EKG Basics

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EKG Basics

• In 1790, the usually sedate audience of
  scientists gasped in disbelief as Luigi Galvani,
  in a flare of showmanship, made a dead frogs leg
  dance by electrical stimulation.

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EKG Basics

• Galvani knew that the electrical current would
  stimulate the frogs legs to jump, and with
  repeated stimuli, he could make them dance.

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EKG Basics

• In the 1790s, bringing a dead frog back to
  life was a shocking and ghastly supernatural
  feat.
• Galvani loved shocking people!

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EKG Basics

• While conducting research in 1855, Kollicker and
  Mueller found that when the motor nerve to a
  frogs leg was laid over its isolated beating
  heart, the leg kicked with each heartbeat.

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EKG Basics

• Eureka! they thought, the same electrical
  stimulus that causes a frogs leg to kick must
  cause the heart to beat.
• Therefore, the beating of the heart must be due
  to a rhythmic discharge of electrical stimuli.

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EKG Basics

• In the mid 1880s, while using sensor electrodes
  placed on a mans skin, Ludwig and Waller
  discovered that the hearts rhythmic electrical
  activity could be monitored from a persons skin.
• However, their apparatus was not sensitive enough
  for clinical use.

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EKG Basics

• Enter Willem Einthoven, a brilliant scientist who
  suspended a silvered wire between the poles of a
  magnet.
• Two skin sensors (electrodes) placed on a man
  were then connected across the silvered wire,
  which ran between the two poles of the magnet.

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EKG Basics

• The silvered wire (suspended in the magnetic
  field) twitched to the rhythm of the subjects
  heartbeat.
  
• This was very interesting, but Einthoven wanted a
  timed record.

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EKG Basics

• So Einthoven projected a tiny light beam through
  holes in the magnets poles, across the twitching
  silvered wire.
• The wires rhythmic movements were recorded as
  waves (named P, QRS, and T) on a moving scroll of
  photographic paper.

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EKG Basics

• The rhythmic movements of the wire (representing
  the heartbeat) created a series of distinct waves
  in repeating cycles.
• The waves were named P, QRS, and T.
• The clever Einthoven reasoned that he could
  record a hearts abnormal electrical activity and
  compare it to the normal.

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EKG Basics

• Thus, a great diagnostic tool, Einthovens
  Electrokardiogram was created in 1901.

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EKG Basics

• The electrocardiogram (EKG) records the
  electrical activity of the heart, providing a
  record of cardiac electrical activity, as well as
  valuable information about the hearts function
  and structure.

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EKG Basics

• The EKG is often recorded on a ruled piece a
  paper that gives a written record of cardiac
  activity.
• Cardiac monitors and cardiac telemetry provides
  the same information on a display screen.

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EKG Basics

• The EKG records the electrical impulses that
  stimulate the heart muscle (myocardium) to
  contract.

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EKG Basics

• The hearts dominant pacemaker, the SA Node,
  begins the impulse of depolarization which
  spreads outward in wave fashion, stimulating the
  atria to contract.

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EKG Basics

• The SA Node is the hearts dominant pacemaker,
  and its pacing activity is known as Sinus
  Rhythm.
• The ability to generate pacemaking stimuli is
  known as automaticity.
• Other regions of the heart also have
  automaticity, at slower rates than the SA Node.

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The P Wave

• The electrical impulse, originating at the SA
  Node, spreads as a wave of depolarization through
  both atria, and this produces the P Wave on the
  EKG.

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The P Wave

• Thus, the P wave represents the electrical
  activity (depolarization) of both atria, and it
  also represents the simultaneous contraction of
  the atria.

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The AV Node

• The atrial depolarization stimulus reaches the AV
  Node, where depolarization slows, producing a
  brief pause, thus allowing the blood in the atria
  to enter the ventricles.

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The AV Node

• Remember, the AV Node is the only electrical
  conduction pathway between the atria and the
  ventricles.

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HIS Bundle and Left and Right Bundle Branches

• Depolarization passes through the AV Node slowly,
  but upon reaching the ventricular conduction
  system, depolarization conducts very rapidly
  through the HIS Bundle, and the Left and Right
  Bundle Branches.

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Purkinje Fibers

• The left and right Bundle Branches transmits the
  wave of electrical activity to the Purkinje
  Fibers.
• The Purkinje Fibers distribute the depolarization
  stimulus to the ventricular myocardial cells,
  producing a QRS complex on the EKG.

