ECG BasicsECG Basics

Dr.Ola TorkDr.Ola Tork

MD.PhysiologyMD.Physiology

OutlineOutline

1.1. Basic laws of ECG Basic laws of ECG

2.2. Review of the conduction systemReview of the conduction system

3.3. ECG waveforms and intervalsECG waveforms and intervals

4.4. ECG leadsECG leads

5.5. Determining heart rateDetermining heart rate

6.6. Cardiac RhythmCardiac Rhythm

7.7. Determining QRS axisDetermining QRS axis8.8. ATRIAL HYPERTROPHY &ventricular hypertrophyATRIAL HYPERTROPHY &ventricular hypertrophy

What is an ECG?What is an ECG?

The electrocardiogram (ECG) is a The electrocardiogram (ECG) is a record of the sum of all electrical record of the sum of all electrical activity of the heart from the surface of activity of the heart from the surface of the body as the body fluids act as the body as the body fluids act as electrical conductors .electrical conductors .

Propagating Activation WavefrontPropagating Activation Wavefront

When the cells are at rest, they have a When the cells are at rest, they have a negative transmembrane voltage – negative transmembrane voltage – surrounding media is positivesurrounding media is positive

When the cells depolarize, they switch to a When the cells depolarize, they switch to a positive transmembrane voltage – positive transmembrane voltage – surrounding media becomes negativesurrounding media becomes negative

This leads to a propagating electric vector This leads to a propagating electric vector (pointing from negative to positive)(pointing from negative to positive)

Basic laws of ECGBasic laws of ECG

Propagating Activation WavefrontPropagating Activation Wavefront Depol. toward positive electrode

Positive SignalRepol. toward positive electrode

Negative Signal

Depol. away from positive electrodeNegative Signal

Repol. Away from positive electrodePositive Signal

The Normal Conduction SystemThe Normal Conduction System

ECG SignalECG SignalThe excitation begins at the The excitation begins at the sinus (SA) node and spreads sinus (SA) node and spreads along the atrial wallsalong the atrial walls

The resultant electric vector The resultant electric vector is shown in yellowis shown in yellow

Cannot propagate across the Cannot propagate across the boundary between atria and boundary between atria and ventricleventricle

The projections on Leads I, II The projections on Leads I, II and III are all positiveand III are all positive

ECG Signal

• Atrioventricular (AV) node located on atria/ventricle boundary and provides conducting path

• Pathway provides a delay to allow ventricles to fill

• Excitation begins with the septum

ECG Signal

• Depolarization continues to propagate toward the apex of the heart as the signal moves down the bundle branches

• Overall electric vector points toward apex as both left and right ventricles depolarize and begin to contract

ECG Signal• Depolarization of the right

ventricle reaches the epicardial surface

• Left ventricle wall is thicker and continues to depolarize

• As there is no compensating electric forces on the right, the electric vector reaches maximum size and points left

• Note the atria have repolarized, but signal is not seen

ECG Signal

• Depolarization front continues to propagate to the back of the left ventricular wall

• Electric vector decreases in size as there is less tissue depolarizing

ECG Signal

• Depolarization of the ventricles is complete and the electric vector has returned to zero

ECG Signal• Ventricular repolarization

begins from the outer side of the ventricles with the left being slightly dominant

• Note that this produces an electric vector that is in the same direction as the depolarization traveling in the opposite direction

• Repolarization is diffuse and generates a smaller and longer signal than depolarization

ECG Signal

• Upon complete repolarization, the heart is ready to go again and we have recorded an ECG trace

Waveforms and IntervalsWaveforms and Intervals

What types of pathology can we What types of pathology can we identify and study from EKGs?identify and study from EKGs?

ArrhythmiasArrhythmiasMyocardial ischemia and infarctionMyocardial ischemia and infarctionPericarditisPericarditisChamber hypertrophyChamber hypertrophyElectrolyte disturbances (i.e. Electrolyte disturbances (i.e. hyperkalemia, hypokalemia)hyperkalemia, hypokalemia)Drug toxicity (i.e. digoxin and drugs which Drug toxicity (i.e. digoxin and drugs which prolong the QT interval)prolong the QT interval)

Normal ECGNormal ECG

5 waves:P, Q, R,S ,T5 waves:P, Q, R,S ,T

1.1. P wave : caused by atrial depolarizationP wave : caused by atrial depolarization

2.2. QRS complex: caused by ventricular QRS complex: caused by ventricular depolarizationdepolarization

3.3. T wave :caused by ventricular T wave :caused by ventricular repolarizationrepolarization

Intervals :Intervals :

P-R interval = 0.12 -0.2s P-R interval = 0.12 -0.2s

ECG LeadsECG LeadsIn 1908, Willem In 1908, Willem Einthoven developed a Einthoven developed a system capable of system capable of recording these small recording these small signals and recorded signals and recorded the first ECG.the first ECG.The leads were based The leads were based on the Einthoven on the Einthoven triangle associated with triangle associated with the limb leads.the limb leads.Leads put heart in the Leads put heart in the middle of a trianglemiddle of a triangle

