Pathologic Q Waves

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This is part of: Myocardial Infarction
A pathologic Q wave

Pathologic Q waves are a sign of previous myocardial infarction. They are the result of absence of electrical activity. A myocardial infarction can be thought of as an elecrical 'hole' as scar tissue is electrically dead and therefore results in pathologic Q waves. Pathologic Q waves are not an early sign of myocardial infarction, but generally take several hours to days to develop. Once pathologic Q waves have developed they rarely go away. However, if the myocardial infarction is reperfused early (e.g. as a result of percutaneous coronary intervention) stunned myocardial tissue can recover and pathologic Q waves disappear. In all other situations they usually persist indefinitely.

The precise criteria for pathologic Q waves have been debated. Here we present the latest definition as accepted by the ESC and ACC.[1]

Definition of a pathologic Q wave
Any Q-wave in leads V2–V3 ≥ 0.02 s or QS complex in leads V2 and V3
Q-wave ≥ 0.03 s and > 0.1 mV deep or QS complex in leads I, II, aVL, aVF, or V4–V6 in any two leads of a contiguous lead grouping (I, aVL,V6; V4–V6; II, III, and aVF)
R-wave ≥ 0.04 s in V1–V2 and R/S ≥ 1 with a concordant positive T-wave in the absence of a conduction defect

Notes

  • Absence of pathologic Q waves does not exclude a myocardial infarction!
  • Lead III often shows Q waves, which are not pathologic as long as Q waves are absent in leads II and aVF (the contiguous leads)

For those interested: the Minnesota Code Classification System for Electrocardiographic Findings contains a very extensive definition of pathologic Q waves.

The Novacode system further classifies ischemic abnormalities in patients with no known history of myocardial infarction:[2]

  • High risk of ischemic injury/ Q wave MI:
    • Major Q waves: Q >= 50ms or Q >= 40 ms AND R/Q < 4,
  • Moderate risk of ischemc injury / possible Q wave MI:
    • Q >= 30 ms and ST deviation > 0.20 mV (minor Q waves with STT abnormalities)
    • Q >= 40 ms and ST deviation < 0.20mV (moderate Q waves without STT abnormalities)
  • Marginal risk of ischemic injury / possible Q wave MI:
    • Isolated T wave abnormalities
    • Minor Q waves (shallow Q < 30ms) and ST deviation < 0.15 mV
  • Low risk of ischemic injury
    • No significant Q waves or STT abnormalities


References

  1. Thygesen K, Alpert JS, White HD, Jaffe AS, Apple FS, Galvani M, Katus HA, Newby LK, Ravkilde J, Chaitman B, Clemmensen PM, Dellborg M, Hod H, Porela P, Underwood R, Bax JJ, Beller GA, Bonow R, Van der Wall EE, Bassand JP, Wijns W, Ferguson TB, Steg PG, Uretsky BF, Williams DO, Armstrong PW, Antman EM, Fox KA, Hamm CW, Ohman EM, Simoons ML, Poole-Wilson PA, Gurfinkel EP, Lopez-Sendon JL, Pais P, Mendis S, Zhu JR, Wallentin LC, Fernández-Avilés F, Fox KM, Parkhomenko AN, Priori SG, Tendera M, Voipio-Pulkki LM, Vahanian A, Camm AJ, De Caterina R, Dean V, Dickstein K, Filippatos G, Funck-Brentano C, Hellemans I, Kristensen SD, McGregor K, Sechtem U, Silber S, Tendera M, Widimsky P, Zamorano JL, Morais J, Brener S, Harrington R, Morrow D, Lim M, Martinez-Rios MA, Steinhubl S, Levine GN, Gibler WB, Goff D, Tubaro M, Dudek D, and Al-Attar N. Universal definition of myocardial infarction. Circulation 2007 Nov 27; 116(22) 2634-53. doi:10.1161/CIRCULATIONAHA.107.187397 pmid:17951284. PubMed
  2. Rautaharju PM, Park LP, Chaitman BR, Rautaharju F, and Zhang ZM. The Novacode criteria for classification of ECG abnormalities and their clinically significant progression and regression. J Electrocardiol 1998 Jul; 31(3) 157-87. pmid:9682893. PubMed
  3. Alpert JS, Thygesen K, Antman E, and Bassand JP. Myocardial infarction redefined--a consensus document of The Joint European Society of Cardiology/American College of Cardiology Committee for the redefinition of myocardial infarction. J Am Coll Cardiol 2000 Sep; 36(3) 959-69. pmid:10987628. PubMed