understanding ecg

UNDERSTANDI NG ECG

By

Dr. Sy e d Sa ifudd in.

History

Development as a clinically useful tool – later half of nineteenth century.

12 lead standard ECG – early 20 th century – 1940

Alexander Muirhead – first to record human ECG.

Augustus D Waller – first to publish in 1887, of Robert Goswell.

Nomenclature

Waller - ABCD for the 4 deflectionsLater based on mathematical notation –

PQRST was started.First used by Einthoven.

What does the ECG actually record

Electrical activity of the heart.Also other muscles – skeletal muscles.A ECG from relaxed patient is easy to

elicit.

ECG Paper: Dimensions5 mm

1 mm

0.1 mV

0.04 sec

0.2 sec

Speed = rate

Voltage ~Mass

Measurements

ECG graphs:1 mm squares5 mm squares

Paper Speed:25 mm/sec standard

Voltage Calibration: 10 mm/mV standard

How does ECG look at the heart?

Electrodes vs leadsLimb vs chest leadsBipolar vs unipolar leadsCoranal vs transverse view

ECG Leads

The standard ECG has 12 leads:3 Standard Limb Leads

3 Augmented Limb Leads

6 Precordial Leads

The axis of a particular lead represents the viewpoint from The axis of a particular lead represents the viewpoint from which it looks at the heart.which it looks at the heart.

+-

RA

RA

LL+

+

--LA

LL

LA

LEAD II

LEAD I

LEAD III

Remember, the RLis always the ground

• By changing the arrangement of which arms or legs are positive or negative, three unipolar leads (I, II & III ) can be derived giving three "pictures" of the heart's electrical activity from 3 angles.

The Concept of a “Lead”

Leads I, II, and III

I

II III

Precordial Leads

Summary of Leads

Limb Leads Precordial Leads

Bipolar I, II, III(standard limb leads)

-

Unipolar aVR, aVL, aVF (augmented limb leads)

V1-V6

Direction of ECG deflection & direction of current

Generation of waves

Wave forms

Duration of waves & segments

Normal Heart rate = 60 – 100 bpm PR interval = 0.12 – 0.20 sec QRS interval <0.12 SA Node discharge = 60 – 100 / min AV Node discharge = 40 – 60 min Ventricular Tissue discharge = 20 – 40 min

Summary

Determining the Heart Rate

Rule of 300

10 Second Rule

Rule of 300

Take the number of “big boxes” between neighboring QRS complexes, and divide this into 300. The result will be approximately equal to the rate

Although fast, this method only works for regular rhythms.

10 Second Rule

As most ECGs record 10 seconds of rhythm per page, one can simply count the number of beats present on the ECG and multiply by 6 to get the number of beats per 60 seconds.

This method works well for irregular rhythms.

The QRS Axis

By near-consensus, the normal QRS axis is defined as ranging from -30° to +90°.

-30° to -90° is referred to as a left axis deviation (LAD)

+90° to +180° is referred to as a right axis deviation (RAD)

-90°-60°

-30°

0°

aVL

I

30°

60°

aVR

II

90°

120°III

150°

180°

-150°

-120°

aVF

Marked RAD

LAD

RAD

Normal Axis

-30° to +100°

Using leads I, II, III

LEAD 1 LEAD 2 LEAD 3

Normal UPRIGHT UPRIGHT UPRIGHT

Physiological Left Axis UPRIGHT

UPRIGHT / BIPHASIC NEGATIVE

Pathological Left Axis

UPRIGHT NEGATIVE NEGATIVE

Right Axis NEGATIVEUPRIGHTBIPHASICNEGATIVE

UPRIGHT

Extreme Right Axis

NEGATIVE NEGATIVE NEGATIVE

Normal Sinus Rhythm

Heart Rate Rhythm P Wave

PR Interval(sec.)

QRS (Sec.)

