Introduction to the basics of 12Lead EKG Interpretation

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Introduction to the basics of 12-Lead EKG
Interpretation

• Jennifer Rodgers, MSN, ARNP
• Wichita State University
• Summer 2006

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INTRODUCTION

• 12-Lead EKG machine developed in 1903 timeless
  invention
• Inexpensive, easily accessible
• Goals
• 1. Review basic cardiac physiology
• 2. Develop systematic approach to 12-Lead
• interpretation
• 3. Practice interpreting EKG strips

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12-Lead EKG

• Electrical recording of the hearts electrical
  activity
• Cardiac cells resting state polarized (negative
  inside positive outside)
• Ensure appropriate distribution of ions
  (potassium, sodium, chloride, calcium)
• Depolarization-fundamental electrical event of
  the heart, stimulationgtmuscle begins to work
• Propagated from cell to cellgtwave throughout
  entire heartgtflow of electricity

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TYPES OF CELLS

• PACEMAKER-electrical source
• ELECTRICAL CONDUCTING-hard wiring
• MYOCARDIAL-contractile machinery

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PACEMAKER CELLS

• Small 5-10 cm in length
• Depolarize spontaneously _at_ particular rate
• Located in Right Atrium-Sinoatrial (sinus) node
• Typical 60-100 beats/minute
• Dependent on autonomic nervous system and body
  demands

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ELECTRICAL CONDUCTING CELLS

• Long-Thin cells
• Rapidly carry currents to distant regions of heart

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Myocardial Cells

• Heavy labor cells
• Constantly contracting relaxinggt delivering
  blood to the periphery
• Contain contractile proteinsgt actin myosin
• Depolarizationgtmyocardial cellgtcalcium released
  within cellgtcontract

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Time Voltage

• Waves on EKG primarily reflect electrical
  activitygtmyocardial cells
• Waves-3 characteristics
• 1. Duration-measured fraction/second
• 2. Amplitude-measured millivolts (mV)
• 3. Configuration-shape/appearance

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EKG PAPER

• Light lines small squares- 1 X 1 mm
• Bold lines large squares 5 X 5 mm
• Horizontal axistime
• 1. Distance across small square0.04 sec.
• 2. Distance across large square0.2 sec.
• Vertical axisvoltage
• 1. Distance across small square0.1 mV
• 2. Distance across large square0.5 mV
• 6 second strip to figure rate (X 10) (30 lg6)

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SINUS NODE

• STARTS EACH CARDIAC CYCLE OF CONTRACTION
  RELAXATION BY SPONTANEOUS DEPOLARIZATION THIS IS
  NOT SEEN ON THE EKG

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ATRIOVENTRICULAR (AV) NODE

• Electrical Gatekeeper between atria and
  ventricles
• Allows atrial contraction to end empty contents
  into the ventricle before ventricular contraction
  begins

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VENTRICULAR DEPOLARIZATION

• WAVE DEPOLARIZATION SPREADS THROUGH THE 3
  PARTS-Bundle of His (intrinsic 40-60 bpm)gt Bundle
  Branchesgt Purkinje Fibers (intrinsic 20-40 bpm)
  out into the ventricular myocardium
• Beginning ventricular depolarizationgtQRS complex

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VENTRICULAR REPOLARIZATION

• Brief refractory period
• Restore electro negativity of their interiors
• T wave
• Atrial repolarization is not seen

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PR INTERVAL

• Includes P wave the first straight line
  connecting it to the QRS interval
• Measures the time from the start of atrial
  depolarization to the start of ventricular
  depolarization
• Normal 0.12-0.20 sec
• gt0.20 delay in AV conduction
• lt0.12 shortens as HR increases

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ST SEGMENT

• The straight line connecting the end of the QRS
  complex with the beginning of the T wave
• Measures the time from the end of ventricular
  depolarization to the start of ventricular
  depolarization

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QT INTERVAL

• Includes the QRS complex, ST segment, T wave
• Measures the time from the beginning of
  ventricular depolarization to the end of
  ventricular repolarization
• Normal duration QRS 0.06-0.10 seconds

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RATE MEASURMENT

• 1. COUNT THE OF QRS COMPLEXES IN 6 SECONDS X
  10, MOST COMMON
• 2. COUNT OF LG. BOXES BETWEEN 2 R WAVES /BY
  300
• 3. COUNT OF SM. BOXES BETWEEN 2 R WAVES /BY
  150

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STEPWISE APPROACH STRIP INTERPRETATION

• A. Determine Atrial Ventricle Rate
• 1. V-measure R-R, A-measure P-P
• 2. gt100 Tachycardia, lt60 Bradycardia
• B. R-R Interval Regular?
• C. P wave Formation
• 1. Precede QRS, occur regularly,
• similar size
• 2. P wave (SA Node) OR -/absent (AV
• Junction)
• D. QRS wide or narrow

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SINUS NODE DYFUNCTION

• SINUS ARRHYTHMIA
• SINUS TACHYCARDIA
• SINUS BRADYCARDIA

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SINUS ARRHYTHMIA

• A. Rate 60-100 bpm
• B. R-R irregular
• C. Normal P wave
• D. Normal PR interval 0.12-0.20 sec.
• E. Normal QRS complex lt/0.10 sec.
• Phasic slowing quickening, benign, normal
  response to respirations, asymptomatic
• Except in elderlygtSick Sinus Syndrome, not
  usually seen in infants

