What Makes ECG

MYOCYTES PRODUCE Electrical impulse

Human body conducting impulse

Electrodes pick up potential difference

ECG Machine read potential difference ,

and draw a graph

What is electrode ?

Special Sensor devices Connected to certain

areas in the body Pick up potential

difference They known as leads

Types of leads ( Electrodes )

Leads

Limb LeadsBipolar

Unipolar

Chest leads V1 to V6

What is Bipolar leads

Lead 1

• +ve LA• -ve RA

Lead 11

• +ve LL• -ve RA

Lead 111

• +ve LL• -ve LA

Bipolar Limb Leads

Can be located at any part of the limb 10 cm from the heart

They form equilateral triangle Einthoven triangle

Augmented Unipolar leads

aVR

aVF

aVL

• +ve• RA

• +ve• Lf

• +ve• LA

Augmented Unipolar leads

• No Negative pole• Instate the reference is

the other two leads• The machine change

the leads without addition of attached devices

Chest leads Location

V1 Rt 4th IC

V4 LT 5th IC

V2 Lt 4th IC

V5 5th IC , AAL

V3 HALF WAY

V2&V4

V5 5th IC ,MAL

Hexaxial system• Two victors(leads) are equal

in intensity ,and polarity as long as they are parallel

• Accordingly we can shit the leads to a point passing through the heart center, and they will be the same

• The location of the lead is determined by its positive pole

• Direction of the Lead is from Positive to Negative electrode

• The direction of the unipolar lead is towards the center of the corresponding limb of the triangle, otherwise same is applied as in bipolar leads

Hexaxial system

Anatomical representations of the leads

Anatomical representations of the leads

ECG paper

ECG paper

ECG paper

Calibration Box Found at edge of ECG

paper Standard 10 mm

height (1MV ) .2 second width To confirm standard

ECG format

ECG Components

• A deflections from the base line represent cardiac event

• P- QRS- T wavesWaves

• A specific portion of the complex• PR – ST Segment

• Distance measured as time between two cardiac events

• QT- PR- TPInterval

Waves

Waves represent : Atrial , or ventricular

depolarization , repolarization and conduction

Can be positive ,negative or biphasic deflection from the baseline

Baseline from one TP segment to the next

ECG Representation of cardiac events

• Atrial depolarizatio• Atrial Repolarization• Conduction • Ventricular depolarization• Ventricular Repolarization• Conduction

ECG Segments & Intervals

Segments

PR

ST

Intervals

PR

QT

Additional intervals

RR

PP

P- Wave

• First wave after TP • Represent atrial depolarization

and conduction• Duration 0.08 – 0.11 second• Direction of the impulse is

downwards & to the left• It is upright in leads 11,111,& aVf• Downwards in aVR• It must be upright in Leads 11 &

aVF to say sinus rhythm

TP wave

• Represent repolarization of Atria

• Usually not seen • It occurs when there is

no QRS after P as in Av dissociation

• It can also be seen in PR or ST depression

PR Segment

• From end of P to beginning of QRS

• Usually at the base line• Depression of up to

0.8 mm is accepted as normal

• Pathological depression in pericarditis and atrial ischemia

PR Interval

• Include P wave ,and PR segment

• Cover the event from initiation of impulse at SA node to start of ventricular depolariz.

• Duration o.12 sec. to 0.20 sec.

• < 0.11 shortening• > 0.20 1st degree heart

block

QRS Complex

• Composed of two or more waces

• Represent ventricular depolarization

• Duration is up to 0.12 second

How to identify different waves

• The first negative wave after P wave

Q wave

• The first Positive wave after P wave

R wave

• The first negative deflection after R wave

S wave

An X Prime wave

• Extra wave in QRS• It isn't an actual wave • Change in QRS • QRS become bizarre• S wave : only when

cross the baseline

Q Wave

Can be significant if : 0.03 second or wider Equal to or greater than

1/3rd of height of R wave

Non significant Q wave Commonly found in

Leads : 1 , aVL & V6

The Intrinsicoid Deflection

• Beginning of QRS to the beginning of negative down slope of the R wave when no Q wave

• Represent the time of electrical impulse from purkinje fibers to surface of epicardium

• It is longer in left preicordial leads V5, V6

• Prolongation in LVH , BBB

The ST Segment

• End of QRS to Beginning of T • Usually along the base line

with normal variation of 1 mm in limbs leads & 3 mm in Right chest leads

• The point of junction with QRS is called J point

• Represent the period from depol. to repol. of ventricles

The T Wave

• Represent ventricular repolarization

• negative or positive deflection after ST Segment

• Should be The same direction of QRS

• It is asymmetric , begin sloping and end is faster

How to measure asymmetry

• Draw a line from the peak of T wave to the base line , and measure each side

• Asymmetry is usually a sign of pathology , but may be normal

QT Interval

QRS + ST + T Represent all the event of

ventricular systoleVaries with Rate ,age sex ,

and electrolyte abnormality

prolongation predispose to arrhythmias

Best way to measure QT Interval

• Normal QT Is less than the half of R-R Interval• Accordingly lengthen when the heart rate

slow, and shorten when fast • This makes it hard to calculate the interval at

which QT is normal

QTc Interval

• Stand for QT corrected Interval• Corrected for the heart rate• QTc interval calculation is the best way.• Normal QTc : 0.410 second• prolonged QTc : > 0.419 second

QTc Interval Equation

QT 1.75(VR-60) QTc

U - Wave

• A small flat wave sometimes seen after the T wave

• Representation unknown• Clinical significance : Hypokalemia Hyperkalemia Inaccuracy in measuring QT segment

Additional Intervals

• R-R Interval• The distance between

peaks of R waves in two consecutive QRS

• P-P interval• Distance between two

identical points of one P to the next

• These intervals are useful in evaluation of Rhythm