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8/4/2019 adeel ECG @

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Dr. ADEEL AHMED WAHEED

HOUSE OFFICER

M-4


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ECG Basics


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Electrocardiography (ECG or EKG[from the GermanElektrokardiogramm]) is

a transthoracic (across the thorax orchest) interpretation of the electricalactivity of the heart over a period of time,as detected by electrodes attached to theouter surface of the skin and recorded bya device external to the body.

The recording produced by thisnoninvasive procedure is termed anelectrocardiogram (also ECG or EKG).
http://en.wikipedia.org/wiki/German_languagehttp://en.wikipedia.org/wiki/Thoraxhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Hearthttp://en.wikipedia.org/wiki/Electrodehttp://en.wikipedia.org/wiki/Non-invasive_(medical)http://en.wikipedia.org/wiki/Non-invasive_(medical)http://en.wikipedia.org/wiki/Electrodehttp://en.wikipedia.org/wiki/Hearthttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Thoraxhttp://en.wikipedia.org/wiki/German_language


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Impulse Conduction & the ECG

Sinoatrial node

AV node

Bundle of His

Bundle Branches

Purkinje fibers


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The PQRST

P waveAtrial depolarization

T wave -Ventricular

repolarization

QRSVentricular

depolarization


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The PR Interval

Atrial depolarization

+

delay in AV junction

(AV node/Bundle of His)

(delay allows time forthe atria to contractbefore the ventricles

contract)


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The ECG Paper

Horizontally

One small box - 0.04 s

One large box - 0.20 s

Vertically

One large box - 0.5 mV


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The ECG Paper (cont)

Every 3 seconds (15 large boxes) ismarked by a vertical line.

This helps when calculating the heart rate.NOTE: the following strips are not marked

but all are 6 seconds long.

3 sec 3 sec


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Rhythm Analysis

Step 1: Calculate rate.

Step 2: Determine regularity.

Step 3: Assess the P waves. Step 4: Determine PR interval.

Step 5: Determine QRS duration.


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Step 1: Calculate Rate

Option 1

Count the # of R waves in a 6 second rhythmstrip, then multiply by 10.

Interpretation?

9 x 10 = 90 bpm

3 sec 3 sec


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Option 2

Find a R wave that lands on a bold line.

Count the # of large boxes to the next Rwave. If the second R wave is 1 large boxaway the rate is 300, 2 boxes - 150, 3 boxes -100, 4 boxes - 75, etc. (cont)

R wave


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Option 2 (cont)

Memorize the sequence:

300 - 150 - 100 - 75 - 60 - 50

Interpretation?

300

150

100

75

60

50

Approx. 1 box less than

100 = 95 bpm


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Step 2: Determine regularity

Look at the R-R distances (using a caliper ormarkings on a pen or paper).

Regular (are they equidistant apart)?

Occasionally irregular? Regularly irregular?Irregularly irregular?

Interpretation? Regular

R R


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Step 3: Assess the P waves

Are there P waves?

Do the P waves all look alike?

Do the P waves occur at a regular rate? Is there one P wave before each QRS?Interpretation? Normal P waves with 1 P

wave for every QRS


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Step 4: Determine PR interval

Normal: 0.12 - 0.20 seconds.

(3 - 5 boxes)

Interpretation? 0.12 seconds


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Step 5: QRS duration

Normal: 0.04 - 0.12 seconds.

(1 - 3 boxes)

Interpretation? 0.08 seconds


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Rhythm Summary

Rate 90-95 bpm Regularity regular

P waves normal

PR interval 0.12 s QRS duration 0.08 s

Interpretation? Normal Sinus Rhythm


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Normal Sinus Rhythm (NSR)

Etiology: the electrical impulse is formed

in the SA node and conducted normally.

This is the normal rhythm of the heart;

other rhythms that do not conduct via thetypical pathway are called arrhythmias.


