ELECTROCARDIOGRAPHY (ECG)

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ELECTROCARDIOGRAPHY (ECG)

  1. 1. ©Dr. Anwar SiddiquiPhysiology Seminar15/01/2013ELECTROCARDIOGRAPHYPRACTICAL PHYSIOLOGY1
  2. 2. INTRODUCTION ECG is a three letter acronym for ElectroCardioGraphy. The word is derived from electro(greek forelectricity),cardio(greek for heart) and graph(Greek rootmeaning "to write“) It is a transthoracic interpretation of the electrical activityof the heart over time captured and externally recordedby skin electrodes. The device used to produce this non invasive record iscalled the electrocardiograph. ECG is the gold standard for the noninvasive diagnosis ofcardiac diseases and may occasionally be the only markerfor the presence of heart disease.2
  3. 3. INDICATIONS OF ECG Gold standard for diagnosis of cardiac arrhythmias Helps detect electrolyte disturbances (hyper- &hypokalemia) Allows for detection of conduction abnormalities Screening tool for ischemic heart disease during stresstests Helpful with non-cardiac diseases (e.g. pulmonaryembolism or hypothermiaAn ECG is a diagnostic tool, NOT a treatmentNo one is ever cured by an ECG!!3
  4. 4. ELECTROCARDIOGRAPHY TIMELINE 1872:Alexander Muirhead attached wires to a feverishpatients wrist to obtain a record of the patients heartbeatSt Bartholomews Hospital. 1887:British physiologist Augustus D. Waller of St MarysMedical School, London publishes the first humanelectrocardiogram. The trace from the heartbeat wasprojected onto a photographic plate which was itself fixedto a toy train 1893:Dutch physiologist Willem Einthoven introduces theterm electrocardiogram at a meeting of the Dutch MedicalAssociation. 1895: Willem Einthoven distinguishes five deflectionswhich he names P, Q, R, S and T4
  5. 5. 1902: Einthoven publishes the first electro -cardiogram recorded on a string galvanometer.1912: Einthoven addresses the Chelsea ClinicalSociety in London and describes an equilateraltriangle formed by his standard leads I, II and IIIlater called Einthovens triangle.1924: Willem Einthoven wins the Nobel prize forinventing the electrocardiograph.5
  6. 6. • Figure depicting Einthoven recording his first ECGin 1902 by placing limbs in buckets of conductingsolution!6
  7. 7. BASIC ELECTROPHYSIOLOGYPHYSIOLOGICAL PROPERTIES OF MYOCARDIAL CELLAutomaticity: ability to initiate an impulseExcitability: ability to respond to a stimulusConductivity: ability to transmit an impulse Contractility: ability to respond with pumpingactionDepolarization and repolarization of a cardiac cellgenerates action potentialECG is the composite representation of actionpotential of all cardiac cell.7
  8. 8. ELECTRICAL CONDUCTION SYSTEM OF THE HEART The electrical discharge for each cardiac cycle normallystarts in a special area of the right atrium called the‘sinoatrial (SA) node’. Depolarization then spreads through the atrial musclefibres. There is a delay while the depolarization spreads throughanother special area in the atrium, the ‘atrioventricular(AV) node’. Thereafter, the electrical discharge travels very rapidly,down specialized conduction tissue: first a singlepathway, the ‘bundle of His’, which then divides in theseptum between the ventricles into right and left bundlebranches. 8
  9. 9.  Within the ventricular mass, conduction spreads somewhatmoreslowly, through specialized tissue called ‘Purkinjefibres’.9
  10. 10. Conduction speed of cardiac tissue10TISSUE CONDUCTIONRATE (m/s)SA node 0.05Atrial pathway 1AV node 0.05Bundle of His 0.05Purkinje system 4Ventricular muscle 1
  11. 11. CONDUCTION OF THE IMPULSE:Normal resting membrane potential=-90mvIf the potential rises from -90 to 0, then this excites afurther rise of potential, called the action potential.The action potential is transmitted throughout thecell and forms the impulse.During the rise of potential, the membrane becomespermeable to Sodium ions and the potential rises to apositive direction. This phenomena is calleddepolarization.The Sodium channels close and there is rapiddiffusion of K+ ions into the exterior, reestablishingthe resting membrane potential. This is called Depolarization is followed by muscle contraction andrepolarisation is followed by muscle relaxation.11
