Cardiac Electrophysiology

1. Basic Arrhythmias Basic Arrhythmias
InterpretationInterpretation
Cardiac Cardiac
ElectrophysiologyElectrophysiology
Natalie Bermudez, RN, BSN, MSNatalie Bermudez, RN, BSN, MS
Clinical Educator for TelemetryClinical Educator for Telemetry

2. Myocardial Cardiac Cell TypesMyocardial Cardiac Cell Types
P Cells
•Pacemaker cells
–Responsible for generation of action
potentials
–electrical activity
Cardiomyocytes
•Myocardial Cells
–Contractile cells that generate force
–Mechanical activity

3. Cardiac Cell ActivityCardiac Cell Activity
Electrical activity ALWAYS
precedes mechanical activity
Electrical activity can occur
without a mechanical response
(i.e. pulse).
This is known as pulseless
electrical activity (PEA).

4. Primary Characteristics of
Cardiac Cells
Automaticity
Excitability
Conductivity
Contractility
ECG Workout Textbook: p. 10

5. Is it GOOD or BAD???
ALL ELECTRICAL CARDIAC CELLS ARE
CAPABLE OF AUTOMATICITY!!!
IRRITABILITY!!!
AutomaticityAutomaticity
It is definitely
REALLY
GOOD
THING!!
But it can also
be a
REALLY
BAD THING!!

6. Electrolytes and Cardiac Cells
•Electrolyte solution surrounds cardiac cells
•K
+
primary intracellular ion
•Na
+
primary extracellular ion
•Ready State: Inside of the cell
more negative
•Cell stimulated; membrane permeability
changes

7. PolarizationPolarization
DepolarizationDepolarization

RepolarizationRepolarization
Electrical Activity at the Cellular LevelElectrical Activity at the Cellular Level

8. Cardiac Action Potential
•As cardiac cells reverse polarity, the electrical
impulse generated during that event creates an
energy stimulus that travels across the cell
membrane
•High-speed, self-producing current (heart only)

9. Slow-Response Cells
•SA node & AV node
•Spontaneously depolarize slowly
•Shorter, non-prominent plateau phase with
slower repolarization period

10. Fast-Response Cells
•Purkinje cells and working myocardial
cells
•Rapid depolarization
•Then, a period of sustained depolarization
– plateau phase

11. Phases of Action Potential
Phase 0
•Cellular depolarization is initiated as + ions enter the
cell (Na
+
and Ca
++
)
•Working cells rapidly depolarize as Na
+
enters the
cells through Na
+
fast channels (fast response)
•SA/AV node depolarize as Ca
++
enters the cell
through Ca
++
slow channels (slow-response)

12. Phases of Action Potential
Phase 1
•Small, early, rapid repolarization as K
+
exits the
intracellular space
Phase 2
•The plateau phase as Ca
++
ions enter the intracellular
space

13. Phases of Action Potential
Phase 3
•Completion of repolarization and return of cell to
resting state
Phase 4
•Resting phase before the next depolarization (Na
+
out, K
+
in)

15. POLARIZATIONPOLARIZATION
Electrical charges are balanced and
ready for discharge.

16. The discharge of energy that accompanies
the transfer of electrical charges across
the membrane.
The process of electrical discharge and flow
of electrical activity.
An electrical event that can be recorded on
an EKG or rhythm strip.
DEPOLARIZATIONDEPOLARIZATION

17. The return of electrical charges across
the cell membrane.
REPOLARIZATIONREPOLARIZATION

18. Refractory PeriodRefractory Period
Absolute: The brief period during repolarization
when the cell CAN’T respond to any stimulus,
no matter how strong.
*Relative: The brief period during repolarization
when excitability is depressed. If stimulated, the
cell may respond, but a stronger than usual
stimulus is required.
Supernormal: The cells will respond to a weaker
than normal stimulus (this period occurs just
before the cells have completely repolarized)

19. What is an EKG?
•Think of it as a map that shows the road
traveled by an electrical impulse

•Each waveform indicates the location of
the electrical impulse and if has traveled
through that location “normally”

