1. Dr.Ola Tork MD.Physiology
ECG Basics
Dr.Ola Tork
MD.Physiology

2. Outline Basic laws of ECG Review of the conduction system
ECG waveforms and intervals
ECG leads
Determining heart rate
Cardiac Rhythm
Determining QRS axis
ATRIAL HYPERTROPHY &ventricular hypertrophy

3. What is an ECG?
The electrocardiogram (ECG) is a record of the sum of all electrical activity of the heart from the surface of the body as the body fluids act as electrical conductors .

4. Propagating Activation Wavefront
When the cells are at rest, they have a negative transmembrane voltage – surrounding media is positive
When the cells depolarize, they switch to a positive transmembrane voltage – surrounding media becomes negative
This leads to a propagating electric vector (pointing from negative to positive)

5. Basic laws of ECG

6. Propagating Activation Wavefront
Depol. toward positive electrode
Positive Signal
Repol. toward positive electrode
Negative Signal
Depol. away from positive electrode
Negative Signal
Repol. Away from positive electrode
Positive Signal

7. The Normal Conduction System

8. ECG Signal
The excitation begins at the sinus (SA) node and spreads along the atrial walls
The resultant electric vector is shown in yellow
Cannot propagate across the boundary between atria and ventricle
The projections on Leads I, II and III are all positive

9. ECG Signal
Atrioventricular (AV) node located on atria/ventricle boundary and provides conducting path
Pathway provides a delay to allow ventricles to fill
Excitation begins with the septum

10. ECG Signal
Depolarization continues to propagate toward the apex of the heart as the signal moves down the bundle branches
Overall electric vector points toward apex as both left and right ventricles depolarize and begin to contract

11. ECG Signal
Depolarization of the right ventricle reaches the epicardial surface
Left ventricle wall is thicker and continues to depolarize
As there is no compensating electric forces on the right, the electric vector reaches maximum size and points left
Note the atria have repolarized, but signal is not seen

12. ECG Signal
Depolarization front continues to propagate to the back of the left ventricular wall
Electric vector decreases in size as there is less tissue depolarizing

13. ECG Signal
Depolarization of the ventricles is complete and the electric vector has returned to zero

14. ECG Signal
Ventricular repolarization begins from the outer side of the ventricles with the left being slightly dominant
Note that this produces an electric vector that is in the same direction as the depolarization traveling in the opposite direction
Repolarization is diffuse and generates a smaller and longer signal than depolarization

15. ECG Signal
Upon complete repolarization, the heart is ready to go again and we have recorded an ECG trace

16. Waveforms and Intervals

18. What types of pathology can we identify and study from EKGs?
Arrhythmias
Myocardial ischemia and infarction
Pericarditis
Chamber hypertrophy
Electrolyte disturbances (i.e. hyperkalemia, hypokalemia)
Drug toxicity (i.e. digoxin and drugs which prolong the QT interval)

19. Normal ECG 5 waves:P, Q, R,S ,T
P wave : caused by atrial depolarization
QRS complex: caused by ventricular depolarization
T wave :caused by ventricular repolarization
Intervals :
P-R interval = s

20. ECG Leads
In 1908, Willem Einthoven developed a system capable of recording these small signals and recorded the first ECG.
The leads were based on the Einthoven triangle associated with the limb leads.
Leads put heart in the middle of a triangle

21. EKG 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)

22. EKG Leads The standard EKG has 12 leads: 3 Standard Limb Leads
3 Augmented Limb Leads
6 Precordial Leads
The axis of a particular lead represents the viewpoint from which it looks at the heart.

23. Standard Limb Leads

24. Standard Limb Leads

25. Augmented Limb Leads

26. All Limb Leads

27. Precordial Leads
Adapted from:

28. Precordial Leads

29. aVR, aVL, aVF (augmented limb leads)
Summary of Leads
Limb Leads
Precordial Leads
Bipolar
I, II, III
(standard limb leads) -
Unipolar
aVR, aVL, aVF (augmented limb leads)
V1-V6

30. Arrangement of Leads on the EKG

32. Anatomic Groups (Septum)

33. Anatomic Groups (Anterior Wall)

34. Anatomic Groups (Lateral Wall)

35. Anatomic Groups (Inferior Wall)

36. Anatomic Groups (Summary)

37. Determining the Heart Rate
Rule of 300
10 Second Rule

38. Rule of 300
Take the number of “big boxes” between neighboring QRS complexes, and divide this into The result will be approximately equal to the rate
Although fast, this method only works for regular rhythms.

