ECG INTERPRETATION

Dr. P.S.INDURKAR

professor in Anesthesia,

DY Patil Medical college, Mauritius

ECG

This short course reviews

• the main features of ECG tracings.

• A method for analyzing ECGs .

• assessment of rhythm, calculating heart rate

• observing P-wave forms, measurement of ECG

intervals and segments

• and the evaluation of other relevant waves.

Leads The 12 leads on the ECG (I, II, III, aVL , aVF, aVR, V1 - 6) are

formed using only 9 electrodes (and a neutral)?

• Lead I is formed using the right arm electrode (red) as the

negative electrode and the left arm (yellow) electrode as the

positive.

• Lead II is formed using the right arm electrode (red) as the

negative electrode and the left leg electrode as the positive.

• Lead III is formed using the left arm electrode as the negative

electrode and the left leg electrode as the positive.

• aVL, aVF and aVR are composite leads, using the information

from the other leads .also known as augmented leads. They

are derived from the same three electrodes as leads I, II, and

III. However, they view the heart from different

angles(Einthoven,s law, Einthoven,s triangle)

Each lead can be thought of as looking at an area of myocardium

Limb leads look at the heart in the coronal plane

• aVL, , I and II = lateral

• II, III and aVF = inferior

• aVR = right side of the heart

Chest leads

• V1 to V6 look at the heart on the transverse plain

• V1 and V2 look at the anterior of the heart and R ventricle

• V3 and V4 = anterior and septal

• V5 and V6 = lateral and left ventricle

• ECG tracings are recorded on grid paper. The horizontal axis of

the ECG paper records time, with black marks at the top

indicating 3 second intervals.

• Each second is marked by 5 large grid blocks. Thus each large

blocks equals 0.2 second. The vertical axis records ECG

amplitude (voltage). Two large blocks equal 1 millivolt (mV).

Each small block equals 0.1 mV.

Within the large blocks are 5 small blocks, each representing

0.04 seconds

• 1mm (small square) = 0.04 sec

• 5mm (big square) = 0.2 sec

• Normal ECG tracings consist of waveform

components which indicate electrical events during

one heart beat. These waveforms are labeled P, Q, R,

S, T and U. (The following descriptions are with

respect to Lead II).

• P wave is the first deflection and is normally a

positive (upward) waveform. It indicates atrial

depolarization (Contraction).

• QRS complex follows the P wave. It normally begins with a downward deflection Q; a larger upwards deflection R; and then a downwards S wave.

• The QRS complex represents ventricular depolarization and contraction.

• T wave is normally a modest upwards waveform, representing ventricular repolarization.

• U wave indicates the recovery of the Purkinje conduction fibers. This wave component may not be observable.

ECG interpretation should be performed using a standard procedure. For this course, we are using an eight step procedure: 1) Rhythm 5) QRS Interval

2) Rate 6) T Wave

3) P Wave 7) QT Interval

4) PR Interval 8) ST Segment

RHYTHM • Sinus Rhythm

Definition--Cardiac impulse originates from the sinus

node. Every QRS must be preceded by a P wave.

• Sinus bradycardia

Rhythm originates in the sinus node . Rate of less

than 60 beats per minute

• Sinus tachycardia

Rhythm originates in the sinus node. Rate of greater

than 100 beats per minute

RHYTHM

Rhythm means---are the heartbeats regular, meaning

that each heart beat's R-R interval is equal. Small

variations of up to 10% are considered equal.

Is the rhythm (R-R intervals) regularly irregular or

completely irregular? For example is there a pattern,

such as increasing R-R durations?

For ventricular rhythm, examine the R to R intervals on

the ECG strip. Calipers or paper marks can be used to

fix the distance for one R-R interval and then this

distance can be compared to other R-R pairs.

Is the rhythm regular?

• The easiest way to tell is to take a sheet of paper and

line up one edge with the tips of the R waves on the

rhythm strip.

• Mark off on the paper the positions of 3 or 4 R wave

tips

• Move the paper along the rhythm strip so that your

first mark lines up with another R wave tip

• See if the subsequent R wave tips line up with the

subsequent marks on your paper

• If they do line up, the rhythm is regular. If not, the

rhythm is irregular

RATE

There are several methods for determining heart rate.