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Ventricular Conduction System
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The Q Wave

• The Q Wave is the first downward stroke of the
  QRS Complex, and it is followed by an upward R
  Wave.
• The Q Wave is often not present.

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QRS Complex

• The upward R Wave is followed by a downward S
  Wave. This total QRS Complex represents the
  electrical activity of ventricular depolarization.

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ST Segment

• Following the QRS complex, there is a segment of
  horizontal baseline known as the ST Segment, and
  then a broad T Wave appears.
• The ST Segment represents the initial phase of
  Ventricular Repolarization.

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ST Segment

• The ST Segment should be flat and level with the
  baseline.
• If the ST Segment is elevated or depressed beyond
  the baseline, it is a sign of serious problems.

ST Normal ST
Elevation
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T Wave

• The T Wave represents the final rapid phase of
  ventricular repolarization.
• At this time, the ventricular myocardial cells
  recover their resting negative charge, so they
  will be ready to depolarize again.

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QT Interval

• The QT Interval represents the duration of
  ventricular systole (contraction of the
  ventricles) and is measured from the beginning of
  the QRS until the end of the T Wave.

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The Cardiac Cycle

• The Cardiac Cycle is represented by the P Wave,
  QRS Complex, the T Wave, and the baseline that
  follows until another P Wave appears. This cycle
  is repeated continuously.

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The Cardiac Cycle
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The Cardiac Cycle

• The P Wave represents atrial depolarization
  (contraction).
• The PR Segment represents the pause at the AV
  Node.
• The QRS Complex represents ventricular
  depolarization (contraction).
• The ST Segment represents the initial phase of
  ventricular repolarization.
• The T Wave represents the final, rapid phase of
  ventricular repolarization.

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EKG Paper

• The EKG is recorded on ruled (graph paper).
• The smallest divisions are 1 millimeter (mm)
  squares.
• The large black square has sides that are 5 mm
  long.

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EKG Paper

• The horizontal axis represents time.
• Each small box represents .04 seconds.
• Each large black box represents .2 seconds.

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EKG Paper

• By measuring along the horizontal axis, we can
  determine the duration of any part of the cardiac
  cycle.

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EKG Leads

• The standard EKG is composed of 12 separate leads
  (or wires) that are attached to electrodes
  (sensors).
• There are 6 limb leads recorded by using arm and
  leg electrodes.
• There are 6 chest leads obtained by placing
  electrodes at different positions on the chest.

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EKG Leads
Limb Leads Chest Leads
I V1
II V2
III V3
AVR V4
AVL V5
AVF V6
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EKG Lead Location
Leads What they are looking at
V1, V2 Right side of heart -Anterior Descending Artery
V3, V4 Septum between ventricles -Anterior Descending Artery
V5, V6, I, AVL Left (lateral) side of heart -Circumflex Artery
II, III, AVF Inferior part of heart -Right or Left Coronary Artery

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Heart Rate

• When examining an EKG, you should first consider
  the rate.
• The rate is read as cycles per minute.

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Heart Rate

• The SA Node is the hearts dominant pacemaker,
  generating a sinus rhythm.
• The SA Node paces at a resting rate range of 60
  to 100 per minute.

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Heart Rate

• When the SA Node paces the heart rate slower than
  60 per minute, it is called Sinus Bradycardia.
• When the SA Node paces the heart rate faster than
  100 per minute, it is called Sinus Tachycardia.

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Heart Rate

• Other potential pacemakers, known as ectopic foci
  have the ability to pace the heart (at a slower
  rate), if the normal SA Node pacemaking fails.
• These foci are located in the
• -Atrial Foci rate of 60-80 per minute
• -Junctional Foci rate of 40-60 per minute
• -Ventricular Foci rate of 20-40 per minute
• Rapid pacemaking activity suppresses slower
  activity

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Determining the Heart Rate from an EKG

• Step 1
• -Find a specific R Wave that peaks on a
  heavy black line (this will be the start line)

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Determining the Heart Rate from an EKG

• Step 2
• -Count off 300, 150, 100 for every thick
  black line that follows the start line, naming
  each line as shown

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Determining the Heart Rate from an EKG

• Step 3
• -Count off the next three lines after 300,
  150, 100 as 75, 60, 50.

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Determining the Heart Rate from an EKG

• Step 4
• -Where the next R Wave falls, determines the
  heart rate.
• -Its that simple!

