EKG Basics 2

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EKG Basics 2

• That Squigglely Line -
• What Does It Really Mean ?
• Part 2
• David Arnall, Ph.D., P.T. (2000)

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The V Leads

• The Precordial Chest Leads Record The Hearts
  Electrical Activity In The Transverse Or
  Horizontal Plane.

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http//www.publicsafetynet.net/12lead_dx.htmelect
rode
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• To Create The Six Precordial Chest Leads, Each
  Chest Lead Is Made Positive The Whole Body Is
  Considered Negative.

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Lead Positioning

• V1 Is Placed In The Fourth Intercostal Space To
  The Right Of The Sternum.
• V2 Is Placed In The Fourth Intercostal Space To
  The Left Of The Sternum.

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• V3 Is Placed In Between V2 And V4.
• V4 Is Placed In The Fifth Intercostal Space In
  The Midclavicular Line Near The Nipple.

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• V5 Is Placed In Between V4 And V6.
• V6 Is Placed In The Fifth Intercostal Space In
  The Midaxillary Line.

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http//endeavor.med.nyu.edu/courses/physiology/cou
rseware/ekg_pt1/EKGprecordial.html
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• When placing the precordial chest leads across
  the thorax, the clinician places the electrodes
  under the pectoralis major not over the breasts.

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• In The Chest Cavity, The Heart Is Positioned With
  The Right Ventricle Lying Anteriorly Medially
  While The Left Ventricle Lies Anterolaterally
  Posteriorly

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• Therefore, Leads V1 V2 Lie Directly Over The
  Right Ventricle. Their Line Of Sight Is To View
  The Electrical Activity Coming From The Right
  Ventricle.

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• Leads V3 V4 Lie Directly Over The
  Interventricular Septum. Their Line Of Sight Is
  To View The Electrical Activity Of The
  Interventricular Septum.

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http//endeavor.med.nyu.edu/courses/physiology/cou
rseware/ekg_pt1/EKGprecolead.html
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• Leads V5 V6 Lie Over The Left Ventricle.
  Therefore, These Leads View The Electrical
  Activity Of The Left Ventricle.

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• The Precordial Chest Leads Can Be Divided Up Into
  Areas Of The Heart They View.

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• Leads V1, V2, V3, V4 Are The Anterior Leads.

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• Leads V5 V6 Look At The Left Lateral Wall.

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In Review

• Anterior Chest Leads
• V1, V2, V3 V4

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• Left Lateral Wall Leads
• aVL, Lead I , V5 V6

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• Inferior Chest Leads
• Lead II, Lead III, Lead aVF

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• No Mans Land
• aVR

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• A Review Of The Waves
• Intervals Of The EKG

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The P Wave

• The P Wave Is The Signal That Electrical
  Potential Has Left The SA Node, Swept Across The
  Atria, Has Initiated Atrial Contraction.

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What Is A Normal P Wave ?

• Duration The Normal Duration Of A P Wave is
  2.0 - 2.5 mm (.04 - .1 sec)
• If It Is Greater Than 2.75 mm (.11 sec) It Is
  Considered To Be An Abnormal P Wave.

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http//www.ovcnet.uoguelph.ca/ClinStudies/Courses/
Public/Cardiology/Concepts/ECGConcepts13-16.htm
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• Amplitude
• A Normal Amplitude For A
• P Wave Is 2-3 mm.

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• The P Wave Should Always Be Gently Rounded -
  Never Pointed Or Peaked.

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• Abnormal Amplitude Of The P Wave Is Often Seen In
  Cor Pulmonale, A-V Valve Disease, Hypertension
  In Patients With Congenital Heart Disease

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• P Waves Within The Same Lead That Are Multiformic
  Indicate The Presence Of More Than One Pacemaker
  In The Right Atrium.

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• In The Six Limb Leads, You Will Generally See P
  Waves In The Upright Position Except In aVR V1
  Where They Are Negatively Deflected.

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http//bioscience.org/images/normalh.gif
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• You Will Frequently See Biphasic P Waves In Lead
  III, Lead V2 Occasionally In Lead aVL.

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BiPhasic P Wave In V1
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The PR Interval

• After The P Wave There Is A Silent Period Where
  Nothing Is Happening In The EKG Tracing. This
  Quiescent Period Is Called The PR Interval.

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• The PR Interval Is A Time Lag And Represents The
  Period During Which There Is AV Nodal Capture Of
  The SA Node Signal.

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• The PR Interval Allows The Atria To Contract
  (atrial systole) Which Tops Off The Ventricles
  With Blood - An Event Called Atrial Kick.

