Cardiac Electrophysiology


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Cardiac Electrophysiology

  1. 1. Basic Arrhythmias Interpretation Cardiac Electrophysiology Natalie Bermudez, RN, BSN, MS Clinical Educator for Telemetry
  2. 2. Myocardial Cardiac Cell Types <ul><li>P Cells </li></ul><ul><li>Pacemaker cells </li></ul><ul><ul><li>Responsible for generation of action potentials </li></ul></ul><ul><ul><li>electrical activity </li></ul></ul><ul><li>Cardiomyocytes </li></ul><ul><li>Myocardial Cells </li></ul><ul><ul><li>Contractile cells that generate force </li></ul></ul><ul><ul><li>Mechanical activity </li></ul></ul>
  3. 3. Cardiac Cell Activity <ul><li>Electrical activity ALWAYS precedes mechanical activity </li></ul><ul><li>Electrical activity can occur without a mechanical response (i.e. pulse). </li></ul><ul><li>This is known as pulseless electrical activity (PEA). </li></ul>
  4. 4. Primary Characteristics of Cardiac Cells <ul><li>Automaticity </li></ul><ul><li>Excitability </li></ul><ul><li>Conductivity </li></ul><ul><li>Contractility </li></ul><ul><li>ECG Workout Textbook: p. 10 </li></ul>
  5. 5. Is it GOOD or BAD ??? <ul><li>ALL ELECTRICAL CARDIAC CELLS ARE CAPABLE OF AUTOMATICITY!!! </li></ul><ul><li>IRRITABILITY!!! </li></ul>Automaticity It is definitely REALLY GOOD THING!! But it can also be a REALLY BAD THING!!
  6. 6. Electrolytes and Cardiac Cells <ul><li>Electrolyte solution surrounds cardiac cells </li></ul><ul><li>K + primary intracellular ion </li></ul><ul><li>Na + primary extracellular ion </li></ul><ul><li>Ready State: Inside of the cell </li></ul><ul><li>more negative </li></ul><ul><li>Cell stimulated; membrane permeability changes </li></ul>
  7. 7. Polarization Depolarization Repolarization Electrical Activity at the Cellular Level
  8. 8. Cardiac Action Potential <ul><li>As cardiac cells reverse polarity, the electrical impulse generated during that event creates an energy stimulus that travels across the cell membrane </li></ul><ul><li>High-speed, self-producing current (heart only) </li></ul>
  9. 9. Slow-Response Cells <ul><li>SA node & AV node </li></ul><ul><li>Spontaneously depolarize slowly </li></ul><ul><li>Shorter, non-prominent plateau phase with slower repolarization period </li></ul>
  10. 10. Fast-Response Cells <ul><li>Purkinje cells and working myocardial cells </li></ul><ul><li>Rapid depolarization </li></ul><ul><li>Then, a period of sustained depolarization – plateau phase </li></ul>
  11. 11. Phases of Action Potential <ul><li>Phase 0 </li></ul><ul><li>Cellular depolarization is initiated as + ions enter the cell (Na + and Ca ++ ) </li></ul><ul><li>Working cells rapidly depolarize as Na + enters the cells through Na + fast channels (fast response) </li></ul><ul><li>SA/AV node depolarize as Ca ++ enters the cell through Ca ++ slow channels (slow-response) </li></ul>
  12. 12. Phases of Action Potential <ul><li>Phase 1 </li></ul><ul><li>Small, early, rapid repolarization as K + exits the intracellular space </li></ul><ul><li>Phase 2 </li></ul><ul><li>The plateau phase as Ca ++ ions enter the intracellular space </li></ul>
  13. 13. Phases of Action Potential <ul><li>Phase 3 </li></ul><ul><li>Completion of repolarization and return of cell to resting state </li></ul><ul><li>Phase 4 </li></ul><ul><li>Resting phase before the next depolarization (Na + out, K + in) </li></ul>
  14. 15. POLARIZATION <ul><li>Electrical charges are balanced and ready for discharge. </li></ul>
  15. 16. <ul><li>The discharge of energy that accompanies the transfer of electrical charges across the membrane. </li></ul><ul><li>The process of electrical discharge and flow </li></ul><ul><li>of electrical activity. </li></ul><ul><li>An electrical event that can be recorded on </li></ul><ul><li>an EKG or rhythm strip. </li></ul>DEPOLARIZATION
