ECG

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ECG
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Fundamentals of Electrocardiography

• The conduction system is the mechanism by which
  the heart contracts. Contraction is controlled
  by specialized cells within the heart that
  generate and distribute electrical impulses

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Fundamentals of Electrocardiography Path of
Impulse

• SA Node
• ?
• AV Node
• ?
• AV Bundle (Bundle of His)
• ?
• Right and Left Bundle Branches
• ?
• Purkinje Fibers
• www.clevelandclinic.org/heartcenter/pub/guide/hert
  works/heratpics.htm

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Fundamentals of ElectrocardiographyPath of
Impulse

• The pulse begins in the sinoatrial (SA) node.
  The cells within the SA node spontaneously
  depolarize to trigger contraction. The
  contraction begins in the upper atria and spreads
  toward the atrioventricular (AV) valves. This
  helps move blood from the atria to the ventricles.

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Fundamentals of Electrocardiography Path of
Impulse

• The pulse travels to the AV node which is located
  within the interatrial septum. It than proceeds
  to the AV bundle (Bundle of His). The bundle of
  His then divides into the left and right bundle
  branches. Each branch travels down the septum.
  At the apex, the branches called purkinje fibers
  transverse the ventricles back toward the base of
  the heart.

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Fundamentals of Electrocardiography

• Depolarization causes contraction of heart
• Repolarization causes relaxation of heart
• Contraction state of heart is systole
• Relaxation state of heart is diastole

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Fundamentals of ElectrocardiographyPurpose of ECG

• Identify cardiac rate
• Identify any abnormalities in rhythm
• Identify presence of abnormal transmission
  impulses through conduction system of heart

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Fundamentals of ElectrocardiographyIndications
for ECG

• Chest pain
• Rhythm disturbances
• Routine physical
• Pre-Op evaluation

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Fundamentals of ElectrocardiographyBasic ECG
Tracing

• The basic ECG tracing consists of
• P wave
• Q wave
• R wave
• S wave
• T wave

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Fundamentals of ElectrocardiographyBasic ECG
Tracing

• P wave (normal lt.2 sec or 5 boxes)
• First deflection from baseline
• Is a positive deflection (upward)
• Corresponds to atrial depolarization
• Q wave
• Small negative (downward) deflection preceding
  the R wave

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Fundamentals of ElectrocardiographyBasic ECG
Tracing

• R wave
• Large positive deflection preceding the S wave
• S wave
• Small negative deflection

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Fundamentals of ElectrocardiographyBasic ECG
Tracing

• QRS Complex
• All 3 Q, R, and S waves together(normally lt 3
  boxes)
• Corresponds with ventricular depolarization,
  resulting in ventricle contraction
• If Q wave is absent, then QRS complex is measured
  from the beginning of the first positive
  deflection after the PR interval

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Fundamentals of ElectrocardiographyBasic ECG
Tracing

• T wave
• Follows QRS complex
• Positive deflection
• Corresponds to ventricular repolarization and
  relaxation

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Fundamentals of ElectrocardiographyBasic ECG
Tracing

• ST Segment
• Interval time from end of ventricular
  depolarization to beginning of ventricular
  repolarization
• Should normally be at baseline
• Hearts resting period between ventricular
  depolarization and repolarization

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Fundamentals of ElectrocardiographyBasic ECG
Tracing

• PR Interval
• Measured from beginning of P wave to beginning of
  QRS Complex (normal lt.2 sec or 5 boxes)
• Is the time between atrial depolarization and
  beginning of ventricular depolarization
• The impulse travels from the SA node to the
  ventricle

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Fundamentals of ElectrocardiographyBasic ECG
Tracing

• QT Interval
• Period between onset of QRS complex and end of T
  wave
• It represents the entire time of ventricular
  depolarization and repolarization

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Fundamentals of ElectrocardiographyStandard
12-Lead ECG

• Consists of 6 chest leads and 6 limb leads
• Only ten electrodes are utilized to obtain a
  12-Lead ECG

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Fundamentals of ElectrocardiographyLead Placement

• Limb Leads
• Right arm
• Right leg
• Left arm
• Left Leg

• Chest Leads
• V1 just to the right of the sternum
• V2 just to the left of the sternum
• V3 placed next to below V2
• V4 placed next to below V3
• V5 laterally and over to the left side of the
  heart
• V6 laterally next to V5

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Fundamentals of ElectrocardiographyBasic ECG
Tracing-Limb Leads

• Lead I Right arm and Left arm
• Lead II Right arm and Left leg
• Lead III Left arm and Left leg
• AVR midway between left arm and left leg to
  right arm
• AVL midway between right arm and left leg to
  left arm
• AVF midpoint between right and left arms to
  left leg

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Fundamentals of ElectrocardiographyBasic ECG
Tracing

• Right leg lead is the ground lead
• V1, V2 and AVR are the right heart leads
• V3 and V4 are the septal leads (transition
  between right and left sides of heart)
• V5, V6, I and AVL are the lateral leads (left
  side of the heart)
• II, III, and AVF are the inferior heart leads

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Fundamentals of ElectrocardiographyLead Placement

• Lead placement of the six chest leads

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Fundamentals of ElectrocardiographyHeart Rates
Rhythm

• Sinus rhythm 60-100 bpm and rhythm originates
  in SA node (Normal rhythm is when there is equal
  distance between the R-R intervals)
• Sinus tachycardia SA node paces the heart
  faster than 100 bpm
• Sinus bradycardia SA node paces the heart
  slower than 60 bpm
• Flutter 250-350 bpm
• Fibrillation gt350 bpm

