Introduction to ECGs
EMS Professions Temple College
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Discussion Topics
ECG Monitoring Basics Standardized Methods & Devices Components & Measurements of the ECG Complex ECG Analysis
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ECG Monitoring
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ECG Monitoring
Recording of Electrical Activity Uses Bipolar or Unipolar leads
The ECG DOES NOT provide a recording or evaluation of Mechanical Activity!!!
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ECG Monitoring
Bipolar Leads
1 positive and 1 negative electrode
RA always negative LL always positive
Traditional limb leads are examples of these
Lead I Lead II Lead III
Provide a view from a vertical plane
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ECG Monitoring
Unipolar Leads
1 positive electrode 1 negative “reference point”
calculated by using summation of 2 negative leads
Augmented Limb Leads
aVR, aVF, aVL vertical plane
Precordial or Chest Leads
V1-V6 horizontal plane
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ECG Monitoring
Einthoven’s Triangle
Each lead “looks” from a different perspective Can determine the direction of electrical impulses Upright electrical recording indicates electricity flowing towards the + electrode
positive deflection
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Standardized Methods & Devices
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Standardized Methods & Devices
ECG Paper Device Paper Speed Device Calibration Electrode Placement
Variations Do Exist!
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Standardized Methods & Devices
ECG Graph Paper
Vertical
1
axis- voltage axis - time
small box = 1 mm = 0.1 mV
Horizontal
1
small box = 1 mm = 0.04 sec.
Every
5 lines (boxes) are bolded
Horizontal
axis - 1 and 3 sec marks
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Standardized Methods & Devices
ECG Paper Examples
Vertical
No.
Axis
of mm in 10 small boxes? No. of small boxes in 2 mm?
Horizontal
No.
Axis
of seconds in 5 small boxes? No. of small boxes in 0.2 second? No. of small boxes in 1 second?
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Standardized Methods & Devices
Paper Speed & Calibration
Paper
Speed - 25 mm/sec standard of Voltage is Automatic
Calibration
Both
Speed and voltage calibration can be changed on most devices
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Standardized Methods & Devices
Electrode Placement
Standardization
improves accuracy of comparison ECGs 3 Lead and 12 Lead Placement are most common Assure good conduction gel Prep area with alcohol prep Avoid
Bone Large muscles or hairy areas Limb vs. Chest placement
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Standardized Methods & Devices
Electrode Placement
Poor
placement or preparation
Often results in artifact
Stray energy from other sources can also lead to poor ECG tracings (noise)
60 cycle interference
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Components of the ECG
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Components of the ECG Complex
Components & Their Representation
P, Q , R, S, T Waves PR Interval
QRS Interval
ST Segment
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Components of the ECG Complex
P Wave
first upward deflection represents atrial depolarization usually 0.10 seconds or less usually followed by QRS complex
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Components of the ECG Complex
QRS Complex
Composition of 3 Waves
Q, R & S represents ventricular depolarization much variability
usually < 0.12 sec
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Components of the ECG Complex
Q Wave
first negative deflection after P wave depolarization of septum not always seen
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Components of the ECG Complex
R Wave
first positive deflection following P or Q waves subsequent positive deflections are R’, R”, etc
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Components of the ECG Complex
S Wave
Negative deflection following R wave subsequent negative deflections are S’, S”, etc may be part of QS complex
absent R wave in aberrant conduction
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Components of the ECG Complex
PR Interval
time impulse takes to move through atria and AV node from beginning of P wave to next deflection on baseline (beginning of QRS complex) normally 0.12 - 0.2 sec may be shorter with faster rates
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Components of the ECG Complex
QRS Interval
time impulse takes to depolarize ventricles from beginning of Q wave to beginning of ST segment usually < 0.12 sec
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Components of the ECG Complex
J Point
point where QRS complex returns to isoelectric line beginning of ST segment critical in measuring ST segment elevation
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Components of the ECG Complex
ST Segment
early repolarization of ventricles measured from J point to onset of T wave elevation or depression may indicate abnormality
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Components of the ECG Complex
T Wave
repolarization of ventricles concurrent with end of ventricular systole
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ECG Analysis
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ECG Analysis
Rate Rhythm/Regularity QRS Complex P Waves Relationships & Measurements
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ECG Analysis
Ventricular Rate
Triplicate
R-R
method
300-150-100-75-60-50
method
divide
300 by # of large squares between consecutive R waves # of R waves in a 6 second strip by 10
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Second method
multiply
Rate
meter unreliable!!!
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ECG Analysis
Rhythm
Measure
R-R intervals across strip Should find regular distance between R waves Classification
Regular Irregular
• Regularly irregular • Irregularly irregular
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ECG Analysis
QRS Complex
Narrow
<
0.12 seconds (3 small boxes) is normal indicates supraventricular origin (AV node or above) of pacemaker
Wide
>
0.12 seconds is wide indicates ventricular or supraventricular w/aberrant conduction
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ECG Analysis
P Waves
Present? Do
they all look alike? Regular interval Upright or inverted in Lead II?
Upright
= atria depolarized from top to bottom Inverted = atria depolarized from bottom to top
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ECG Analysis
Relationships/Measurements
PR
Interval
than 0.20 seconds (1 large bx)
Constant? Less
P
to QRS Relationship
wave before, during or after QRS? 1 P wave for each 1 QRS? Regular relationship?
P
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ECG Analysis
A monitoring lead can tell you:
How
often the myocardium is depolarizing How regular the depolarization is How long conduction takes in various areas of the heart The origin of the impulses that are depolarizing the myocardium
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ECG Analysis
A monitoring lead can not tell you:
Presence
or absence of a myocardial infarction Axis deviation Chamber enlargement Right vs. Left bundle branch blocks Quality of pumping action Whether the heart is beating!!!
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ECG Analysis
An ECG is a diagnostic tool, NOT a treatment No one was ever cured by an ECG!!
Treat the PATIENT not the Monitor!!!
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