20. Isoelectric Line & WaveformsIsoelectric Line & Waveforms
Isoelectric Line:
electrically neutral
baseline of an EKG
complex.
Waveform: any part of
the EKG tracing that
moves away from &
returns to the
isoelectric line
(baseline)

21. DeflectionsDeflections
Deflection: a waveform
on an EKG strip that
denotes electrical
activity; may be
positive (upright)
and/or negative
(downward).
Monophasic or
Biphasic
See Overhead slide 1-0

22. Positive & Negative PolesPositive & Negative Poles
Electrical activity that
travels towards a
positive pole appears
upright on an EKG
appears and is called
a positive deflection.
Electrical activity that
travels towards a
negative pole
appears inverted
(downward) on an
EKG and is called a
negative deflection

23. Positive & Negative PolesPositive & Negative Poles
See Overhead Slide 1-1

24. Cardiac Monitors
Electrodes, Poles, Wires, Leads,
and Electrode Placement

25. Five-Leadwire System

26. Electrode Pad PlacementElectrode Pad Placement
Electrode
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

27. Poles & Lead IIPoles & Lead II
Lead II consists of the
following electrode
placement:
•Right Limb Lead (negative
pole): the 2
nd
intercostal
space on the right
•Left Limb Lead (positive
pole): the 8
th
intercostal
space on the left
•Grounding Lead: 8
th

intercostal space to the right

28. LEAD II
Lead II is used alone quite frequently.
Normal rhythms present with a prominent
P wave and a tall QRS.

29. Irritability versus EscapeIrritability versus Escape
Irritability – a site that speeds up and takes
over as the pacemaker.
Escape – when the normal pacemaker slows
down or fails and a lower site assumes pace
making responsibility.
Either of these may exist as a beat or rhythm!

30. More EKG
Terminology
Focus, Ectopy, Aberrancy, Artifact

31. Important TerminologyImportant Terminology
Focus - The starting point of an electrical
impulse
Ectopic – An impulse that originates from a
focus other than the primary pacemaker.

32. AberrancyAberrancy
Aberrancy – abnormal conduction of an electrical
impulse
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”

33. ArtifactArtifact
Electrical activity displayed on graph
paper that is superimposed on cardiac
tracings, interfering with interpretation of
the rhythm.
Can be caused by outside electrical
soures, muscle tremors, patient
movement; also called interference.

34. Cardiac Electrophysiology
The Electrical Conduction Pathway

35. Nervous System StimulationNervous System Stimulation
Sympathetic Nervous System: causes
an increase in heart rate, increase in AV
conduction , and increase in ventricular
contractility
The increase is caused a release of
norepinephrine
(catecholamine/neurotransmitter)

36. Nervous System StimulationNervous System Stimulation
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
The decrease is caused a release of
acetylcholine
(catecholamine/neurotransmitter)

37. PacemakerPacemaker
Pacemaker – the SA node is the natural/normal
pacemaker of the heart.
Latent Pacemaker Cells – Cells in the electrical
conduction system located below the SA node with
the property of automaticity
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.
a.k.a. – Subsidiary pacemaker cells

38. The Electrical Conduction Pathway

39. SA Node
•ie. Sinoatrial Node or Sinus Node
•Posesses the highest level of automaticity
•SA Node is the primary pacemaker of the
heart
•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

40. AV Node (The Gatekeeper)
Three main functions:
•Slows conduction to allow time for the
atria to contract & empty its contents
(atrial kick) before the ventricles contract
•Secondary pacemaker (40 – 59 bpm)
•Blocks some of the impulses from being
conducted to the ventricles when atrial
rate is rapid

41. AV Node (The Gatekeeper)
Three Regions:
•Atrial-Nodal (upper region)
Pacemaker cells
•Nodal (middle region)
No pacemaker cells (area responsible
for delay)
•Nodal-His (lower region)
Pacemaker cells

42. Ventricular Conduction
Impulses moves rapidly through the
ventricles:
•Bundle of His
•Left & Right Bundle branches (LBB divides
into the anterior fascicle and posterior
fascicle)
•Purkinje fibers
Tertiary pacemaker (20 – 39)

43. EKG COMPLEXEKG COMPLEX

44. PQRST = One EKG complex = One Cardiac Cycle
Total Duration of a Cardiac Cycle = ___________ seconds

45. P WaveP Wave
•Depicts the firing of
the SA node and
atrial depolarization
(contraction).
•P waves are upright
& rounded (in Lead
II).
•Precedes a QRS
•Both atria depolarize
simultaneously.

