THE PHYSIOLOGICAL THE PHYSIOLOGICAL BASIS OF THE EKGBASIS OF THE EKG

Dr. Guido E. SantacanaDr. Guido E. Santacana

ProfessorProfessor

Dept. of PhysiologyDept. of Physiology

After this section you should be able to:After this section you should be able to:

Differentiate between an intracellular action potential and the Differentiate between an intracellular action potential and the electrocardiogram as an extracellular recording.electrocardiogram as an extracellular recording.

Recognize the concept of the dipole and electrical potential vector and how it Recognize the concept of the dipole and electrical potential vector and how it applies to the heart and EKG recording.applies to the heart and EKG recording.

Recognize that the cumulative electrical activity of the heart forms dipoles or Recognize that the cumulative electrical activity of the heart forms dipoles or electrical potential vectors in different directions as the activation of the heart electrical potential vectors in different directions as the activation of the heart progresses.progresses.

Recognize that the multiple dipoles or electrical potential vectors generated by Recognize that the multiple dipoles or electrical potential vectors generated by the heart produce the EKG recording.the heart produce the EKG recording.

Learn the 12 EKG Leads and their projection of the lead vectors in three Learn the 12 EKG Leads and their projection of the lead vectors in three orthogonal planes.orthogonal planes.

Understand how each EKG wave is generated using Lead I as an example.Understand how each EKG wave is generated using Lead I as an example. Perform a simple sequential analysis of the EKG.Perform a simple sequential analysis of the EKG. Learn the standards of the EKG recording paper.Learn the standards of the EKG recording paper. Understand the origin of the Mean QRS Axis concept.Understand the origin of the Mean QRS Axis concept. Using the Electrical Axis Circle of the heart learn to estimate Mean Electrical Using the Electrical Axis Circle of the heart learn to estimate Mean Electrical

Axis.Axis. Calculate the Mean QRS Axis by vector analysis using three or two standard Calculate the Mean QRS Axis by vector analysis using three or two standard

leads.leads. Recognize the effect of left or right hypertrophy on the Mean QRS Axis. Recognize the effect of left or right hypertrophy on the Mean QRS Axis. Recognize the effect of left or right Bundle Branch Block on the Mean Electrical Recognize the effect of left or right Bundle Branch Block on the Mean Electrical

Axis.Axis. Understand the concept of current of injury and its clinical implications.Understand the concept of current of injury and its clinical implications. Learn to estimate the site of an ischemic injury using the concept of the J Point.Learn to estimate the site of an ischemic injury using the concept of the J Point.

The Conduction System of the The Conduction System of the HeartHeart

Action Potentials = Change in membrane potential occurring in nerve, muscle, heart and other cells

The ECG is not an action potential butreflects their cumulative effect at the level of the skin where the recordingelectrodes are located.

THE DIPOLE CONCEPTTHE DIPOLE CONCEPT

0 +2-2

+- AB

C

D POS

NEG+

-

+ -BATTERY

JAR

METER

EINTHOVEN’S TRIANGLEEINTHOVEN’S TRIANGLEAND LIMB LEADSAND LIMB LEADS

B A

B A

Einthoven’s Original EKG RecorderEinthoven’s Original EKG Recorder

String Galvanometer BasedEKG Recorder. Patient withhands submerged in strong salt solution.

String GalvanometerSchematic.

What are we looking at in the EKG What are we looking at in the EKG waves?waves?

TIME!!

Duration in fractions of a second

VOLTAGE!!

As amplitude inMillivolts.

Baseline at 0mv

Atrial DepolarizationAtrial DepolarizationP wave (Lead I)P wave (Lead I)

P +

-

0

B A

+

-

Zero potential

PeakPotential

Ventricular Conducting SystemVentricular Conducting System

AV Node

Right BundleBranch

Left Bundle Branch

Septal fascicle

Left Posterior Fascicle

Left AnteriorFascicle

P

P

P= Purkinje Fibers

Bundle of His

Ventricular Septal Ventricular Septal Depolarization- the Q Wave Depolarization- the Q Wave

Q

+

-

0

B A

-+

Ventricular Depolarization-the R WaveVentricular Depolarization-the R Wave

3

4

R

+

-

0

B A

-

+

Ventricular Depolarization-The S WaveVentricular Depolarization-The S Wave

SS

+

-

0

B. A

-

+

B.

