Understanding the Electrocardiogram
Transcript of Understanding the Electrocardiogram
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Understanding the Electrocardiogram
David C. Kasarda M.D. FAAEM
St. Luke’s Hospital, Bethlehem
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Overview
1. History
2. Review of the conduction system
3. EKG: Electrodes and Leads
4. EKG: Waves and Intervals
5. Determining heart rate
6. Determining Rhythm
7. Determining QRS Axis
8. To be continued
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History
� Luigi Galvani (1786)
� Studying the effects of electricity on animal tissue
� Notes that a dissected frog leg twitches when
exposed to an electric field
� Galvinometer
� Instrument for measuring and recording electricity
� EKG is essentially a sensitive Galvinomter
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History
� Willem Einthoven (1893)
� Introduces the term electrocardiogram at a
meeting of the Dutch Medical Society
� Later he credits A.D. Waller
� (1895) using an improved electrometer
� Distinguishes five deflections
� P,Q,R,S,T
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Augustus D. Waller
� (1887) Publishes the first recorded human
ECG in 1887
� Capillary electrometer
� (1889) First International
Congress of Physiologists
� Willem Einthoven sees Waller
demonstrate the technique on
“Jimmy”
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History
� Evolution
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Overview
1. History
2. Review of the conduction system
3. EKG: Electrodes and Leads
4. EKG: Waveforms and Intervals
5. Determining heart rate
6. Determining Rhythm
7. Determining QRS Axis
8. To be continued
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It’s Electric
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The Cardiac Conduction System
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Overview
1. History
2. Review of the conduction system
3. EKG: Electrodes and Leads
4. EKG: Waveforms and Intervals
5. Determining heart rate
6. Determining Rhythm
7. Determining QRS Axis
8. To be continued
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EKG Electrodes
� The EKG records the
electrical activity of
the heart using skin
sensors called
electrodes
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EKG Electrodes
� As a positive wave of depolarization within
the heart cells advances TOWARD a
positive electrode, an UPWARD deflection
is recorded on the EKG
Electrode
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EKG Electrodes
� As a positive wave of depolarization
within the heart cells advances AWAY
from positive electrode, a DOWNWARD
deflection is recorded on the EKG
Electrode
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EKG Electrodes
� If a wave of
depolarization within
the heart cells occurs
at a 90 degree angle
respective to a positive
electrode, an
ISOELECTRIC
deflection is recorded
on the EKG
Electrode
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EKG Electrodes
� Therefore, the size and direction of the recorded impulse is directly related to the direction of depolarization as viewed from the POSITIVE electrode
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EKG Electrodes
� The EKG uses multiple electrode
combinations (Leads) to record:
� The SAME cardiac impulse…
� From DIFFERENT perspectives
� Gives the observer (you) more information about
the electrical activity of the heart
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EKG Leads
� Leads measure the difference in electrical
potential between either:
� Two different points on the body
� Bipolar Leads
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EKG Leads
� OR:
� One point on the body and a virtual reference point with zero electrical potential, located in the center of the heart
� Unipolar Leads
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Summary of Leads
Limb Leads Precordial Leads
Bipolar I, II, III(standard limb leads)
-
Unipolar aVR, aVL, aVF (augmented limb leads)
V1-V6
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Lead Placement: Limb Leads
� White on RIGHT ARM
� Black to LEFT ARM
� Red to LEFT LEG
� Green to RIGHT LEG
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Lead Placement: Precordial Leads
V1: Right 4th intercostal space, parasternal
V2: Left 4th intercostal space, parasternal
V4: Left 5th intercostal space, mid-clavicular line
V3: Halfway between V2 and V4
V5: Horizontal to V4, anterior axillary line
V6: Horizontal to V5, mid-axillary line
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Anatomic Groups(Summary)
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Overview
1. History
2. Review of the conduction system
3. EKG: Electrodes and Leads
4. EKG: Waveforms and Intervals
5. Determining heart rate
6. Determining Rhythm
7. Determining QRS Axis
8. To be continued
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The EKG
� The electrocardiogram (EKG) is a
representation of the electrical events that
occur during the cardiac cycle
� Each event has a distinctive waveform, the
study of which can lead to insight into a
patient’s cardiac pathophysiology
PATTERN RECOGNITION
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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)
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EKG: Standard
� The calibration box
confirms that the EKG
is performed using
standard format
� Run at 25 mm/sec
� Voltage 10mm/mV
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EKG: Standard
� When set to run at
25mm/sec
� 0.2 sec wide
� When set at
10mm/mV
� 10 boxes high
0.2 sec
1 mV
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EKG: Standard
� When set to run at
50mm/sec
� 0.4 sec wide
� Can help sort out
underlying rhythms
when heart rate is fast
0.4 sec
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EKG: Standard
� Can be set to run at ½
standard
� 5mm/mV
� Useful in children or
when voltage is high5mm/mV
