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Pathogenesis and diagnosis of Q waves on the electrocardiogram

Author
Ary L Goldberger, MD
Section Editor
David M Mirvis, MD
Deputy Editor
Gordon M Saperia, MD, FACC

INTRODUCTION

By definition, a Q wave on the electrocardiogram (ECG) is an initially negative deflection of the QRS complex. Thus, a Q wave indicates that the net direction of early ventricular depolarization forces is oriented away from (by more than 90º) the positive axis of the lead in question. Although prominent Q waves are a characteristic finding in myocardial infarction (MI), they can also be seen in a number of noninfarct settings. Failure to appreciate the other causes of Q waves can lead to important diagnostic errors. (See "Basic principles of electrocardiographic interpretation".)

The presence of a Q wave does not indicate any specific electrophysiological mechanism. To the contrary, Q waves can be related to one or more of the following four factors (table 1) [1,2]:

Physiologic and positional effects

Myocardial injury or replacement

Ventricular enlargement

             

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Literature review current through: Aug 2015. | This topic last updated: May 12, 2015.
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References
Top
  1. Goldberger, AL, Goldberger, ZD, Shvilkin AS. Goldberger’s Clinical Electrocardiography: A Simplified Approach, 8th edition, Elsevier, Philadelphia, 2012.
  2. Mirvis, DM, Goldberger, AL. Electrocardiography. In: Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 9th ed, Bonow, RO, Mann, DL, Zipes, DP, Libby, P (Eds), W.B. Saunders Company, Philadelphia 2014.
  3. Delewi R, Ijff G, van de Hoef TP, et al. Pathological Q waves in myocardial infarction in patients treated by primary PCI. JACC Cardiovasc Imaging 2013; 6:324.
  4. Pirwitz MJ, Lange RA, Landau C, et al. Utility of the 12-lead electrocardiogram in identifying underlying coronary artery disease in patients with depressed left ventricular systolic function. Am J Cardiol 1996; 77:1289.