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NSR Parameters

Rate 60 - 100 bpm

Regularity regular P waves normal

PR interval 0.12 - 0.20 s

QRS duration 0.04 - 0.12 s

Any deviation from above is sinus tachycardia, sinusbradycardia or an arrhythmia


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AV Nodal Blocks

1st Degree AV Block

2nd Degree AV Block, Type I

2nd Degree AV Block, Type II

3rd Degree AV Block


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Rhythm #1

60 bpm

Rate? Regularity? regular

normal

0.08 s

P waves?

PR interval? 0.36 s QRS duration?

Interpretation? 1st Degree AV Block


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1st Degree AV Block

Deviation from NSR

PR Interval > 0.20 s


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1st Degree AV Block

Etiology: Prolonged conduction delay in

the AV node or Bundle of His.


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Rhythm #2

50 bpm

Rate? Regularity? regularly irregular

nl, but 4th no QRS

0.08 s

P waves?

PR interval? lengthens QRS duration?

Interpretation? 2nd Degree AV Block, Type I

(Wenckebach phenomenon)


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Deviation from NSR

PR interval progressively lengthens,then the impulse is completely blocked(P wave not followed by QRS).


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Etiology: Each successive atrial impulse

encounters a longer and longer delay inthe AV node until one impulse (usually the3rd or 4th) fails to make it through the AV

node.


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Rhythm #3

40 bpm


nl, 2 of 3 no QRS

0.08 s

P waves?

PR interval? 0.14 s QRS duration?

Interpretation? 2nd Degree AV Block, Type II


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Deviation from NSR

Occasional P waves are completelyblocked (P wave not followed by QRS).


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Etiology: Conduction is all or nothing (no

prolongation of PR interval); typicallyblock occurs in the Bundle of His.


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Rhythm #4

40 bpm


no relation to QRS

wide (> 0.12 s)

P waves?

PR interval? none QRS duration?

Interpretation? 3rd Degree AV Block


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3rd Degree AV Block

Deviation from NSR

The P waves are completely blocked inthe AV junction; QRS complexesoriginate independently from below the

junction.


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3rd Degree AV Block

Etiology: There is complete block of

conduction in the AV junction, so the atriaand ventricles form impulsesindependently of each other. Without

impulses from the atria, the ventricles ownintrinsic pacemaker kicks in at around 30 -45 beats/minute.


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AxisAxis refers to the mean QRS axis (or vector) duringventricular depolarization. As you recall when theventricles depolarize (in a normal heart) the direction ofcurrent flows leftward and downward because most of

the ventricular mass is in the left ventricle. We like toknow the QRS axis because an abnormal axis can suggestdisease such as pulmonary hypertension from apulmonary embolism.


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We can quickly determine whether the QRS axis is normalby looking at leads I and II.

If the QRS complex isoverall positive (R > Q+S)in leads I and II, the QRSaxis is normal.

QRS negative (R < Q+S)

In this ECG what leadshave QRS complexesthat are negative?equivocal?

QRS equivocal (R = Q+S)


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How do we know the axis is normal when the QRS

complexes are positive in leads I and II?


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The answer lies in the fact that each frontal leadcorresponds to a location on the circle.

0

o

30o

-30o

60o

-60o-90o

-120o

90o120o

150o

180

o

-150o

I

IIavF

avLavR

Limb leads

I = +0o

II = +60o

III = +120o

Augmented leads

avL = -30o

avF = +90o

avR = -150o

I

IIIII


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The normal QRS axis falls between -30o and +90o becauseventricular depolarization is leftward and downward.

Left axis deviation occurs when the axis falls between -30o and -90o.

Right axis deviation occurs when the axis falls between +90o and+150o.

Right superior axis deviation occurs when the axis falls betweenbetween +150o and -90o.

QRS Complexes

AxisI II

+ +

+ -

- +

- -

normal

left axis deviation

right axis deviation

right superioraxis deviation

A quick way to determinethe QRS axis is to look at theQRS complexes in leads Iand II.


