Basics of Basics of ElectrocardiographyElectrocardiography

Dr.K.SubramanyamDr.K.Subramanyam

23-3-200923-3-2009

OutlineOutline

1.1. Review of the conduction systemReview of the conduction system

2.2. ECG leads and recording ECG leads and recording

3.3. ECG waveforms and intervalsECG waveforms and intervals

4.4. Normal ECG and its variantsNormal ECG and its variants

5.5. Interpretation and reporting of an ECGInterpretation and reporting of an ECG

What is an ECG?What is an ECG?

An ECG is the recording (gram) An ECG is the recording (gram)

of the electrical activity(electro) of the electrical activity(electro) generated by the cells of the generated by the cells of the heart(cardio) heart(cardio)

that reaches the body that reaches the body surface.surface.

Recording ECGRecording ECG

William Einthoven

Useful in diagnosis of…Useful in diagnosis of…

Cardiac ArrhythmiasCardiac Arrhythmias

Myocardial ischemia and infarctionMyocardial ischemia and infarction

PericarditisPericarditis

Chamber hypertrophyChamber hypertrophy

Electrolyte disturbancesElectrolyte disturbances

Drug effects and toxicityDrug effects and toxicity

Recording an ECGRecording an ECG

BasicsBasics

ECG graphs:ECG graphs:

– 1 mm squares1 mm squares

– 5 mm squares 5 mm squares

Paper Speed:Paper Speed:

– 25 mm/sec standard25 mm/sec standard

Voltage Calibration: Voltage Calibration:

– 10 mm/mV standard10 mm/mV standard

ECG Paper: DimensionsECG Paper: Dimensions5 mm

1 mm

0.1 mV

0.04 sec

0.2 sec

Speed = rate

Voltage ~Mass

ECG LeadsECG Leads

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

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

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

+-

RA

RA

LL+

+

--LA

LL

LA

LEAD II

LEAD I

LEAD III

Remember, the RLis always the ground

• By changing the arrangement of which arms or legs are positive or negative, three unipolar leads (I, II & III ) can be derived giving three "pictures" of the heart's electrical activity from 3 angles.

The Concept of a “Lead”

Leads I, II, and III

I

II III

ECG LeadsECG Leads

The standard ECG has 12 leads:The standard ECG 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.

ECG LEADSECG LEADS

Gold Berger :aV frontal leadsGold Berger :aV frontal leads

Wilson & co-workwers :chest leadsWilson & co-workwers :chest leads

Standard Limb LeadsStandard Limb Leads

Precordial LeadsPrecordial Leads

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

Limb Leads (Einthoven leads)Limb Leads (Einthoven leads)

Einthoven triangle

Einthoven Rule

I+II+III==0

I+(-II)+III=0

I+III=II

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)

Localising the arterial territoryLocalising the arterial territory

InferiorII, III, aVF

LateralI, AVL, V5-V6

Anterior / SeptalV1-V4

Standard sites unavailableStandard sites unavailable

Patient pathologyPatient pathology

Amputation or burns or bandagesAmputation or burns or bandages should be placed as closely as possible to should be placed as closely as possible to the standard sitesthe standard sites

Specific cardiac abnormalitiesSpecific cardiac abnormalities

Situs inversus dextrocardiaSitus inversus dextrocardia right & left right & left arm electrodes should be reversedarm electrodes should be reversed

pre-cordial leads should be recorded from pre-cordial leads should be recorded from V1R(V2) to V6V1R(V2) to V6

RVH & RV infarction:V3R & V4RRVH & RV infarction:V3R & V4R

Continuous monitoringContinuous monitoring

Bed side: Bed side:

Holter monitoring:Holter monitoring:

TMT: Mason Likar systemTMT: Mason Likar system

Other practical pointsOther practical points

Electrodes should be selected for Electrodes should be selected for maximum adhesiveness and minimum maximum adhesiveness and minimum discomfort,electrical noise,and skin-discomfort,electrical noise,and skin-electrode impedanceelectrode impedance

Effective contact between electrode and Effective contact between electrode and skin is essential.skin is essential.

ECG :calibrationECG :calibration

ECG :paper speedECG :paper speed

Electrical artifacts:external or internalElectrical artifacts:external or internal

external can be minimized by straightening external can be minimized by straightening the lead wiresthe lead wires

internal can be due to muscle internal can be due to muscle tremors,shivering ,hiccoughs .tremors,shivering ,hiccoughs .

Supine positionSupine position

Interpretation of an ECGInterpretation of an ECG

Steps involvedSteps involved

Heart RateHeart Rate

RhythmRhythm

AxisAxis

Wave morphologyWave morphology

Intervals and segments analysisIntervals and segments analysis

Chamber enlargementChamber enlargement

Specific changesSpecific changes

Wave formsWave forms

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.

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.

