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 
Thanks again for an interesting article. I read another article from you just a couple of days ago which I also found very interesting. I will bookmark your blog and keep visiting!
By the way, I just started my own blog, The Ecg Blog. Have a look if you want! 🙂
Excellent explanation my dear friend….you are absolutely right, and as an experienced cardiologist at Standford, I could not have explained it more clearly, concisely and ever so eloquently. The indians do good for this world, and their techniques transends mere surgical novelty and finess. Bravo!
@ dr venkatesan ,thanks,for this excellent explanations on this point! recently I had two cases of stemi evolving to nonQ mi. both had classical history suggestive of mi first one had aw stemi on ecg with raised cardiac enzymes with positive trop -t ,was given iv stk within one hour of symptom onset .post ivstk ecgs showed st settling to isoelectric, no q developed and t inverted in the anterior leads so I feel his reperfussion was successful .the second had classical history of mi, initial 2 ecgs were normal and then showed transient st rise in anterior leads , his cardiac enzymes remained normal , serial ecgs evolved to non q mi .both remained in killip class 1 . was this second case a case of ‘prolonged’prinzmetal’s or by duration of angina [more than two hours,so presumed mi ] a case of ‘stunned’ myocardium??so they were stemi crossing over to nstemi erstwhile called nonQ mi? request your opinion especially on the second case.thanks
Hi Dr Ray
Thank you for your comments.
Yes, as you have mentioned the first patient in all probability had a very successful thrombolysis and evolved into a non q MI.
The second patient, i understand did not show any evidence for myocardial necrosis .The confusion around prinzmetal angina is
mostly due to our poor understanding about the concept of coronary spasm.I think my blog has an article on this topic.
The simple fact that , spasm if sustained , can result in infarct should be appreciated.
In the early hours of STEMI it is believed IRA must have a spastic component , the quantum of which shall determine the distal flow .
So , the final outcome can be anything between a aborted MI to full fledged QMI or Non Q mi .
Here , I would like to know the echo findings in your patient .That may throw some light.But it should be remembered , 2D echo is less sensitive to detect
WMA in non q MI. Tissue doppler velocity is supposed to help here.
Thanks again
May I know which institution are you attached
Dr Venkatesan
Chennai