ECG: Indication and Interpretation

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ECG: Indication and Interpretation

  1. 1. Guide Dr. J. Singh Madam Rakesh Verma
  2. 2.  The electrocardiogram (EKG) is a graphical representation of the electrical events of the cardiac cycle.  1895 - William Einthoven, credited for the invention of EKG  1924 - William Einthoven got the Noble prize for the same
  3. 3.  SA node is the pacemaker where the electrical impulse is generated.  Located along the posterior wall of the right atrium right beneath the opening of the SVC.  It is crescent shaped and about 3 mm wide and 1 cm long.  The impulse travels from the SA node through the internodal pathways to the atrioventricular node (AV node).
  4. 4.  The AV node is responsible for conduction of the impulse from the atria to the ventricles.  The impulse is delayed slightly at this point to allow complete emptying of the atria before the ventricles contract.  The impulse continues through the AV bundle and down the left and right bundle branches of the Purkinje fibers.
  5. 5. The Purkinje fibers conduct the impulse to all parts of the ventricles
  6. 6.  Turn on machine  Calibrate to 10mm/ mV  Rate at 25mm/ s  Record and print  Label the tracing - Name, DOB, Hospital number, date and time
  7. 7.  10 electrodes in total are placed on the patient  The 10 leads are lubricated with jelly then placed over the respective sites
  8. 8.  Chest leads are labelled “V”(vector) and are numbered from 1 to 6.  The placement of these electrodes needs to be exact to give the optimum information.
  9. 9.  V1 fourth intercostal space, right sternal edge  V2 fourth intercostal space, left sternal edge  V4 at the apex (fifth ICS mid clavicular line)  V3 midway between V2 and V4  V5 same level as V4 but on the anterior axillary line  V6 same level as V4 and V5 but on the mid mid-axillary line
  10. 10.  Electrical impulse (wave of depolarisation) picked up by placing electrodes on patient  The voltage change is sensed by measuring the current change across 2 electrodes – a positive electrode and a negative electrode  If the electrical impulse travels towards the positive electrode this results in a positive deflection  If the impulse travels away from the positive electrode this results in a negative deflection
  11. 11.  P wave: Activation (depolarization) of the right and left atria  QRS complex: right and left ventricular depolarization  T wave: ventricular repolarization
  12. 12.  PR interval: time interval from onset of atrial depolarization (P wave) to onset of ventricular depolarization (QRS complex)  QRS duration: duration of ventricular muscle depolarization  QT interval: duration of ventricular depolarization and repolarization  RR interval: duration of ventricular cardiac cycle (an indicator of ventricular rate)  PP interval: duration of atrial cycle (an indicator of atrial rate)
  13. 13.  Symtoms Palpitation, cyanosis, chest pain, syncope, seizure, poisoning  Signs tachycardia, bradycardia, hypothermia, murmur, Shock  Evaluation of rheumatic heart disease, congenital heart diseases  Evaluation of suspected electrolyte imbalance  Evaluation of cases like drowning, electrocution  During cardiopulmonary resuscitation (CPR).  Evaluation of patients with implanted defibrillators and pacemakers  To detect myocardial injury, ischemia, and the presence of prior infarction as well.  Effects and side effects of pharmacotherapy  Evaluation of metabolic disorders processes among others. Contraindications  No absolute contraindications patient refusal, exist. patients allergies to adhesive used to affix the leads
  14. 14. Limb leads Poles E.g. Bipolar Positive and negative poles I, II, III Unipolar Positive and zero poles aVL, aVR, aVF, chest leads
  15. 15. Calibration Rate Rhythm Axis
  16. 16.  Horizontally ◦ One small box - 0.04 s ◦ One large box - 0.20 s  Vertically ◦ One large box - 0.5 mV ◦ 25mm = 1s
