Ecg basics


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ECG for beginners

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Ecg basics

  1. 1. Dr Jain T Kallarakkal MD,FRCP,DM Consultant Interventional Cardiologist
  2. 2.  Electrocardiogram  Tracing of heart heart’s electrical activity
  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, causing contraction
  6. 6. Introduce, Privacy, Explain procedure, Permission  Lay patient down  Expose chest, wrists, ankles  Clean electrode sites  May need to shave  Apply electrodes  Attach wires correctly 
  7. 7.  Turn on machine  Calibrate to 10mm/ mV  Rate at 25mm/ s  Record and print  Label the tracing - Name, DOB, Hospital number, date and time  Disconnect if adequate and remove electrodes
  8. 8.  10 electrodes in total are placed on patient  Firstly self self-adhesive ‘dots’ attached to the patient.  The 10 leads on the ECG machine then clipped onto the contacts of ‘dots’ the are are the
  9. 9.     Chest leads are labelled “V” and are numbered from 1 to 6. The placement of these electrodes needs to be exact to give the optimum information. If the electrodes are placed incorrectly on the chest, the tracing will reveal duplication of some information, while other areas will not be represented properly. Incorrect placement of the electrodes can lead to serious errors of interpretation.
  10. 10. 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 
  11. 11.  Pacemaker = sinoatrial node  Impulse travels across atria  Reaches AV node  Transmitted along interventricular septum in Bundle of His  Bundle splits in two (right and left branches)  Purkinje fibres
  12. 12.     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
  13. 13.  Anteroseptal: V1, V2, V3, V4  Anterolateral: V4–V6, I, aVL  High Lateral: I and aVL  Inferior: II, III, and aVF  Inferolateral: II, III, aVF, and V5 and V6
  14. 14. P wave: Activation (depolarization) of the right and left atria  QRS complex: right and left ventricular depolarization  T wave: ventricular repolarization
  15. 15.      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)
  16. 16.  Check Name DoB Time and date Indication Any previous or subsequent ECGs Is it part of a serial ECG sequ ence? In which case it may be numbered
  17. 17.  Calibration  Rate  Rhythm  Axis  Elements lead of the tracing in each
  18. 18.      Height 10mm = 1mV Look for a reference pulse which should be the rectangular looking wave somewhere near the left of the paper. It should be 10mm (10 small squares) tall Paper speed 25mm/ s 25 mm (25 small squares / 5 large squares) equals one second
  19. 19. 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
  20. 20. 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 
  21. 21.      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.  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
  23. 23.  Wolff-Parkinson-White syndrome can cause both Left and Right axis deviation  Right ight Axis Deviation - Right ventricular hypertrophy, Anterolateral MI, Left Posterior Hemiblock  Left eft Axis Deviation- Ventricular tachycardia, Inferior MI, Left ventricular hypertrophy, Left Anterior hemiblock
  24. 24.  Represents atrial depolarisation  It is thought of as being made up of two separate waves due to right atrial depolarisation and left atrial depolarisation.  Right atrial depolarisation occurs first
  25. 25.  Height - a P wave over 2.5mm should arouse suspicion  A tall P wave (over 2.5mm) is called P pulmonale  Occurs due to right atrial enlargement/hypertrophy  Causes include: pulmonary hypertension, pulmonary stenosis, tricuspid stenosis
  26. 26.  Length - a P wave longer than 0.08s (2 small squares) should arouse suspicion  A P wave with a length >0.08 seconds (2 small squares) and a bifid shape is called P mitrale  It is caused by left atrial hypertrophy and delayed left atrial depolarisation  Causes include: Mitral valve disease, LVH
  27. 27. The PR interval is measured between the beginning of the P wave to the beginning of the QRS complex  if there is a Q wave before the R wave the PR interval is measured from the beginning of the P wave to the beginning of the Q wave, not the start of the R wave  PR interval corresponds to the time period between depolarisation of the atria and ventricular depolarisation. 
  28. 28.    A normal PR interval is between 0.12 and 0.2 seconds (3-5 small squares) If the PR interval is short (less than 3 small squares) it may signify that there is an accessory electrical pathway between the atria and the ventricles, hence the ventricles depolarise early giving a short PR interval. One example of this is Wolff-Parkinson-White syndrome where the accessory pathway is called the bundle of Kent.
  29. 29.     If the PR interval is long (> 5 small squares or 0.2s):1st st degree heart block First degree heart block is a longer than normal delay in conduction at the AV node If the PR interval looks as it is widening in every beat and then a QRS complex is missing: 2nd degree heart block, Mobitz type I. The lengthening of the PR interval is known as the Wenckebach phenomenon
  30. 30.  If the PR interval is constant with a missed QRS complex: 2nd degree heart block, Mobitz type II  If there is no discernable relationship between the P waves and the QRS complexes: 3rd degree heart block
  31. 31. A Q wave can be pathological if it is: ◦Deeper than 2 small squares (0.2mV) ◦Wider than 1 small square (0.04s)  If the complexes in the chest leads look very tall, consider left ventricular hypertrophy (LVH)
  32. 32.  The width of the QRS complex should be less than 0.12 seconds (3 small squares)  Some texts say less than 0.10 seconds (2.5 small squares)  If the QRS is wider than this, it suggests a ventricular conduction problem usually right or left bundle branch block (RBBB or LBBB)
  33. 33. The ST segment should sit on the isoelectric line  It is abnormal if there is planar (i. e. flat) elevation or depression of the ST segment  Planar ST elevation can represent an MI or Prinzmetal’s (vasospastic) angina  Planar ST depression can represent ischemia 
  34. 34. T wave generally shouldn’t be taller than half the size of the preceding QRS complex  Seen in :Hyperkalemia, Acute myocardial infarction  If the T wave is flat, it may indicate hypokalemia  If the T wave is inverted it may indicate ischemia
  35. 35. The QT interval is measured from the start of the QRS complex to the end of the 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: QTc = QT/ √RR (QTc = corrected QT) 
  36. 36.  The normal range for QTc is 0.38- 0.42 A short QTc may indicate hypercalcemia  A long QTc has many causes  Long QTc increases the risk of developing an arrhythmia
  37. 37. ◦Drugs (Na channel blockers) ◦Hypocalcemia, hypomagnesemia, hypokalemia ◦Hypothermia ◦AMI ◦Congenital ◦Increased ICP
  38. 38. 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
  39. 39. THANK YOU