QRS axisQRS axis

Dr.K.SubramanyamDr.K.Subramanyam

9-4-20099-4-2009

Genesis of QRSGenesis of QRS

Initially there is a small vector from left to Initially there is a small vector from left to right through the IVS ,followed by a larger right through the IVS ,followed by a larger vector from right to left through the free vector from right to left through the free wall of the LVwall of the LV

Effect of left oriented leadEffect of left oriented lead

Small septal vector ,directed away from Small septal vector ,directed away from the positive pole resulting in a small q the positive pole resulting in a small q wavewave

Larger vector of the free wall ,directed Larger vector of the free wall ,directed towards the positive pole resulting in a tall towards the positive pole resulting in a tall R waveR wave

Effect of right oriented leadEffect of right oriented lead

Small septal vector which is directed Small septal vector which is directed towards the positive pole,hence a small r towards the positive pole,hence a small r wavewave

Large vector of free LV wall which is Large vector of free LV wall which is directed away from the lead and hence a directed away from the lead and hence a large s wavelarge s wave

Transition zoneTransition zone

Transition from rS to qR pattern which is Transition from rS to qR pattern which is usually seen in V3 /V4usually seen in V3 /V4

Rotation of the heartRotation of the heart

Around AP axis;here the axis runs through Around AP axis;here the axis runs through the IVS from the ant to post surface of the the IVS from the ant to post surface of the heartheartHorizontal position;main body of the LV is Horizontal position;main body of the LV is oriented upwards and to the left:towards oriented upwards and to the left:towards leads I and avL(left axis)leads I and avL(left axis)Vertical position;main body of the LV is Vertical position;main body of the LV is oriented to leads II and avF(right and oriented to leads II and avF(right and inferior)inferior)

Around oblique axis;the axis runs through Around oblique axis;the axis runs through the IVS from apex to basethe IVS from apex to base

Anatomical rotation Anatomical rotation clock-wise and clock-wise and counter clock wise rotationcounter clock wise rotation

Counter clock-wise Counter clock-wise more anterior more anterior position of LVposition of LV

Results in transition zone shifting to leftResults in transition zone shifting to left

Clock wise rotation;here th RV assumes a Clock wise rotation;here th RV assumes a more anterior position so that the IVS lay more anterior position so that the IVS lay parallel to the chest wallparallel to the chest wall

There is a shift of the transition zone to the There is a shift of the transition zone to the rightright

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.

Abnormalities of axis can hint at:Abnormalities of axis can hint at:

Ventricular enlargementVentricular enlargement

Conduction blocks (i.e. hemiblocks)Conduction blocks (i.e. hemiblocks)

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.

Example 1Example 1

Negative in I, positive in aVF RAD

Example 2Example 2

Positive in I, negative in aVF Predominantly positive in II

Normal Axis (non-pathologic LAD)

-90°-60°

-30°

0°

aVL

I

30°

60°

aVR

II

90°

120°III

150°

180°

-150°

-120°

aVF

Marked RAD

LAD

RAD

Normal Axis

-30° to +100°

Example 1Example 1

Equiphasic in aVF Predominantly positive in I QRS axis ≈ 0°

Example 2Example 2

Equiphasic in II Predominantly negative in aVL QRS axis ≈ +150°

Using leads I, II, IIIUsing leads I, II, III

LEAD 1LEAD 1 LEAD 2LEAD 2 LEAD 3LEAD 3

NormalNormal UPRIGHTUPRIGHT UPRIGHTUPRIGHT UPRIGHTUPRIGHT

PhysiologicPhysiological Left Axisal Left Axis UPRIGHTUPRIGHT UPRIGHT / UPRIGHT /

BIPHASICBIPHASIC NEGATIVENEGATIVE

Pathological Pathological Left AxisLeft Axis UPRIGHTUPRIGHT NEGATIVENEGATIVE NEGATIVENEGATIVE

Right AxisRight Axis NEGATIVENEGATIVEUPRIGHTUPRIGHT

BIPHASICBIPHASIC

NEGATIVENEGATIVEUPRIGHTUPRIGHT

Extreme Extreme Right AxisRight Axis NEGATIVENEGATIVE NEGATIVENEGATIVE NEGATIVENEGATIVE

Common causes of LADCommon causes of LAD

May be normal in the elderly and very May be normal in the elderly and very obeseobeseDue to high diaphragm during pregnancy, Due to high diaphragm during pregnancy, ascites, or ABD tumorsascites, or ABD tumorsInferior wall MIInferior wall MILeft Anterior HemiblockLeft Anterior HemiblockLeft Bundle Branch BlockLeft Bundle Branch BlockWPW SyndromeWPW SyndromeCongenital LesionsCongenital LesionsRV Pacer or RV ectopic rhythmsRV Pacer or RV ectopic rhythmsEmphysemaEmphysema