  17. 17.  Height 10mm = 1mV  Half standardisation 5mm=1mV  One fourth standardisation 2.5mm= 1mV  (only amplitude is changed not speed)  Paper speed = 25mm/ s  25 mm (25 small squares / 5 large squares) equals one second
  18. 18. If the heart rate is regular  Count the number of large squares between R waves i. e. the RR interval in large squares  Rate = 300/RR(no. of large boxes) = 1500/RR(no. of small boxes)
  19. 19.  If the rhythm is irregular it may be better to estimate the rate using the rhythm strip at the bottom of the ECG (usually lead II)  The rhythm strip is usually 25cm long (250mm i. e. 10 seconds)  Count the number of R waves on that strip and multiple by 6 you will get the rate Heart rate Regular slow 300/RR (large square) Regular fast 1500/RR (small square) Irregular R wave in rhythm strip X 6
  20. 20.  New born 110-150/min  2year 85-125/min  4year 75-125/min  6year 65-100/min  > 6 year 60-100/min  Tachycardia  Sinus tachcardia  Supraventrical  Ventricular  Atrial flutter and fibrillation  Bradycardia  Sinus bradycardia  Heart block
  21. 21.  Normal rhythm must have a P wave before each QRS complex  The easiest way to tell is to take a sheet of paper and line up one edge with the tips of the R waves on the rhythm strip.  Mark off on the paper the positions of 3 or 4 R wave tips  Move the paper along the rhythm strip so that your first mark lines up with another R wave tip  See if the subsequent R wave tips line up with the subsequent marks on your paper  If they do line up, the rhythm is regular. If not, the rhythm is irregular
  22. 22.  Absent P wave – indicate non sinus rhythm  SA block  AV rhythm (may be present)  Atrial fibrillation  Idioventricular rhythm  Multiple P waves ◦ Atrial flutter ◦ Atrial fibrillation ◦ 2nd ar 3rd degree block  Changing P wave shape ◦ Wandering atrial pacemaker
  23. 23. The axis is the overall direction of the cardiac impulse or wave of depolarisation of the heart  An abnormal axis (axis deviation) can give a clue to possible pathology
  24. 24. Lead I Lead aVF Mean axis
  25. 25. Lead I Lead aVF Mean axis
  26. 26. Equiphasic method
  27. 27. Lead (mm) = R-S amplitude Lead I = 4-0 = 4mm Lead aVF = 13-2 = 11mm Lead I Lead aVF Mean axis
  28. 28. Lead I Lead aVF Lead I = 5+ (-10)= -5mm Lead aVF = 17-4 = 13mm
  29. 29.  Right Axis Deviation - Right ventricular hypertrophy, Anterolateral MI, Left Posterior Hemi-block, COPD, pulmonary arterial hypertension or large pulmonary embolism  Left Axis Deviation- Ventricular tachycardia, Left ventricular hypertrophy, Left Anterior hemi-block  Wolff-Parkinson-White syndrome can cause both Left and Right axis deviation
  30. 30. Normal values 1. up in all leads except aVR. 2. Duration. < 2.5 mm. 3. Amplitude. < 2.5 mm. Abnormalities 1. Inverted P-wave  Junctional rhythm. 2. Wide P-wave (P- mitrale)  LAE 3. Peaked P-wave (P- pulmonale)  RAE 4. Saw-tooth appearance  Atrial flutter 5. Absent normal P wave  Atrial fibrillation
  31. 31. Definition: the time interval between beginning of P- wave to beginning of QRS complex. Normal PR interval <3yrs – 0.08sec 3-16 yrs – 0.10sec >16 – 0.12sec Abnormalities 1. Short PR interval  WPW syndrome 2. Long PR interval  First degree heart block
  32. 32. Slide 44
  33. 33.  If the PR interval is constant with a missed QRS complex: 2nd degree heart block, Mobitz type II, each QRS followed after P wave  If there is no relationship between the P waves and the QRS complexes: 3rd degree heart block Block Relation Electrical origin 1st degree Each P has QRS SA node 2nd degree Each QRS has P SA node 3rddegree No Relation Fasciular,Ventricular, or other
  34. 34.  Q waves <0.04 second.  That’s is less than one small square duration.  Present commonly in I,II,III,aVF, and always present in V5 and V6 (lateral leads)  Absent in V1  Height < 1/4 of R wave height.
  35. 35.  The width of the QRS complex should be less than 0.12 seconds (3 small squares)  Height of R wave is (V1-V6) >8 mm in at least one of chest leads.  Morphology: progression from Short R and deep S (rS) in V1 to tall R and short S in V6 (qRs).