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Acute

Myocardial

Infarction


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The 12-Lead ECG

The 12-Lead ECG sees the heartfrom 12 different views.

Therefore, the 12-Lead ECG helpsyou see what is happening in

different portions of the heart.


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The 12-Leads

The 12-leads include:

3 Limb leads(I, II, III)

3 Augmented leads

(aVR, aVL, aVF)

6 Precordial leads(V1- V6)


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Views of the Heart

Some leads get agood view of the:

Anterior portion

of the heart

Lateral portion

of the heart

Inferior portion

of the heart


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ST Elevation

One way todiagnose an

acute MI is tolook forelevation of the

ST segment.


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ST Elevation (cont)

Elevation of theST segment

(greater than 1small box) in 2leads is

consistent with amyocardialinfarction.


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Anterior View of the Heart

The anterior portion of the heart is bestviewed using leads V1- V4.


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Anterior Myocardial Infarction

If you see changes in leads V1 - V4 thatare consistent with a myocardial

infarction, you can conclude that it isan anterior wall myocardial infarction.


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Putting it all Together

Do you think this person is having amyocardial infarction. If so, where?


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Interpretation

Yes, this person is having an acute anteriorwall myocardial infarction.


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Other MI Locations

First, take a lookagain at thispicture of theheart.

Anterior portion

of the heart

Lateral portion

of the heart

Inferior portion

of the heart


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Other MI Locations

The limb and augmented leads seeelectrical activity moving inferiorly (II, IIIand aVF), to the left (I, aVL) and to the

right (aVR). Whereas, the precordial leadssee electrical activity in the posterior toanterior direction.


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Anterior MI

The anterior portion of the heart is bestviewed using leads V1- V4.

Precordial Leads


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Lateral MI

Lateral portionof the heart is

best viewed

Leads I, aVL,

and V5- V6


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Inferior MI

For inferiorportion of the

heart

Leads II, III and

aVF


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Now, where do you think this person ishaving a myocardial infarction?


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Inferior Wall MI

This is an inferior MI. Note the STelevation in leads II, III and aVF.


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How about now?


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Anterolateral MI

This persons MI involves both the anterior wall(V2-V4) and the lateral wall (V5-V6, I, and aVL)!


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ST Elevation andnon-ST Elevation MIs


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ST Elevation and non-ST Elevation MIs

When myocardial blood supply is abruptlyreduced or cut off to a region of the heart, asequence of injurious events occur beginning

with ischemia (inadequate tissue perfusion),followed by necrosis (infarction), andeventual fibrosis (scarring) if the blood supplyisn't restored in an appropriate period oftime.

The ECG changes over time with each ofthese events


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ECG Changes

Ways the ECG can change include:

Appearanceof pathologicQ-waves

T-waves

peaked flattened inverted

ST elevation &depression


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ST Elevation Infarction

ST depression, peaked T-waves,then T-wave inversion

The ECG changes seen with a ST elevation infarction are:

Before injury Normal ECG

ST elevation & appearance ofQ-waves

ST segments and T-waves return tonormal, but Q-waves persist

Ischemia

Infarction

Fibrosis


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Heres a diagram depicting an evolving infarction:

A. Normal ECG prior to MI

B. Ischemia from coronary artery occlusion

results in ST depression (not shown) andpeaked T-waves

C. Infarction from ongoing ischemia results inmarked ST elevation

D/E. Ongoing infarction with appearance ofpathologic Q-waves and T-wave inversion

F. Fibrosis (months later) with persistent Q-waves, but normal ST segment and T-

waves


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Heres an ECG of an inferior MI:

Look at theinferior leads

(II, III, aVF).Question:What ECGchanges doyou see?

ST elevationand Q-waves

What is therhythm?

Atrial fibrillation (irregularly irregular with narrow QRS)!


