EKG Basics # 2


Click here to start

Table of Contents

EKG Basics # 2

The V Leads


To Create The Six Precordial Chest Leads, Each Chest Lead Is Made Positive & The Whole Body Is Considered Negative.

Lead Positioning

V3 Is Placed In Between V2 And V4.

V5 Is Placed In Between V4 And V6.


When placing the precordial chest leads across the thorax, the clinician places the electrodes under the pectoralis major & not over the breasts.

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

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.

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


Leads V5 & V6 Lie Over The Left Ventricle. Therefore, These Leads View The Electrical Activity Of The Left Ventricle.

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

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

Leads V5 & V6 Look At The Left Lateral Wall.

In Review

Left Lateral Wall Leads

Inferior Chest Leads

No Manís Land

A Review Of The Waves

PPT Slide

The P Wave

What Is A Normal P Wave ?



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

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

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

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


You Will Frequently See Biphasic P Waves In Lead III, Lead V2 & Occasionally In Lead aVL.

BiPhasic P Wave In V1

The PR Interval

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

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

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.

PPT Slide


The PR Interval Represents The Time Period Encompassing Atrial Depolarization Up To But Not Including The Start Of Ventricular Depolarization.

ďA 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 systemĒ.

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)

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

The PR Interval Shortens During Exercise Because Of The Sympathetic Tone That Predominates Over The Heart.

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.

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

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

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

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

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

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

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

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

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.

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.

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.

W-P-W occurs in ~ .15% - .20% of the population or 2:1,000 people. Patients with W-P-W are otherwise healthy.

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.

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



The Q Wave

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

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

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

Q Waves Are An Indication Of Ventricular Septal Wall Depolarization.

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.

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

Significant Q Waves

1. They Are Between 25% - 33% Of The Amplitude Of The R Wave.

Q waves of any size are normal in leads aVR.

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.

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.

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.

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.

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

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


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.

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

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

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


QRS Complex Generalities

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

The QRS Complex Signals The Depolarization Of The Ventricles.

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

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

The ST Segment

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

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

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

Normal Up Sloping Of The ST Segment May Be 1-2 mm In Indo-Europeans And As Much As 4 mm In African-Americans

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

ST Segment Elevation

ST Segment Elevation

ST Segment Elevation

So...., The Classic Signs Of An Acute MI In Progress Are :

Signs Of An

Anterior Wall Infarction

ST Segment Changes With An Acute Anterior MI

Acute Anterior Myocardial Infarction http://homepages.enterprise.net/djenkins/ami.html

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

ST Segment Changes With An Acute Inferior MI

Acute Inferior Myocardial Infarction http://homepages.enterprise.net/djenkins/ami.html

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

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

Acute Lateral Wall MI

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

For All Types Of MIís, 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

ST Segment Depression

Types Of ST Segment Depression

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

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

The ST segment depression will begin to appear as the heart becomes ischemic

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

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

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

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

Normal Amplitude For The T Wave Is Highly Variable.

T Waves Get Taller During GXTís And Exercise.

T Waves During Infarction

The QT Interval

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

The QT Interval Becomes Shorter As The Heart Rate Increases.

Summary Of Durations & Amplitudes Of The P-QRS-T

Q Waves

QRS Complex

T Wave

Author: Preferred Customer

Email: David.Arnall@NAU.EDU , DAArnall@AOL.COM

Home Page: http://jan.ucc.nau.edu/~daa/heartlung/

Download presentation source