1. Introduction to Clinical Electrocardiography Gari Clifford, PhD Andrew Reisner, MD Roger Mark, MD PhD

2. Electrocardiography  The heart is an electrical organ, and its activity can be measured non- invasively  Wealth of information related to: The electrical patterns proper The geometry of the heart tissue The metabolic state of the heart  Standard tool used in a wide-range of medical evaluations

3. A heart Blood circulates, passing near every cell in the body, driven by this pump …actually, two pumps… Atria = turbochargers Myocardium = muscle Mechanical systole Electrical systole

4. To understand the ECG:  Electrophysiology of a single cell  How a wave of electrical current propagates through myocardium  Specific structures of the heart through which the electrical wave travels  How that leads to a measurable signal on the surface of the body

5. Part I: A little electrophysiology

6. Once upon a time, there was a cell: ATPase

7. time Intracellular millivoltage -90 Resting comfortably a myocyte

8. time Intracellular millivoltage Depolarizing trigger

9. time Intracellular millivoltage Na channels open, briefly

10. time Intracellular millivoltage In: Na + Mystery current

11. time Intracellular millivoltage In: Na + Ca ++ is in balance with K + out

12. time Intracellular millivoltage In: Na + Excitation/Contraction Coupling : Ca ++ causes the Troponin Complex (C, I & T) to release inhibition of Actin & Myosin

13. time Intracellular millivoltage In: Na + Ca ++ in; K + out More K + out; Ca ++ flow halts

14. time Intracellular millivoltage In: Na + In: Ca ++ ; Out: K + Out: K + Sodium channels reset

15. time Intracellular millivoltage In: Na + Higher resting potential Few sodium channels reset Slower upstroke

16. time Intracellular millivoltage a pacemaker cell Slow current of Na + in; note the resting potential is less negative in a pacemaker cell-55

17. time Intracellular millivoltage a pacemaker cell Threshold voltage-40

18. time Intracellular millivoltage Ca ++ flows in

19. time Intracellular millivoltage... and K + flows out

20. time Intracellular millivoltage... and when it is negative again, a few Na+ channels open

21. How a wave of electrical current propagates through myocardium  Typically, an impulse originating anywhere in the myocardium will propagate throughout the heart  Cells communicate electrically via “gap junctions”  Behaves as a “syncytium”  Think of the “wave” at a football game!

22. The dipole field due to current flow in a myocardial cell at the advancing front of depolarization. Vm is the transmembrane potential.

23. Cardiac Electrical Activity

24. Important specific structures  Sino-atrial node = pacemaker (usually)  Atria  After electrical excitation: contraction  Atrioventricular node (a tactical pause)  Ventricular conducting fibers (freeways)  Ventricular myocardium (surface roads)  After electrical excitation: contraction

25. The Idealized Spherical Torso with the Centrally Located Cardiac Source (Simple dipole model)

26. Excitation of the Heart

28. Cardiac Electrical Activity

29. Recording the surface ECG

30. Clinical Lead Placement  Einthoven Limb Leads:

31. Precordial leads

32. 12 Lead ECG

34. The temporal pattern of the heart vector combined with the geometry of the standard frontal plane limb leads.

35. Normal features of the electrocardiogram.

36. Normal sinus rhythm

37. What has changed?

38. Sinus bradycardia

39. time Intracellular millivoltage Neurohumeral factors Vagal stimulation makes the resting potential MORE NEGATIVE...

40. time Intracellular millivoltage Neurohumeral factors... and the pacemaker current SLOWER...

41. time Intracellular millivoltage... and raise the THRESHOLD

42. time Intracellular millivoltage Catecholamines make the resting potential MORE EXCITED...

43. time Intracellular millivoltage... and speed the PACEMAKER CURRENT...

44. time Intracellular millivoltage... and lower the THRESHOLD FOR DISCHARGE...

45. time Intracellular millivoltage Vagal Stimulation:

46. time Intracellular millivoltage Adrenergic Stim.

47. Sinus arrhythmia

48. Atrial premature contractions (see arrowheads)

50.  Usually just a spark; rarely sufficient for an explosion  “Leakiness” leads to pacemaker-like current  Early after-depolarization  Late after-depolarization

51. What’s going on here?

52. Wave-front Trajectory in a Ventricular Premature Contraction.

53. Is this the same thing?

54. What’s going on here?

56. Non-sustained ventricular tachycardia (3 episodes)

57. Slow Refractory Quick Refractory KeyWords: Heterogeneous, Circus, Self-Perpetuating Side “ A ”Side “ B ”

58. No Longer Refractory KeyWords: Heterogeneous, Circus, Self-Perpetuating Side “ A ”Side “ B ”

59. KeyWords: Heterogeneous, Circus, Self-Perpetuating Side “ A ”Side “ B ”

60. KeyWords: Heterogeneous, Circus, Self-Perpetuating Side “ A ”Side “ B ”

61. KeyWords: Heterogeneous, Circus, Self-Perpetuating Side “ A ”Side “ B ”

62. KeyWords: Heterogeneous, Circus, Self-Perpetuating Side “ A ”Side “ B ”

63. INCREASED Refractory Side “ A ”Side “ B ”

64. INCREASED Refractory Side “ A ”Side “ B ”

65. INCREASED Refractory Side “ A ”Side “ B ”

66. INCREASED Refractory Side “ A ”Side “ B ”

67. INCREASED Refractory Side “ A ”Side “ B ”

68. INCREASED Refractory Side “ A ”Side “ B ”

69. Ventricular Fibrillation

74. Heart attack

75. Hyperkalemia

76. Understanding the ECG: A Cautionary Note  Basic cell electrophysiology, wavefront propagation model, dipole model: Powerful, but incomplete  There will always be electrophysiologic phenomena which will not conform with these explanatory models  Examples: metabolic disturbances anti-arrhythmic medications need for 12-lead ECG to record a 3-D phenomenon

77. Questions?