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Non-ST Elevation Infarction

ST depression & T-waveinversion

The ECG changes seen with a non-ST elevation infarction are:

Before injury Normal ECG

ST depression & T-wave inversion

ST returns to baseline, but T-waveinversion persists

Ischemia

Infarction

Fibrosis


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When analyzing a 12-lead ECG for evidence of aninfarction you want to look for the following:

Abnormal Q waves

ST elevation or depression Peaked, flat or inverted T waves

ST elevation (or depression) of 1 mm in 2 or morecontiguous leads is consistent with an AMI

There are ST elevation (Q-wave) and non-ST elevation(non-Q wave) MIs


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Bundle Branch Blocks


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Normal Impulse ConductionSinoatrial node

AV node

Bundle of His

Bundle Branches

Purkinje fibers


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So, depolarization ofthe Bundle Branchesand Purkinje fibers

are seen as the QRScomplex on the ECG.

Therefore, a conductionblock of the BundleBranches would bereflected as a change inthe QRS complex.

RightBBB


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With Bundle Branch Blocks you will see twochanges on the ECG.

1. QRS complex widens (> 0.12 sec).

2. QRS morphology changes (varies depending on ECG

lead, and if it is a right vs. left bundle branch block).


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Why does the QRS complex widen?

When the conduction

pathway is blocked itwill take longer forthe electrical signalto pass throughout

the ventricles.


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Right Bundle Branch Blocks

What QRS morphology is characteristic?

V1

For RBBB the wide QRS complex assumes aunique, virtually diagnostic shape in those

leads overlying the right ventricle (V1 and V2).

Rabbit Ears


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Left Bundle Branch Blocks

LBBB is best seen inV6,where there isa broad complex with a notchedtop,which resembles the letterM

Normal


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In this step of the 12-lead ECG analysis, we use

the ECG to determine if any of the 4 chambers ofthe heart are enlarged or hypertrophied. Wewant to determine if there are any of thefollowing:

Right atrial enlargement (RAE)

Left atrial enlargement (LAE)

Right ventricular hypertrophy (RVH)

Left ventricular hypertrophy (LVH)


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Right atrial enlargement

To diagnose RAE you can use the following criteria: II P > 2.5 mm, or

V1 or V2 P > 1.5 mm

Remember 1 smallbox in height = 1 mm

A cause of RAE is RVH from pulmonary hypertension.

> 2 boxes (in height)

> 1 boxes (in height)


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Left atrial enlargement To diagnose LAE you can use the following criteria:

II > 0.04 s (1 box) between notched peaks, or

V1 Neg. deflection > 1 box wide x 1 box deep

Normal LAE

A common cause of LAE is LVH from hypertension.


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Right ventricular hypertrophy Compare the R waves in V1, V2 from a normal ECG and one

from a person with RVH. Notice the R wave is normally small in V1, V2 because the right

ventricle does not have a lot of muscle mass.

But in the hypertrophied right ventricle the R wave is tall in V1,V2.

Normal RVH


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Right ventricular hypertrophy

To diagnose RVH you can use the following criteria: Right axis deviation, and

V1 R wave > 7mm tall

A commoncause of RVHis left heart

failure.


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Left ventricular hypertrophy Take a look at this ECG. What do you notice about the axis

and QRS complexes over the left ventricle (V5, V6) and rightventricle (V1, V2)?

There is left axis deviation (positive in I, negative in II) and thereare tall R waves in V5, V6 and deep S waves in V1, V2.

The deep S wavesseen in the leads overthe right ventricle arecreated because theheart is depolarizingleft, superior andposterior (away fromleads V1, V2).


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Left ventricular hypertrophy To diagnose LVH you can use the following

criteria*: R in V5 (or V6) + S in V1 (or V2) > 35 mm, or

avL R > 13 mm

A common cause of LVHis hypertension.

* There are severalother criteria for thediagnosis of LVH.

S = 13 mm

R = 25 mm


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