1) Count the number of QRS complexes over a 6 second

interval. Multiply by 10 to determine heart rate. This method

works well for both regular and irregular rhythms.

In this image , we can count 7 QRS complexes, so the heart rate

is 70.

2)The second method uses small boxes. Count the number of

small boxes for a typical R-R interval. Divide this number into

1500 to determine heart rate. In the above image, the number of

small boxes for the R-R interval is 22.5. The heart rate is

1500/21.5, which is 69.8.

3)Count the number of large squares between R waves i. e. the

RR interval in large squares .

• Rate = 300 /RR

• e. g. RR = 4 large squares , 300/ 4= 75 beats per minute

P-wave The P wave represents atrial depolarization. In

normal ECGs, the P-wave precedes the QRS

complex. It looks like a small bump upwards from

the baseline. The amplitude is normally 0.05 to

0.25mV (0.5 to 2.5 small boxes). Normal duration

is 0.06-0.11 seconds (1.5 to 2.75 small boxes). The

shape of a P-wave is usually smooth and rounded.

P-wave assessment

Are they present?

Do they occur regularly?

Is there one P-wave for each QRS complex?

Are the P-Waves smooth, rounded, and upright?

Do all P-Waves have similar shapes?

PR Interval

• The PR Interval indicates AV conduction time.

It is measured from where the P wave begins

until the beginning of the QRS complex.

Calipers, marked paper or counting small

boxes methods can be used to determine PR

Intervals. Normally this interval is 0.12 to 0.20

seconds (3 to 5 small boxes) in adults, longer

in elderly people.

• This interval shortens with increased heart

rate.

PR Interval • Also evaluate if PR Intervals are constant or varying across the

ECG strip. If they vary, determine if the variations are a steady

lengthening until the point where an expected QRS does not

appear.

PR Interval assessment while reading ECG:

1) Does the PR-Interval fall within the norm of 0.12-0.20

seconds?

2) Is the PR-Interval constant across the ECG tracing?

QRS complex • The QRS complex indicates ventricular depolarization.

Depolarization triggers contraction of the ventricles.

Because of the larger tissue mass, the QRS complex is bigger

than the P wave. A typical QRS complex consists of three wave

components, one or two of these components may be

missing.

Measure the QRS interval from the end of the PR interval to

the end of the S wave. Use calipers, marking paper or by

counting small boxes. Normally this interval is 0.06 to 0.12

seconds (1.5 to 3 boxes).

• QRS assessment:

1) Does the QRS interval fall within the range of 0.08-

0.12 seconds?

2) Are the QRS complexes similar in appearance

across the ECG tracing?

T wave • The T wave indicates the repolarization of the ventricles. It is a

slightly asymmetrical waveform which follows (after a pause),

the QRS complex. (Take note of T waves which have a

downward (negative) deflection or of T waves with tall,

pointed peaks.

T wave abnormalities

• Hyper acute T waves

• Inverted T waves

• Biphasic T waves-Causes-MI, Hypokalemia

• Ca el Hu p T waves--There are two causes:

1)Prominent U waves fused to the end of the T

wave, as seen in severe hypokalemia

2)Hidden P waves embedded in the T wave, as

seen in sinus tachycardia and various types of heart

block

• Flattened T waves-----it may indicate hypokalemia

• Peaked T waves

• Tall, narrow, symmetrically peaked T-waves are

characteristically seen in hyperkalaemia.

• Hyperacute T waves

• Broad, as etri all peaked or h pera ute T-

waves are seen in the early stages of ST-elevation MI

(STEMI) and often precede the appearance of ST

elevation and Q waves. They are also seen with

Prinzmetal angina.

Inverted T waves are seen in the following conditions:

• Normal finding in children

• Persistent juvenile T wave pattern

• Myocardial ischemia and infarction

• Bundle branch block

• Ve tri ular h pertroph strai patter s

• Pulmonary embolism

• Hypertrophic cardiomyopathy

• Raised intracranial pressure

Inferior T wave inversion due to acute ischaemia

Inferior T wave inversion with Q waves due to prior inferior MI

U-wave • The U-wave is a small upright, rounded bump.

• U waves occur after the T wave and are often

difficult to see. They are thought to be due to

repolarization of the atrial septum

• Prominent U waves can be a sign of

hypokalemia , hyperthyroidism

QT interval

• The QT interval represents the time of ventricular

activity including both depolarization and

repolarization.

