interpreting ecg

Dr…………………………..

Interpreting ECG

Topics:

1. Coronary circulation.2. Electrical conduction system of the heart3. Electrocardiography elements4. Electrical events & the waveform in a normal

ECG.5. ECG interpretation6. Identify lethal cardiac diseases7. The learning

Coronary circulation

Coronary Circulation Review

Figure 1

Superior & Inferior Vena Cava

Right Atrium

Tricuspid Valve

Right Ventricle

Pulmonary Semi-lunar Valve

Pulmonary Trunk

Right & Left Pulmonary Arteries

Left Atrium

Pulmonary Veins

Mitral Valve

Left Ventricle

Aortic Semi-lunar Valve

Right Coronary Artery

Supplies blood to: Right Atrium Right Ventricle The SA Node and in 55% of population the LV

inferior wall The LV posterior wall and ⅓ of the posterior

interventricular septum in 90% of the population

Left Circumflex Artery

Supplies blood to: the Left Atrium the LV lateral wall the SA Node in 45% of the population and to the LV

posterior wall ⅓ of the interventricular septum AV Node and Bundle of His in 10% of the population

Left Anterior Descending Artery

Supplies blood to: the LV anterior and lateral walls the Left and Right Bundle Branches the anterior ⅔ of the interventricular septum

Coronary Artery Blood Supply

Recall: The Right Coronary Artery supplies both the Right

and Left heart. The Left Coronary Artery and its branches only

supply the Left heart.

Electrical conduction of the heart

Cardiac Conduction

The Conduction System of the Heart

Cardiac Conduction

The SA Node is the primary pacemaker for the heart at 60-100 beats/minute

The AV Node is the “back-up” pacemaker of the heart at 40-60 beats/ minute.

The Ventricles (bundle branches & Purkinje fibers) are the last resort and maintain an intrinsic rate of only 20-40 beats/minute

Cardiac Conduction

The normal conduction pathway:

SA Node AV Node

Bundle of His

Right & Left Bundle

Branches

Purkinje Fibers

Cardiac Conduction

Correlation of the mechanical activity with the electrical activity….

Cardiac Conduction

Depolarization occurs when sodium channels open fast and the inside of the membrane becomes less negative (electrical stimulation). This is manifested as the P wave on an ECG, which

signifies atrial muscle depolarization. The plateau that immediately follows the P

wave represents atrial systole, when calcium channels open slowly and potassium channels close (at this time mechanical contraction of the atria takes place).

Cardiac Conduction

The PR interval on an ECG reflects conduction of an electrical impulse from the SA node through the AV node. PR = 0.12 – 0.20 seconds

Cardiac Conduction

The QRS complex of an ECG reflects ventricular muscle depolarization (the electrical impulse moves through the Bundle of His, the left and right bundle branches and Purkinje fibers). QRS = 0.08 – 0.10 seconds

The QT interval measures the time from the start of ventricular depolarization to the end of ventricular repolarization. QT interval = < 0.43 seconds or ½ of the R-to-R

interval.

Cardiac Conduction

The ST segment reflects the early ventricular repolarization and lasts from the end of the QRS complex to the beginning of the T wave.

The T-wave on an ECG reflects ventricular muscle repolarization (when the cells regain a negative charge - the “resting state”) and mechanical relaxation, which is also known as diastole.

ECG elements

Heart Revisited

Myocardial Cells = the mechanical cells of the heart. They contract when they receive an electrical impulse from the pacemaker cells. Myocardial = Muscle

Pacemaker Cells are very small cells within the conduction system which spontaneously generate electrical impulses. Pacemaker = Power Source

Electrical Conducting Cells rapidly carry current to all areas of the heart. Conducting Cells = Hard Wiring of Heart

What is an ECG?

An electrocardiogram (ECG) is a graphic recording of the electrical activity of the heart.

The machine is called Electrocardiograph while the recording is called Electocardiogram & is used as a diagnostic tool to assess cardiac function..

ECG Paper

ECG paper comes in a roll of graph paper consisting of horizontal and vertical light and dark lines.

The horizontal axis measures time

The vertical axis measures voltage.