A

QRS ConfigurationsQRS Configurations

QRSRSR’

RS QRQS

Ventricular Repolarization- the T WaveVentricular Repolarization- the T Wave

TT

+

-

+

-

0

SS

AB

+

-

Review of the Sequence in the Review of the Sequence in the Formation of the EKGFormation of the EKG

Intervals and Segments of the Intervals and Segments of the Normal EKGNormal EKG

INTERVALS AND SEGMENTS !INTERVALS AND SEGMENTS ! PR Interval- Onset of P wave to PR Interval- Onset of P wave to

onset of QRS. (.12-.20sec or 3-5 onset of QRS. (.12-.20sec or 3-5 small squares)small squares)

QRS Interval-Beginning and end QRS Interval-Beginning and end of QRS wave.(<.12sec duration of QRS wave.(<.12sec duration or 3 small squares)or 3 small squares)

QT interval- Beginning of QRS to QT interval- Beginning of QRS to end of T wave.( Calculated as end of T wave.( Calculated as corrected QT = .42 sec)corrected QT = .42 sec)

ST segment ( no elevation or ST segment ( no elevation or depression)depression)

B A B B

A A

0° 60° 120°

-150°-30°

90°

Limb Leads=Frontal Plane

Chest Leads = Horizontal Plane

+

-

+

-

-

+

A

B

A

B

A

B

B

A

The Chest or Precordial LeadsThe Chest or Precordial Leads

V1 V2 V3 V4

V5

V6

Over rightventricle

Over Interventricular Septum

Over the Left Ventricle

Projection of the 12 Lead EKG Vectors Projection of the 12 Lead EKG Vectors in Three Orthogonal Planesin Three Orthogonal Planes

Review of what each EKG Lead Review of what each EKG Lead looks at.looks at.

Inferior LeadsII,III,AVF

Left lateralLeadsI, AVL,V5V6

Anterior LeadsV1,V2,V3,V4

X

Y

Z

MEAN QRS AXIS BASICSMEAN QRS AXIS BASICSWHAT IS THE MEAN QRS AXIS?IT REPRESENTS THE AVERAGE DIRECTION OF THE INSTANTANEOUS FORCES GENERATED DURING THE SEQUENCE OF VENTRICULAR DEPOLARIZATION.

NORMAL RANGE= -30 TO +90 DEGREES

NORMAL VALUE= 59 DEGREES

MORE - THAN -30 = LEFT AXIS DEVIATION

MORE + THAN +90 = RIGHT AXIS DEVIATION

Instantaneous and Mean Vectors ofInstantaneous and Mean Vectors ofVentricular DepolarizationVentricular Depolarization

-90°

+90°

180° 0°

A B C DEFG

Mean Vector

The Electrical Axis CircleThe Electrical Axis CircleWhere does it come from?Where does it come from?

Lead I

LeadII

Lead III

REMEMBER EINTHOVEN

Lead I

LeadII

Lead III

0°

60°

120°

The three Leads with a Common The three Leads with a Common CenterCenter

Lead I

LeadII

Lead III

0°

60°

120°

THE ELECTRICAL AXIS CIRCLE!THE ELECTRICAL AXIS CIRCLE!

I- 0°

aVF- + 90°

aVL - -30°aVR- -150°

II - +60°III- +120°

+180°

+30°

-90°-60°

-120°

+150°

Normal

Range

Using the Circle to Estimate MEAUsing the Circle to Estimate MEA

I-0°

-90°

+180°

+90° II - +60°

-30°

+90°

NORMAL AXIS

-30°

+150°Lead IQRS UP

Lead II QRS UPTO ESTIMATE QRS AXIS

The Isoelectric QRS and its use!The Isoelectric QRS and its use!

aVL

-30°

+60II

Lead perpendicular to theisoelectric QRS

Why is a Wave Biphasic?Why is a Wave Biphasic?

------------------++++++++++

0+-

Cardiac Muscle

Lead

Meter

-------Lead

----------+++++

++++

0- +

Cardiac Muscle

Meter

Lead

++++

-------

----------+++++

0- +

Cardiac Muscle

Meter

A B C

Electrode Perpendicular to Direction of Depolarization

Why is Lead aVL Biphasic?Why is Lead aVL Biphasic?

