Acute coronary syndrome (ACS) is currently classified as STEMI and NSTEMI.This classification came into vogue primarily to triage patients for thrombolysis eligibility , as ST elevation is the only criteria for thrombolysis.The earlier term non q MI is largely used to denote the present day NSTEMI. In the past q MI was referring to transmural MI non q MI to non transmural pathologically.(Of course , now we know the relationship between q waves and transmurality is not good )
So when can we still use term non q MI ?
These terminologies of STEMI and NSTEMI are made on admission at the emergency room. ACS being a dynamic entity these patients can have rapidly changing ST shifts , from depression to elevation and vice versa. Fresh T wave changes can also occur .Q waves may or may not develop , depending upon the damage sustained to the myocardium and the efficacy of thrombolysis / PCI. So it should be emphasised here STEMI, NSTEMI , q MI , non q MI are the descriptions of the same group of patients in different time frames. The common mode of evolution of STEMI is to q MI and NSTEMI into non q MI. Cross overs can occur.
The problem here is NSTEMI getting converted into STEMI is quiet common and has no nomenclature issues . But when STEMI down grades into NSTEMI there is apparent nomenclature incompatibility .This category of patients have no other labelling option other than “A STEMI evolving into non q MI”. Because one can’t label STEMI evolving into NSTEMI as many of them will have a residual ST elevation as well.
What is the final message ?
The term non q MI is still relevant and is used at discharge , in a patient with STEMI when he or she evolves without a q wave .In the setting of unstable angina , NSTEMI has largely replaced the term non q MI either on admission or at discharge.
Before I close
The important point to remember here is NSTEMI getting converted into STEMI is an adverse outcome and in fact, it is a complication and the patient should get an immediate thrombolysis or PCI , while a STEMI getting converted into non Q MI is generally a major therapeutic success.( Effective salvaging and preventing q waves )
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Dr.S.Venkatesan MD 