ECG Paper

One small square = 0.04 seconds

One large square = 0.2 seconds Or [One small square(0.04)] x 5

ECG Paper

The light lines circumscribe small squares of 1 x 1 mm. One small square = 0.1 mV

The dark lines delineate large squares of 5 x 5 mm One large square = 0.5 mV

Electrocardiogram

ECG is a painless procedure that is performed by placing disposable electrodes on the skin of a person’s chest wall, upper & lower extremities.

In the ECG, the 12 lead one is the most commonly used tool to diagnose cardiac conduction abnormalities, arrhythmias, myocardial infarction and ischemia.

Electrocardiogram

The ECG represents the electrical impulses that the heart transmits and are recorded as wave tracings on specialized graph paper.

Electrocardiogram – 12 leads

6 limb leads 6 precordial leads Positioning measures 12 perspectives or views

of the heart The 12 perspectives are arranged in vertical

columns Limb leads are I, II, III, AVR, AVL, AVF Precordial leads are V1, V2, V3, V4, V5, V6 Horizontal marks time Vertical marks amplitude

Electrocardiogram - 12-Leads

Each limb lead I, II, III, AVR, AVL, AVF records from a different angle

All 6 limb leads intersect and visualize a frontal plane

The 6 chest leads (precordial) V1, V2, V3, V4, V5, V6 view the body in the horizontal plane to the AV node

The 12 lead ECG forms a camera view from 12 angles

Electrocardiogram - 12-Leads

I and AVL

II, III and AVF

V3 & v4

V1 & v2

V5 & v6

Where the positive electrode is positioned, determines what part of the heart is seen!

Electrocardiogram Lead Placement

Each positive electrode acts as a camera looking at the heart

10 leads attached for 12 lead diagnostics. The monitor combines 2 leads.

Mnemonic for limb leads White on right Smoke(black) over

fire(red) Snow(white) on

grass(green)

Unipolar and Bipolar leads

Limb leads I, II, III are bipolar and have a negative and positive pole Electrical potential differences are measured between the

poles AVR, AVL and AVF are unipolar

No negative lead The heart is the negative pole Electrical potential difference is measured betweeen the lead

and the heart Chest leads are unipolar

The heart also is the negative pole

Precordial leads

Anteroseptal: V1, V2, V3, V4 Anterior: V1–V4 Anterolateral: V4–V6, I, aVL Lateral: I and aVL Inferior: II, III, and aVF Inferolateral: II, III, aVF, and

V5 and V6

Precordial leads

V5 and V6

Precordial leads

The 12-Lead ECG

Color Coding ECG’s Anterior

Yellow indicates V1, V2, V3, V4 Anterior infarct with ST

elevation Left Anterior Descending

Artery (LAD) V1 and V2 may also indicate

septal involvement which extends from front to the back of the heart along the septum

Left bundle branch block Right bundle branch block 2nd Degree Type2 Complete Heart Block

Anterior MI

2004 Anna Story 40

Color Coding ECG- Inferior

Blue indicates leads II, III, AVF Inferior Infarct with ST

elevations Right Coronary Artery

(RCA) 1st degree Heart Block 2nd degree Type 1, 2 3rd degree Block N/V common, Brady

Inferior MI

Color Coding ECG- Lateral

Red indicates leads I, AVL, V5, V6 Lateral Infarct with ST

elevations Left Circumflex Artery Rarely by itself Usually in combo

Lateral MI

Color Coding ECG- Posterior

Green indicates leads V1, V2 Posterior Infarct with ST Depressions and/ tall R

wave RCA and/or LCX Artery

Understand Reciprocal changes The posterior aspect of the

heart is viewed as a mirror image and therefore depressions versus elevations indicate MI

Rarely by itself usually in combo

Posterior MI

Color Coding ECG- SubEndo

No color for SubEndocardial infarcts since they are not transmural

Look for diffuse or localized changes and non – Q wave abnormalities T-wave inversions ST segment

depression

SubEndo MI

More colors show abnormality

A combination of infarcts such as: Anterolateral yellow and red Inferoposterior blue and green Anteroseptal yellow and green

ECG Distribution

V5 and V6

The 12-Lead ECG

The 12-Lead view

Deflection on leads

When an electrical current moves toward a positive electrode, the deflection on the ECG strip will be positive (up).