  16. 17. <ul><li>The return of electrical charges across the cell membrane. </li></ul>REPOLARIZATION
  17. 18. Refractory Period <ul><li>Absolute: The brief period during repolarization when the cell CAN’T respond to any stimulus, no matter how strong. </li></ul><ul><li>*Relative: The brief period during repolarization when excitability is depressed. If stimulated, the cell may respond, but a stronger than usual stimulus is required. </li></ul><ul><li>Supernormal: The cells will respond to a weaker than normal stimulus (this period occurs just before the cells have completely repolarized) </li></ul>
  18. 19. What is an EKG? <ul><li>Think of it as a map that shows the road traveled by an electrical impulse </li></ul><ul><li>Each waveform indicates the location of the electrical impulse and if has traveled through that location “normally” </li></ul>
  19. 20. Isoelectric Line & Waveforms <ul><li>Isoelectric Line: electrically neutral baseline of an EKG complex. </li></ul><ul><li>Waveform : any part of the EKG tracing that moves away from & returns to the isoelectric line (baseline) </li></ul>
  20. 21. Deflections <ul><li>Deflection: a waveform on an EKG strip that denotes electrical activity; may be positive (upright) and/or negative (downward). </li></ul><ul><li>Monophasic or Biphasic </li></ul><ul><li>See Overhead slide 1-0 </li></ul>
  21. 22. Positive & Negative Poles <ul><li>Electrical activity that travels towards a positive pole appears upright on an EKG appears and is called a positive deflection . </li></ul><ul><li>Electrical activity that travels towards a negative pole appears inverted (downward) on an EKG and is called a negative deflection </li></ul>
  22. 23. Positive & Negative Poles See Overhead Slide 1-1
  23. 24. Cardiac Monitors Electrodes, Poles, Wires, Leads, and Electrode Placement
  24. 25. Five-Leadwire System
  25. 26. Electrode Pad Placement <ul><li>Electrode </li></ul>An electrode pad is the medium through electrical activity is registered/recorded Proper placement of the electrode pad is the most important step in obtaining a good quality and accurate EKG tracing An EKG lead provides a view of the heart’s electrical activity between two points or poles (one positive & one negative) The EKG waveforms are recorded via an electrode/wire system – i.e. five-leadwire system
  26. 27. Poles & Lead II <ul><li>Lead II consists of the following electrode placement: </li></ul><ul><li>Right Limb Lead (negative pole): the 2 nd intercostal space on the right </li></ul><ul><li>Left Limb Lead (positive pole): the 8 th intercostal space on the left </li></ul><ul><li>Grounding Lead: 8 th intercostal space to the right </li></ul>
  27. 28. LEAD II <ul><li>Lead II is used alone quite frequently. Normal rhythms present with a prominent P wave and a tall QRS. </li></ul>
  28. 29. Irritability versus Escape <ul><li>Irritability – a site that speeds up and takes over as the pacemaker. </li></ul><ul><li>Escape – when the normal pacemaker slows down or fails and a lower site assumes pace making responsibility. </li></ul><ul><li>Either of these may exist as a beat or rhythm! </li></ul>
  29. 30. More EKG Terminology Focus, Ectopy, Aberrancy, Artifact
  30. 31. Important Terminology <ul><li>Focus - The starting point of an electrical impulse </li></ul><ul><li>Ectopic – An impulse that originates from a focus other than the primary pacemaker. </li></ul>
  31. 32. Aberrancy <ul><li>Aberrancy – abnormal conduction of an electrical impulse </li></ul><ul><li>Aberrant Ventricular Conduction – An impulse that originates from the SA node, atria, or AV junction that is abnormally conducted through the ventricles producing a wider than normal QRS complex: a.k.a “aberrancy” </li></ul>
