Carton, Daly & Ramani: Clinical Pathology 
'Ask the Author' Forum
Figures from the bookCarton, Daly & Ramani: Clinical Pathology
December 2006: Non-Q-wave myocardial infarction
Q. I find your description of acute coronary syndromes (unstable angina and NSTEMI) and STEMI really clear - the best I've read in any book. My one remaining uncertainty is how non-Q-wave MI (=subendocardial MI) fits into this classification. Is it part of ACS or STEMI or is it an old term that is no longer really used?
A. Many thanks for the question and also for your positive comments.
Q-wave and non-Q wave myocardial infarction are indeed older terms which were used before measurement of cardiac troponin became widely available as a highly specific and sensitive marker of myocardial necrosis. The terms are no longer in routine clinical use and do not fit into the new ACS/non-STEMI/STEMI classification.
Q-wave MI referred to full thickness myocardial infarction and equates to what we now call STEMI. The Q wave on the ECG is thought to represent the reciprocal R wave from the ventricular wall opposite the area of infarction; this is transmitted through to the ECG leads because the dead myocardium acts as an electrically inactive "window".
Non-Q-wave MI referred to partial thickness, or subendocardial, infarction (what we now called non-STEMI). This typically causes ST depression and T wave inversion but does not cause prominent ST elevation or the development of Q waves.
I hope this clarifies things.
James Carton
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