When an electrical current moves toward a negative electrode, the deflection on the ECG strip will be negative(down).

Electrical events and the waveform in ECG

ECG Analysis

Rate Rhythm (including intervals and blocks) P - waves PR Interval QRS Complex

Axis Hypertrophy Ischemia

ECG Analysis

ECG Rate Analysis

Rate What’s the normal heart rate for an adult human

being?▪ 60 – 100 beats/ minute

Remember: In terms of rate computation, heart rate generally

refers to the number of ventricular contractions that occur in 60 seconds or one minute.

When calculating rates, if there is a P-wave in front of every R-wave, the atrial and ventricular rates will be the same.

ECG Rate Analysis

Atrial rate can be calculated by measuring the interval of time between P-waves (the P-to-P intervals).

Ventricular rate can be calculated by measuring the time intervals between QRS complexes (the R-to-R intervals).

Check: Is the rate in the strip too fast or too slow?

ECG Rate Analysis

Why is it necessary to know both the atrial and ventricular rates? There are instances, such as 2nd and 3rd degree

AV block, in which the atrial rate and ventricular rates are different.

This is why it is important to know how to determine both atrial and ventricular rates.

ECG Rate Computation

Rules Count the number of QRS’s in a 6 - second strip,

then multiply that number by 10. Determine the time between R-R intervals, then

divide that number by 60. For example:

▪ 40 ÷ (20 small boxes x 0.04 seconds each)▪ = 50 beats per minute

Rules Memorize these numbers: 300, 150, 100, 75, 50

Normal Heart rate for an adult = 60 -100 bpm This means that 3 to 5 large blocks should exist

between R – R intervals. Bradycardia = more than 5 large blocks Tachycardia = less than 3 large blocks.

Rule of 300- Divide 300 by the number of boxes between each QRS = rate

HR of 60-100 = normal HR > 100 = tachycardia HR < 60 = bradycardia

ECG Rate Analysis

Let’s Practice with an Example:

What is the rate based on Rule #1? If it is 50 bpm…., you are Correct!!!

ECG Rate Analysis

Let’s Practice with an Example:

What is the rate based on Rule #1? 300/6= 50 bpm

ECG Analysis

Rhythm

Sinus Originating from SA

node P wave before every

QRS P wave in same

direction as QRS

Normal Intervals

PR 0.20 sec (less than one

large box) QRS

0.08 – 0.10 sec (1-2 small boxes)

QT 450 ms in men, 460 ms

in women Based on sex / heart rate Half the R-R interval with

normal HR

Prolonged QT

Normal Men 450ms Women 460ms

Corrected QT (QTc) QTm/√(R-R)

Causes Drugs (Na channel

blockers) Hypocalcemia,

hypomagnesemia, hypokalemia

Hypothermia AMI Congenital Increased ICP

Blocks

AV blocks1. First degree block

▪ PR interval fixed and > 0.2 sec

2. Second degree block, Mobitz type 1 ▪ PR gradually lengthened, then drop QRS

3. Second degree block, Mobitz type 2 ▪ PR fixed, but drop QRS randomly

4. Type 3 block ▪ PR and QRS dissociated

ECG Rhythm Analysis

Are the P waves regular or irregular?

Are the R-to-R intervals regular or irregular?

ECG Analysis

ECG P-wave Analysis

Are there P-waves in the rhythm strip?

Is there a P-wave for each QRS complex? Do all of the P-waves look the same?

ECG Analysis

ECG PR Interval Analysis

Is the PR Interval measurement normal?

PR = 0.12 – 0.20 seconds Is the PR Interval measurement constant?

ECG Analysis

ECG QRS Analysis

Is the QRS wide? > 0.10

Is it normal? QRS = 0.08 – 0.10 seconds Or is it narrow? < 0.08

ECG QRST analysis

Is the T-wave peaked, inverted or flat?

Is the ST segment elevated, depressed or normal?

Is the QT Interval < 0.43 seconds? Is there any ectopy present?

ECG Analysis

QRS Axis and deviation

Represents the overall direction of the heart’s activity and Axis of –30 to +90 degrees is normal.