60 - 100

Regular Before each QRS, Identical

.12 - .20 <.12

Sinus Rhythms

Sinus Bradycardia


PR Interval(sec.)

QRS (Sec.)

<60 Regular Before each QRS, Identical

.12 - .20 <.12

Sinus Rhythms

Sinus Tachycardia


PR Interval(sec.)

QRS (Sec.)

>100 Regular Before each QRS, Identical

.12 - .20 <.12

Sinus Rhythms

Sinus Arrhythmia


PR Interval(sec.)

QRS (Sec.)

Var. Irregular Before each QRS, Identical

.12 - .20 <.12

Sinus Rhythms

Sinus Arrest


PR Interval(sec.)

QRS (Sec.)

NA Irregular Before each QRS, Identical

.12 - .20 <.12

Sinus Rhythms

Sinus Arrest

Sinus Rhythms

Stop of sinus rhythm

New rhythm starts

One dropped beat is a sinus pause

Beats walk through

Sinus Pause

Atrial Fibri l lation


PR Interval(sec.)

QRS (Sec.)

Var. Irregular Wavy irregular NA <.12

Atrial Rhythms

Atrial Fibrillation No discernable p-waves preceding the QRS complex

The atria are not depolarizing effectively, but fibrillating Rhythm is grossly irregular HR <100 - controlled a-fib if >100 - rapid ventricular response AV node acts as a “filter”. Often a chronic condit ion, medical attention only

necessary if patient becomes symptomatic.

Atrial Rhythms

Atrial Flutter

Heart Rate Rhythm P WavePR

Interval(sec.)

QRS (Sec.)

Atrial=250 – 400

VentricularVar.

Irregular SawtoothNot

Measur-able

<.12

Atrial Rhythms

Ventricular RhythmsVentricular Tachycardia


PR Interval(sec.)

QRS (Sec.)

100 – 250

Regular

No P waves corresponding to

QRS, a few may be seen

NA >.12

Ventricular Rhythms

Ventricular Tachycardia No discernable p-waves with QRS Rhythm is regular Atrial rate cannot be determined, ventricular

rate is between 150-250 beats per minute Must see 4 beats in a row to classify as v-tach

Ventricular Rhythms

Ventricular Fibri l lation


PR Interval(sec.)

QRS (Sec.)

0 Chaotic None NA None

Ventricular RhythmsVentricular Fibrillation

No discernable p-waves No regularity Unable to determine rate Multiple irritable foci within the ventricles all

firing simultaneously May be coarse or fine This is a deadly rhythm

Patient will have no pulse Call a code and begin CPR

Asystole


PR Interval(sec.)

QRS (Sec.)

None None None None None

Heart Block

First Degree Heart Block


PR Interval(sec.)

QRS (Sec.)

Norm.

Regular Before each QRS, Identical

> .20 <.12

Heart BlockSecond Degree Heart BlockMobitz Type I (Wenckebach)


PR Interval(sec.)

QRS (Sec

.)

Norm. can be

slow

Irregular

Present but some not

followed by QRS

Progressively longer

<.12

Heart BlockSecond Degree Heart BlockMobitz Type II (Classical)


PR Interval(sec.)

QRS (Sec.)

Usually slow

Regular or

irregular

2 3 or 4 before each QRS,

Identical

.12 - .20

<.12 depend

s

Heart Block

Third Degree Heart Block(Complete)


PR Interval(sec.)

QRS (Sec.)

30 – 60

RegularPresent but no

correlation to QRS may be hidden

Varies<.12

depends

Identifying the cardiac rhythm

I hope that the advise given here will be sufficient to keep you out of trouble when trying to identify the cardiac rhythm in an emergency.

However, the recognition of some arrhythmias can be difficult, even for the specialist.

REMEMBER

IF IN DOUBT ABOUT A PATIENT’S CARDIAC RHYTHM, DONOT HESITATE TO SEEK THE ADVISE OF A CARDIOLOGIST.

