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Ischemia Injury & Infarction

12 Lead Ischemia, Injury and Infarct 1

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Ischemia, Injury & Infarction• Definitions• Injury/Infarct Recognition• Localization & Evolution• Reciprocal Changes• The High Acuity Patient


The Three I’s• Ischemia• lack of oxygenation• ST segment depression or T wave inversion• Injury• prolonged ischemia• ST segment elevation• Infarct• death of tissue• may or may not show a Q wave


Review of WaveformComponents


Waveform ComponentsR Wave• First positivedeflection• R wave includes thedown strokereturning to thebaseline


Waveform ComponentsQ Wave• First negativedeflection before theR wave• Q wave includes thenegative downstroke and return tobaseline


Waveform ComponentsS Wave• Negative deflectionfollowing the R wave• S wave includesdeparture from andreturn to baseline


Waveform ComponentsQRS• Q waves• Can occur normally in several leads• Normal Q waves called physiologic• Physiologic Q waves• < .04 sec (40ms)• Pathologic Q• >.04 sec (40ms)


Waveform ComponentsQRS• Q wave• Measure width• Pathologic if greater than or equal to 0.04seconds (1 small box)


Waveform ComponentsQS Complex• Entire complex isnegatively deflected• No R wave is present


Waveform ComponentsJ-Point• Junction betweenthe end of QRS andbeginning of STsegment• Where QRS stopsand makes a suddensharp change indirection


Waveform ComponentsST Segment• Segment betweenJ-Point and beginningof T wave


Waveform ComponentsST Segment• Need reference point• Compare to TP segment• DO NOT use PR segment as reference!


Waveform ComponentsPracticeFind the J Point and ST segment


Waveform ComponentsPracticeJ POINTSST SEGMENT


Injury/Infarct RecognitionWell Perfused MyocardiumEpicardial Coronary ArterySeptumLateral Wall of LVInterior Wall of LVPositive Electrode


Injury/Infarct RecognitionNormal ECG


Injury/Infarct RecognitionIschemiaEpicardial Coronary ArterySeptumLeftVentricularCavityLateral Wall of LVPositive ElectrodeInterior Wall of LV


Injury/Infarct Recognition• Ischemia• Inadequate oxygen to tissue• Represented by ST depression orT inversion• May or may not result in infarctor Q waves


Injury/Infarct RecognitionST Segment Depression


Injury/Infarct RecognitionInjuryThrombusIschemia


Injury/Infarct Recognition• Injury• Prolonged ischemia• Represented by ST elevation• referred to as an “injury pattern”• Usually results in infarct• may or may not develop Q wave


Injury/Infarct RecognitionST Segment Elevation


Injury/Infarct RecognitionInfarctInfarcted AreaElectrically SilentDepolarization


Injury/Infarct Recognition• Infarct• Death of tissue• Represented by Q wave• Not all infarcts develop Q waves


Injury/Infarct RecognitionQ Waves


Injury/Infarct RecognitionThrombusInfarcted AreaElectrically SilentIschemiaDepolarization


Injury/Infarct Recognition• What to Look for:• ST segmentelevation• Present in two ormoreanatomicallycontiguous leads


Injury/Infarct Recognition:PracticeLook at J points and ST segments


LocalizationIIIIIIaVRaVLaVFV1V2V3V4V5V6Inferior: II, III, AVFSeptal: V1, V2Anterior: V3, V4Lateral: I, AVL, V5, V6


LocalizationWhich coronary arteries are mostlikely associated with each group ofcontiguous leads?I LateralaVRV1 SeptalV4 AnteriorII InferioraVL LateralV2 SeptalV5 LateralIII InferioraVF InferiorV3 AnteriorV6 Lateral


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