The Quadrant Approach

QRS up in I and up in aVF = Normal

What is the axis?

Normal- QRS up in I and aVF

Hypertrophy

Add the larger S wave of V1 or V2 in mm, to the larger R wave of V5 or V6.

Sum is > 35mm = LVH

ECG Analysis

Cardiac ischaemia changes

Ischaemia….. Usually indicated by ST segment changes

1. Elevation = Infarction▪ Any elevation in the ST segment that is greater than 2 small boxes

is indicative of myocardial injury.

2. Depression = Ischemia▪ Any ST segment depression greater than 2 small boxes indicates

myocardial ischemia.

Can manifest as T wave changes Remote ischemia shown by Q waves

ECG Changes : Ischemia

T-wave inversion ( flipped T) ST segment depression T wave flattening Biphasic T-waves

Baseline

ECG Changes: Injury

ST segment elevation of greater than 1mm in at least 2 contiguous leads

Heightened or peaked T waves Directly related to portions of myocardium

rendered electrically inactive

Baseline

ECG Changes: Infarct

Significant Q-wave where none previously existed Why?

▪ Impulse traveling away from the positive lead▪ Necrotic tissue is electrically dead

No Q-wave in Subendocardial infarcts Why?

▪ Not full thickness dead tissue▪ But will see a ST depression▪ Often a precursor to full thickness MI

Criteria Depth of Q wave should be 25% the height of the R wave Width of Q wave is 0.04 secs Diminished height of the R wave

Evolving MI & AMI Hallmarks

1 year

Q wave

ST Elevation

T wave inversion

ECG interpretation

ECG Interpretation

Let’s try an example…..

Is the rhythm regular or irregular?

Are the P-waves identical? Is there a P-wave for each QRS complex?

Is the PR Interval 0.12 – 0.20?

Regular

Yes for both!

Yes, PR = 0.16

ECG Interpretation

Let’s try an example…..

Is the Is the QRS wide, normal or narrow??

Is the T-wave peaked, inverted or flat?

Is the ST segment elevated or depressed?

Is the QT Interval < 0.43?

Normal QRS = 0.08

No, it’s normal

Yes, QT Interval= 0.36

ECG Interpretation

Is there any ectopy present in this rhythm?

ECG Interpretation

So, the rhythm is …..

Normal sinus rhythm

Identify lethal cardiac diseases

Cardiac Arrhythmias

The cardiac arrhythmias that are almost always associated with death include:1. Atrial Fibrillation

2. Atrial Flutter

3. Ventricular Fibrillation

4. Ventricular Tachycardia

5. 1st , 2nd and 3rd degree AV Block

6. Asystole

7. Ischaemia

Cardiac arrythmias

Atrial fibrillation…..

Rhythm

P-waves

PR interval

Atrial fibrillation is irregular + chaotic; Ventricular rhythm is very irregularAtrial is > 350 bpm; Ventricular is 120-200 bpmNot consistent (they are fine and fibrillating)Not measurable

Cardiac arrythmias

Atrial flutter…..

Rhythm

P-waves

PR interval

Atrial flutter is usually regular;

Atrial is 250- 350 bpm; Ventricular rate depends on AV conductioncharacterized by “saw tooth” pattern

cannot be determined; more flutter waves than QRS complexes

Cardiac arrythmias

Ventricular fibrillation…..

Rhythm

P-waves

PR interval

Ventricular rhythm is totally erratic

Ventricular rate is 350-450 bpm

Cardiac arrythmias

Ventricular tachycardia….. Aka widow maker

Rhythm

P-waves

PR interval

Typically regular, but can be irregular

Ventricular rate is 100-220 bpm

can be present but have no correlation to QRS complex0.12 seconds with odd “tomb –stone” shape

ECG Rhythm Analysis

Type 1st degree AV block

PR is fixed and longer than 0.2 sec

ECG Rhythm Analysis

Type 1 - 2nd degree AV block [Wenckebach]

ECG Rhythm Analysis

Type 2 - 2nd degree AV block

Dropped QRS

Cardiac arrythmias

3rd degree AV block….. Complete heart block

Rhythm

P-waves

PR interval

40-60 bpm (narrow QRS and junctional); 20-40 bpm (wide QRS and ventricular)Normal, but usually more P-waves than QRS’s

Cardiac arrythmias

Asystole…..

