Presentation on theme: "EKG Basics # 2 That Squigglely Line - What Does It Really Mean ? What Does It Really Mean ? Part # 2 David Arnall, Ph.D., P.T. (2000)"— Presentation transcript:
EKG Basics # 2 That Squigglely Line - What Does It Really Mean ? What Does It Really Mean ? Part # 2 David Arnall, Ph.D., P.T. (2000)
The V Leads l The Precordial Chest Leads Record The Heart’s Electrical Activity In The Transverse Or Horizontal Plane.
l To Create The Six Precordial Chest Leads, Each Chest Lead Is Made Positive & The Whole Body Is Considered Negative.
Lead Positioning l V1 Is Placed In The Fourth Intercostal Space To The Right Of The Sternum. l V2 Is Placed In The Fourth Intercostal Space To The Left Of The Sternum.
l V3 Is Placed In Between V2 And V4. l V4 Is Placed In The Fifth Intercostal Space In The Midclavicular Line Near The Nipple.
l V5 Is Placed In Between V4 And V6. l V6 Is Placed In The Fifth Intercostal Space In The Midaxillary Line.
l When placing the precordial chest leads across the thorax, the clinician places the electrodes under the pectoralis major & not over the breasts.
l In The Chest Cavity, The Heart Is Positioned With The Right Ventricle Lying Anteriorly & Medially While The Left Ventricle Lies Anterolaterally & Posteriorly
l 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.
l Leads V3 & V4 Lie Directly Over The Interventricular Septum. Their Line Of Sight Is To View The Electrical Activity Of The Interventricular Septum.
l Leads V5 & V6 Lie Over The Left Ventricle. Therefore, These Leads View The Electrical Activity Of The Left Ventricle.
l The Precordial Chest Leads Can Be Divided Up Into Areas Of The Heart They View.
l Leads V1, V2, V3, & V4 Are The Anterior Leads.
l Leads V5 & V6 Look At The Left Lateral Wall.
In Review Anterior Chest Leads V1, V2, V3 & V4
Left Lateral Wall Leads aVL, Lead I, V5 & V6 aVL, Lead I, V5 & V6
Inferior Chest Leads Lead II, Lead III, & Lead aVF Lead II, Lead III, & Lead aVF
No Man’s Land aVR
A Review Of The Waves & Intervals Of The EKG & Intervals Of The EKG
The P Wave l The P Wave Is The Signal That Electrical Potential Has Left The SA Node, Swept Across The Atria, & Has Initiated Atrial Contraction.
What Is A Normal P Wave ? l Duration : The Normal Duration Of A P Wave is mm ( sec) l If It Is Greater Than 2.75 mm (.11 sec) It Is Considered To Be An Abnormal P Wave.
Amplitude A Normal Amplitude For A A Normal Amplitude For A P Wave Is 2-3 mm. P Wave Is 2-3 mm.
The P Wave Should Always Be Gently Rounded - Never Pointed Or Peaked.
l Abnormal Amplitude Of The P Wave Is Often Seen In Cor Pulmonale, A-V Valve Disease, Hypertension & In Patients With Congenital Heart Disease
l P Waves Within The Same Lead That Are Multiformic Indicate The Presence Of More Than One Pacemaker In The Right Atrium.
l In The Six Limb Leads, You Will Generally See P Waves In The Upright Position Except In aVR & V1 Where They Are Negatively Deflected.
l You Will Frequently See Biphasic P Waves In Lead III, Lead V2 & Occasionally In Lead aVL.
BiPhasic P Wave In V1
The PR Interval l 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.
l The PR Interval Is A Time Lag And Represents The Period During Which There Is AV Nodal Capture Of The SA Node Signal.
l The PR Interval Allows The Atria To Contract (atrial systole) Which “Tops Off” The Ventricles With Blood - An Event Called Atrial Kick.
l 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.
l The PR Interval Represents The Time Period Encompassing Atrial Depolarization Up To But Not Including The Start Of Ventricular Depolarization.
l “ 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 ”. Marriott’s Practical Electrocardiography, 9th ed., Galen S. Wagner, pg 39, 1994
l Duration : The Adult PR Interval Is Normally Between 3-5 mm Or Seconds In Duration. Some Cardiologists Will Say It Is Normal Out To.22 Seconds (5 1/2 mm)
l If The PR Interval Is Longer Than 5 mm, It Is Called A Prolonged PR Interval & May Indicate The Presence Of An AV Block.