  36. 36.  New born +125  1 month +90  3 years +60  Adult +50  Preterm 0.04s  Full term 0.0.5s  1 -3yrs 0.06s  >3 years 0.07s  Adult 0.08s
  37. 37.  LAD ◦ LVH ◦ LBBB ◦ Left anterior hemiblock  RAD ◦ RVH ◦ RBBB  Superiorly oriented axis ◦ Left anterior hemiblock, particularly with endocardial cushion defect ◦ RBBB  Bundle branch block  Preexication (WPW)  Intraventricular block  Idioventricular rhythm  Ventricular implanted pacemaker
  38. 38.  Abnormally large deflections (positive or negative) ◦ Ventricular hypertrophy ◦ Ventricular conduction defects like - BBB, preexication,artificial ventricular pacemaker  Low voltage complex – limb lead less than 5mm ◦ Myocarditis ◦ Pericardial effusion ◦ Hypothyroidism ◦ Pericarditis
  39. 39.  Right axis deviation of +110° or more.  Dominant R wave in V1  Dominant S wave in V5 or V6  Right atrial enlargement (P pulmonale).  Right ventricular strain pattern = ST depression / T wave inversion in the right precordial (V1-4) and inferior (II, III, aVF) leads.
  40. 40.  Left axis deviation  Increased R wave amplitude in the left-sided ECG leads (I, aVL and V4-6) and  Increased S wave depth in the right-sided leads (III, aVR, V1-3).  The thickened LV wall leads to prolonged depolarisation and delayed repolarisation (ST and T-wave abnormalities) in the lateral leads.  Left atrial enlargement (P mitrale).  Left ventricular strain pattern = ST depression / T wave inversion in the lateral (I, aVL,V5-V6) leads.
  41. 41. In RBBB, activation of the right ventricle is delayed as depolarisation has to spread across the septum from the left ventricle. The left ventricle is activated normally, meaning that the early part of the QRS complex is unchanged. The delayed right ventricular activation produces a secondary R wave (R’) in the right precordial leads (V1-3) and a wide, slurred S wave in the lateral leads (V5-6) Delayed activation of the right ventricle also gives rise to secondary repolarization abnormalities, with ST depression and T wave inversion in the right precordial leads (V1-3)  QRS duration ≥ 120ms  rSR’ pattern or notched R wave in V1-3 along with T wave inversion  Wide S wave in I and V6
  42. 42.  Normally the septum is activated from left to right, producing small Q waves in the lateral leads.  In LBBB, the normal direction of septal depolarisation is reversed (becomes right to left), as the impulse spreads first to the RV to the LV via the septum.  Eliminates the normal septal Q waves in the lateral leads. .  The overall direction of depolarisation (from right to left) produces tall R waves in the lateral leads (I, V5-6) and deep S waves in the right precordial leads (V1-3)  As the ventricles are activated sequentially (right, then left) rather than simultaneously, this produces a broad or notched (‘M’-shaped) R wave in the lateral leads.  QRS duration ≥ 120ms  Broad R wave in I, aVL, and V5-6  Prominent QS wave in V1-3  Absence of q waves (including physiologic q waves) in I and V6
  43. 43.  The ST segment should sit on the isoelectric line (at least in the begining)  It is abnormal if there is planar (i.e. flat) elevation or depression of the ST segment
  44. 44. 1. ST elevation: More than one small square  Infarcts  Angina.  Acute pericarditis.  Early repolarization ST depression: More than one small square  Ischemia.  Ventricular strain.  BBB.  Hypokalemia.  Digoxin effect.
  45. 45. ST depression
  46. 46.  T wave is best measured in left precordial leads  In V5 <1yr 11mm >1yr 14mm Abnormalities: 1. Peaked T-wave: Posterior wall MI. Hyperkalemia. . 2. T- inversion:  Ischemia.  Myocardial infarction.  Myocarditis  Ventricular strain  BBB.  Hypokalemia.  Digoxin effect.
  47. 47.  The normal range for QT is 0.38-0.42 (≤ 11mm ) Definition: Time interval between beginning of QRS complex to the end of T wave. QT interval varies with heart rate - As the heart rate gets faster, the QT interval gets shorter It is possible to correct the QT interval with respect to rate by using the following formula: Bazzet’s formula QTc = QT/ √RR (QTc = corrected QT)
  48. 48.  Long QTc – causes ◦ Drugs – procanamide, quinidine ◦ Hypocalcemia, ◦ hypomagnesemia, ◦ hypokalemia ◦ Hypothermia ◦ AMI ◦ Congenital  Jerwell and Lange-Neilsen syndrome  Romano- Ward syndrome  Short QT interval: hypercalcemia, digitalis Abnormalities:
  49. 49.  U waves occur after the T wave and are often difficult to see  They are thought to be due to repolarisation of the atrial septum  Prominent U waves can be a sign of hypokalaemia
  50. 50. THANKS

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