• It is measured from the beginning of the QRS

complex to the end of the T wave. Normally, the QT

interval is 0.36 to 0.44 seconds (9-11 boxes). The QT

interval will vary with patient gender, age and heart

rate. Another guideline is that normal QT Intervals is

less than half of the R-R Interval for heart rates

below 100 bpm.

QT interval

ST segment • The ST segment represents the early part of

ventricular repolarization.

• The ST segment is from the end of the QRS complex

to beginning of the T wave. Normally the ST segment

is flat, being neither positive or negative relative to

the baseline. The most important cause of ST

segment abnormality (elevation or depression) is

myocardial ischemia or infarction

Exercise--Calculate the Heart rate

Calculate the Heart rhythm

P Wave shape varies

PR Interval varies

Wide QRS Interval

• Interpretation (adults)

• 60–100 beats/min

– Normal

• >100 beats/min

– Tachycardia

• <60 beats/min

– Bradycardia

• Normal Heart Rates in Children

• Newborn: 110 – 150 bpm

• 2 years: 85 – 125 bpm

• 4 years: 75 – 115 bpm

• 6 years+: 60 – 100 bpm

Axis deviation Definition

• the mean direction of electrical forces in the frontal plane ( limb leads) as

measured from the zero reference point (lead 1)

• Normal values

– P wave: 0 to 75 degrees

– QRS complex: -30 to 90 degress

– T wave: QRS-T angle <45 degrees frontal or <60 degrees precordial

Axis deviation

• The simplest method of identifying gross deviations

in axis is to look at the QRS complexes in leads I and

aVF. Lead I is a left-sided lead, and as aVF is

perpendicular to lead I, it can be considered a right-

sided lead.

– Both leads I and aVF have mainly positive QRS

complexes = normal axis.

– Lead I is positive and aVF is negative = left axis

deviation (LAD).

– Lead I is negative and aVF is positive = right axis

deviation (RAD).

– Both leads negative = e tre e ‘AD or North-

West a is

Axis in the normal range

Lead aVF is the isoelectric lead.

•The t o perpe di ulars to aVF are 0° and

180°.

•Lead I is positi e i.e., orie ted to the left . •Therefore, the a is has to e °.

Axis in the left axis deviation (LAD) range

Lead aVR is the smallest and isoelectric lead.

•The t o perpe di ulars are -60° and +120°.

•Leads II a d III are ostl egati e i.e., moving away from the + left leg)

•The a is, therefore, is -60°.

Axis in the right axis deviation (RAD) range

ead aVR is closest to being isoelectric

(slightly more positive than negative)

•The t o perpe di ulars are -60° and

+120°

•Lead I is ostl egati e; lead III is ostl positive.

•Therefore the a is is lose to + °.

Because aVR is slightly more positive, the

axis is slightly beyond +120° (i.e., closer to

the positive right arm for aVR).

Right Axis Deviation (RAD)

Differential diagnosis

• Right Ventricular Hypertrophy (RVH) — most common

• Left Posterior Fascicular Block (LPFB) — diagnosis of exclusion

• Lateral and apical MI

• Acute Right Heart Strain, e.g. acute lung disease such as pulmonary embolus

• Chronic lung disease, e.g. COPD

• Dextrocardia

• Ventricular pre-excitation (WPW) — LV free wall accessory pathway

• Ventricular ectopy

• Hyperkalemia

• Sodium-channel blockade, e.g. tricyclic toxicity

• Secundum ASD — rSR patter

• Normal in infants and children

• Normal young or slender adults with a horizontally positioned heart can also demonstrate a rightward QRS axis on the ECG.