First Degree AV Block
l The PR Interval Shortens During Exercise Because Of The Sympathetic Tone That Predominates Over The Heart.
l 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.
l In Young Children, The PR Interval Is Shorter Than In Adults. The Child’s Heart Rate Is Also Faster.
l In A 1 Year Old Child At Rest, The Normal P-R Interval Is Typically.11 sec. Or Slightly Under 3 mm.
l For Children Who Are 6 Years Of Age, The P-R Interval At Rest Is.13 Seconds Or Slightly Over 3 mm.
l In Children 12 Years Of Age, The P-R Interval At Rest Will Be.14 Seconds Or About 3.5 mm.
l In Grown Adults 18 Years Of Age And Older, The P-R Interval At Rest Will Be 3-5 mm In Length.
l Prolonged P-R Intervals Are Symptomatic Of : AV Blocks Due To Coronary Disease & Rheumatic Fever.
l 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.
Pathologies Resulting In PR Interval Shortening
l Shortened P-R Intervals Are Seen In Patients With Pheochromocytoma And Wolfe-Parkinson-White Syndrome
l 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.
l 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.
l 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.
l W-P-W occurs in ~.15% -.20% of the population or 2:1,000 people. Patients with W-P-W are otherwise healthy.
l 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.
l Patients with W-P-W often complain of episodic symptoms that include chest discomfort, dizziness, and palpitations.
The Q Wave l Definition : The Q Wave Is The First Downward Deflection After The P Wave & Before The R Wave.
l Sometimes Q Waves Are Present & Sometimes They Are Absent Depending On The Lead.
l It is common to normally see Q waves in leads I, II, aVL and in V4-6.
l A Normal Q Wave Is Not Wider In Duration Than 0.5 mm Or About.02 Seconds. Its Normal Amplitude Is < 1 mm.
l Q Waves Are An Indication Of Ventricular Septal Wall Depolarization.
l 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.
l Q Waves Of Normal Size Have No Diagnostic Meaning In Normal Hearts Except That The Septum Has Depolarized.
Significant Q Waves l Q waves In Leads I, II, aVF, & aVL Can Mean Something If...
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.
l Q waves of any size are normal in leads aVR.
l 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.
l 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.
l 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.
l 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.
l 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.
The R Wave l Definition : The R Wave Is The First Upward Deflection After The P Wave.
l 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
l 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.
l Loss of the R wave progression is abnormal and signals the possible presence of bundle branch blocks or the occurrence of a myocardial infarction.
The S Wave l Definition : The S Wave Is Defined As The First Downward Deflection After The R Wave.
l There is a normal progressive decrease in the size of the S wave in the precordial leads.
l V1 through V2 should have large S waves with a decreasing appearance of S through V5 and V6.
QRS Complex Generalities l Mostly Upward Deflected QRS Complexes Are Found In Leads I, II, III, aVF, aVL, V4, V5, and V6.
l Mostly Downward Deflected QRS Complexes Will Be Seen In Leads aVR And V1,V2, And Sometimes V3.
l The QRS Complex Signals The Depolarization Of The Ventricles.
l A Normal QRS Complex Has A Duration of ~ Sec. Or About mm.
l If The QRS Is >3mm, The Medical Staff Will Construe It To Mean There Is An Abnormal Intraventricular Conduction Pathway.
The ST Segment l 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.
l It Symbolizes The End Of Ventricular Depolarization To The Start Of Ventricular Repolarization.
l It Is During This Phase Of The EKG When The Heart Is Being Passively Perfused - The Windkessel Effect.
l The ST Segment Slopes Gently Up Toward The Isoelectric Line From The J Point And Ends At The Beginning Of The T Wave.
The ST Segment
Normal EKG w/ J Point In aVL
l Normal Up Sloping Of The ST Segment May Be 1-2 mm In Indo- Europeans And As Much As 4 mm In African-Americans
l The Normal Duration Of The ST Segment Is About 2-3 mm.
ST Segment Elevation l 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.