39. What is the heart rate?
(300 / 6) = 50 bpm

40. What is the heart rate?
(300 / ~ 4) = ~ 75 bpm

41. What is the heart rate?
(300 / 1.5) = 200 bpm

42. The Rule of 300 It may be easiest to memorize the following table:
# of big boxes
Rate 1
300 2
150 3
100 4 75 5 60 6 50

43. 10 Second Rule
As most ECGs record 10 seconds of rhythm per page, one can simply count the number of beats present on the ECG and multiply by 6 to get the number of beats per 60 seconds.
This method works well for irregular rhythms.

44. What is the heart rate? 33 x 6 = 198 bpm
The Alan E. Lindsay ECG Learning Center ;
33 x 6 = 198 bpm

45. Cardiac Rhythm: Supraventricular
NORMAL SINUS RHYTHM Impuses originate at S-A node at normal rate
                      
                                                                           
SINUS TACHYCARDIA Impuses originate at S-A node at rapid rate
                      
                                                                           
All complexes normal, evenly spaced Rate > 100/min
SINUS TACHYCARDIA Impuses originate at S-A node at rapid rate
                      
                                                                           
All complexes normal, rhythm is irregular Longest R-R interval exceeds shirtest > 0.16 s

46. Cardiac Rhythm: Supraventricular
ATRIAL FLUTTER Impulses travel in circular course in atria – No interval between T and P
                      
                                                                           
Rapid flutter waves, ventricular response irregular
ATRIAL FIBRILLATION Impuses have chaotic, random pathways in atria
                      
                                                                           
Baseline irregular, ventricular response irregular

47. Cardiac Rhythm: Ventricular
PREMATURE VENTRICULAR CONTRACTION A single impulse originates at right ventricle
                      
                                                                           
Time interval between normal R peaks is a multiple of R-R intervals
VENTRICULAR TACHYCARDIA Impulse originate at ventricular pacemaker – odd/wide QRS complex - often due to myocardial infarction
                      
                                                                           
Wide ventricular complexes Rate> 120/min

48. Cardiac Rhythm: Ventricular
VENTRICULAR FIBRILLATION Chaotic ventricular depolarization – ineffective at pumping blood – death within minutes
                      
                                                                           
Rapid, wide, irregular ventricular complexes
PACER RHYTHM Impulses originate at transvenous pacemaker
                      
                                                                           
Wide ventricular complexes preceded by pacemaker spike Rate is the pacer rhythm

49. Activation Sequence Disorders
A-V BLOCK, FIRST DEGREE Atrio-ventricular conduction lengthened
                      
                                                                           
P-wave precedes each QRS-complex but PR-interval is > 0.2 s
A-V BLOCK, SECOND DEGREE Sudden dropped QRS-complex
                      
                                                                           
Intermittently skipped ventricular beat

50. Bundle-branch Block
RIGHT BUNDLE-BRANCH BLOCK QRS duration greater than 0.12 s Wide S wave in leads I, V5 and V6
                                                                                          

51. The QRS Axis
The QRS axis represents the net overall direction of the heart’s electrical activity.

52. The QRS Axis
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)

53. Determining the Axis
The Quadrant Approach
The Equiphasic Approach

54. Determining the Axis Predominantly Positive Predominantly Negative
Equiphasic

55. 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.

56. 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.

57. Quadrant Approach: Example 1
The Alan E. Lindsay ECG Learning Center
Negative in I, positive in aVF  RAD

58. Quadrant Approach: Example 2
The Alan E. Lindsay ECG Learning Center
Positive in I, negative in aVF  Predominantly positive in II 
Normal Axis (non-pathologic LAD)

59. Deviation of Electric Axis of the Heart
Deviation to R: increased activity in R vent. – obstruction in lung, pulmonary emboli, some heart disease
Deviation to L: increased activity in L vent. – hypertension, aortic stenosis, ischemic heart disease

60. Atrial Hypertropy: Enlarged Atria
RIGHT ATRIAL HYPERTROPHY Tall, peaked P wave in leads I and II
LEFT ATRIAL HYPERTROPHY Wide, notched P wave in lead II Diphasic P wave in V1
                                             

61. Ventricular Hypertropy: Enlarged Ventricle
LEFT VENTRICULAR HYPERTROPHY Large S wave in leads V1 and V2 Large R wave in leads V6 and V6
                                                                                          

62. Myocardial Ischemia and Infarction
Oxygen depletion to heart can cause an oxygen debt in the muscle (ischemia)
If oxygen supply stops, the heart muscle dies (infarction)
The infarct area is electrically silent and represents an inward facing electric vector…can locate with ECG