Left Axis Deviation (LAD)

Differential diagnosis

• Left ventricular hypertrophy (LVH)

• Left Anterior Fascicular Block (LAFB) —

diagnosis of exclusion

• LBBB

• inferior MI

• ventricular ectopy

• paced beats

• Ventricular pre-excitation (WPW)

• Primum ASD — rSR patter

• Extreme Axis Deviation

– 180 to -90 degrees

• rare

Differential diagnosis

• Right Ventricular Hypertrophy (RVH)

• Apical MI

• VT

• Hyperkalemia

Axis Deviation

Wolff--Parkinson --White syndrome can cause

both Left and Right axis deviation

short PR interval, less than 3 small squares

(120 ms)

slurred upstroke to the QRS indicating pre-

excitation (delta wave)

broad QRS

secondary ST and T wave changes

Classic Wolff-Parkinson-White electrocardiogram with short PR, QRS >120 ms,

and delta wave

Heart block

• Conduction system

Heart block

• Sino-Atrial Exit Block

• Atrio-Ventricular (AV) Block – 1st Degree AV Block

– 2nd Degree AV Block :Type I (Wenckebach)

– 2nd Degree AV Block: Type II (Mobitz)

– Complete (3rd Degree) AV Block

– AV Dissociation

• Intraventricular Blocks – Right Bundle Branch Block

– Left Bundle Branch Block

– Left Anterior Fascicular Block

– Left Posterior Fascicular Block

– Bifascicular Blocks

– Nonspecific Intraventricular Block

– Wolff-Parkinson-White Preexcitation

Types of Heart Block

• First-degree heart block – The electrical impulses are slowed

as they pass through the conduction system, but they all

successfully reach the ventricles. First-degree heart

block rarely causes symptoms or problems. Well-trained

athletes may have first-degree heart block. Medications can

also cause this condition. No treatment is generally needed

for first-degree heart block.

• Second-degree heart block (Type I) – The electrical impulses

are delayed further and further with each heartbeat until a

beat fails to reach to the ventricles entirely. It sometimes

causes dizziness and/or other symptoms. People with normal

conduction systems may sometimes have type 1 second

degree heart block when they sleep.

• Second-degree heart block (Type II) – With this condition,

some of the electrical impulses are unable to reach the

ventricles. This condition is less common than Type I, and is

more serious. Usually, a pacemaker recommend to treat type II

second degree heart block, as it frequently progresses to third

degree heart block.

• Third-degree heart block – With this condition, also called

complete heart block, none of the electrical impulses from the

atria reach the ventricles. When the ventricles do not receive

electrical impulses from the atria, they may generate some

impulses on their own, called junctional or ventricular escape

eats. Ve tri ular es ape eats, the heart s aturall o urri g backups, are usually very slow.

• Patients C/O -Light headedness or dizziness, Palpitations,

Fatigue, Chest pressure or pain, Shortness of breath, Fainting

spells

• Bundle Branch Block – With this condition, the electrical impulses are slowed or

blocked as they travel through the specialized conducting tissue in one of the two

ventricles.

• Types of bundle branch blocks-Depending on the anatomical location of the

defect:

1)Right bundle branch block

2)Left Bundle branch block

The left bundle branch block can be further sub classified into:

a)Left anterior fascicular block. In this case only the anterior half of the left

bundle branch (fascicle) is involved

b)Left posterior fascicular block. Only the posterior part of the left bundle branch

is involved

Other classifications of bundle branch blocks are;

Bifascicular block--This is a combination of right bundle branch block (RBBB) and

either left anterior fascicular block (LAFB) or left posterior fascicular block (LPFB)

Trifascicular block--This is a combination of right bundle branch block with either

left anterior fascicular block or left posterior fascicular block together with a first

degree AV block.

Read more: http://www.hrsonline.org/Patient-Resources/Heart-Diseases-Disorders/Heart-Block#ixzz3EgcjiMKI

Symptoms of Heart Block

• Some people with heart block will not experience any symptoms. Others will have symptoms that may include the following:

• Fainting ( syncope)

• Dizziness Lightheadedness

• Chest pain

• Shortness of breath

Risk factors for Heart Block

• Some medical conditions increase the risk for developing heart block. These medical conditions include:

• Heart failure

• Prior heart attack

• Heart valve abnormalities

• Heart valve surgery

• Some medications or exposure to toxic substances

• Lyme disease

• Aging Read more: http://www.hrsonline.org/Patient-Resources/Heart-Diseases-Disorders/Heart-Block#ixzz3Egd0vug3

LBBB

• ƒƒ If left bundle branch block is present, the QRS

o ple a look like a W i V a d/or a M shape i V6.

•ƒƒ (New onset LBBB with chest pain consider Myocardial infarction. Not possible to

interpret the ST segment)

RBBB

It is also called RSR pattern . If right bundle

branch block is present, there may be an

M i V a d/ or a W i V6. Can occur in healthy people with normal QRS

width--partial RBBB

Myocardial infarction

• The leads affected determine the site of the

infarct.