  12. 12. • Fig depicting the mechanism of depolarisation andrepolarisationDepol RepolRestoration of ionicbalance12
  13. 13. NORMAL SINUS RYTHEMThe adjacent figure shows the normal sinus rythemA normal sinus rythem comprises of the followingwaves:-• P waves- denotes atrial depolarization(electricalvector is directed from the SA node towards the AVnode)• QRS complex- denotes depolarization of ventricles aswell as repolization of atrium• T waves- denotes the repolarization (or recovery) ofthe ventricles. The interval from the beginning of theQRS complex to the apex of the T wave is referred to asthe absolute refractory period. The last half of the Twave is referred to as the relative refractory period.As depicted in the fig:-•PR interval- beginning of the P wave to the beginningof the QRS complex•ST segment- connects the QRS complex and the Twave.•QT interval- the beginning of the QRS complex to theend of the T wave.13
  14. 14. What differentiates a segment from an interval? A segment is a straight line connecting two waves. An interval encompasses at least one wave plus theconnecting straight line.14
  15. 15.  J point- J-point is the point at which the QRS complex meets the ST wave. Its an isoelectric point and its importance lies in the fact that ST segmentelevation is measured with respect to it J WAVE AND U WAVE:These are two abnormal waves that may be seensumtime in the ecg recordings.o J wave• also known as camel-hump sign, late delta wave, hathook junction, hypothermicwave, prominent J wave ,[1] K wave, H wave or current of injury• positive deflections occurring at the junction between the QRS complex and STsegment(j point)• observed in people suffering from hypothermia with a temperature of less than32o U wave• typically small, and, by definition, follows the T wave• Prominent U waves are most often seen in hypokalemia, but may be presentin hypercalcemia, thyrotoxicosis15
  16. 16. Fig representing the J pointFig representing the J wave in anhypothermic individualThe arrow in the figure representsthe U wave in a hypokalemicpatient16
  17. 17. RECORDING THE ELECTROCARDIOGRAMTHE E.C.G PAPER ECG machines record changes in electrical activity bydrawing a trace on a moving paper strip. The electrocardiograph uses thermal paper, which is agraph paper & runs normally at a speed of 25mm/sec Time is plotted on the X axis & voltage is plotted on the Yaxis. In X axis, 1 second is divided into 5 large squares each ofwhich represents 0.2 sec. Each large square is furtherdivided into 5 small squares which represents 0.04 sec. The ECG machine is calibrated in such a way that anincrease of voltage by 1 mVolt should move the stylusvertically by 1cms.17
  18. 18. ECG PAPER• Fig adjacent shows a callibrationgraph.By callibration we mean that anincrease of voltage by 1mVolt shouldmove the stylus vertically by 1cms. . Thecalibration signal should be includedwith every record18
  19. 19. ELECTROCARDIOGRAPHIC LEADS - CONVENTIONAL 12 conventional leads, physiologically divided into two groupsviz:Bipolar leads- 3 Standard limb leadsUnipolar leads-3 Augmented limb leads and 6 precordialchest leads Bipolar leads : These record the actual difference in potentialacross the two electrodes. There are three standard limblead:-• Lead I Left arm Right arm• Lead II Left foot Right arm• Lead III Left foot Left armo The lead axes form the sides of an equilateral triangle withthe heart at the center ( Einthovens triangle)19
  20. 20. o The sum total of the potential in the three leads equals zeroand mathematically it co uld be demonstrated that thepotential in L II equals sum of the potentials in L I and L III i.e,Einthovens law. Unipolar limb leads:• Constituted by the indifferent electrode which forms thenegative electrode and the exploring electrode which formsthe positive electrode.• The indifferent electrode is constituted by connecting all limblead electrodes together through an electrical resistancethere by maintaining the zero potential. The positiveelectrode records the true potential at a given point. Here therecord is of low voltage.• Goldberger augmented these leads for properrecording,came to be known as augmented unipolar limbleads, represented by aVR, aVF, aVL leads20
  21. 21. According to Kirchhoffs law these lead voltages have the following relationship:VI + VIII = VII21
