The Q-wave and non-Q wave myocardial infarction: Differences and similarities

Abstract

I T IS STANDARD medical practice to divide myocardial infarctions into two types: the “transmural” infarction and the “nontransmural” or “subendocardial” infarction. Clinically, this distinction is made on the basis of the occurrence of new Q waves on the ECG. Customarily, if only ST segment or T wave changes occur without the development of Q waves, the infarction is classified as subendocardial, whereas those infarcts accompanied by new Q waves are considered to be transmural. Recently, however, there has been a major reevaluation of the differentiation between transmural and subendocardial myocardial infarctions.‘-3 The prognosis of patients sustaining subendocardial infarcts has traditionally been regarded as better than patients with transmural infarcts”; however, several recent studies have not supported this view.8-‘2 Even the value of the ECG criteria has been questioned because of the lack of specificity of the Q wave in identifying the transmural extent of infarction.‘3,‘4 The traditional view has been based primarily on the concept that since a smaller amount of myocardium is involved in a subendocardial infarct, the overall effect on left ventricular function is less. In addition, the in-hospital mortality for subendocardial infarcts was thought to be less. However, it is now increasingly clear that the outer myocardial layers remain in jeopardy after a subendocardial infarction, exposing the patient to the risk of a subsequent event following hospital discharge. Similarly, the validity of the Q wave to estimate the transmural depth of infarction, and by inference, to predict the likely shortand long-term course of such patients has been reevaluated as well. Is there enough evidence to support the continued use of the terms subendocardial and transmural and what are the consequences for patient management?