Common causes of RADCommon causes of RAD

Normal variantNormal variant

Right Ventricular HypertrophyRight Ventricular Hypertrophy

Anterior MIAnterior MI

Right Bundle Branch BlockRight Bundle Branch Block

Left Posterior HemiblockLeft Posterior Hemiblock

Left Ventricular ectopic rhythms or Left Ventricular ectopic rhythms or pacingpacing

WPW Syndrome WPW Syndrome

The Normal ECGThe Normal ECG

Dr.K.SubramanyamDr.K.Subramanyam

30-3-200930-3-2009

Normal Sinus RhythmNormal Sinus Rhythm

Originates in the sinus nodeOriginates in the sinus nodeRate between 60 and 100 beats per minRate between 60 and 100 beats per minP wave axis of +45 to +65 degrees, ie. P wave axis of +45 to +65 degrees, ie. Tallest p waves in Lead IITallest p waves in Lead IIMonomorphic P wavesMonomorphic P wavesNormal PR interval of 120 to 200 msecNormal PR interval of 120 to 200 msecNormal relationship between P and QRSNormal relationship between P and QRSSome sinus arrhythmia is normalSome sinus arrhythmia is normal

Sinus ArrhythmiaSinus Arrhythmia

ECG Characteristics: Presence of sinus P waves

Variation of the PP interval which cannot be attributed to either SA nodal block or PACs

When the variations in PP interval occur in phase with respiration, this is considered to be a normal variant. When they are unrelated to respiration, they may be caused by the same etiologies leading to sinus bradycardia.

Normal P waveNormal P wave

Atrial depolarisationAtrial depolarisation

Duration 80 to 100 msecDuration 80 to 100 msec

Maximum amplitude 2.5 mmMaximum amplitude 2.5 mm

Axis +45 to +65Axis +45 to +65

Biphasic in lead V1Biphasic in lead V1

Terminal deflection should not exceed 1 Terminal deflection should not exceed 1 mm in depth and 0.03 sec in duration mm in depth and 0.03 sec in duration

Normal P waveNormal P wave

P’ waveP’ wave

Results in negative wave form in leads Results in negative wave form in leads II,III and avFII,III and avF

Axis;-80 to -90Axis;-80 to -90

Retrograde activation of atria due to Retrograde activation of atria due to impulse arising from or passing through impulse arising from or passing through AV nodeAV node

Dome & dart p waveDome & dart p wave

Low left atrial rhythmLow left atrial rhythm

Initial dome-like deflexion and a terminal Initial dome-like deflexion and a terminal sharp & spike like deflexionsharp & spike like deflexion

Normal QRS complexNormal QRS complex

Completely negative in lead aVR , maximum Completely negative in lead aVR , maximum positivity in lead IIpositivity in lead IIrS in right oriented leads and qR in left oriented rS in right oriented leads and qR in left oriented leads (septal vector)leads (septal vector)Transition zone commonly in V3-V4Transition zone commonly in V3-V4RV5 > RV6 normallyRV5 > RV6 normallyNormal duration 50-110 msec, not more than Normal duration 50-110 msec, not more than 120 msec120 msecPhysiological q wave not > 0.03 secPhysiological q wave not > 0.03 sec

ECG showing qR pattern in lead ECG showing qR pattern in lead III ,disappears on deep inspiration III ,disappears on deep inspiration q q wave not significantwave not significant

Mech:shift in the QRS axisMech:shift in the QRS axis

QRS-T angleQRS-T angle

The normal t wave axis is similar to the The normal t wave axis is similar to the QRS axisQRS axis

Normally the QRS-T angle does not Normally the QRS-T angle does not exceed 60 degexceed 60 deg

Amplitude of QRSAmplitude of QRS

Depends on the following factorsDepends on the following factors

1.electrical force generated by the 1.electrical force generated by the ventricular myocardiumventricular myocardium

2.distance of the sensing electrode from 2.distance of the sensing electrode from the ventriclesthe ventricles

3.Body build;a thin individual has larger 3.Body build;a thin individual has larger complexes when compared to obese complexes when compared to obese individualsindividuals

4.direction of the frontal QRS axis4.direction of the frontal QRS axis

Normal T waveNormal T wave

Same direction as the preceding QRS Same direction as the preceding QRS complexcomplex

Blunt apex with asymmetric limbsBlunt apex with asymmetric limbs

Height < 5mm in limb leads and <10 mm Height < 5mm in limb leads and <10 mm in precordial leadsin precordial leads

Smooth contoursSmooth contours

May be tall in athletesMay be tall in athletes

ST segmentST segment

Merges smoothly with the proximal limb of Merges smoothly with the proximal limb of the T wavethe T wave

