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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

EISLO’sEISLO’s

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Myocardial A&PMyocardial A&P

http://www.healthline.com/vpvideo/how-the-heart-works

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Heart wall - Three layersHeart wall - Three layers

Epicardium (outer)visceral layer of pericardiumthin, transparentsmooth, slippery

Myocardium (middle)mass of cardiac muscle

Endocardium (inner)endothelium over thin connective tissuesmooth lining for the chambers and valvescontinuous with blood vessel endothelium

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Cardiac EnzymesCardiac Enzymes• Myoglobin

– Released by all striated muscle

– Rises fast (2 hours) after myocardial infarction

– Peaks at 6 - 8 hours– Returns to normal in

20 - 36 hours

• CK– Released by all muscles

in the body– Rises in 4-6 hours after

injury– Peaks in 24 hours– Returns to normal in 3-4

days– CK-MB is myocardial

“specific”• Peaks in 3-4 hours • Returns to normal in

2 days

• Troponin– More specific for

myocardial injury– Rises 2-6 hours after

injury– Peaks in 12 hours– Remains elevated for 5-14

days

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Arteries Arteries first branches off the aortablood moves more easily into the myocardium when it is relaxed between beats during diastoleblood enters coronary capillary beds

Coronary Coronary Blood Blood FlowFlow

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Collateral CirculationCollateral Circulation

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Coronary CirculationCoronary Circulation

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Coronary Circulation PathologiesCoronary Circulation Pathologies

Compromised coronary circulation due to:Compromised coronary circulation due to:emboli: blood clots, air, amniotic fluid, tumor fragmentsfatty atherosclerotic plaquessmooth muscle spasms in coronary arteries

ProblemsProblemsischemia (low supply of nutrients)hypoxia (low supply of O2)infarct (cell death)

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Internodal tracts

Bundle of His

Right Bundle Branch

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SA NodeSA Node

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Intranodal PathwaysIntranodal Pathways

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AV Node ConductionAV Node Conduction

Normal conduction pathway from atria to ventricles

Limits number of atrial impulses sent to the ventricles

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Bundle BranchesBundle Branches

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Action PotentialAction Potential

Phase 0Begins at -70 mV with a slow influx of sodium ions; gradually raising the potential toward threshold When threshold is reached fast sodium channels open; causing the cell to fire

Phase 1Rapid sodium pumps are slowed by influx of potassium

Phase 2Plateau phaseSodium influx slows; calcium begins to enter the cellCalcium stimulates cellular contraction by stimulating the myocyte

Phase 3Reverse pumps open; rapid repolarization

Phase 4Back to the -70 mV resting potential

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Myocardial Action PotentialDepolarization

Phase 1 of the action potentialStimulation of the cardiac cell by the pacemaker cell causing an influx of Na and Ca, outflow of K.

Repolarization Phase 2 of the action potentialNo impulse entering the cells can cause it to depolarize

Relative refractory periodPhase 3 of the action potentialImpulses entering the cardiac cell now can cause serious, uncontrolled reactions.

Absolute refractory periodPhase 4 of the action potentialThe return of the cardiac cells to resting state.

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EKG BasicsEKG Basics

25 mm per secEach small box - horizontally = 0.4 secEach small box - vertically = 1 mm

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EKG Review - AnalysisEKG Review - Analysis

RhythmRegular or irregular

RateToo fast, too slow, just right

P wavesUpright, inverted, not there, not related

P-R Interval0.12-0.20; >0.20; <0.12

QRS complex<0.12

QT Interval.34-.44

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P wave: Represents positive and negative deflections of atrial contraction and relaxation

PR Interval: Distance between the P wave and the Q/R wave .12 -20

QRS Complex: represents ventricular depolarization

•Q wave: First negative deflection

•R Wave: First positive deflection

•S Wave: second negative deflection

ST Segment: Essentially isoelectric, slopes gently upward•Normal > .08 sec

J point: the point where the S wave meets the isoelectric line

T Wave: Ventricular repolarization•always upright in leads I, II, V2-V6•aVR is always negative.•Leads III, aVL, aVF, and V1 can be positive or negative

U Wave: unclear etiology, commonly seen in V2-V3 due to proximity to ventricular mass; common in bradycardia, hypokalemia, digitalis

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QT intervalbeginning of the QRS complex to the end of the T wave represents ventricular depolarization and repolarization ---- Changes with heart rate

QTcQT corrected for heart rate QT / R-R = QTcEvaluates the recovery of the ventricle

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

Myocardial injuryMyocardial injuryInjury always points outward from the surface that is injured with ST segment elevation

Myocardial infarctionMyocardial infarctiondeath of heart muscle

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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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40EKG 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.

42EKG 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

45HyperkalemiaHyperkalemia

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.

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Inferior-Anterior-LateralInferior-Anterior-Lateral

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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, aVLV5, V6

V1

Posterior Posterior Descending (RCA)

V7, V8, V9 - elevation

V1, V2 -ischemia

Septal Septal Perforating (LAD)Posterior Descending (RCA

Possible loss of R wave in

V1, V2, 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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CASE STUDY – EVOLUTION of MICASE STUDY – EVOLUTION of MI

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

heart wallheart wall

View of InferiorInferior 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 LateralLateral 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 LateralLateral 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 LateralLateral 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

75EKG 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 SeptalSeptal 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

80PATHOLOGICAL 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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LBBB

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