ElectroCardioGraph (ECG) Basic Principles

ElectroCardioGram (ECG)Introduction Of Basic PrinciplesDian Puspita SariObjectivesAt the end of this session, students expected to be able to:Explain definition of ECG and the use of ECGExplain about electrodes and leadsExplain about procedure of ECGExplain about Unipolar and Bipolar LeadsExplain about principles of ECG waves and normal pattern of ECGMention how to asses Heart rhythm, heart rate, axis, and several important abnormalitiesIntroductionECG records potential differences caused by cardiac excitationGive information about:Heart position, Relative chamber size, Heart rhythm, Impulse origin/propagation, Rhythm/conduction disturbances, Extent and location of cardiac inschaemia/infarct, Changes in electrolyte concentrationTypical ECG report shows cardiac cycles from 12 vantage points by using 10 electrodesTermsElectrode : electrical recording device, placed in patients bodyLimbs electrodes : Right Arm (RA), Left Arm (LA), Left Leg(LL), Right Leg (ground)Precordial electrodes : V1, V2,, V6Lead : electrical picture of the heart; picture in each lead can be different depend on the direction of electrical impulse. Electrodes

Limbs ElectrodePrecordial ElectrodeLocation for Precordial ElectrodeV1 : right 4th intercostal space, parasternal lineV2: left 4th intercostal space, parasternal lineV3 : between V2 and V4V4 : left 5th intercostal space, midclavicular lineV5 : horizontal to V4, anterior axillary lineV6: horizontal to V5, mid axillary lineECG Leads2 Basic types:Unipolar leads : lead aVR, aVL, aVF, V1 V6 point where electrode is placed is the (+) pole, and negative pole is combination of other electrodes

Bipolar leads : lead I, II, III lead between 2 electrodes, where one electrodes serve as (-) pole and other as (+) pole

Unipolar Leads

Frontal PlanePerpendicular PlaneBipolar Leads

Bipolar Leads(-) electrodes(+) electrodesIRALAIIRALLIIILALL

Axial Reference System

Principles of ECG WavesAn electrical force directed toward the (+) pole of a lead results in an upward deflection on ECG recording of that leadForces that head away form the (+) electrode result in a downward deflectionMagnitude of deflection, either upward or downward, reflects how parallel the electrical force is to the axis of lead being examined. The more parallel the electrical force to the lead, the greater the magnitude of the deflectionAn electrical force directed perpendicular to an ECG lead does not register any activity by that lead (a flat line on recording)LARALL3 Bipolar Limb Leads:I = RA vs. LA (+)ECG Recordings (QRS Vector pointing leftward, inferiorly & posteriorly)12LARALL3 Bipolar Limb Leads:I = RA vs. LA (+)II = RA vs. LL (+)ECG Recordings (QRS Vector pointing leftward, inferiorly & posteriorly)13LARALL3 Bipolar Limb Leads:I = RA vs. LA (+)II = RA vs. LL (+)III = LA vs. LL (+)ECG Recordings (QRS Vector pointing leftward, inferiorly & posteriorly)14LARALL3 Bipolar Limb Leads:I = RA vs. LA (+)II = RA vs. LL (+)III = LA vs. LL (+)3 Augmented Limb Leads:aVR = (LA-LL) vs. RA(+)ECG Recordings (QRS Vector pointing leftward, inferiorly & posteriorly)15LARALL3 Bipolar Limb Leads:I = RA vs. LA (+)II = RA vs. LL (+)III = LA vs. LL (+)3 Augmented Limb Leads:aVR = (LA-LL) vs. RA(+)aVL = (RA-LL) vs. LA(+)ECG Recordings (QRS Vector pointing leftward, inferiorly & posteriorly)16LARALLECG Recordings (QRS Vector pointing leftward, inferiorly & posteriorly)3 Bipolar Limb Leads:I = RA vs. LA (+)II = RA vs. LL (+)III = LA vs. LL (+)3 Augmented Limb Leads:aVR = (LA-LL) vs. RA(+)aVL = (RA-LL) vs. LA(+)aVF = (RA-LA) vs. LL(+)17V1V2V3V4V5V66 Precordial (Chest) LeadsSpineSternum18ECG Waves

