How to read ECG

How to read ECG

ECGRepresentation of Electrical activity of heart

ECG Leads12 lead ECG6 limb leads: Lead I, II, IIIaVL, aVR, aVF6 Chest Leads: V1, V2,V3, V4, V5, V6

ECG paperSpeed 25mm/s1 large square= 5 small square [5mm]Voltage 10mm =1mV

Appearance of wavesPositive deflection [upward]If electrical impulses flowing towards that leadNegative deflection [downward]If electrical impulses flowing away from that lead

Origin of waves

P waveAtrial depolarizationPR intervalAtrial depolarization to start of ventricular depolarizationQRS complexVentricular depolarizationT waveVentricular repolarizationQT intervalVentricular depolarization & repolarizationU wave? Interventricular septal repolarization

Systematic approachThe following 14 points should be analyzed carefully in every ECG:Standardization Heart rateRhythm P waves PR interval QRS voltages

QRS interval QT intervalMean QRS axisPrecordial R-wave progressionAbnormal Q waves ST segments T waves U waves

Standardization

Heart Rate1500/RR

If HR is irregularCount no. of QRS complexes in 30 large squares= 6 secMultiply it with 10HR [per min]

Rate calculationMemorize the number sequence: 300, 150, 100, 75, 60, 50

ECG machines: print out HRDO NOT RELY ON IT!!!!Always Calculate yourself.Bradycardia: 100/min

Rhythm Rhythm strip: prolonged recording of Lead IISinus rhythm ?Each QRS complex preceded by P waveRegular/ irregular?

RegularSinus rhythm

Irregular

QRS AXISIndicator of overall direction that wave of depolarization takes when passing through ventriclesAlso called ANGLEMeasured in degrees

Photo

Right axis deviation [RAD] Beyond +90Left Axis Deviation [LAD]Beyond -30

Method 1Most precise methodUse of vectorsMeasure overall height of QRS in lead I & aVFPlot in graph paperMeasure the ANGLE of vector

Method 2Quick methodIdentify limb lead in which QRS complex is isoelectric[with equal positive & negative deflection]Implies: electric flow is at Right angle to this lead

Method 3For quick assessmentLook at QRS complexes in lead I & II

Predominantlypositive QRS in lead IAxis between -90 to +90Excludes RAD

Predominantly positive QRS in lead II Axis between -30 to +150Excludes LAD

Lead ILead IICardiac AxisQRS PositiveQRS PositiveNormal AxisQRS PositiveQRS NegativeLeft Axis DeviationQRS NegativeQRS PositiveRight Axis Deviation

LADWPW syndromeLBBBInferior wall MIRADRVHWPW syndromeAnterolateral MIDextrocardia

P wavePresent or not?Sinus rhythmIf completely absentAtrial FibrillationHyperkalemia If intermittently absentSinus arrest

Inverted P waves?Incorrect positioned electrodesDextrocardiaAbnormal atrial depolarization

Height of P waves> 2.5 mm: tallIndicative of Right Atrial enlargementP Pulmonale

P PULMONALEP MITRALE

Width of P waves>2mm width: abnormalBifid P waveIndicates Left Atrial enlargementP Mitrale

PR IntervalFrom start of P wave to start of R waveNormallyNot 5 small squaresConsistent

Short PR IntervalAV junctional rhythmWPW syndromeLown Ganong-Levine syndrome

Long PR IntervalDenotes delay in conduction through AV nodeFirst Degree BlockPR prolonged, constant

Second degree BlockMobitz Type IPR progressively increase until one P wave fails to produce QRS complex

Mobitz Type IIPR interval normal & fixed, But occasional P waves fail to produce QRS

Third Degree Block [Complete AV Block]No relationship between P waves & QRS complex

2:1 BlockAlternate P waves are not followed by QRS complex

Q WAVEFirst negative deflection in QRS complex? Pathological Q wavesIf>2 small squares deep>1 small square wide>25% of height of the following R wave in depth

QRS complexAppearance of QRS Complex vary from lead to lead

Width: Narrow/ wideWide QRS:> 3 small squaresBundle branch blockVentricular arrhythmia

Size of QRS complexSmall:Pericardial effusion?incorrect calibration

Big QRS complexVentricular hypertrophy: R/LWPW syndrome

Progression of R waveV1: small R wave , large S wave,Gradually R wave increases, S wave decreases V6: small Q wave, large R waveV3 and V4 : located midway between V1 and V6, QRS complex nearly isoelectric in one of these leads

Progression of R wave

Left ventricular HypertrophyR Wave in V5 or V6 >25mmS Wave in V1 or V2 > 25mmSum of R wave in V5 Or V6 & S wave in V1 or V2 >35mm

LVH

Right Ventricular HypertrophyRight axis deviationDeep S Waves in leads V5 & V6R>S in V1RBBB

RBBBRight Bundle Branch BlockBroad QRS complexSmall r wave in V1, small Q wave in V6S wave in V1, R wave in V6R wave in V1, S wave in V6

LBBBLeft Bundle Branch BlockBroad QRSSmall Q wave in V1, Small r wave in V6R wave in V1, S wave in V6S wave in V1, R wave in V6

WILLIAM MORROWWilliam: W in V1 & M in V6: LBBBMorrow: M in V1 & W in V6: RBBB

LBBBIschemic Heart DiseaseCardiomyopathyLVHFibrosis RBBBIschemic heart diseaseCardiomyopathyASDMassive pulmonary embolism

ST SegmentFrom end of S wave to start of T WaveNormally: Isoelectric? Depressed/ elevated

Elevated ST segmentAcute MIPrinzmetals anginaPericarditisLV aneurysmHigh take off

Depressed ST segmentMyocardial ischemiaPosterior MIVentricular hypertrophy with StrainDrugs: Digoxin

Ventricular Hypertrophy with strain patternTall R wavesDeep S wavesST segment depressionT wave inversion

T Wave

T waveInverted?Normal in aVRV1,V2, IIISizeNormal: not > size of preceeding QRS complexToo small?Too large?

Tall T wavesHyperkalemiaAcute MI

Too small T WavesHypokalemiaPericardial effusionhypothyroidism

Inverted T wavesNormal in few leads: aVR, V1, V2, IIIMIMyocardial ischemiaVentricular hypertrophy with strainDigoxin toxicity

QT IntervalFrom start of QRS complex to end of T waveVaries with HR

Corrected QT intervalQTCQTC =QT/RRNormal: 0.35-0.43 sec

Prolonged QTcIf 0.44 secHypocalcemiaAcute myocarditisTorsades de pointes

U wavesMostly in anterior chest leadsDifficult to identify clearly

Prominent U WavesHypoklemiaHypercalcemiaHyperthyroidism

Common ECG Problems

ACUTE MI

Ischemia

HYPERKALEMIA

LVH WITH STRAIN

PERICARDITIS