46. P Wave AbnormalitiesP Wave Abnormalities
p mitrale = Wide & Notched P wave
___________________________________
___________________________________
p pulmonale = Tall, peaked P wave
____________________________________
___________________________________
_

47. PR SegmentPR Segment
The PR segment represents delay in the
AV node
Flat = Baseline

48. QRS ComplexQRS Complex
Depicts the electrical impulse traveling through
the ventricles and ventricular depolarization
(contraction).
Not all QRS complexes have a Q, R, and S.

49. QRS ComplexQRS 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 endsSee Overhead Slide 1-3

50. QRS Complex VariationsQRS Complex Variations
Overhead Slide 1-2

51. ST-SegmentST-Segment
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.

52. ST-Segment Elevation & ST-Segment Elevation &
DepressionDepression
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)

53. ST-Segment DepressionST-Segment Depression
Most often seen with acute
myocardial ischemia
Other Causes:
Left and right ventricular hypertrophy
Left and Right BBB
Hypokalemia
Drug Effects (i.e. digitalis)

54. ST-Segment ElevationST-Segment Elevation
Most often seen with acute
myocardial injury or infarction
Other Causes:
Coronary vasospasm (Prinzmetal’s Angina)
Pericarditis
Ventricular Aneurysm
Hyperkalemia
Early repolarization (a normal variant)

55. T WaveT Wave
Depicts ventricular repolarization
Refractory Period

56. T WavesT Waves
Positive Deflection
(above baseline < 5 mm)
Should appear rounded and
symmetrical
Peak is closer to the end of the wave

57. Elevated T WavesElevated T Waves
Positive Deflection
(above baseline > 5 mm)
Tall, peaked (tented)
HYPERKALEMIA
or MYOCARDIAL INJURY

58. Inverted T WavesInverted T Waves
Negative Deflection
(below baseline)
Causes:
Myocardial Ischemia
Myocardial Infarction
Pericarditis
Ventricular Enlargement
Bundle Branch Block
Subarachnoid Hemorrhage
Certain Drugs (quinidine or procainamide)

59. U WaveU Wave
Depicts last phase of ventricular
repolarization or endocardial
repolarization???

60. U WaveU Wave
U Wave < 2 mm
Seen most commonly with BRADYCARDIC
rate
Can cause inaccuracies when measuring QT
intervals

61. U WaveU Wave
U Wave < 2 mm
Large = hypokalemia, cardiomyopathy,
LV enlargement
Some drugs may cause a large U wave
May cause Torsades de Pointes

62. Atrial Repolarization ???Atrial Repolarization ???
Hidden beneath the QRS complex.

64. EKG Graph PaperEKG Graph Paper

65. Waveform Measurements

66. PR IntervalPR Interval
Measurement:
0.12 – 0.20
seconds
Represents the
time from SA
node firing to
the end of AV
node delay

67. PRI AbnormalitiesPRI Abnormalities
Prolonged or
Inconsistent PRI’s may
indicate a type of heart
block:
1
st
degree AVB
Mobitz 1 or Mobitz 2
Complete AVB

68. PRI AbnormalitiesPRI Abnormalities
Shortened or
Nonexistent PRI’s may
indicate:
Tachycardic Rhythms
WPW Syndrome
Junctional Rhythms
Ectopic Atrial Rhythms
Ventricular Rhythms

69. PRI AbnormalitiesPRI Abnormalities
See Overhead Slide 1-4

70. PR IntervalPR Interval
PRI=
PRI=

71. QRS DurationQRS Duration
Measurement:
0.04 – 0.10
seconds
Represents the
travel time of
electrical
activity through
the ventricles