Lead aVL

+

Lead I

+

Lead II

+

RA

LA

RV

LV-

+

Mean QRS

Quick Estimation of Axis DeviationQuick Estimation of Axis Deviation

ExtremeRight axisdeviation

Right axisdeviation.

Normal axis

Left axisdeviation

+90° Lead AVF

0° Lead I

I

AVF

I

AVFAVF

I

AVF

I

Ventricular Hypertrophy 1Ventricular Hypertrophy 1Limb Leads

Precordial Leads

Ventricular Hypertrophy 2Ventricular Hypertrophy 2Precordials

R exceeding 18mm

R exceeding 26mm

S wave

Review of Vectors and Review of Vectors and Vectorial Analysis of the Vectorial Analysis of the

EKGEKGGuido E. Santacana Ph.D.Guido E. Santacana Ph.D.

ProfessorProfessor

Department of PhysiologyDepartment of Physiology

Basis for Vectorial AnalysisBasis for Vectorial AnalysisThe Boat example!!!

20 knots

Wind 10 knots

Actual Direction(Resultant Vector)

y

x

Graphical Representation

Vectorial Analysis of the Mean Vectorial Analysis of the Mean Electrical AxisElectrical Axis

EKG (LEAD I): Projected Vectors for EKG (LEAD I): Projected Vectors for different Mean Electrical Axesdifferent Mean Electrical Axes

LEAD I

Tilted Mean Vectors

Partial Voltage Reading

Perpendicular Mean Vectors

LEAD I

No Voltage Reading

+

-

-

+Parallel Mean Vectors

Higher Voltage Reading

+-

NO PROJECTED VECTOR!!!!!

LEAD I

The Concept of the Projected The Concept of the Projected VectorVector

Figure A

Figure B

A=Mean VectorB=Projected Vector

Projected Vectors for theThree Projected Vectors for theThree Standard LeadsStandard Leads

Ventricular Depolarization Analysis Ventricular Depolarization Analysis Using the Projected VectorsUsing the Projected Vectors

.01 sec .02 sec

.035 sec.05 sec

.06 sec

Ventricular Repolarization Analysis Ventricular Repolarization Analysis Using the Projected VectorsUsing the Projected Vectors

What is the Vectorcardiogram?What is the Vectorcardiogram?

It is simply the path marked by the positive ends ofThe depolarization vectors.

How to Plot the Mean Electrical How to Plot the Mean Electrical Axis Using Two EKG LeadsAxis Using Two EKG Leads

R wave only = 6mmor .6mv

RS wavesR= 8mmS= -2mmTotal = 8-2=6mmor .6mv

Mean Electrical Axis

6mm

6mm

Abnormal Ventricular Conditions Abnormal Ventricular Conditions That Cause Axis DeviationThat Cause Axis Deviation

Change in position of the heart in the Change in position of the heart in the chest.chest.

Hypertrophy of one ventricle.Hypertrophy of one ventricle. Bundle Branch Block.Bundle Branch Block.

Vectorial Analysis of Ventricular Vectorial Analysis of Ventricular HypertrophyHypertrophy

Left ventricular hypertrophy in a hypertensive heart.Reasons for deviation are LV mass and conduction time.

-15°

Vectorial Analysis of Right Vectorial Analysis of Right Ventricular HypertrophyVentricular Hypertrophy

RV Hypertrophy caused by Pulmonary Valve Stenosis

170°

Notice also theHigh voltageEKG in Lead I

170°

Vectorial Analysis in Bundle Branch Vectorial Analysis in Bundle Branch BlockBlock

Left axis deviation caused by a Left Bundle Branch Block

ProlonguedQRS due toSlowerConductionTime ThroughBlock

-50° left deviation

Vectorial Analysis in Bundle Branch Vectorial Analysis in Bundle Branch BlockBlock

Right Bundle Branch Block producing a right axis deviation.Again observe the longer QRS interval. Longer QRS intervalsCan distinguish axis deviations due to BBBs vs. hypertrophies.

Low Voltage EKGLow Voltage EKG

Normal voltage between R waveand S wave shouldbe from .5 to 2mv

If the sum of thevoltages in the QRSof leads I,II,III isgreater than 4mvthe EKG is consideredas high voltage.

Low voltage EKG due to myocardial infarction.Low voltage EKG is also caused by pericardial effusion, pleural effusionand pulmonary emphysema.