ST Segment Elevation
l So...., The Classic Signs Of An Acute MI In Progress Are : – Elevated ST Segment – Inverted T Wave – Presence Of A Q Wave
Signs Of An Anterior Wall Infarction
l An anterior wall MI is usually caused by an occlusion of the LAD l EKG changes are seen in any of the precordial chest leads - V1 - V6
ST Segment Changes With An Acute Anterior MI l ST segment elevation in V1-V6 and in Leads I and aVL (the lateral wall leads). l Reciprocal ST segment depression in Leads II, III & aVF (the inferior leads)
Acute Anterior Myocardial Infarction
l In An Uncomplicated MI, These EKG Changes Will Largely Disappear Once The Infarction Has Frankly Resolved - Usually In About 3 Or More Days.
Mature Anterior Wall MI
Signs Of An Inferior Wall Infarction
l This infarction occurs on the diaphragmatic surface of the heart. l It is frequently caused by an occlusion to blood flow through the right coronary
ST Segment Changes With An Acute Inferior MI l ST segment elevations in Leads II, III and aVF l Reciprocal ST segment changes in Leads I, aVL, V1-V6.
Acute Inferior Myocardial Infarction
l In An Uncomplicated MI, These EKG Changes Will Largely Disappear Once The Infarction Has Frankly Resolved - Usually In About 3 Days.
A Mature Inferior Wall MI
Old Inferior Wall MI
Signs Of A Lateral Wall Infarction
l This type of MI involves the lateral wall of the heart - the left ventricle. l It is often caused by an occlusion to blood flow through the circumflex artery.
l ST segment elevations will be seen in the lateral chest leads - Leads I, aVL and V5 and V6.
Acute Lateral Wall MI
l In An Uncomplicated MI, These EKG Changes Will Largely Disappear Once The Infarction Has Frankly Resolved - Usually In About 3 Days.
Mature Lateral Wall Infarct
l For All Types Of MI’s, The Q Wave Often Remains As The Only Residual Sign That An Infarction Has Occurred. Also, The ST Segment May Be Permanently Depressed.
ST Segment Depression l When The ST Segment Is Depressed, Then It Is Usually A Sign Of Cardiac Ischemia.
ST Segment Depression
Types Of ST Segment Depression
l ST Segment Depression May Be A Permanent Part Of The EKG Tracing.
l At Rest The Patient May Have A Normal ST Segment. However, It May Become Depressed As The Person’s Exercise Level Is Increased Above The Heart’s Ability To Receive Adequate Perfusion.
l The ST segment depression will begin to appear as the heart becomes ischemic l It will continue to be more depressed the more ischemic the heart becomes.
l 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.
The T Wave l The T Wave Represents Repolarization Of The Ventricles. l Repolarization Proceeds From The Apex Of The Heart To The Base Of The Heart.
l In Normal Hearts, The T Wave Is Usually Upright In Leads I, II, III, aVF, aVL, & V2-V6.
l In Normal Hearts, The T Wave Will Usually Be Upside Down In aVR And V1.
l The Normal Duration Of The T Wave Is About 1-2 mm.
l Normal Amplitude For The T Wave Is Highly Variable.
l T Waves Get Taller During GXT’s And Exercise.
T Waves During Infarction l With infarction, the T wave usually becomes tall and narrow - referred to as “peaking”. l With time and the onset of ischemia, the T wave will invert.
The QT Interval l The QT Interval Encompasses The Time From The Beginning Of The Q Or R Wave Through The End Of The T Wave.
l The QT Interval Represents 40% Of The Normal Cardiac Cycle Whether At Rest Or During Exercise.
l The QT Interval Becomes Shorter As The Heart Rate Increases.
Summary Of Durations & Amplitudes Of The P-QRS-T l P Waves ¤ Normal Duration : 2.5 mm ¤ Normal Amplitude : 2-3 mm l PR Intervals ¤ Normal Duration : 3-5 mm
l Q Waves ¤ Normal Duration : <.5 mm ¤ Normal Amplitude : <25% of R amplitude or ~ 1.0 mm
l QRS Complex ¤ Normal Duration : < 3.0 mm ¤ Normal Amplitude : Variable l ST Segment ¤ Normal Amplitude : 1-2 mm ¤ Normal Duration : 2-3 mm
l T Wave ¤ Normal Duration : 2 mm ¤ Normal Amplitude : < 5 mm in Limb Leads & < 10 mm in Precordial Leads