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Introduction to ECGs

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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 axis- voltage

1 small box = 1 mm = 0.1 mV

Horizontal axis - time 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 Axis

No. of mm in 10 small boxes? No. of small boxes in 2 mm?

Horizontal Axis No. 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

Calibration of Voltage is Automatic

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 method 300-150-100-75-60-50

R-R method divide 300 by # of large squares

between consecutive R waves 6 Second method

multiply # of R waves in a 6 second strip by 10

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 Constant? Less than 0.20 seconds (1 large bx)

P to QRS Relationship P wave before, during or after QRS? 1 P wave for each 1 QRS? Regular relationship?

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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!!!