B.Based on the Location of NSTEMI .
Currently , NSTEMI simply means there is an infarct some where in the heart ? Should we not localise it ? Is it not surprising , we have not attempted to localise NSTEMI so far ?
C.Based on the coronary anatomy : RCA NSTEMI vs LAD vs LCX NSTEMI.
The reason is two fold.
1.NSTEMI is often patchy , subendocardial . Some times only islands of infarct can occur.But , .How common is segmental NSTEMI ? May not be common, still if wall motion defect occur it must be an segmental MI.Some estimate wall motion defect in NSTEMI is around 25%.
2.Is there any clinical purpose for localising NSTEMI ?
Some would think there is no real purpose. That does not mean , we should not attempt to do it. In fact there is an important reason , we need to localise NSTEMI. Triple vessel disease , is the common pathology underlying NSTEMI. They often have multiple critical lesions as well. Identifying the the culprit lesion is not an easy task. If we know the site of infarct , however small it may be , it helps us fix the coronary artery.
A real dilemma could occur in patients with NSTEMI , who has a 90 % lesion in RCA and 50 % proximal LAD lesion . We ( tend to !) take it as granted , RCA lesion is likely to be responsible for the NSTEMI. But the real culprit could be the recannalised LAD . If it is so , the 50% LAD lesion could be more important and if you leave it free there is a strong likely hood of recurrent UA. If we could some how located the NSTEMI in the LAD region in this patient , he could get a PCI for LAD as well.
Of course , there is an universal approach available “Doing PCI for all suspected culprit lesion however mild it may be ” . Unfortunately , it increases the metal load for the patient, which is an independent risk factor for a future ACS.
How to locate NSTEMI ?
So , it is often helpful to locate NSTEMI . Of course , it needs little more efforts. A very meticulous echoc cardiography can aid in locating the subtle wall motion defects in NSTEMI . Perfusion studies/PET studies may be indicated in occasional patients.Myocardial contrast echo can be useful.
Difference between Anterior NSTEMI and inferior NSTEMEI