  22. 22.  Unipolar chest leads Constituted by an indifferent electrode resulting from aconnection between all three standard limb leads and anexploring electrode placed on 6 different points on thechest wall. The indifferent electrode forms the negative terminal&the exploring electrode forms the positive terminal. Placement of precordial leads.V 1 - 4th intercostal space , right of sternum.V 2 - 4th ICS left of sternumV 4 - 5th ICS midclavicular lineV 3 - Midway between V2 and V4V 5 - 5th ICS anterior axillary line.V 6 - 5th ICS mid axillary line. 22
  23. 23. Diagram depicting the einthoven’sTriangle along with the position ofvarious electrodes used in the ECGLegend:RA-right armLA-left armL leg-left legV1 to V6-precordial chest leadaVR-augmented vector right armaVL-augmented vector left armaVF-augmented vector left foot23
  24. 24.  Leads I, II and aVL look at the left lateral surface of the heart leads III and aVF at the inferior surface, and lead aVR looks at theright atrium The V leads are attached to the chest wall by means of asuction electrode• leads V1 and V2 look at the right ventricle• V3 and V4 look at the septum between the ventricles and theanterior wall of the left ventricle• V5 and V6 look at the anterior and lateral walls of the left ventricle24
  25. 25. • An overview of the electrocardiographic leads25
  26. 26. MAKING A RECORDING Good contact between body surface and electrode is necessary. Itmight be essential to shave the chest and apply electro cardiographic jelly The patient must lie down and relax to prevent muscle tremor Connect up the limb electrodes to the correct limb.limb electrodeshave marking on them and also they are colour coded(red –rightarm,yellow-left arm,gren left leg and black-right leg) Calibrate the record with 1mv signal.There shouldn’t beoverdamping or underdamping. Any metallic object like watch or jwelleary should be removef fromthe patients body 4-5 recording of each lead is recorded26
  27. 27. FUNDAMENTAL PRINCIPLES BEHIND THE RECORDING An electromagnetic force, current or vector has bothmagnitude and direction. When this force is directed tothe positive electrode of a lead, the ECG will record anupward or positive deflection When the vector is directed away from the positiveelectrode the ECG will record a downward or negativedeflection, if at 90degree to the electrode the wavetouches the baseline physiologically, left ventricle and inter ventricular septumconstitutes the dominant part,and hence maximallyinfluences variations in ECG.27
  28. 28. WAVES FORMATION28A wave of depolarisation moving toward a positive electrode records a positive deflectionA wave of depolarisation moving away from the elec trode causes negative deflewction
  29. 29. • EKG recording if the positive electrode is placedin the middle of the cell29
  30. 30. 30 We can easily apply these concepts to the entire heart. Electrodes placed on the surface of the body will recordwaves of depolarization and repolarization as they sweepthrough the heart.
  31. 31. HOW TO REPRT AN ECG Ecg strip should be correctly labelled(the patients particular andall the lead markings) The ecg recording should be described under the following heads:• Heart rate• Rythem• Various conduction intervals (pr interval ,qt interval)• Description of QRS complex ,ST segment and T waves• Cardiac axis• Any abnormal wave like J and U waves Heart rate:calculated by dividing 1500 by number of small boxbetween two consecutive R waves• Sinus tachycardia-heart rate more than 100 beats per minute.• Sinus bradycardia-heart rate less than 60 beats per minute31
  32. 32.  Rhythm- rhythm controlled by sinus node at a rate of 60-100beats/min; each P wave followed by QRS and each QRS precededby a P wave.Specific Arrhythmias• Sinus bradycardia• Sinus tachycardia• Sick sinus syndrome- disturbance of SA nodal function that resultsin a markedly variable rhythm (cycles of bradycardia andtachycardia).• Atrial flutter - sinus rate of 250-350 beats/min• AV nodal blocks - a conduction block within the AV node (oroccasionally in the bundle of His) that impairs impulse conductionfrom the atria to the ventricles.• Ventricular flutter - very rapid ventricular depolarizations >250/min• Ventricular fibrillation - uncoordinated ventricular depolarizations;leads to death if not quickly corrected32