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Determining the Heart Rate from an EKG
What is this patients Heart Rate?
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Determining the Heart Rate from an EKG

• In the previous EKG, the heart rate was 60, and P
  Waves were absent.
• Which ectopic foci acted as the pacemaker for
  this case of bradycardia?

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Determining the following Heart Rates
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Determining the rhythm on an EKG

• The EKG provides the most accurate means of
  identifying cardiac arrhythmias (abnormal
  rhythms).

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Determining the rhythm on an EKG

• On an EKG, there is a consistent distance
  (duration) between similar waves during a normal
  , regular cardiac rhythm.
• This is due to the automaticity of the SA Node,
  which maintains a constant cycle of pacing
  impulses.

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Determining the rhythm on an EKG

• An EKG is scanned for the repetitive continuity
  of a regular rhythm. Breaks in the continuity,
  such as a pause, presence of an early (premature)
  beat, or sudden rate change warn us of a rhythm
  disturbance.

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Irregular Rhythms

• Wandering Pacemaker
• An irregular rhythm produced by the pacemaker
  activity wandering from the SA Node to nearby
  atrial foci.
• This produces cycle length variation as well as
  variation in the shape of the P Wave

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Wandering Pacemaker
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Multifocal Atrial Tachycardia

• Multifocal Atrial Tachycardia (MAT) is a rhythm
  of patients with Chronic Obstructive Pulmonary
  Disease (COPD).
• The heart rate is over 100 bpm with P waves of
  various shapes, since three or more atrial foci
  are involved.

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Multifocal Atrial Tachycardia
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Atrial Fibrillation

• Atrial Fibrillation is caused by the continuous,
  rapid firing of multiple atrial foci. Since no
  single impulse depolarizes the atria completely,
  and only one occasional atrial depolarization
  gets through the AV Node to stimulate the
  ventricles, an irregular ventricular rhythm is
  produced.

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Atrial Fibrillation
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A
B
C
What is pacing the rhythm of EKG C?
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Premature Beats

• Premature beats occur when an irritable foci
  fires a single stimulus
• Premature Atrial Contraction (PAC)
• Premature Ventricular Contraction (PVC)

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Premature Atrial Contraction

• A Premature Atrial Contraction (PAC) originates
  suddenly in an irritable atrial foci, and it
  produces an abnormal P Wave earlier than
  expected.
• The abnormal P Wave leads to a QRS Complex that
  occurs out of its normal rhythm.

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Premature Atrial Contraction
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Premature Ventricular Contraction

• A Premature Ventricular Contraction (PVC)
  originates suddenly in an irritable ventricular
  foci.
• It produces a giant ventricular complex (big and
  wide QRS)on the EKG.
• There is no P Wave before the abnormal QRS
  Complex, because the atria have not depolarized
  (contracted).

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Premature Ventricular Contraction
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Tachyarrhythmias

• A Tachyarrhythmia originates in a very irritable
  foci that paces rapidly. Sometimes more than one
  active foci is generating the pacing stimuli.
• Paroxysmal Tachycardia 150-250 bpm
• Flutter 250-350 bpm
• Fibrillation 350-450 bpm

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First Degree AV Heart Block

• Normally, there is a pause at the AV Node, which
  allows blood to enter the ventricles.
• In First Degree AV Block, there is a longer than
  normal pause before ventricular stimulation.
• This is seen on an EKG as a PR Interval longer
  than one large square (.2 Seconds).

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Myocardial Infarction

• Myocardial Infarction (MI) results from the
  complete occlusion of a coronary artery.
• The area of the myocardium supplied by the
  occluded coronary artery becomes non-viable and
  neither depolarizes or contracts.

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Myocardial Infarction

• The classic triad of myocardial infarction is
• Ischemia
• Injury
• Infarction

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Myocardial Infarction

• Ischemia a decrease in blood supply from the
  coronary arteries to the myocardium of the heart.
• Characterized by inverted T Waves on the EKG

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Myocardial Infarction

• Injury indicates the acuteness of an infarct.
• ST Elevation denotes myocardial injury.

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Myocardial Infarction

• Infarction permanent damage to the myocardium is
  called an infarction.
• A Significant Q Wave is one that is at least 1
  small square wide (.04 sec), or 1/3 the height
  (or greater) of the QRS amplitude (Height).
• Significant Q Waves indicate permanent damage to
  the myocardium from a heart attack.

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Myocardial Infarction
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Myocardial Infarction
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Myocardial Infarction