Analysing the rhythm

Two questions in your mind—

1. Where does the impulse come from?

2. How is the impulse conducted?

Narrowing down on the possible diagnosis!!!

1. How is the patient?

2. Is ventricular activity present?

3. What is the ventricular rate?

4. Is the ventricular rhythm regular or irregular?

5. Is the QRS complex width normal or broad?

6. Is atrial activity present?

7. How is the atrial activity and ventricular activity related?

How is the patient?

Never analyse ECG without the clinical context in which it was recorded.

NSR vs PEA Arrhythmia vs Artifact ALWAYS ---

1. Insist on knowing the clinical context

2. Make a note of the clinical context at the top of the ECG

Is ventricular activity present?

Check for the electrical activityAsystole – check for the electrodes and of

course the patientP waves only – responds to emergency

pacing manoeuvresIf QRS present – proceed next

What is the ventricular rate?

Bradycardia - <60 beats/minNormal - 60-100 beats/minTachycardia - 100 beats/min

Is the ventricular rhythm regular or irregular?

Spacing of the QRS complexes1. Regular – equal2. Irregular – variable Using a strip of paper Irregular cardiac rhythms –1. Atrial fibrillation2. Sinus arrhythmia3. Any supraventricular rhythm with intermittent

AV block4. Ectopic beats

Is the QRS complex width normal or broad?

Clue about the origin of the rhythm.Narrowed to one half of the heart.Supraventricular vs ventricularVentricular repolarisation via AV node –

0.12s – narrow QRS complex.Any block/impulse directly from ventricular

muscle – myocyte to myocyte conduction – prolonged depolarisation - broad QRS complex.

Broad QRS complex –

1. Ventricular rhythm

2. Supraventricular rhythm with aberrant conduction.

A GOOD GENERAL RULE IS THAT BROAD COMPLEX TACHYCARDIA IS ALWAYS ASSUMED TO BE VT UNLESS PROVEN OTHERWISE.

VT vs SVT

Elderly H/o Cardiac disease Atypical broad

complexes Diagnostic of VT –

Independent P wave activity, fusion beats, capture beats.

Young No H/o Cardiac

disease Typical LBBB/RBBB

morphology.

Is atrial activity present?

4 categories –

1. P waves (atrial depolarization) – check for orientation

2. Flutter waves – 300/min

3. Fibrillation waves – 400-600/min

4. Unclear activity – Hidden in QRS complex – AVNRT Absent – SA block / sinus arrest

How is the atrial activity and ventricular activity related?

Association between QRS complex and P wave –

Every QRS followed by P wave – activated by common source – SA / AV node

More P waves than QRS – Block (partly/completely)

More QRS complexes than P waves – AV dissociation

ST segment changes

Anatomic Groups(Summary)

Ventricular hypertrophy

Bundle branch blocks

Artefacts

If you encounter abnormalities that appear atypical or do not fit with the patients clinical condition, always consider the possibility that they are artefacts caused by –

1. Electrode misplacement

2. External electrical interference

3. Incorrect calibration

4. Incorrect paper speed

5. Patient movement

Deflections occurring at a rate of 400-to-500 times/minute especially in view of the morphology, irregularity, and clinical history (of tremor) in this case.

ventricular fibrillation in a awake and alert patient.

ALWAYS KEEP THINGS SIMPLE AND TRY TO AVOID GETTING SIDE TRACKED BY UNNESSARY DETAIL – THE DIAGNOSIS WILL OFTEN OFTEN BE OBVIOUS ONCE YOU HAVE IDENTIFIED THE KEY FEATURES OF ECG.

--- THANK YOU !!!

Study resources

www.ecglibrary.com www.skillstat.com/6sECG_rdm.html http://www.randylarson.

rhythmst.htmlcom/acls/master/ Rapid Interpretation of EKG’s, Dale Dubin M.D.

understanding ecg

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