• Inferior--II, III, aVF.

• Anteroseptal--V1-V4

• Anterolateral--V4 V6, I, aVL

• Posterior--Tall ide ‘ a d “T↓ i V a d V

Myocardial infarction

• Within hours: T wave may become peaked, ST

segment may begin to rise

• Within 24 hours: T wave inverts (may or may

not persist) ST elevation may persist

• Within a few days: pathological Q waves can

form and usually persists.

Inferior MI

Supraventricular tachycardias

These are tachycardias where the impulse is

initiated in the atria ( sinoatrial node, atrial wall

or atrioventricular node)

• If there is a normal conduction pathway when

the impulse reaches the ventricles, a narrow

QRS complex is formed, hence they are

narrow complex tachycardias However if there

is a conduction problem in the ventricles such

as LBBB, then a broad QRS complex is formed.

This would result in a form of broad complex

tachycardia

Atrial Fibrillation

• Features: There may be tachycardia The

rhythm is usually irregularly irregular.

• No P waves are discernible

• instead there is a shaky baseline This is

because there is no order to atrial

depolarization, different areas of atrium

depolarise at will

Atrial Fibrillation

Symptoms of AF

• Palpitation

• Shortness of breath

• Weakness

• Chest pain

• Dizziness or fainting

• Fatigue

• Confusion

Causes of AF • High blood pressure is the most common cause.

• ischemic heart disease.

• Other conditions and situations that may trigger AF to develop include:

– An overactive thyroid gland (hyperthyroidism)

– Pneumonia

– Pulmonary embolus

– Obesity

– Lung cancer

– Drinking a lot of alcohol.

– Drinking a lot of caffeine (tea, coffee, etc).

• AF occurs in some people with heart valve problems, pericardial disease, dilated cardiomyopathy and hypertrophic cardiomyopathy

Atrial Fibrillation

Atrial flutter There is a saw-tooth baseline which rises above and

dips below the isoelectric line. Atrial rate 250/ min

This is created by circular circuits of depolarisation

set up in the atria

Premature ventricular complex/contractions

Definition--A premature beat arising from an

ectopic focus within the ventricles.

Features:

• Broad QRS complex ≥ 120 ms) with abnormal

morphology & Premature i.e. occurs earlier than

would be expected for the next sinus impulse.

• Variable ST segment and T wave changes.

• Usually followed by a full compensatory pause.

(Retrograde capture of the atria may or may not

occur).

PVCs may be either:

• Unifocal --Arising from a single ectopic focus; each PVC is identical.

• Multifocal --Arising from two or more ectopic foci; multiple QRS morphologies.

PVCs often occur in repeating patterns:

1. Bigeminy — every other beat is a PVC.

2. Trigeminy — every third beat is a PVC.

3. Quadrigeminy — every fourth beat is a PVC.

4. Couplet — two consecutive PVCs.

5. Triplet — three consecutive PVCs.

Causes

• Anxiety

• Sympathomimetics

• Beta-agonists

• Excess caffeine

• Hypokalaemia

• Hypomagnesaemia

• Digoxin toxicity

• Myocardial ischemia

Ventricular Tachycardia

• QRS complexes are wide and irregular in shape. Usually secondary to infarction. Circuits of depolarisation are set up in damaged myocardium This leads to recurrent early repolarisation of the ventricle leading to tachycardia.

• As the rhythm originates in the ventricles, there is a broad QRS complex Hence it is one of the causes of a broad complex tachycardia

• Need to differentiate with supraventricular tachycardia with aberrant conduction

Ventricular Tachycardia

Ventricular Fibrillation • Completely disordered ventricular

depolarisation

• Not compatible with a cardiac output

• Results in a completely irregular trace

consisting of broad QRS complexes of varying

widths, heights and rates

References

1. www.thh.nhs.uk

2. www.practicalclinicalskills.com

3. ecg.utah.edu

4. cdn.lifeinthefastlane.com

5. www.ecglibrary.com

6. emedicine.mediscape.com

7. www.nhlbi.nih.gov

8. www.hrsonline.org

9. www.mayoclinic.org

Thank you