  32. 33. Artifact <ul><li>Electrical activity displayed on graph paper that is superimposed on cardiac tracings, interfering with interpretation of the rhythm. </li></ul><ul><li>Can be caused by outside electrical soures, muscle tremors, patient movement; also called interference. </li></ul><ul><li>     </li></ul>
  33. 34. Cardiac Electrophysiology The Electrical Conduction Pathway
  34. 35. Nervous System Stimulation <ul><li>Sympathetic Nervous System: causes an increase in heart rate, increase in AV conduction , and increase in ventricular contractility </li></ul><ul><li>The increase is caused a release of norepinephrine (catecholamine/neurotransmitter) </li></ul>
  35. 36. Nervous System Stimulation <ul><li>Parasympathetic Nervous System: (from the vagus nerve) causes a slowing of the heart rate, a decrease in AV conduction, and a slight decrease in ventricular contractility </li></ul><ul><li>The decrease is caused a release of acetylcholine (catecholamine/neurotransmitter) </li></ul>
  36. 37. Pacemaker <ul><li>Pacemaker – the SA node is the natural/normal pacemaker of the heart. </li></ul><ul><li>Latent Pacemaker Cells – Cells in the electrical conduction system located below the SA node with the property of automaticity </li></ul><ul><li>These cells hold the property of automaticity in reserve in case the SA node fails to function properly or electrical impulses fail to be conducted. </li></ul><ul><li>a.k.a. – Subsidiary pacemaker cells </li></ul>
  37. 38. The Electrical Conduction Pathway
  38. 39. SA Node <ul><li>ie. Sinoatrial Node or Sinus Node </li></ul><ul><li>Posesses the highest level of automaticity </li></ul><ul><li>SA Node is the primary pacemaker of the heart </li></ul><ul><li>If it fails to fire or slows down less than its inherent firing rate (60 – 100), another pacemaker that is lower in the conduction system will take over </li></ul>
  39. 40. AV Node (The Gatekeeper) <ul><li>Three main functions: </li></ul><ul><li>Slows conduction to allow time for the atria to contract & empty its contents (atrial kick) before the ventricles contract </li></ul><ul><li>Secondary pacemaker (40 – 59 bpm) </li></ul><ul><li>Blocks some of the impulses from being conducted to the ventricles when atrial rate is rapid </li></ul>
  40. 41. AV Node (The Gatekeeper) <ul><li>Three Regions: </li></ul><ul><li>Atrial-Nodal (upper region) </li></ul><ul><li>Pacemaker cells </li></ul><ul><li>Nodal (middle region) </li></ul><ul><li>No pacemaker cells (area responsible </li></ul><ul><li>for delay) </li></ul><ul><li>Nodal-His (lower region) </li></ul><ul><li>Pacemaker cells </li></ul>
  41. 42. Ventricular Conduction <ul><li>Impulses moves rapidly through the ventricles: </li></ul><ul><li>Bundle of His </li></ul><ul><li>Left & Right Bundle branches (LBB divides into the anterior fascicle and posterior fascicle) </li></ul><ul><li>Purkinje fibers </li></ul><ul><li>Tertiary pacemaker (20 – 39) </li></ul>
  42. 43. EKG COMPLEX
  43. 44. PQRST = One EKG complex = One Cardiac Cycle Total Duration of a Cardiac Cycle = ___________ seconds
  44. 45. P Wave <ul><li>Depicts the firing of the SA node and atrial depolarization (contraction). </li></ul><ul><li>P waves are upright & rounded (in Lead II). </li></ul><ul><li>Precedes a QRS </li></ul><ul><li>Both atria depolarize simultaneously. </li></ul>
  45. 46. P Wave Abnormalities <ul><li>p mitrale = Wide & Notched P wave ______________________________________________________________________ </li></ul><ul><li>p pulmonale = Tall, peaked P wave </li></ul><ul><li>________________________________________________________________________ </li></ul>
  46. 47. PR Segment <ul><li>The PR segment represents delay in the AV node </li></ul><ul><li>Flat = Baseline </li></ul>
  47. 48. QRS Complex Depicts the electrical impulse traveling through the ventricles and ventricular depolarization (contraction). Not all QRS complexes have a Q, R, and S.
