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1. EKG 12 Leads Internal Medicine 2010

2. Electrocardiography A recording of the electrical activity of the heart over time Gold standard for diagnosis of cardiac arrhythmias Helps detect electrolyte disturbances Allows for detection of conduction abnormalities Screening tool for ischemic heart disease (stress tests) Helpful with non-cardiac diseases

3. ECG Leads The standard EKG has 12 leads: 3 Standard Limb Leads 3 Augmented Limb Leads 6 Precordial Leads

4. ECG Limb Leads Leads are electrodes which measure the difference in electrical potential between either: 1. Two different points on the body (bipolar leads) 2. One point on the body and a virtual reference point with zero electrical potential, located in the center of the heart (unipolar leads)

5. Recording of the ECG Limb leads are I, II, II. Each of the leads are bipolar; i.e., it requires two sensors on the skin to make a lead. If one connects a line between two sensors, one has a vector. There will be a positive end at one electrode and negative at the other. The positioning for leads I, II, and III were first given by Einthoven (Einthoven’s triangle).

6. ECG Limb Leads

7. Precordial Leads

8. Summary of Leads

9. Arrangement of Leads on the EKG

10. Anatomic Groups

11. Anatomic Groups

12. Anatomic Groups

13. Anatomic Groups

14. Anatomic Groups

15. ECG Graph Paper Runs at a paper speed of 25 mm/sec Each small block of ECG paper is 1 mm2 At a paper speed of 25 mm/s, one small block equals 0.04 s Five small blocks make up 1 large block which translates into 0.20 s 5 large blocks per second Voltage: 1 mm = 0.1 mV between each individual block vertically

16. The Normal Conduction System

18. ECG Tracing

19. Guide in ECG Reading Rhythm Rate: Atrial and Ventricular Axis P wave: morphology and duration P – R interval QRS complex: morphology and duration ST segment T wave U wave Q – T interval

20. Determining the Rhythm Regular or Irregular Accessing whether the PP intervals and RR intervals are regularly spaced If the rhythm is irregular, determine if: Occasionally irregular Regularly irregular (there is the pattern of irregularity) Irregularly irregular (no pattern of irregularity)

21. Determining the Heart Rate Rule of 300 Take the number of “big boxes” between neighboring QRS complexes, and divide this into 300. The result will be approximately equal to the rate Although fast, this method only works for regular rhythms. 10 Second Rule As most EKGs record 10 seconds of rhythm per page, one can simply count the number of beats present on the EKG and multiply by 6 to get the number of beats per 60 seconds. This method works well for irregular rhythms.

22. The QRS Axis The QRS axis represents the net overall direction of the heart’s electrical activity. By near-consensus, the normal QRS axis is defined as ranging from -30° to +90°. -30° to -90° is referred to as a left axis deviation (LAD) +90° to +180° is referred to as a right axis deviation (RAD)

23. The QRS Axis

24. The QRS Axis The Quadrant Approach 1. Examine the QRS complex in leads I and aVF to determine if they are predominantly positive or predominantly negative. The combination should place the axis into one of the 4 quadrants below.

25. The QRS Axis The Quadrant Approach 2. In the event that LAD is present, examine lead II to determine if this deviation is pathologic. If the QRS in II is predominantly positive, the LAD is non-pathologic (in other words, the axis is normal). If it is predominantly negative, it is pathologic.

26. P-wave Depolarization of both atria Relationship between P and QRS helps distinguish various cardiac arrhythmias Shape and duration of P may indicate atrialenlargement

27. ECG Tracing

28. P wave morphology I AVR Upright P Inverted P V1 Biphasic P 4

29. PR interval from onset of P wave to onset of QRS Normal duration = 0.12-2.0 sec (120-200 ms) (3-4 horizontal boxes) Represents atria to ventricular conduction time (through His bundle) Prolonged PR interval may indicate a 1st degree heart block

30. ECG Tracing

31. P – R interval Normal = 0.12 – 0.22 Short = < 0.12 Prolonged = > 0.22

32. QRS complex Ventricular depolarization Larger than P wave because of greater muscle mass of ventricles Normal duration = 0.08-0.12 seconds