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Fundamentals of ElectrocardiographyRate
Determination

• On ECG paper, count the number of R waves in any
  6 sec. interval. Multiply that number by 10 to
  calculate HR
• 300, 150, 100, 75, 60, 50 method

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Fundamentals of ElectrocardiographyCauses of
Arrhythmias

• Fast or slow HR
• Skipped beats
• Heart disease
• Smoking
• Caffeine
• Alcohol
• Medications
• Stress

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Fundamentals of ElectrocardiographyAtrial Flutter

• Saw-tooth appearance

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Fundamentals of ElectrocardiographyAtrial
Fibrillation

• Caused by continuous, uncontrolled firing of
  multiple foci in atria, resulting in an
  ineffective quivering of the cardiac muscle
• Characterized by irregular ventricular rhythm and
  absence of P wave
• Difficult to get adequate pacing trigger for
  gated studies

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Fundamentals of ElectrocardiographyPVCs

• Premature ventricular contractions
• Originate from an ectopic focus in the ventricle
• It produces a wide QRS complex
• Can be unifocal or multifocal (couplet, triplet
  or a run) and can occur as bigeminy or trigeminy

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Fundamentals of ElectrocardiographyVentricular
Bigeminy

• A repeating pattern followed by a normal beat

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Fundamentals of ElectrocardiographyVentricular
Trigeminy

• A pattern of PVCs followed by two normal beats

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Fundamentals of ElectrocardiographyVentricular
Tachycardia

• The appearance of 3 or more rapid consecutive
  PVCs.
• If not controlled, can lead to V-flutter or V-fib

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Fundamentals of ElectrocardiographyVentricular
Flutter

• ECG tracing becomes wavy and irregular with no
  discernible QRS complex or P wave

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Fundamentals of ElectrocardiographyHeart Block

• An electrical conduction disorder from the SA, AV
  nodes or Purkinje fibers
• Heart blocks are classified by the extent of the
  conduction abnormality

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Fundamentals of ElectrocardiographyHeart Block

• First-Degree
• Electrical impulse is conducted more slowly than
  normal
• Second-Degree
• The electrical impulse may or may not be
  conducted
• Third-Degree
• The electrical impulse is totally blocked

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Fundamentals of ElectrocardiographyHeart Blocks

• Sinus block
• Atrioventricular block
• Bundle branch block (BBB)

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Fundamentals of ElectrocardiographyHeart
Block-AV Block

• The AV block delays the stimulation of the
  ventricles

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Fundamentals of ElectrocardiographyHeart
Block-AV Blocks

• First-Degree
• PR interval is prolonged beyond 0.2 second
  because of a delay in conduction through the AV
  node
• Second-Degree
• PR interval becomes gradually longer and QRS
  complex fails to occur
• Third-Degree
• None of the atrial impulses are conducted to the
  ventricles and the ventricles pace independently

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Fundamentals of ElectrocardiographyHeart
Block-Bundle Branch Blocks

• BBB are the most common block. It originates in
  the left or right bundle branches. BBBs are
  caused by a block of depolarization in the right
  or left bundle branches. The peak of the QRS
  complex is notched.

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Bundle Branch Blocks

• Right bundle branch blocks appear in leads V1 and
  V2
• Left bundle branch blocks appear in leads V5 and
  V6

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Fundamentals of ElectrocardiographyIschemia/Infar
ction

• ST segment depression may be seen in
  subendocardial infarction, in patients on
  Digitalis and in transient exercise-induced
  ischemia.
• T wave inversion represents ischemia. Its
  appearance may be anything from moderately
  flattened to significantly inverted.

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Fundamentals of Electrocardiography

• ST Depression
• T wave inversion

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Fundamentals of ElectrocardiographyIschemia/Infar
ction

• ST segment elevation represents acute ischemia
  resulting in injury. Degree of elevation denotes
  severity of ischemic injury.
• Presence of Q wave denotes myocardial infarction.
  Q wave is not usually visualized. The
  anatomical location of the infarction is
  determined by the presence of a Q wave on a given
  lead.

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Fundamentals of Electrocardiography

• ST segment elevation
• Presence of Q wave

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Fundamentals of ElectrocardiographyAbnormalities
on ECG Determines Infarct Location

• Anteroseptal V2 V3
• Anterior V3 V4, not on V5 or V6
• Anterolateral V4 V5
• Lateral I, AVL, V5 V6
• Inferior II, III, AVF

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Fundamentals of ElectrocardiographyArtificial
Pacemakers

• An electric device used to stimulate the heart to
  beat when the electrical conduction system is
  unable to function properly. Can be used for
  atrial, ventricular or dual-chamber pacing. It
  causes a narrow line (the pacemaker spike) in the
  ECG tracing.

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Fundamentals of ElectrocardiographyArtificial
Pacemakers
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References

• Crawford, MS, CNMT, Elpida S., and Syed Sajid
  Husain, MD, MAS. Nuclear Cardiac Imaging,
  Terminology and Technical Aspects. Reston
  Society of Nuclear Medicine, 2003.
• Taylor, MD, Andrew, David Schuster, MD, and Naomi
  Alazraki, MD. A Clinicians Guide to Nuclear
  Medicine. Reston Society of Nuclear Medicine,
  2000.
• Introduction to Nuclear Cardiology (Third
  Edition). Du Pont Pharma ( a professional
  education service), 1993.

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References

• University of Utah School of Medicine website,
  www.medstat.med.utah.edu/kw/ecg