  33. 33. 33NORMAL SINUS RHYTHM Impulses originate at S-A node at normal rateSINUS TACHYCARDIA Impulses originate at S-A node at rapid rateATRIAL FLUTTER Impulses travel in circular course in atria – No interval between T and P
  34. 34. 34ATRIAL FIBRILLATION Impluses have chaotic, random pathways in atriaVENTRICULAR TACHYCARDIAImpulse originate at ventricular pacemaker – odd/wide QRS complexVENTRICULAR FIBRILLATIONChaotic ventricular depolarization – ineffective at pumping blood – death within minutes
  35. 35. 35A-V BLOCK, FIRST DEGREE Atrio-ventricular conduction lengthenedP-wave precedes each QRS-complex but PR-interval is > 0.2 sA-V BLOCK, SECOND DEGREE Sudden dropped QRS-complexIntermittently skipped ventricular beat
  36. 36.  PR interval and QT interval• The PR interval extends from the start of the P wave to thevery start of the QRS complex.• A normal value is 0.12 to 0.20 seconds• Its significance lies in assessing the nodal blocks• QT interval is a measure of the time between the start of the Qwave and the end of the T wave• Normal values for the QT interval are between 0.30 and 0.44 secs• If abnormally prolonged or shortened, there is a risk of developingventricular arrythmias QRS complex and ST segment• The QRS complex is 0.08 to 0.12 sec• Not every QRS complex contains a Q wave, an R wave, and an S wave• The duration, amplitude, and morphology of the QRS complex is useful indiagnosing, arrythmias, conduction abnormality, myocardialinfarction,and other disease states.36
  37. 37. • ST segment connects theQRS complex and theT wave and has a duration of0.08 to 0.12 sec• ST segment elevation or depression is associated with various cardiacabnormalityConditions causing ST segment elevationAcute myocardial infarctionPericarditisLeft Ventricular HypertrophyLeft Bundle Branch BlockhyperkalemiaConditions causing ST segment depressionIschemic heart diseaseHypokalemiaSecondary ST segment changes with conduction abnormalities (e.g., RBBB,LBBB, WPW, etchypokalemia37
  38. 38. Morphology of ST segment elevation AMI usually demonstrate straight/convex STE Concave shaped STE-non AMI causes38
  39. 39.  Cardiac axis• The electrical axis of the heart is the mean direction of the actionpotentials traveling through the ventricles during ventricularactivation (depolarization)• The QRS complex, which represents ventricular depolarization, isused for the determination of the electrical heart axis.• The normal electrical axis of the heart is situated between -30degrees and +90 degrees (positive 90 degrees) with respect to thehorizontal line• Left axis deviation: the electrical heart axis is between -30 degreesand -90 degrees with respect to the horizontal line.• Right axis deviation: the electrical heart axis is between +90degrees and 180 degrees with respect to the horizontal line.• Extreme axis deviation (also known as northwest axis or no man’sland): the electrical heart axis is between +180 degrees and -90degrees with respect to the horizontal line.39
  40. 40. Fig showing the cardiac axis in hexaxial referrance systemcauses of right axis deviation•normal finding in children and tall thin adults•right ventricular hypertrophy•chronic lung•anterolateral myocardial infarction•left posterior hemiblock•Wolff-Parkinson-White syndrome - left sided accessory pathway•atrial septal defect•ventricular septal defect 40
  41. 41. causes of left axis deviation• left anterior hemiblock• Q waves of inferior myocardial infarction• emphysema• hyperkalaemia• Wolff-Parkinson-White syndrome - right sided accessory pathway• tricuspid atresia• ostium primum ASD• injection of contrast into left coronary arterycauses of a Northwest axis (no mans land)• emphysema• hyperkalaemia• lead transposition• artificial cardiac pacing• ventricular tachycardia41
  42. 42. REFERENCES• Only EKG Book Youll Ever Need, Thaler, Malcom S, 2007 LippincottWilliams & Wilkins 5th Edition• Schamroth L. Electrical axis. In : Schamroth C. (ed)An introductionto Electrocardiography, Blackwell Science Ltd. Massachusetts 1990;34–48.• John.R.Hampton the ECG made easy 6th edition ,ChurchillLivingstone publicationthe end….. thank you42

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