The Current of InjuryThe Current of Injury

Cardiac abnormalities specially those Cardiac abnormalities specially those that damage the heart muscle cause that damage the heart muscle cause part of the heart to remain partially part of the heart to remain partially or totally depolarized all the time.or totally depolarized all the time.

The current that flows even between The current that flows even between heartbeats from the pathologically heartbeats from the pathologically depolarized area to the normal area depolarized area to the normal area is the CURRENT OF INJURY.is the CURRENT OF INJURY.

Causes of the Current of InjuryCauses of the Current of Injury

Mechanical Trauma.Mechanical Trauma. InfectionsInfections Ischemia caused by coronary Ischemia caused by coronary

occlusions. (Most common cause)occlusions. (Most common cause)

The Current of InjuryThe Current of Injury

Currentof injuryremains afterthe heart hasRepolarized.

EKG Generation in Normal vs. EKG Generation in Normal vs. Infarcted HeartInfarcted Heart

NORMALINFARCTED

The J Point and the Current of The J Point and the Current of Injury Vector AnalysisInjury Vector Analysis

J Point is thezero potentialline from whichthe directionof the injury current is determined

Injury Potential in Anterior Wall Injury Potential in Anterior Wall InfarctionInfarction

Respective J PointsIn Leads I and III

J point in V2an anterior Lead

Injury Potential in Posterior Wall Injury Potential in Posterior Wall Apical InfarctionApical Infarction

J Points ofLeads II &III.

J point of V2

Cardiac ArrhythmiasCardiac Arrhythmias

Result from disturbances of

IMPULSE PROPAGATION

IMPULSE INITIATION

Conduction BlocksReentry rhythms

SA NodeEctopic Foci

Alteration of SA RhythmAlteration of SA Rhythm

Autonomic nervous system usually Autonomic nervous system usually involved.involved.

P, QRS, T waves normal.P, QRS, T waves normal. Duration of Cardiac Cycle P-P interval Duration of Cardiac Cycle P-P interval

shortened or prolonged.shortened or prolonged. Sinus Bradycardia- Slow Rhythm.Sinus Bradycardia- Slow Rhythm. Sinus Tachycardia- Fast Rhythm.Sinus Tachycardia- Fast Rhythm. Cardiac frequency changes gradually.Cardiac frequency changes gradually.

BradycardiaBradycardia

Normal Rhythm

Bradycardia

bradycardia occurs when the hearts rate is slower than 60 beats per minute.

TachycardiaTachycardia

Normal Rhythm

Tachycardia

Sinus tachycardia occurs when the sinus rhythm is faster than 100 beats per minute

AV Transmission BlocksAV Transmission Blocks

Impulse transmission through Impulse transmission through conduction tissue blocked.conduction tissue blocked.

His Bundle Electrogram may be used His Bundle Electrogram may be used to localize block.to localize block.

His Bundle ElectrogramHis Bundle Electrogram

A H

VAtrial WaveHis BundleWave Ventricular wave

Prolongation of eitherthe A-H or H-V intervalindicates block above or below the Bundle of His

Paroxysmal TachycardiaParoxysmal Tachycardia

Abrupt onset and termination.Abrupt onset and termination. Origin is ectopic site.Origin is ectopic site. Reentry circus movements most Reentry circus movements most

frequent cause.frequent cause. High frequency.High frequency. Can cause lightheadedness or Can cause lightheadedness or

syncope.syncope. Rapid contractions reduce ventricular Rapid contractions reduce ventricular

filling.filling.

Paroxysmal Supraventricular Paroxysmal Supraventricular TachycardiaTachycardia

Originate in atria or AV tissue.Usually from a reentry loop in atrial, AV tissue or both.

Paroxysmal Ventricular Paroxysmal Ventricular TachycardiaTachycardia

From ectopic foci in the ventricles.From considerable ischemic damage.Bizarre QRS complexesMay be a precursor of Ventricular FibrillationResults from digitalis toxicity.

FibrillationFibrillation

Arrhythmia that is ineffectual in Arrhythmia that is ineffectual in pumping blood.pumping blood.

Atria or Ventricles may be involved.Atria or Ventricles may be involved. Is due to fragmentation of reentry Is due to fragmentation of reentry

loop into multiple irregular circuits.loop into multiple irregular circuits.