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• The PR Interval Is Measured From The Beginning Of
  The P Wave To The Beginning Of The Q Wave Or The
  Beginning Of The R Wave If The Q Wave Is Absent.

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http//doyle.ibme.utoronto.ca/EKG/rhythm/EKGTUTORI
AL.htm
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• The PR Interval Represents The Time Period
  Encompassing Atrial Depolarization Up To But Not
  Including The Start Of Ventricular
  Depolarization.

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• A major portion of the PR interval reflects the
  slow conduction through the AV node which is
  controlled by the sympathetic-parasympathetic
  balance within the autonomic nervous system.
• Marriotts Practical Electrocardiography, 9th
  ed., Galen S. Wagner, pg 39, 1994

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• Duration The Adult PR Interval Is Normally
  Between 3-5 mm Or .12 - .20 Seconds In Duration.
  Some Cardiologists Will Say It Is Normal Out To
  .22 Seconds (5 1/2 mm)

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• If The PR Interval Is Longer Than 5 mm, It Is
  Called A Prolonged PR Interval May Indicate The
  Presence Of An AV Block.

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First Degree AV Block
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• The PR Interval Shortens During Exercise Because
  Of The Sympathetic Tone That Predominates Over
  The Heart.

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• If The PR Interval Could Not Shorten, Along With
  Other Segments In The EKG, Then Acceleration Of
  Heart Rate During Exercise Would Be Difficult If
  Not Impossible.

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• In Young Children, The PR Interval Is Shorter
  Than In Adults. The Childs Heart Rate Is Also
  Faster.

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• In A 1 Year Old Child At Rest, The Normal P-R
  Interval Is Typically .11 sec. Or Slightly Under
  3 mm.

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• For Children Who Are 6 Years Of Age, The P-R
  Interval At Rest Is .13 Seconds Or Slightly Over
  3 mm.

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• In Children 12 Years Of Age, The P-R Interval At
  Rest Will Be .14 Seconds Or About 3.5 mm.

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• In Grown Adults 18 Years Of Age And Older, The
  P-R Interval At Rest Will Be 3-5 mm In Length.

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• Prolonged P-R Intervals Are Symptomatic Of AV
  Blocks Due To Coronary Disease Rheumatic Fever.

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• Sometimes, Prolonged P-R Intervals Not Related To
  Heart Disease, Can Be Seen In Healthy Athletes -
  An Aberration Called A Normal Variant. This Can
  Be Seen In About 1 - 2 Of The Healthy, Young
  Population.

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• Pathologies Resulting In PR Interval Shortening

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• Shortened P-R Intervals Are Seen In Patients With
  Pheochromocytoma And Wolfe-Parkinson-White
  Syndrome

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• Pheochromocytoma is a tumor in the adrenal
  medulla that results in a greater-than-normal
  release of catecholamines. The high blood
  concentration of catecholamines causes the heart
  rate to accelerate.

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• Wolff-Parkinson-White Syndrome is a medical
  condition in which atrioventricular myocardial
  accessory pathways electrically pre-excite the
  ventricles to contract producing an extremely
  short PR interval.

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• These accessory electrical pathways are remnants
  of fetal pathways that did not disappear after
  birth. The Bundle Of Kent has been implicated as
  a common aberrant pathway in W-P-W.

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• W-P-W occurs in .15 - .20 of the population
  or 21,000 people. Patients with W-P-W are
  otherwise healthy.

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• W-P-W effects men more than women and can evolve
  into atrial and ventricular dysrhythmias with a
  general mortality up to 4 of the effected
  population.

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• Patients with W-P-W often complain of episodic
  symptoms that include chest discomfort,
  dizziness, and palpitations.

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http//homepages.enterprise.net/djenkins/ecghome.h
tml
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http//www.heartinfo.org/physician/ecg/wpw.htm
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The Q Wave

• Definition The Q Wave Is The First Downward
  Deflection After The P Wave Before The R Wave.

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• Sometimes Q Waves Are Present Sometimes They
  Are Absent Depending On The Lead.

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• It is common to normally see Q waves in leads I,
  II, aVL and in V4-6.

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• A Normal Q Wave Is Not Wider In Duration Than 0.5
  mm Or About .02 Seconds. Its Normal Amplitude Is
  lt 1 mm.

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• Q Waves Are An Indication Of Ventricular Septal
  Wall Depolarization.

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• They Appear Before The QRS Complex Because The
  Fascicle That Conducts The Signal Is Higher Than
  The Right And Left Bundle Branch That Give You
  The QRS Complex.