72. QRS Complex VariationsQRS Complex Variations
Wide and/or notched QRS
complexes:
- BBB’s
- Aberrant ventricular conductivity
- Rhythms with Ventricular Focus

73. Aberrant QRS ComplexAberrant QRS Complex
See Overhead Slide 1-5

74. QRS DurationQRS Duration
QRS=
QRS=

75. QT IntervalQT 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

76. QT Rate CorrectedQT Rate Corrected
HR ↑ = QT interval ↓

HR ↓ = QT interval ↑
QTc =
QT + 1.75 (ventricular rate – 60)

77. QT IntervalQT Interval
QT= QTc=
QT= QTc=

78. Prolonged QT IntervalsProlonged QT Intervals
Represents a
prolonged time to
repolarization
May lead to
R-on-T
Phenomenon and
ventricular
dysrhythmias!!!

79. Basics to Interpreting StripsBasics to Interpreting Strips
Rhythm
Rate
P Wave
PR Interval (PRI)
QRS Duration

80. RHYTHMRHYTHM
Determine regularity or irregularity
Use calipers for accuracy
Measure distance from R-R wave
Regular Rhythm = R-R distance does not vary (less
than 3 small boxes of variation does not count)
Irregular Rhythm = R-R distance varies (3 small
small boxes or greater)

81. HEART RATEHEART RATE
Use 1500-rule and the 6-second
rule for all regular rhythms
6-second rule only for irregular
rhythms

82. Calculating Heart RatesCalculating Heart Rates
The 6-Second Rule
The Rule of 300’s
The 1500 Rule

83. 6-Second Strip6-Second Strip
Count number of R waves in a 6-second strip and
multiply by 10
A.K.A. Rapid Rate Calculation
HR = # R waves x 10
•Not very accurate
•Used only for very quick estimate

84. Rule of 300’sRule of 300’s
Count number of large
squares between 2
consecutive R waves and
divide into 300.
HR = 300 / # large squares
•Very quick
•Used only with regular
rhythms
•Not very accurate with
fast rates

85. Rule of 300’sRule of 300’s
Scale of 300Scale 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

86. 1500 Rule1500 Rule
Count number of small squares between 2
consecutive R waves and divide into 1500
A.K.A. – Precise Rate Calculation
•Most accurate
•Used only with regular rhythms
•Time-consuming

87. P WavesP Waves
•Upright
•Uniform
•Precedes each QRS complex
•Any extra P waves

88. PRIPRI
•Measure from beginning of P
wave to the end of the PR
segment
•0.12 – 0.20 seconds
•Constant

89. QRS ComplexQRS Complex
•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)
•0.04 – 0.10 seconds
•Notched???, Wide, etc.

90. QT Interval or QTcQT Interval or QTc
•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
•QTc = QT + 1.75 (ventricular rate – 60)

91. Extras???Extras???
•P waves without QRS complexes
•ST-segment depression or
elevation

93. ReferencesReferences
Chernecky, C., et al. (2002). Real world nursing survival guide: ECG’s & the heart. United States
of America: W. B. Saunders Company.
Garcia, T. B., & Holtz, N. E. (2001). 12-lead ecg: The art of interpretation. Sudbury, MA: Jones
and Bartlett Publishers.
Huff, J. (2006). ECG workout: Exercises in arrhythmia interpretation (5
th
ed.). United States of
America: Lippincott, Williams & Wilkins.
Smeltzer, S. C., et al. (2008). Brunner and suddarth’s testbook of medical-surgical nursing, (11
th

ed.). Philadelphia, PA: Lippincott, Williams & Wilkins.
Walraven, G. (1999). Basic arrhythmias (5
th
ed.). United States of America: Prentice-Hall, Inc.
Woods, S. L., et al. (2005). Cardiac nursing, (5
th
ed.). Philadelphia, PA: Lippincott, Williams &
Wilkins.
www.madsci.com/manu/ekg_rhy.htm