Atrial FibrillationAtrial Fibrillation

Atria do not contract and relax sequentially.No contribution to ventricular filling.No P waves. Irregular fluctuations or f waves.Normal QRS complexes but irregular rhythm.Compatible with life and full physical activity.20-30% reduction in ventricular pumping.

Ventricular FibrillationVentricular Fibrillation

Irregular continuous twitching of the ventricular muscle.No pumping of blood possible.Loss of conciousness occurs rapidlyIrregular fluctuations in the EKGOften initiated by a premature impulse arriving in thevulnerable phase.Vulnerable phase coincides with downslope of theT wave.Electric shock used to treat VF by leaving the ventricles temporarily refractory and allowingthe SA node to take over again.

Mechanism of Ventricular Mechanism of Ventricular FibrillationFibrillation

Long Pathway= dilated heartsDecreased velocity of conduction=blockade of Purkinje SystemGreatly shortened refractory period= Epinephrine

Causes of reentryCircus movements

60 Hz AC Induced VF60 Hz AC Induced VF

60Hz 120VACApplied here

End result

Atrial FlutterAtrial Flutter

F wave

Normal EKG

Wolf Parkinson-White SyndromeWolf Parkinson-White SyndromeNormal

Wolf Parkinson White

Alternate Conduction PathwayBundle of Kent

SEQUENTIAL APPROACH TO SEQUENTIAL APPROACH TO THE EKGTHE EKG

Gain familiarity with the normal EKG.Gain familiarity with the normal EKG. Evaluate the rhythm.Evaluate the rhythm. Calculate rate.Calculate rate. Evaluate each P wave, QRS, ST segment Evaluate each P wave, QRS, ST segment

and T wave in each lead.and T wave in each lead. Mean QRS AxisMean QRS Axis Abnormalities of the P waveAbnormalities of the P wave Abnormalities of the QRSAbnormalities of the QRS ST and T wave abnormalities.ST and T wave abnormalities.

The Normal EKG - 12 leadThe Normal EKG - 12 lead

Reading the EKG PaperReading the EKG PaperBASICSBASICS

Each individual Each individual horizontal and vertical horizontal and vertical line is ruled in 1 mmline is ruled in 1 mm

Each horizontal space Each horizontal space represent a time represent a time interval of 0.04 secinterval of 0.04 sec

Each vertical space Each vertical space represents a voltage represents a voltage change of 0.1 mvchange of 0.1 mv

0.2 sec.

0.5

mv

HEART RHYTHMHEART RHYTHM

Every P wave followed by a QRS.Every P wave followed by a QRS. Every QRS preceded by a P waveEvery QRS preceded by a P wave P wave upright in leads I, II, IIIP wave upright in leads I, II, III PR interval greater than .12 secPR interval greater than .12 sec P wave rate 60-100BPM with < 10% P wave rate 60-100BPM with < 10%

variation. < 60 - sinus bradycardia, variation. < 60 - sinus bradycardia, >100sinus tachycardia. Variation of >100sinus tachycardia. Variation of more than 10% = Sinus arrhythmiamore than 10% = Sinus arrhythmia

CALCULATE HEART RATECALCULATE HEART RATE

STANDARD EKG PAPER SPEED OF 25MM SEC

HEART RATE = 25MM SEC X 60SEC/MIN MM/BEAT OR!!

= 1500 # of small boxes between 2 beats

ExampleExample

There are 23 mm between the There are 23 mm between the two QRS complexes, therefore:two QRS complexes, therefore:

Heart rate = 1500/23 = 65 Heart rate = 1500/23 = 65 beats/minbeats/min

23

Analyzing The Normal EKGAnalyzing The Normal EKG

Left Atrial EnlargementLeft Atrial Enlargement

Right Atrial EnlargementRight Atrial Enlargement

Sample Abnormality of the Sample Abnormality of the P waveP wave

P waves not visiblerandom rhythmright ventricular hypertrophyatrial fibrillation

MITRALSTENOSIS

AV BLOCKAV BLOCK

Exercise Intolerance Ventricular Escape Rythm

HyperkalemiaHyperkalemia

Small or absent P wavesAtrial FibrillationWide QRSShortened or absent ST segmentWide and tall T wavesVentricular fibrillation (sometimes)

Haemodialysis

HypokalemiaHypokalemia

Small or absent T waves1st or 2nd degree heart AV blockslight depression of ST segment

Vomiting (prolonged)