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• Q Waves Of Normal Size Have No Diagnostic Meaning
  In Normal Hearts Except That The Septum Has
  Depolarized.

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Significant Q Waves

• Q waves In Leads I, II, aVF, aVL Can Mean
  Something If ...

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• 1. They Are Between 25 - 33 Of The Amplitude Of
  The R Wave.
• 2. They Are Greater Than 0.04 Seconds (1 mm) In
  Duration.

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• Q waves of any size are normal in leads aVR.

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• If They Are 25-33 Of The Total Amplitude Of The
  R Wave, Then They Are Significant For The
  Presence Of An MI In The Lead Where The Q Wave
  Appears.

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• In Other Words, If The Significant Q Wave Appears
  In Leads II, III Or aVF, Then The MI Must Have
  Occurred In The Inferior Portion Of The Heart -
  The Right Coronary Is Blocked.

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• If The Significant Q Wave Appeared In Lead I Or
  aVL, Then The MI Must Have Occurred In The
  Antero-Lateral Or Lateral Portions Of The Left
  Ventricle.

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• Since Lead I aVL Cover The Lateral Wall Of The
  Left Ventricle, Then The Occlusion Likely
  Occurred In The Circumflex Or The Marginal
  Branches Of The Left Coronary.

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• Use The Precordial Chest Leads To Look For
  Significant Q Waves For The Presence Of An MI In
  The Anterior Portion Of The Heart - V1 - V6 - The
  LAD Is Occluded.

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The R Wave

• Definition The R Wave Is The First Upward
  Deflection After The P Wave.

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• In the precordial chest leads, there should be an
  R wave progression - i.e. - an ever increasing
  amplitude of the R wave from V1 through V6

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http//www.heartinfo.org/physician/ecg/norm.htm
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• R wave progression occurs because the precordial
  chest leads sweep across the thoracic cage
  looking from the thinner right ventricle across
  to the thicker left ventricle.

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• Loss of the R wave progression is abnormal and
  signals the possible presence of bundle branch
  blocks or the occurrence of a myocardial
  infarction.

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The S Wave

• Definition The S Wave Is Defined As The First
  Downward Deflection After The R Wave.

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• There is a normal progressive decrease in the
  size of the S wave in the precordial leads.

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• V1 through V2 should have large S waves with a
  decreasing appearance of S through V5 and V6.

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http//www.heartinfo.org/physician/ecg/norm.htm
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QRS Complex Generalities

• Mostly Upward Deflected QRS Complexes Are Found
  In Leads I, II, III, aVF, aVL, V4, V5, and V6.

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• Mostly Downward Deflected QRS Complexes Will Be
  Seen In Leads aVR And V1,V2, And Sometimes V3.

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• The QRS Complex Signals The Depolarization Of The
  Ventricles.

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• A Normal QRS Complex Has A Duration of .06 -
  .12 Sec. Or About 1.5 - 3.0 mm.

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• If The QRS Is gt3mm, The Medical Staff Will
  Construe It To Mean There Is An Abnormal
  Intraventricular Conduction Pathway.

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The ST Segment

• The ST Segment Is The Pause After The QRS Complex
  - The Interval Between The End Of The QRS Complex
  The Beginning Of The T Wave.

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• It Symbolizes The End Of Ventricular
  Depolarization To The Start Of Ventricular
  Repolarization.

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• It Is During This Phase Of The EKG When The Heart
  Is Being Passively Perfused - The Windkessel
  Effect.

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• The ST Segment Slopes Gently Up Toward The
  Isoelectric Line From The J Point And Ends At The
  Beginning Of The T Wave.

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The ST Segment
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Normal EKG w/ J Point In aVL
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• Normal Up Sloping Of The ST Segment May Be 1-2 mm
  In Indo-Europeans And As Much As 4 mm In
  African-Americans

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• The Normal Duration Of The ST Segment Is About
  2-3 mm.

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ST Segment Elevation

• When The ST Segment Is Elevated In A Patient With
  Known Disease, It Is Usually A Sign Of An
  Evolving Transmural Infarction - An MI In
  Progress.

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ST Segment Elevation
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ST Segment Elevation
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• So...., The Classic Signs Of An Acute MI In
  Progress Are
• Elevated ST Segment
• Inverted T Wave
• Presence Of A Q Wave

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• Signs Of An
• Anterior Wall Infarction

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Anterior Wall Infarction

• An anterior wall MI is usually caused by an
  occlusion of the LAD
• EKG changes are seen in any of the precordial
  chest leads - V1 - V6

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ST Segment ChangesWith An Acute Anterior MI

• ST segment elevation in V1-V6 and in Leads I and
  aVL (the lateral wall leads).
• Reciprocal ST segment depression in Leads II, III
  aVF (the inferior leads)

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Acute Anterior Myocardial Infarctionhttp//homepa
ges.enterprise.net/djenkins/ami.html
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• In An Uncomplicated MI, These EKG Changes Will
  Largely Disappear Once The Infarction Has Frankly
  Resolved - Usually In About 3 Or More Days.

