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==Criteria for a previous myocardial infarction==
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{{Chapter|Myocardial Infarction}}
[[Image:PathoQMeasure.png|thumb| A pathological is Een pathologische golf (''x'') is dieper dan 1/3 van de hoogte van het QRS complex (''x+y'') en breder (''d'') dan 0,04 sec.]]
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[[Image:PathoQ.png|thumb| A pathologic Q wave]]
[[Image:PathoQ.png|thumb| Een pathologische Q golf]]
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Pathologic Q waves are a sign of '''previous [[Myocardial Infarction|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'''.
Pathologic Q waves are a sign of absence of electrical activity. They can be thought of as an elecrical 'hole'. Myocardial infarction results in scar tissue that is electrically dead and therefore results in pathologic Q waves.
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The precise criteria for pathologic Q waves have been debated. Here we present the latest definition as accepted by the ESC and ACC.<cite>Alpert</cite>
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The precise criteria for pathologic Q waves have been debated. Here we present the latest definition as accepted by the ESC and ACC.<cite>Thygesen</cite>
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;Definition of a pathologic Q wave:
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;Definition of a pathologic Q wave
:Any Q wave in leads V1-V3
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:Any Q-wave in leads V2–V3 ≥ 0.02 s or QS complex in leads V2 and V3
:Q wave > or = to 30ms (0.03s) in leads I, II, aVL, aVF, V4, V4, or V6 (the Q wave changes must be present in any two contiguous lead, and be > or = 1mm in depth).
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: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)
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: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
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'''Note''': Absence of pathologic Q waves does not exclude a myocardial infarction!
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'''Notes'''
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*Absence of pathologic Q waves does not exclude a myocardial infarction!
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*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 [http://www.epi.umn.edu/ecg/mncode.pdf Minnesota Code Classification System for Electrocardiographic Findings] contains a very extensive definition of pathologic Q waves.  
 
For those interested: the [http://www.epi.umn.edu/ecg/mncode.pdf Minnesota Code Classification System for Electrocardiographic Findings] contains a very extensive definition of pathologic Q waves.  
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The Novacode system further classifies ischemic abnormalities in patients with no known history of myocardial infarction:<cite>novacode</cite>
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* High risk of ischemic injury/ Q wave MI:
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** Major Q waves: Q >= 50ms or Q >= 40 ms AND R/Q < 4,
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* Moderate risk of ischemc injury / possible Q wave MI:
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** Q >= 30 ms and ST deviation > 0.20 mV (minor Q waves with STT abnormalities)
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** Q >= 40 ms and ST deviation < 0.20mV (moderate Q waves without STT abnormalities)
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* Marginal risk of ischemic injury / possible Q wave MI:
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** Isolated T wave abnormalities
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** Minor Q waves (shallow Q < 30ms) and ST deviation < 0.15 mV
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* Low risk of ischemic injury
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** No significant Q waves or STT abnormalities
    
{{clr}}
 
{{clr}}
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==Referenties==
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==References==
 
<biblio>
 
<biblio>
 
#Alpert pmid=10987628
 
#Alpert pmid=10987628
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#Thygesen pmid=17951284
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#novacode pmid=9682893
 
</biblio>
 
</biblio>

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