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12-Lead 12-Lead EKGEKG

MEPN Level MEPN Level IVIV

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• Discuss the changes in T wave and ST segment morphology with an MI

• List the criteria for identification of right or left bundle branch blocks.

• List the anatomically congruent leads associated with an inferior, lateral and anterior wall MI

• Describe morphology of Q wave presence

OBJECTIVESOBJECTIVES

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ECG LeadsECG Leads

• 6 limb leads (frontal plane)6 limb leads (frontal plane)– 3 bipolar leads– 3 unipolar leads

• 6 precordial leads (horizontal plane)6 precordial leads (horizontal plane)– V1 – V6

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Lead IRA (-) to LA (+)

Lead IIRA (-) to LL (+)

Lead IIILA (-) to LL (+)

Einthoven’s TriangleEinthoven’s Triangle

Limb LeadsLimb LeadsBIPOLARBIPOLAR

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AUGMENTED (UNIPOLAR) LEADSAUGMENTED (UNIPOLAR) LEADS

Augmented leads combine 2 leads together (the null point) from the center point of the triangle with one positive pole.

aVRaVR (Augmented Voltage Right Arm positive) is a combination of bipolar Leads I and IIaVLaVL (Augmented Voltage Left Arm Positive) is a combination of I and IIIaVF aVF (Augmented Voltage Left Foot positive) is a combination of Bipolar Leads II and III

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I & AVL

II, III & AVF

WHAT ARE THE LEADS

LOOKING AT?

LIMB and AUGMENTEDLEADS

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Precordial Lead PlacementPrecordial Lead Placement

V1 – 4th intercostal space right of sternumV2 - 4th intercostal space left of sternumV4 – 5th intercostal space midclavicular lineV3 – midway between V2 and V4V6 – 5th intercostal space midaxillary lineV5 – same level as V4 at anterior axillary line between V4 and V6

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RIGHT SIDED EKG

Same lead position as left side – looks directly at the

Right ventricle

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Posterior ViewPosterior ViewPosterior leads:

V7 – lateral to V6 at posterior axillary line

V8 – level of V7 at the mid-scapular line

V9 – level of V8 at the paravertebral line (left posterior thorax midway from spine to V8)

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V3 & V4

V1 & V2

V5 & V6

PRECORDIAL LEADS

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calibrationcalibration marker

Bottom line is continuous strip

LIMB LEADS AUGUMENTED LEADS

PRECORDIAL LEADS

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R – Wave ProgressionR – Wave Progression

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R – Wave ProgressionR – Wave Progression

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• Myocardial ischemiaMyocardial ischemia

– Various definitions are used. The term commonly refers to diffuse ST segment depression, usually with associated T wave inversion

• Myocardial injuryMyocardial injury

– Injury always points outward from the surface that is injured with ST segment elevation

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Ischemia, Injury, Infarction Ischemia, Injury, Infarction WaveformsWaveforms

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ST segment should be electrically neutral

ST ST SegmentsSegments

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• Visual aid in determining:– Ischemia or

injury to myocardium

– Normal should be at baseline

– Depressed ST segment - >2 mm below baseline

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21EKG 1

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ST Segment ElevationST Segment Elevation

• ST segment elevation is attributed to impending infarction – but can also be due to pericarditis or

vasospastic (variant) angina.

• The height of the ST segment is measured at a point 2 boxes after the end of the QRS complex– significant if it exceeds 1 mm in a limb

lead or 2 mm in a precordial lead.

23EKG 2

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T WavesT Waves

• T waves are normally positive in leads with a positive QRS

• T waves are normally asymmetrical• T waves are normally not more

than 5 mm high in limb leads or 10 mm high in precordial leads or 2/3 the height of the R wave

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T waveT wave

Hyperkalemia Ischemia

Ischemia

Ischemia

26HyperkalemiaHyperkalemia

EKG 3

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ST-T WaveST-T Wave

• Combination of infarction and often hyperkalemia

• Called Tombstone ‘T’Tombstone ‘T’ because of the shape.

• Usually a sign of impending cardiac death.