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Mature Anterior Wall MI
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• Signs Of An
• Inferior Wall Infarction

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Inferior Wall Infarction

• This infarction occurs on the diaphragmatic
  surface of the heart.
• It is frequently caused by an occlusion to blood
  flow through the right coronary

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ST Segment Changes With An Acute Inferior MI

• ST segment elevations in Leads II, III and aVF
• Reciprocal ST segment changes in Leads I, aVL,
  V1-V6.

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Acute Inferior Myocardial Infarctionhttp//homepa
ges.enterprise.net/djenkins/ami.html
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• In An Uncomplicated MI, These EKG Changes Will
  Largely Disappear Once The Infarction Has Frankly
  Resolved - Usually In About 3 Days.

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A Mature Inferior Wall MI
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Old Inferior Wall MI
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• Signs Of A
• Lateral Wall Infarction

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Lateral Wall Infarction

• This type of MI involves the lateral wall of the
  heart - the left ventricle.
• It is often caused by an occlusion to blood flow
  through the circumflex artery.

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• ST segment elevations will be seen in the lateral
  chest leads - Leads I, aVL and V5 and V6.

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Acute Lateral Wall MI
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• In An Uncomplicated MI, These EKG Changes Will
  Largely Disappear Once The Infarction Has Frankly
  Resolved - Usually In About 3 Days.

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Mature Lateral Wall Infarct
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• For All Types Of MIs, The Q Wave Often Remains
  As The Only Residual Sign That An Infarction Has
  Occurred. Also, The ST Segment May Be
  Permanently Depressed.

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ST Segment Depression

• When The ST Segment Is Depressed, Then It Is
  Usually A Sign Of Cardiac Ischemia.

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ST Segment Depression
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Types Of ST Segment Depression
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• ST Segment Depression May Be A Permanent Part Of
  The EKG Tracing.

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• At Rest The Patient May Have A Normal ST Segment.
  However, It May Become Depressed As The Persons
  Exercise Level Is Increased Above The Hearts
  Ability To Receive Adequate Perfusion.

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• The ST segment depression will begin to appear as
  the heart becomes ischemic
• It will continue to be more depressed the more
  ischemic the heart becomes.

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• The ST segment will normalize once the exercise
  intensity is reduced to a level in which the
  heart receives enough perfusion to support the
  work that is being demanded.

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The T Wave

• The T Wave Represents Repolarization Of The
  Ventricles.
• Repolarization Proceeds From The Apex Of The
  Heart To The Base Of The Heart.

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• In Normal Hearts, The T Wave Is Usually Upright
  In Leads I, II, III, aVF, aVL, V2-V6.

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• In Normal Hearts, The T Wave Will Usually Be
  Upside Down In aVR And V1.

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• The Normal Duration Of The T Wave Is About 1-2 mm.

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• Normal Amplitude For The T Wave Is Highly
  Variable.

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• T Waves Get Taller During GXTs And Exercise.

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T Waves During Infarction

• With infarction, the T wave usually becomes tall
  and narrow - referred to as peaking.
• With time and the onset of ischemia, the T wave
  will invert.

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The QT Interval

• The QT Interval Encompasses The Time From The
  Beginning Of The Q Or R Wave Through The End Of
  The T Wave.

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• The QT Interval Represents 40 Of The Normal
  Cardiac Cycle Whether At Rest Or During Exercise.

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• The QT Interval Becomes Shorter As The Heart
  Rate Increases.

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Summary Of Durations Amplitudes Of The P-QRS-T

• P Waves
• Normal Duration 2.5 mm
• Normal Amplitude 2-3 mm
• PR Intervals
• Normal Duration 3-5 mm

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• Q Waves
• Normal Duration lt .5 mm
• Normal Amplitude lt25 of R amplitude or 1.0
  mm

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• QRS Complex
• Normal Duration lt 3.0 mm
• Normal Amplitude Variable
• ST Segment
• Normal Amplitude 1-2 mm
• Normal Duration 2-3 mm

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• T Wave
• Normal Duration 2 mm
• Normal Amplitude lt 5 mm in Limb Leads lt 10 mm
  in Precordial Leads