EKG LeadsEKG Leads

Leads are electrodes which measure the Leads are electrodes which measure the difference in electrical potential between difference in electrical potential between either:either:

1. Two different points on the body (bipolar leads)1. Two different points on the body (bipolar leads)

2. One point on the body and a virtual reference point 2. One point on the body and a virtual reference point with zero electrical potential, located in the center of with zero electrical potential, located in the center of the heart (unipolar leads)the heart (unipolar leads)

EKG LeadsEKG Leads

The standard EKG has 12 leads:The standard EKG has 12 leads: 3 Standard Limb Leads

3 Augmented Limb Leads

6 Precordial Leads

The axis of a particular lead represents the viewpoint from The axis of a particular lead represents the viewpoint from which it looks at the heart.which it looks at the heart.

Standard Limb LeadsStandard Limb Leads

Standard Limb LeadsStandard Limb Leads

Augmented Limb LeadsAugmented Limb Leads

All Limb LeadsAll Limb Leads

Precordial LeadsPrecordial Leads

Adapted from: www.numed.co.uk/electrodepl.html

Precordial LeadsPrecordial Leads

Summary of LeadsSummary of Leads

Limb LeadsLimb Leads Precordial LeadsPrecordial Leads

BipolarBipolar I, II, IIII, II, III(standard limb leads)(standard limb leads)

--

UnipolarUnipolar aVR, aVL, aVF aVR, aVL, aVF (augmented limb leads)(augmented limb leads)

VV11-V-V66

Arrangement of Leads on the EKGArrangement of Leads on the EKG

Anatomic GroupsAnatomic Groups(Septum)(Septum)

Anatomic GroupsAnatomic Groups(Anterior Wall)(Anterior Wall)

Anatomic GroupsAnatomic Groups(Lateral Wall)(Lateral Wall)

Anatomic GroupsAnatomic Groups(Inferior Wall)(Inferior Wall)

Anatomic GroupsAnatomic Groups(Summary)(Summary)

Determining the Heart RateDetermining the Heart Rate

Rule of 300Rule of 300

10 Second Rule10 Second Rule

Rule of 300Rule of 300

Take the number of “big boxes” between Take the number of “big boxes” between neighboring QRS complexes, and divide this neighboring QRS complexes, and divide this into 300. The result will be approximately into 300. The result will be approximately equal to the rateequal to the rate

Although fast, this method only works for Although fast, this method only works for regular rhythms.regular rhythms.

What is the heart rate?What is the heart rate?

(300 / 6) = 50 bpm

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What is the heart rate?What is the heart rate?

(300 / ~ 4) = ~ 75 bpm

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What is the heart rate?What is the heart rate?

(300 / 1.5) = 200 bpm

The Rule of 300The Rule of 300

It may be easiest to memorize the following table:It may be easiest to memorize the following table:

# of big # of big boxesboxes

RateRate

11 300300

22 150150

33 100100

44 7575

55 6060

66 5050

10 Second Rule10 Second Rule

As most ECGs record 10 seconds of rhythm per As most ECGs record 10 seconds of rhythm per page, one can simply count the number of beats page, one can simply count the number of beats present on the ECG and multiply by 6 to get the present on the ECG and multiply by 6 to get the number of beats per 60 seconds.number of beats per 60 seconds.

This method works well for irregular rhythms.This method works well for irregular rhythms.

What is the heart rate?What is the heart rate?

33 x 6 = 198 bpm

The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/

Cardiac Rhythm: SupraventricularCardiac Rhythm: SupraventricularNORMAL SINUS RHYTHMImpuses originate at S-A node at normal rate

                   

   

                                                                         

  SINUS TACHYCARDIAImpuses originate at S-A node at rapid rate

                   

   

                                                                         

  All complexes normal, evenly spacedRate > 100/min

SINUS TACHYCARDIAImpuses originate at S-A node at rapid rate

                   

   

                                                                         

  All complexes normal, rhythm is irregularLongest R-R interval exceeds shirtest > 0.16 s

Cardiac Rhythm: SupraventricularCardiac Rhythm: Supraventricular

ATRIAL FLUTTERImpulses travel in circular course in atria – No interval between T and P

                   

   

                                                                         

  Rapid flutter waves, ventricular response irregular

ATRIAL FIBRILLATIONImpuses have chaotic, random pathways in atria

                   

   

                                                                         

  Baseline irregular, ventricular response irregular

Cardiac Rhythm: VentricularCardiac Rhythm: VentricularPREMATURE VENTRICULAR CONTRACTIONA single impulse originates at right ventricle

                   

   

                                                                         

