CORRESPONDENCE
Electrocardiogram in myocardial infarction: what is most relevant?
Elena B. Sgarbossa, MDa
a Sections of Cardiology and Critical Care Medicine, Rush Presbyterian–St. Lukes Medical Center, 1750 W. Harrison Street, Chicago, Illinois 60612, USA
Phibbs et al. (1) have recently published an interesting review article on studies comparing Q wave with non–Q wave myocardial infarction (MI). This classification of Q wave/non–Q wave gained widespread use in the prereperfusion era because the rather passive role of clinicians during the acute phase of infarction entailed awaiting Q wave development (or lack thereof) for outcome prediction in survivors. As Phibbs et al. indicated, the dichotomy of Q wave/non–Q wave is inaccurate. The "non Q" category has encompassed infarctions that have produced R-wave changes (i.e., posterior MI, decrease in R-wave amplitude) and are indeed Q wave equivalents. In addition, I believe that the main limitation of the Q/non Q dichotomy is that it erroneously polarized prognostic groups. Several authors have alerted that within the non–Q wave classification there were lumped together infarctions of the T type (which manifest in the electrocardiogram [ECG] only with T wave inversion) and of the ST type (which mainly manifest as ST segment depression) (2,3). The latter type often included patients with a previous infarction, and the underlying anatomy was usually left main occlusion or extensive coronary disease with patchy necrosis. A review of prethrombolytic studies would indicate that, from a prognostic viewpoint, most Q wave infarctions were between the T and the ST types of non–Q wave MI (4). Thus, comparisons of Q versus non–Q wave outcomes have been fraught with the problem that patients and control subjects were often included in the same study arm.
The value of the "T versus ST" classification deserves further evaluation in patients undergoing reperfusion. In a recent study we analyzed over 1,500 patients admitted to the hospital with ST segment elevation. Patients with a history of MI and Q wave equivalences were also included. In this "retrolective" analysis, the favorable prognostic significance of T wave inversion after thrombolysis was confirmed (5). When negative T waves were tested separately from non–Q waves, both variables were associated with similar 30-day survival rates. In a combined four-category plot, patients with negative T waves, but absence of Q waves (i.e., T type of non–Q wave MIs), were the most likely to survive at 30 days; patients in the opposite extreme (i.e., those without negative T waves and with Q wave MIs) were the least likely to survive. Other investigators have suggested that one possible reason for this outcome is a high prevalence of patent culprit coronary arteries (6). We also found that negative T waves were independent, powerful predictors of a nearly four times higher survival rate after adjusting for clinical variables and for new Q waves.
ST segment depression, by contrast, is known to predict cardiac events and death (7), and no benefit from thrombolysis has been shown in this group (8).
Whether or not the categorization "T type/ST type" is prospectively confirmed, the terms "Q wave" and "non–Q wave" should be redimensioned and used as one more ECG element to assist in prognostic stratification, rather than as polar categories.
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References
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1. Phibbs B, Marcus F, Marriott HJC, Moss A, Spodick DH. Q wave versus non–Q wave myocardial infarction: a meaningless distinction. J Am Coll Cardiol. 1999;33:576–582[Free Full Text]
2. Spodick DH. Comprehensive electrocardiographic analysis of acute myocardial infarction by individual and combined waveforms. Am J Cardiol. 1988;62:465–467[CrossRef][Medline]
3. Ramires JA, Serrano CV, Solimene MC, Moffa PJ, Caramelli B, Pileggi F. Prognostic significance of ST-T segment alterations in patients with non–Q wave myocardial infarction. Heart. 1996;75:582–587[Abstract/Free Full Text]
4. Sgarbossa EB, Topol EJ. Semantic ambiguity, the "non-" nosology and myocardial infarction. J Clin Epidemiol. 1994;47:441–446[CrossRef][Medline]
5. Sgarbossa EB, Pinski SL, Pavlovic-Surjancev B, et al. A new hierarchy for ECG stratification of acute myocardial infarction based in T wave polarity (abstr). Circulation. 1998;98(Suppl I):555
6. Kusniec J, Solodky A, Strasberg B, et al. The relationship between the electrocardiographic pattern with TIMI flow class and ejection fraction in patients with a first anterior wall myocardial infarction. Eur Heart J. 1997;18:420–425[Abstract/Free Full Text]
7. MILLIS Study GroupWillich SN, Stone PH, Muller JE, et al. High-risk subgroups of patients with non–Q wave myocardial infarction based on direction and severity of ST deviation. Am Heart J. 1987;114:1110–1119[CrossRef][Medline]
8. ISIS-2 Collaborative Group. Randomised trial of intravenous streptokinase, oral aspirin, both, or neither among 17,187 cases of suspected acute myocardial infarction: ISIS-2. Lancet. 1988;2:349–360[Medline]
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References