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SINUS BRADYCARDIA

• Usual response to reduced demand for blood flow
• A. Rate lt 60 bpm
• B. R-R Regular
• C. Normal P wave
• D. Normal PR interval
• E. Normal QRS Complex
• Asymptomatic Vs. Symptomatic

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SINUS TACHYCARDIA

• ACCELERATION SA NODE
• A. Rate gt110 bpm (110-160)
• B. R-R Regular
• C. Normal P wave
• D. Normal PR Interval 0.12-0.20 sec
• E. Normal QRS Complex lt/0.10 sec
• Response to exercise/stress, OR response illness
  (hypovolemia/hypotension)gtresolves once cause
  fixed

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ATRIAL DYSRHYTHMIAS

• Most common cardiac rhythm disturbance
• Originate in/around SA Node above ventricle
• Can diminish atrial kick gt20 ventricular
  volume
• PSVT-Paroxysmal Supraventricular Tachycardia
• Atrial Fibrillation
• Atrial Flutter

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PSVT

• A. Rate 150-250 bpm
• B. Regular R-R interval
• C. P wave can be buried
• D. PR interval may be hard to find
• E. Normal narrow QRS complex
• Treatment LVEF50gtCCB, BB, Dig., possible
  cardioversion, lt40 No Cardioversion!, Dig.,
  Amiodorone, Diltiazem

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ATRIAL FLUTTER

• A. Atrial Rate 250-350 bpm
• B. R-R Irregular
• C. P wave classic saw tooth OR flutter
• D. PR interval immeasurable
• E. QRS complex narrow
• May have palpitations, OR s/sx reduced C.O.
• If symptomaticgtcardioversion, BB, Sotalol, Dig.

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ATRIAL FIBRILLATION

• Chaotic, asynchronous electrical activity in
  atrial tissuegtmultiple impulses numerous eptopic
  pacemakers
• A. Atrial Rate-indiscernible, V-Rate 60-160
  (RVR-Rapid Ventricular Response)
• B. R-R Irregular
• C. No P wave
• D. No PR interval
• E. QRS narrow

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JUNCTIONAL ESCAPE RHYTHM

• Originates in AV junction escape pacemaker
• A. Rate 40-60 bpm
• B. R-R Regular
• C. Inverted P wave, preceding each QRS
• D. PR Interval short 0.10 sec.
• E. QRS normal
• How is patient tolerating? Loss of atrial
  kickgt can reduce C.O. by 20

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PREMATURE BEATS

• Premature Atrial Contractions (PACs)-originate
  outside AV node, single/multiple ectopic focus
  supersede SA node
• Premature Ventricular Contractions
  (PVCs)-ectopic beats that originate in
  ventricles occur earlier, singles, pairs or in
  clusters

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VENTRICULAR DYSRHYTHMIAS

• VENTRICULAR TACHYCARDIA
• VENTRICULAR FIBRILLATION

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VENTRICULAR TACHYCARDIA (V-TACH)

• Defined as Vent. Rate gt 100 bpm when 3 OR more
  PVCs strike in a row
• Life threatening, unstable, sustained OR
  unsustained
• A. A-rate cant be determined, V-rate100-250
  bpm
• B. R-R regular or slightly irregular
• C. P wave usually absent, dissociated
• D. PR Interval-immeasurable
• E. WIDE QRS gt0.12 sec. Bizarre appearance

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VENTRICULAR FIBRILLATION (V-FIB)

• VF-Full cardiac arrest, no pulse/BP, always check
  patient firstgtDefibrillategtCPR/ACLS
• A. Rate-cant be determined pulseless
• B. R-R cant determine
• C. P wave cant be determined
• D. PR interval cant be determined
• E. QRS complex cant be determined
• Ventricular electrical activity gtfibrillatory
  waves with no recognizable pattern

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A-V BLOCKS

• Interruption/delay in the conduction of
  electrical impulses between the atria
  ventricles
• Classified site of block/severity of conduction
  abnormality
• 1st degree, 2nd degree Mobitz I (Wenkebach), 2nd
  degree Mobitz II, 3rd degree (Complete heart
  block)

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1st Degree AV Block

• Characterized by PR Interval gt 0.20 seconds
• Delay in conduction AV Node
• Prolonged PR Interval constant
• Usually asymptomatic
• Least concerning of the blocks

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2nd Degree Mobitz I (Wenkebach)

• Successive impulses from SA node delayed slightly
  longer than the previous impulse
• Characterized by prolonged PR interval that
  continues until the P wave is dropped (impulse
  doesnt reach ventricle)
• May have hypotension or lightheadedness

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2nd Degree Mobitz II

• Less common, more serious
• Impulses from SA node fail to conduct to
  ventricles
• Hallmark PR Interval constant normal or
  prolonged, doesnt prolong before dropping, not
  followed by QRS, can have gt 1 dropped in a row
• Precursor to 3rd Degree Heart Block

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3RD DEGREE COMPLETE HEART BLOCK

• Indicates complete absence of impulse between the
  atria ventricle
• Atrial rate gt or ventricular rate
• Occur _at_ AV node 40-60 bpm
• Occur _at_ bundle branches lt 40 bpm wide QRS complex
• Decreased C.O., P-P R-R disassociated

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EKG INTERPRETATION

• LETS PRACTICE!!!!