ECG

HISTORY

1842- Carlo Matteucci -electricity is a/w heart beat

1876- Marey - electric pattern of frog’s heart

1895 - William Einthoven - invention of EKG

1924 - Noble prize - Einthoven for EKG

1938 -AHA & Cardiac society of great Britain

defined position of chest leads

1942 -Goldberger increased Wilson’s Unipolar lead

voltage by 50% & made Augmented leads

ELECTROCARDIOGRAM

Is a recording of electrical activity of heart conducted thru ions in body to surface

ECG INTERPRITATION STEPS

Rate Rhythm Cardiac Axis P – wave PR - interval QRS Complex ST Segment QT interval (T & U wave) Other ECG signs

CARDIAC ELECTROPHYSIOLOGY

Electrical activity is governed by multiple trans

membrane ion conductance changes

3 types of cardiac cells

1. Pacemaker cells - SA node, AV node

2. Specialized conducting tissue -

Purkinje fibres

3. Cardiac myocytes

WAVEFORMS AND INTERVALS

ECG GRAPH PAPER

Runs at a paper speed of 25 mm/sec

Each small block of ECG paper is 1 mm2

At speed of 25 mm/s, 1 small block = 0.04 s

Voltage: 1 mm = 0.1 mV between each individual

block vertically

5 mm

1 mm

0.1 mV

0.04 sec

0.2 sec

Speed = rate

Voltage ~Mass

ECG GRAPH PAPER

ECG LEADS

Leads are electrodes which measure the difference in electrical potential between either:

1. Two different points on the body (bipolar leads)

2. One point on the body and a virtual reference point with zero electrical potential, located in the center of the heart (unipolar leads)

+-

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

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 which it looks at the heart.

ECG LEADS

Gold Berger :aV frontal leads

Wilson & co-workwers :chest leads

STANDARD LIMB LEADS

PRECORDIAL LEADS

PRECORDIAL LEADS

STANDARDIZATION

300 number of BIG SQUARE b/w R-R

Rate =

1500 number of SMALL SQUARE b/w R-R

OR

Rate =

RATE

RATE

RHYTHM

P -QRS relationships- Lead II is commonly used

Regular or irregular?

Ventricular rhythm – measured by R-R interval

Atrial rhythm - measured P-P interval.

ECG rhythm -usual rate as per age of child, every P

wave must be followed by a QRS & every QRS is

preceded by P wave.

P wave is upright in leads I and II

Normal Sinus Rhythm

NORMAL SINUS RYTHM

Originates in the sinus node Rate between 60 and 100 beats per min P wave axis of +45 to +65 degrees (Tallest p

waves in Lead II) Monomorphic P waves Normal PR interval of 120 to 200 msec Normal relationship between P and QRS Some sinus arrhythmia is normal

AXIS

Axis refers to general direction of heart's

depolarization wave front (or mean electrical

vector) in the frontal plane.

In healthy conducting system - axis is related to

where the major muscle bulk of heart lies.

William Einthoven developed a system capable of

recording small signals & recorded 1st ECG.

Leads were based on Einthoven triangle a/w limb

leads.

Leads put heart in middle of a triangle

EINTHOVEN TRIANGLE

AXIS

1. Lead I & aVF divide

thorax into quadrants,

(Lt, N , Rt, No Man's)

 

2. If Lead I & aVF are both upright- Axis is normal.

 

3. If lead I is upright & lead aVF is downward - Axis is Left.

AXIS

4. If lead aVF is upright & lead I is downward - Axis is Rt

5. If both leads are downward - Axis is extreme Right Shoulder & most often is Vent. Tachy

Cardiac

Axis

Causes

LAD Pregnancy, obesity; Ascites ,

abdominal distention, tumour ;

LAH, LVH

RAD N finding in children & tall thin

adults, COPD, RVH, Anterolateral

MI.

North

West

Emphysema, Hyperkalaemia ,

Lead transposition, Artificial

cardiac pacing, VT

P WAVE

Depolarization of both atria

Relationship b/w P & QRS - distinguish various

arrhythmias

Shape & duration of P - indicate atrial

enlargement

P WAVE

Always +ve in lead I & II

Always -ve in lead aVR

<2 small sqs - duration

<2 small sqs - amplitude

Biphasic in lead V1

Best seen in lead II

P-PULMONALE P-MITRALE

PR INTERVAL

Onset of P wave to onset of QRS

• Normal = 0.12 - 2.0 sec

• Represents A to V conduction time (via His

bundle)

Prolonged PR interval indicate AV block

PR INTERVAL

Onset of P wave to onset of QRS

• Normal = 0.12 - 2.0 sec

• Represents A to V conduction time (via His

bundle)

Prolonged PR interval indicate AV block

VENTRICULAR DEPOLARIZATION

Includes Bundle of His Bundle Branches

Right Left

SeptalAnteriorPosterior

Terminal Purkinjie fibers

Ventricular Waves

Q wave – 1st downward deflection after P wave

Rwave – 1st upward deflection after Q wave

S wave – 1st downward deflection after R wave

QRS COMPLEX

Ventricular depolarization

• Is > P wave d/t > Ventricular mass

• Normal duration = 0.08 - 0.12 secs

ST SAGMENT

Connects QRS complex & T wave

Duration = 0.08 - 0.12 sec

T WAVE

“small to moderate” size +ve deflection wave

after QRS complex,

Ht is 1/3rd - 2/3rd that of corresponding R wave

U WAVE

Septal repolarization (not always seen on ECG)

QT INTERVAL

Beginning of QRS to end of T wave

Normal QT is usually about 0.40 sec

QT varies based on HR- faster HR ,shorter QT

Bazett’s formula: QTC = QT / √ RR

Fredericia’s formula: QTC = QT / RR 1/3

Framingham formula: QTC = QT + 0.154 (1 – RR)

Hodges formula: QTC = QT + 1.75 (HR– 60)

PROLONGED QT INTERVAL

CAD Cardiomyopathy Severe Bradycardia, High-Grade AV Block Anti-Arrhythmics Psychotropic Drugs Hypocalcemia Autonomic dysfunction Hypothyroid Hypothermia Congenital Long QT Syndrome

SHORT QT INTERVAL

Digitalis effect Hypercalcemia Hyperthermia Vagal stimulation

VENTRICULAR HYPERTROPHY

RVH = R in V1 + S in V6

LVH = S in VI + R in V6

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