  Time interval between normal R peaks is a multiple of R-R intervals

VENTRICULAR TACHYCARDIAImpulse originate at ventricular pacemaker – odd/wide QRS complex - often due to myocardial infarction

                   

   

                                                                         

  Wide ventricular complexesRate> 120/min

Cardiac Rhythm: VentricularCardiac Rhythm: VentricularVENTRICULAR FIBRILLATIONChaotic ventricular depolarization – ineffective at pumping blood – death within minutes

                   

   

                                                                         

  Rapid, wide, irregular ventricular complexes

PACER RHYTHMImpulses originate at transvenous pacemaker

                   

   

                                                                         

  Wide ventricular complexes preceded by pacemaker spikeRate is the pacer rhythm

Activation Sequence DisordersActivation Sequence DisordersA-V BLOCK, FIRST DEGREEAtrio-ventricular conduction lengthened

                   

   

                                                                         

  P-wave precedes each QRS-complex but PR-interval is > 0.2 s

A-V BLOCK, SECOND DEGREESudden dropped QRS-complex

                    

  

                                                                        

   Intermittently skipped ventricular beat

Bundle-branch BlockBundle-branch BlockRIGHT BUNDLE-BRANCH BLOCKQRS duration greater than 0.12 sWide S wave in leads I, V5 and V6

                                                                           

               

The QRS AxisThe QRS Axis

The QRS axis represents the net overall The QRS axis represents the net overall direction of the heart’s electrical activity.direction of the heart’s electrical activity.

The QRS AxisThe QRS Axis

By near-consensus, the normal QRS axis is defined as ranging from -30° to +90°.

-30° to -90° is referred to as a left axis deviation (LAD)

+90° to +180° is referred to as a right axis deviation (RAD)

Determining the AxisDetermining the Axis

The Quadrant ApproachThe Quadrant Approach

The Equiphasic ApproachThe Equiphasic Approach

Determining the AxisDetermining the Axis

Predominantly Positive

Predominantly Negative

Equiphasic

The Quadrant ApproachThe Quadrant Approach1. Examine the QRS complex in leads I and aVF to determine 1. Examine the QRS complex in leads I and aVF to determine

if they are predominantly positive or predominantly if they are predominantly positive or predominantly negative. The combination should place the axis into one negative. The combination should place the axis into one of the 4 quadrants below.of the 4 quadrants below.

The Quadrant ApproachThe Quadrant Approach2. In the event that LAD is present, examine lead II to 2. In the event that LAD is present, examine lead II to

determine if this deviation is pathologic. If the QRS in II is determine if this deviation is pathologic. If the QRS in II is predominantly positive, the LAD is non-pathologic (in other predominantly positive, the LAD is non-pathologic (in other words, the axis is normal). If it is predominantly negative, it words, the axis is normal). If it is predominantly negative, it is pathologic. is pathologic.

Quadrant Approach: Example 1Quadrant Approach: Example 1

Negative in I, positive in aVF RAD

The Alan E. Lindsay ECG Learning Center http://medstat.med.utah.edu/kw/ecg/

Quadrant Approach: Example 2Quadrant Approach: Example 2

Positive in I, negative in aVF Predominantly positive in II

Normal Axis (non-pathologic LAD)

The Alan E. Lindsay ECG Learning Center http://medstat.med.utah.edu/kw/ecg/

Deviation of Electric Axis of the Deviation of Electric Axis of the HeartHeart

Deviation to R: increased activity in R vent. – Deviation to R: increased activity in R vent. – obstruction in lung, pulmonary emboli, some heart obstruction in lung, pulmonary emboli, some heart diseasediseaseDeviation to L: increased activity in L vent. – Deviation to L: increased activity in L vent. – hypertension, aortic stenosis, ischemic heart hypertension, aortic stenosis, ischemic heart diseasedisease

Atrial Hypertropy:Atrial Hypertropy: Enlarged Atria Enlarged AtriaRIGHT ATRIAL HYPERTROPHYTall, peaked P wave in leads I and II

LEFT ATRIAL HYPERTROPHYWide, notched P wave in lead IIDiphasic P wave in V1

                              

               

                              

               

Ventricular Hypertropy:Ventricular Hypertropy: Enlarged Ventricle Enlarged VentricleLEFT VENTRICULAR HYPERTROPHYLarge S wave in leads V1 and V2

Large R wave in leads V6 and V6

                                                                          

                

Myocardial Ischemia and InfarctionMyocardial Ischemia and Infarction

Oxygen depletion to heart Oxygen depletion to heart can cause an oxygen debt in can cause an oxygen debt in the muscle (ischemia)the muscle (ischemia)

If oxygen supply stops, the If oxygen supply stops, the heart muscle dies (infarction)heart muscle dies (infarction)

The infarct area is electrically The infarct area is electrically silent and represents an silent and represents an inward facing electric inward facing electric vector…can locate with ECGvector…can locate with ECG