No true horizontalityNo true horizontality

Normal u waveNormal u wave

Best seen in midprecordial leadsBest seen in midprecordial leads

Height < 10% of preceding T waveHeight < 10% of preceding T wave

Isoelectric in lead aVL (useful to measure Isoelectric in lead aVL (useful to measure QTc)QTc)

Rarely exceeds 1 mm in amplitudeRarely exceeds 1 mm in amplitude

May be tall in athletes (2mm)May be tall in athletes (2mm)

QT intervalQT interval

Normally corrected for heart rateNormally corrected for heart rate

Bazett’s formulaBazett’s formula

Normal 350 to 430 msecNormal 350 to 430 msec

With a normal heart rate (60 to 100), the With a normal heart rate (60 to 100), the QT interval should not exceed half of the QT interval should not exceed half of the R-R interval roughlyR-R interval roughly

Measurement of QT intervalMeasurement of QT interval

The beginning of the QRS complex is best The beginning of the QRS complex is best determined in a lead with an initial q wave determined in a lead with an initial q wave

leads I,II, avL ,V5 or V6leads I,II, avL ,V5 or V6

QT interval shortens with tachycardia and QT interval shortens with tachycardia and lengthens with bradycardia lengthens with bradycardia

Prolonged QTcProlonged QTc

During sleepDuring sleepHypocalcemiaHypocalcemiaAc myocarditisAc myocarditisAMIAMIDrugs like quinidine,procainamide,tricyclic Drugs like quinidine,procainamide,tricyclic antidepressantsantidepressantsHypothermiaHypothermiaHOCMHOCM

Advanced AV block or high degree AV Advanced AV block or high degree AV blockblock

Jervell-Lange –Neilson syndromeJervell-Lange –Neilson syndrome

Romano-ward syndromeRomano-ward syndrome

Shortened QT Shortened QT

Digitalis effectDigitalis effect

HypercalcemiaHypercalcemia

HyperthermiaHyperthermia

Vagal stimulationVagal stimulation

Normal standardizationNormal standardization

1 mV=10 mm1 mV=10 mm

Will result in perfect right angles at each Will result in perfect right angles at each cornercorner

overdampingoverdamping

When the pressure of the stylus is too firm When the pressure of the stylus is too firm on the paper so that it’s movements are on the paper so that it’s movements are retardedretardedThe ecg deflexions are inscribed more The ecg deflexions are inscribed more slowly so that they become fractionally slowly so that they become fractionally widerwiderResults in diminished amplitude of Results in diminished amplitude of deflexionsdeflexions a small s wave may a small s wave may disappeardisappear

Underdamping or overshootUnderdamping or overshoot

When the writing stylus is not pressed When the writing stylus is not pressed firmly enough against the paperfirmly enough against the paper

Results in overshoot of the upswing and Results in overshoot of the upswing and downswing of the writing stylus,resulting in downswing of the writing stylus,resulting in sharp spikes at the cornerssharp spikes at the corners

Effects:deflexions are inscribed more Effects:deflexions are inscribed more rapidly rapidly resulting in fractionally narrower resulting in fractionally narrower complexescomplexes

The ecg deflexions may be increased in The ecg deflexions may be increased in amplitude .amplitude .

An s wave becomes exaggerated An s wave becomes exaggerated

Normal Variants in the ECGNormal Variants in the ECG

Sinus arrhythmiaSinus arrhythmia

Persistent juvenile patternPersistent juvenile pattern

Early repolarisation syndromeEarly repolarisation syndrome

Non specific T wave changesNon specific T wave changes

Persistent juvenile patternPersistent juvenile pattern

Features of ERPSFeatures of ERPS

Vagotonia / athletes’ heartVagotonia / athletes’ heartProminent J pointProminent J pointConcave upwards, minimally elevated ST segmentsConcave upwards, minimally elevated ST segmentsTall symmetrical T wavesTall symmetrical T wavesProminent q waves in left leadsProminent q waves in left leadsTall R waves in left oriented leadsTall R waves in left oriented leadsProminent u wavesProminent u wavesRapid precordial transitionRapid precordial transitionSinus bradycardiaSinus bradycardia

EEarly arly RRecognition ecognition PPrevents revents SStreptokinase infusion !treptokinase infusion !

Reporting an ECGReporting an ECG

1. Patient Details1. Patient Details

“ “ Whose ECG is it ?!”Whose ECG is it ?!”

2. Standardisation and lead 2. Standardisation and lead placementplacement

““Is it properly taken ?”Is it properly taken ?”

3. Analysis of Rate, Rhythm and 3. Analysis of Rate, Rhythm and AxisAxis

4. Segment and wave form 4. Segment and wave form analysis analysis

5. Chamber enlargements5. Chamber enlargements

Final ImpressionFinal Impression

“ “ Does the ECG correlate with Does the ECG correlate with the clinical scenario ?” the clinical scenario ?”

Thank you !Thank you !