  48. 49. QRS Complex Q wave is the FIRST negative deflection R wave is the FIRST positive deflection S wave is the negative deflection that follows the R wave J Point is the point where the QRS complex ends See Overhead Slide 1-3
  49. 50. QRS Complex Variations Overhead Slide 1-2
  50. 51. ST-Segment <ul><li>The ST-segment represents ventricular contraction and period before ventricular repolarization. No electricity is flowing. The ST segment is therefore usually even with the baseline. </li></ul>
  51. 52. ST-Segment Elevation & Depression <ul><li>To be considered a significant elevation or depression the ST must deviate at least 1 mm above or below the baseline (in at least 2 or more correlating leads) </li></ul>
  52. 53. ST-Segment Depression <ul><li>Most often seen with acute myocardial ischemia </li></ul><ul><li>Other Causes: </li></ul><ul><li>Left and right ventricular hypertrophy </li></ul><ul><li>Left and Right BBB </li></ul><ul><li>Hypokalemia </li></ul><ul><li>Drug Effects (i.e. digitalis) </li></ul>
  53. 54. ST-Segment Elevation <ul><li>Most often seen with acute myocardial injury or infarction </li></ul><ul><li>Other Causes: </li></ul><ul><li>Coronary vasospasm (Prinzmetal’s Angina) </li></ul><ul><li>Pericarditis </li></ul><ul><li>Ventricular Aneurysm </li></ul><ul><li>Hyperkalemia </li></ul><ul><li>Early repolarization (a normal variant) </li></ul>
  54. 55. T Wave Depicts ventricular repolarization Refractory Period
  55. 56. T Waves Positive Deflection (above baseline < 5 mm) Should appear rounded and symmetrical Peak is closer to the end of the wave
  56. 57. Elevated T Waves Positive Deflection (above baseline > 5 mm) Tall, peaked (tented) HYPERKALEMIA or MYOCARDIAL INJURY
  57. 58. Inverted T Waves Negative Deflection (below baseline) Causes: Myocardial Ischemia Myocardial Infarction Pericarditis Ventricular Enlargement Bundle Branch Block Subarachnoid Hemorrhage Certain Drugs (quinidine or procainamide)
  58. 59. U Wave Depicts last phase of ventricular repolarization or endocardial repolarization???
  59. 60. U Wave U Wave < 2 mm Seen most commonly with BRADYCARDIC rate Can cause inaccuracies when measuring QT intervals
  60. 61. U Wave U Wave < 2 mm Large = hypokalemia, cardiomyopathy, LV enlargement Some drugs may cause a large U wave May cause Torsades de Pointes
  61. 62. Atrial Repolarization ??? Hidden beneath the QRS complex.
  62. 64. EKG Graph Paper
  63. 65. Waveform Measurements
  64. 66. PR Interval Measurement: 0.12 – 0.20 seconds Represents the time from SA node firing to the end of AV node delay
  65. 67. PRI Abnormalities Prolonged or Inconsistent PRI’s may indicate a type of heart block: 1 st degree AVB Mobitz 1 or Mobitz 2 Complete AVB
  66. 68. PRI Abnormalities Shortened or Nonexistent PRI’s may indicate: Tachycardic Rhythms WPW Syndrome Junctional Rhythms Ectopic Atrial Rhythms Ventricular Rhythms
  67. 69. PRI Abnormalities See Overhead Slide 1-4
  68. 70. PR Interval PRI= PRI=
  69. 71. QRS Duration Measurement: 0.04 – 0.10 seconds Represents the travel time of electrical activity through the ventricles
  70. 72. QRS Complex Variations Wide and/or notched QRS complexes: - BBB’s - Aberrant ventricular conductivity - Rhythms with Ventricular Focus
  71. 73. Aberrant QRS Complex See Overhead Slide 1-5
  72. 74. QRS Duration QRS= QRS=
  73. 75. QT Interval Measurement: < ½ the distance of the preceding R-R interval Represents travel time through ventricles to the end of ventricular repolarization Normally varies according to age, sex, and particularly heart rate
  74. 76. QT Rate Corrected HR ↑ = QT interval ↓ HR ↓ = QT interval ↑ QTc = QT + 1.75 (ventricular rate – 60)
  75. 77. QT Interval QT= QTc= QT= QTc=
  76. 78. Prolonged QT Intervals Represents a prolonged time to repolarization May lead to R-on-T Phenomenon and ventricular dysrhythmias!!!