Rhythm

P-waves

PR interval

No rate as the person that belongs to this rhythm is DEAD

Cardiac ischaemia

What is the diagnosis…..

Acute inferior MI with ST elevation in leads II, III, aVF

Cardiac ischaemia

ST depression II, III, aVF, V3-V6 = ischemia

Cardiac ischaemia

Anterior MI with lateral involvementST elevations V2, V3, V4 ST elevations II, AVL, V5

Cardiac ischaemia

Anteroseptal MIST elevations V1, V2, V3, V4

Cardiac ischaemia

Inferior MIST elevation 2,3 AVF

Cardiac ischaemia

Inferior lateral MIST elevations 2, 3, AVF

ST elevations V5

Cardiac ischaemia

Acute inferior MILateral ischemia

FromSample ECGs

Ventricular tachycardia

Supraventricular tachycardia

Narrow complex, regular; retrograde P waves, rate <220

1st degree heart block

2nd degree heart block – Mobitz type II

(Wenckebach)

PR interval fixed, QRS dropped intermittently

Left Bundle Branch block

Monophasic R wave in I and V6, QRS > 0.12 sec; Loss of R wave in precordial leads; QRS T wave discordance I, V1, V6; Consider ischemia if a new finding

Right Bundle Branch block

V1: RSR prime pattern with inverted T waveV6: Wide deep slurred S wave

Accelerated Idioventricular

Ventricular escape rhythm, 40-110 bpm; Seen in AMI, a marker of reperfusion

Junctional rhythm

Rate 40-60, no p waves, narrow complex QRS

Hyperkalaemia

Tall, narrow and symmetric T waves

Hypokalaemia

U wavesCan also see PVCs, ST depression, small T waves

Wellen’s sign

ST elevation & biphasic T wave in V2 and V3;Sign of large proximal LAD lesion

Wolff-Parkinson-White Syndrome

Short PR interval <0.12 sec; Prolonged QRS >0.10 sec; Delta waveCan simulate ventricular hypertrophy, BBB and previous MI

Brugada syndrome

RBBB or incomplete RBBB in V1-V3 with convex ST elevation

Brugada syndrome

Autosomal dominant genetic mutation of Na+ channels

Causes syncope, v-fib, self terminating VT, and sudden cardiac death

Can be intermittent on ECG Most common in middle-aged males Can be induced in EP lab Need ICD

Premature Atrial Contractions

Trigeminy pattern

Atrial Flutter with Variable Block

Sawtooth waves; Typically at HR of 150

Torsades De Pointes

Notice twisting patternTreatment: Magnesium 2 grams IV

Digitalis

Lateral wall MI

Reciprocal changes

Infero-lateral wall MI

ST elevation II, III, aVFST depression in aVL, V1-V3 are reciprocal changes

Right ventricular MI

Found in 1/3 of patients with inferior MI, Increased morbidity and mortalityST elevation in V4-V6 of Right-sided ECG

Antero-lateral, Inferior wall ischemia

LVH, AV junctional rhythm, bradycardia

Acute Pulmonary Embolism

S1, QIII, TIII in 10-15%; T-wave inversions, especially occurring in inferior and anteroseptal simultaneously; RAD

Additional Practice

1522004 Anna Story

Additional Practice

References

Twelve Lead Electrocardiography for ACLS Providers, D. Bruce Foster, D.O.W.B. Saunders Company

Rapid Interpretation of EKG’s , Dale Dubin, M.D., Cover Publishing Co. 1998

ECG’s Made Easy, Barbara Aehlert, RN, Mosby, 1995 The 12 Lead ECG in Acute Myocardial Infarction, Tim Phalen, Mosby, 1996 Color Coding EKG’s , Tim Carrick, RN, H &H Publishing, 1994 www.ecglibrary.com/ecghome.html www.urbanhealth.udmercy.edu/ekg/read.html www.ecglibrary.com/ecghome.html www.nyerrn.com/h/ekg.htm

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