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Waveforms and Intervals
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Waveforms and Intervals: P Wave
� Best viewed in Lead II
or V1
� Upright in Lead II
� Biphasic in V1
� Max height should be
less than 2.5 mm
� Duration should be
less than 0.12 sec
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Waveforms and Intervals: PR Interval
� PR interval� Includes the P wave and
the PR segment
� PR interval should be between 0.12 and 0.2 seconds
� Depression of PR segment is pathomnemonic for pericarditis
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Waveforms and Intervals: QRS Complex
� Q wave
� First deflection below isoelectric line
� Should be less than one box (0.04 sec wide) and less than 1/4 the height of R wave
� R Wave
� Any deflection above the isoelectric line
� S wave
� Any deflection below the isoelectric line that is NOT a Q wave
� Entire QRS complex should be less than 0.1 seconds
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Waveforms and Intervals: ST segment
� Begins at the junction
or J point
� End of QRS complex
� Start of T wave
� Morpholgy
� Myocardial Injury
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Waveforms and Intervals: T wave
� Represents ventricular
repolarization
� Beginning of QRS to
apex of T wave
� ABSOLUTE refractory
period
� Last half of T wave
� RELATIVE refractory
period
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Waveforms and Intervals: T wave
� Morphology� Follows the direction of
the QRS complex
� Asymmetrical
� Normal
� Symmetrical peaked
� Hyperkalemia
� Flat
� Hypokalemia
� Inverted
� Ischemia, CNS abnl
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Waveforms and Intervals: QT interval
� Indicates how fast the ventricles are repolarized
� How fast they are ready for the next cardiac cycle
� QTi can be prolonged in the presense of:
� Meds, ischemia, electrolyte imbalances
� Prolongation of the QTi can lead to:� Torsades de Pointes
� Ventricular fibrillation
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Waveforms and Intervals: QT interval
� The QT interval is rate
related
� QTi gets shorter as the
heart rate increases
� Calculating the
corrected QTi (QTc)
QTc men < 450 msec
QTc women < 470 msec
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Overview
1. History
2. Review of the conduction system
3. EKG: Electrodes and Leads
4. EKG: Waveforms and Intervals
5. Determining heart rate
6. Determining Rhythm
7. Determining QRS Axis
8. To be continued
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Rule of 300
� Identify an R wave
that falls on or near a
heavy red line
� Where the NEXT R
wave falls determines
the ventricular rate
� MEMORIZE
� 300,150,100,75,60,50
� REGULAR RHYTHM
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What is the heart rate?
� What is the ventricular rate?
� What is the atrial rate?
Start 75 bpm
S
t
a
r
t
3
0
0
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10 Second Rule
� Most EKG’s record 10 seconds of
rhythm per page
� Count the number of beats present
� Rhythm strip
� Multiply by 6 to get the number of
beats per minute
� This method works well for
IRREGULAR RHYTHMS
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What is the heart rate?
33 beats in 10 sec X 6 = 198bpm
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Overview
1. History
2. Review of the conduction system
3. EKG: Electrodes and Leads
4. EKG: Waveforms and Intervals
5. Determining heart rate
6. Determining Rhythm
7. Determining QRS Axis
8. To be continued
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Rhythm: Normal Sinus
� Is there a P wave ?
� Is there a P attached to every QRS ?
� For NSR there must be a P wave for every QRS
complex and QRS complex for each P wave
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Rhythm: Sinus Arrythmia
� P wave for every QRS and vice versa
� IRREGULAR RHYTHM
� Respiratory pattern
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Rhythm: Sinus Tachycardia
� P wave for every QRS and vice
versa
� Rate > 100 bpm
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Rhythm: Sinus Bradycardia
� P wave for every QRS and vice
versa
� Rate < 60 bpm
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Rhythm: Atrial Flutter
� Atrial rate 200-400 bpm
� Saw tooth pattern� Best seen in lead II
� Common pattern (2:1 conduction)� Atrial rate 300
� Venticular rate 150 bpm
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Rhythm: Atrial Fibrillation
� Highly irregular rhythm
� No discernable P waves
� Ventricular rate depends on conduction
� Rapid
� Slow
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Rhythm: Junctional Rhythm
� Regular Rhythm
� Inverted, absent or after QRS
� Ventricular rate (40-60 bpm)
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Rhythm: Wandering Pacemaker
� Irregular Rhythm
� At least 3 P wave morpholgies
� Rate > 100 bpm
� Multifocal Atrial Tachycardia
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Rhythm: PSVT
� Regular Rhythm
� Rate: 120-150 bpm
� P waves hidden or retrograde
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Overview
1. History
2. Review of the conduction system
3. EKG: Electrodes and Leads
4. EKG: Waveforms and Intervals
5. Determining heart rate
6. Determining Rhythm
7. Determining QRS Axis
8. To be continued
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The QRS Axis
� The QRS axis
represents the net
overall direction of the
heart’s electrical activity
� Abnormalities of axis
can hint at:
� Ventricular enlargement
� Conduction blocks (i.e.
hemiblocks)
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The QRS Axis
� Normal axis is defined
as -30° to 90°
� LAD is -30° to -90°
� RAD is 90° to 180°
� NWA is 180° to 270°
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Overview
1. History
2. Review of the conduction system
3. EKG: Electrodes and Leads
4. EKG: Waveforms and Intervals
5. Determining heart rate
6. Determining Rhythm
7. Determining QRS Axis
8. To be continued