28EKG 4

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Pathology of an MIPathology of an MI

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Localization of ECG PathologyLocalization of ECG Pathology

• InferiorInferior: Abnormalities that appear in leads II, III, and aVF (called the inferior leads) indicate pathology on the inferior or diaphragmatic surface of the heart.

• Lateral:Lateral: Leads I, aVF, and V5-V6 are called lateral leads. Abnormality in these leads indicates pathology on the lateral, upper surface of the heart.

• Anterior:Anterior: Anterior pathology is seen in leads V1-V4, and often in lead I.

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Overview of InfarctsOverview of Infarcts

Location of Infarct

Arterial Supply

Indicative Changes

Reciprocal Changes

Anterior LAD V1-V4 II, III, aVF

Inferior RCA II, III, aVF I, aVL

Lateral Circumflex I, aVL, V5, V6

V1

Posterior Posterior Descending (RCA)

None V1, V2

Septal Septal Perforating (LAD)

Posterior Descending (RCA

Loss of R wave in V1, V2, or V3

None

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PathologicalQ Wave

ST Segment Elevation

Q

Q Q

STST

T

T

T Wave Elevation

T Wave Inversion

T

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EKG Changes from InfarctionEKG Changes from Infarction

First Detectable Change in EKG

•Tall T-waves

•increase in height

•more symmetric

•may occur in the first few minutes

Hyper-acute PhaseHyper-acute Phase

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Acute PhaseAcute Phase

•ST Segment Elevation

•Primary indication of injury

•Occurs in first hour to hours

ST Segment Elevation in Leads•1mm or greater in limb leads

•2 mm or greater in chest leads

•Hallmark indication of AMI

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Leads Leads IIII, , IIIIII, , aVFaVF- Looks at inferior Looks at inferior

heart wallheart wall

View of Inferior Heart Wall

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InferiorInferior

EKG 5

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InferiorInferior

EKG 6

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Leads Leads II and and aVLaVL– Looks at lateral heart Looks at lateral heart

wall wall – Looks from the left Looks from the left

arm toward heartarm toward heart

View of Lateral Heart Wall

*Sometimes referred to as High Lateral or

High Apical view*

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Leads Leads V5V5 & & V6V6– Looks at lateral heart Looks at lateral heart

wallwall– Looks from the left Looks from the left

lateral chest toward lateral chest toward heartheart

View of Lateral Heart Wall

*Sometimes referred to as Low

Lateral or Low Apical view*

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Leads Leads II, , aVLaVL, , V5V5, , V6V6

- - Looks at the lateral wall of Looks at the lateral wall of the heart from two different the heart from two different perspectivesperspectives

View of Entire Lateral Heart Wall

Lateral Wall

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LateralLateral

EKG 7

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LateralLateral

EKG 8

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• Leads Leads V3V3, , V4V4– Looks at anterior Looks at anterior

heart wallheart wall– Looks from the left Looks from the left

anterior chestanterior chest

View of AnteriorAnterior Heart Wall

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AnteriorAnterior

EKG 9

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AnteriorAnterior

EKG 10

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Leads Leads V1V1, , V2V2- Looks at septal Looks at septal

heart wallheart wall- Looks along sternal Looks along sternal

bordersborders

View of Septal Heart Wall

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Putting it ALL togetherPutting it ALL together

ANTERIOR

INFERIOR

LATERAL

LATERAL

LATERAL

SEPTAL

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Q WavesQ Waves

• DefinitionDefinition– Septal depolarizationSeptal depolarization– Normally present in I, aVL, V6Normally present in I, aVL, V6

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Two types of Q Two types of Q waveswaves

– Non-pathologic• Narrow, shallow Q

waves• Not visible in all leads

– Pathologic • > 0.04 in duration; at

least 1/4 to 1/3 height of R wave

• Represent an infarcted area of myocardium

51PATHOLOGICAL Q WAVES

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Bundle Branch BlocksBundle Branch Blocks

If the QRS duration is > .12

there is usually an abnormality of conduction of the ventricular impulse

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RBB Block

Most common ventricular conduction defect

Can be acute or chronicAcute RBBB is associated

with an acute anterior MI

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RBBB

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LBB Block

Always indicates a diseased heart

More common in older adults

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EKG 12

LBBB

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