Pay more attention to various shape of normal QRS complexNormal ECG

20SettingVoltage calibration determine the height of waves. Normally, 1mV= 10 mm (2 large boxes)

Speed : normally 25 mm/sec each 1mm = 0.04 secECG InterpretationSettingHeart RhythmHeart RateIntervalsAxis (mean QRS axis)Abnormalities of P waveAbnormalities of QRSAbnormalities of ST and T waveHeart RateHR = (25 mm/sec x 60 sec/min)

Number of mm between beats

HR = 1500

Number of mm between beats

ORHR = 300

Number of large boxes

ORHeart Rate

Heart RhythmSinus Rhythm:Every P wave is followed by a QRS complexEvery QRS is preceed by a P waveP wave is upright in leads I, II, III PR interval is greater 0.12 sec (3 small boxes)Normal Sinus RhythmSinus rhythm with HR between 60-100 x/minIf < 60 x/min Sinus BradycardiaIf> 100x/min Sinus TachycardiaSinus Tachycardia

Sinus Bradycardia

Sinus Arhytmia

IntervalsPR, QRS and QT intervalsCheck the limb leads to asses intervalsLead I, II, III, aVR, aVL, aVFTake measurement in a lead where the interval is longest in durationPR interval : from beginning of P wave until onset of QRS QRS interval: from beginning to the end of QRS complexQT interval : from beginning of QRS to the end of T wave. Corrected QT QT/R-RIntervalsIntervalNormal DurationAnalogQRS 0.12 s3 small boxesPR0.12-0.2 s 3-5 small boxesQT0.410 small boxes or 2 large boxesMean QRS Axis (Axis)Normal Axis : -30o until +90o

Mean QRS Axis (Axis)Right Axis DeviationLeft Axis DeviationNormal Axis

Mean QRS Axis (Axis)Look at Lead I and II; if QRS primarily upward in both lead, then the axis is normal. If not:Determine the mean axisInspect the six limb leads and determine which one contain QRS that is most isoelectric. The mean axis is perpendicular to that.Determine the directionInspect the lead that is perpendicular to lead that contain the isoelectric QRS complex. If QRS in that perpendicular lead is primarily upward,then the mean axis points to the (+) pole of that lead. If primarily negative, than the mean axis points to (-) pole of that lead Axis Deviation

Axis Deviation

P Wave AbnormalitiesP wave represents atrial depolarization (first is right atrium, quickly followed by left atrium)Best visualized in Lead IIAbnormalities of P wave abnormalities of AtriumTall P wave in lead II (>2.5mm in height) right atrial enlargementNegative deflection > 1mm wide and > 1mm deep in lead V1 left atrial enlargement

Right Atrial Enlargement

Left Atrial Enlargement

QRS complexQRS complex represents ventricular depolarizationNormal QRS complex:Small Q waves are permissible in Lead I, aVL, and V6RSR pattern in V1 is normal if less than 0.12 sLook at abN pattern to compare!Abnormalities of QRS complex can describe:Ventricular hypertrophyBundle Branch BlockMyocardial infarctionAbnormalities of QRS complex :Ventricular HypertrophyRight Ventricular HypertrophyR > S in V1Right axis deviationLeft Ventricular Hypertrophy(S in V1) + (R in V5 or V6) 35 mm, ORR in aVL > 11 mm, ORR in lead I > 15 mmLVH

RVH

Abnormalities of QRS complex :Myocardial Infarct Normal Q wave : Short duration ~ 1 small box, and Low magnitude (< 25%of the QRS total height)Pathologic Q wave :Duration > 1 small box, and height > 25% QRS total heightRepresents transmural MIPermanent evidence of infarctLocation of MI can be determinedAbnormalities of ST segmentNormal ST segment : should be isoelectricExample of Abnormalities ST segment :ST elevation infarctST depresion ischaemia ST elevation in Anterior InfarctPicture of ST elevationPicture of ST depression

T waveNormal T wave maybe inverted in :Lead IIILead aVRLead V1Abnormal T wave maybe seen in :Myocardial Infarct (depressed/inverted T wave)Ventricular ArrhytmiaetcECG records were taken from www.learntheheart.comThank you