33. ECG Tracing

34. QRS complex Its duration, amplitude, and morphology are useful in diagnosing cardiac arrhythmias, ventricular hypertrophy, MI, electrolyte derangement, etc. Q wave greater than 1/3 the height of the R wave, greater than 0.04 sec are abnormal and may represent MI

35. QRS morphology and duration I AVR Positive QRS Negative QRS V3 Biphasic QRS 6

36. ST segment Connects the QRS complex and T wave Duration of 0.08-0.12 sec (80-120 msec)

37. ECG Tracing

38. S – T Segment I V1 Normal Elevated V3 Depressed 7

39. T waves Represents repolarization or recovery of ventricles Interval from beginning of QRS to apex of T is referred to as the absolute refractory period

40. ECG Tracing

41. T wave morphology AVR I Upright T Inverted T 8

42. QT Interval Measured from beginning of QRS to the end of the T wave Normal QT is usually about 0.40 sec QT interval varies based on heart rate

43. ECG Tracing

45. Chamber Enlargement Right Atrial Enlargement (RAE) Tall P waves in II, III, AVF > 2.5mm Left Atrial Enlargement (LAE) P wave in I > 0.11 secs Terminal Negativity of P wave in VI = > 1mm Bi-atrial Enlargement RAE + LAE

46. Sinus Bradycardia Heart is slower than 60 beats per minute RR interval is longer P wave followed by QRS complex in 1:1 ratio PR interval slightly prolonged

47. Sinus Tachycardia Sinus rhythm is faster than 100 beats per minute RR interval is shorter, less than 0.6 seconds P wave followed by QRS complex in 1:1 ratio

48. Atrial Flutter atria contract at 200-350 beats per minute F waves are larger than normal P waves and they have a saw-toothed waveform ventricular rate is usually regular but slower than the atrial rate fixed ratio of flutter waves to QRS complexes can be observed, for instance 2:1, 3:1 or 4:1

49. Atrial Flutter

50. Atrial Fibrillation occurs when the atria depolarize repeatedly and in an irregular uncontrolled manner usually at atatrial rate greater than 350 beats per minute no concerted contraction of the atria No P-waves are observed QRS complexes have normal shape, due to normal ventricular conduction. However the RR intervals vary from beat to beat. The ventricular rate may increase to greater than 150 beats per minute if uncontrolled.

51. Atrial Fibrillation

52. Ventricular Tachycardia occurs when electrical impulses originating either from the ventricles cause rapid ventricular depolarization (140-250 beats per minute) QRS complexes are wide and bizarre P-waves may be inverted/may be present but not associated with QRS complexes (AV dissociation) RR intervals are usually regular

53. Ventricular Tachycardia

54. Ventricular Fibrillation occurs when parts of the ventricles depolarize repeatedly in an erratic, uncoordinated manner random, apparently unrelated waves no recognizable QRS complex almost invariably fatal because the uncoordinated contractions of ventricular myocardium electrical defibrillation restores normal regular rhythm

55. Ventricular Fibrillation

56. Wolff-Parkinson-White Syndrome presence of an accessory atrioventicular pathway located between the wall of the right or left atria and the ventricles, known as the Bundle of Kent - allows the impulse to bypass the AV node and activate the ventricles prematurely initial slur to the QRS complex, known as a delta wave may be observed QRS complexes are wide, > 0.11 sec PR is shortened, to less than 0.12 sec

57. Wolff-Parkinson-White Syndrome

58. Right Bundle Branch Block Criteria for right bundle branch block (RBBB) [1] QRS >0,12 sec Slurred S wave in lead I and V6 RSR'-pattern in V1 where R' > R

59. Left Bundle Branch Block QRS duration is 120 msec or greater poor R wave progression in V 1 thru V4 T wave vector is in the opposite direction to the QRS vector (T waves are inverted in I, V5 and V6) conduction abnormality often appears as "rabbit ears" (rsR pattern) on the left side of the chest (V4,5,6)