  77. 79. Basics to Interpreting Strips <ul><li>Rhythm </li></ul><ul><li>Rate </li></ul><ul><li>P Wave </li></ul><ul><li>PR Interval (PRI) </li></ul><ul><li>QRS Duration </li></ul>
  78. 80. RHYTHM <ul><li>Determine regularity or irregularity </li></ul><ul><li>Use calipers for accuracy </li></ul><ul><li>Measure distance from R-R wave </li></ul><ul><li>Regular Rhythm = R-R distance does not vary (less than 3 small boxes of variation does not count) </li></ul><ul><li>Irregular Rhythm = R-R distance varies (3 small small boxes or greater) </li></ul>
  79. 81. HEART RATE <ul><li>Use 1500-rule and the 6-second rule for all regular rhythms </li></ul><ul><li>6-second rule only for irregular rhythms </li></ul>
  80. 82. Calculating Heart Rates The 6-Second Rule The Rule of 300’s The 1500 Rule
  81. 83. 6-Second Strip <ul><li>Count number of R waves in a 6-second strip and multiply by 10 </li></ul><ul><li>A.K.A. Rapid Rate Calculation </li></ul><ul><li>HR = # R waves x 10 </li></ul><ul><li>Not very accurate </li></ul><ul><li>Used only for very quick estimate </li></ul>
  82. 84. Rule of 300’s <ul><li>Count number of large squares between 2 consecutive R waves and divide into 300. </li></ul><ul><li>HR = 300 / # large squares </li></ul><ul><li>Very quick </li></ul><ul><li>Used only with regular rhythms </li></ul><ul><li>Not very accurate with fast rates </li></ul>
  83. 85. Rule of 300’s Scale of 300 1 large square = 300 bpm 2 large squares = 150 bpm 3 large squares = 100 bpm 4 large squares = 75 bpm 5 large squares = 60 bpm 6 large squares = 50 bpm
  84. 86. 1500 Rule <ul><li>Count number of small squares between 2 </li></ul><ul><li>consecutive R waves and divide into 1500 </li></ul><ul><li>A.K.A. – Precise Rate Calculation </li></ul><ul><li>Most accurate </li></ul><ul><li>Used only with regular rhythms </li></ul><ul><li>Time-consuming </li></ul>
  85. 87. P Waves <ul><li>Upright </li></ul><ul><li>Uniform </li></ul><ul><li>Precedes each QRS complex </li></ul><ul><li>Any extra P waves </li></ul>
  86. 88. PRI <ul><li>Measure from beginning of P wave to the end of the PR segment </li></ul><ul><li>0.12 – 0.20 seconds </li></ul><ul><li>Constant </li></ul>
  87. 89. QRS Complex <ul><li>Measure from beginning to the end of QRS complex (1 st deflection from baseline after the PR segment to the beginning of the ST segment) </li></ul><ul><li>0.04 – 0.10 seconds </li></ul><ul><li>Notched???, Wide, etc. </li></ul>
  88. 90. QT Interval or QTc <ul><li>QT Interval = Count the # of small boxes from beginning QRS complex to the end of the T wave. Should be less than ½ the distance of the preceding R-R interval </li></ul><ul><li>QTc = QT + 1.75 (ventricular rate – 60) </li></ul>
  89. 91. Extras??? <ul><li>P waves without QRS complexes </li></ul><ul><li>ST-segment depression or elevation </li></ul>
  90. 93. References <ul><li>Chernecky, C., et al. (2002). Real world nursing survival guide: ECG’s & the heart. United States of America: W. B. Saunders Company. </li></ul><ul><li>Garcia, T. B., & Holtz, N. E. (2001). 12-lead ecg: The art of interpretation. Sudbury, MA: Jones and Bartlett Publishers. </li></ul><ul><li>Huff, J. (2006). ECG workout: Exercises in arrhythmia interpretation (5 th ed.). United States of America: Lippincott, Williams & Wilkins. </li></ul><ul><li>Smeltzer, S. C., et al. (2008). Brunner and suddarth’s testbook of medical-surgical nursing, (11 th ed.). Philadelphia, PA: Lippincott, Williams & Wilkins. </li></ul><ul><li>Walraven, G. (1999). Basic arrhythmias (5 th ed.). United States of America: Prentice-Hall, Inc. </li></ul><ul><li>Woods, S. L., et al. (2005). Cardiac nursing, (5 th ed.). Philadelphia, PA: Lippincott, Williams & Wilkins. </li></ul><ul><li> </li></ul>