Sandipan Dasgupta (10MS12) 3 rd year UG, Department of Biological Sciences Electro Cardio Graphy Sandipan Dasgupta, Indian Institute of Science Education.

E C G

Sandipan Dasgupta (10MS12)

3rd year UG, Department of Biological Sciences

Electro Cardio Graphy

Sandipan Dasgupta, Indian Institute of Science Education and Research Kolkata


In this presentation..

• ECG – A thumbnail account.• Brief history of ECG.• Underlying principle of ECG – Physics• Description of the device – Engineering• Clinical significance – Physiology


ECG – A thumbnail account

German: “Electro” + “kardia” + “graphia”

Also, called “Electro-kardio-graphy (EKG)”

A procedure for recording the electrical activity of heart in the form of a graphical representation.

Note:Electrocardiography: The procedureElectrocardiogram: The recording


A brief history:

1872: Alexandar Muirhead attached wires to the wrist of patients to measure the electrical activity.

1877: Augustus Waller measured heart rate in real time using the Lippman‘s capillary electrometer.

1901: Willem Einthoven discovered the string galvanometer, which was thousands of time more sensitive than capillary electrometer.

1924: Nobel Prize in Medicine.


Basic principle

Moving coil GalvanometerConversion of Electrical energy to

Mechanical energy.Moving charges experience a force

in a magnetic field.Current carrying coil undergoes

rotation (by torque due to magnetic field) , proportional to the current in the coil.


Einthoven’s GalvanometerWillem Einthoven invented this device which consists of a filament placed within strong electro magnetic field. The filament moved sideways in proportion to the current through the filament. The current from the human body was conducted to the filament by salt solution


Einthoven’s Galvanometer


The Cardiac CycleCardiac Cycle: the electrical, pressure and volume changes

that occur in a functional heart between successive heart beats.

• Phase of the cardiac cycle when myocardium is relaxed is termed diastole.

• Phase of the cardiac cycle when the myocardium contracts is termed systole.• Atrial systole: when atria contract.• Ventricular systole: when ventricles contract.


Mechanical Changes1. Ventricular Filling Period

[ventricular diastole, atrial systole]

2. Isovolumetric Contraction Period [ventricular systole]

3. Ventricular Ejection Period [ventricular systole]

4. Isovolumetric Relaxation Period [ventricular diastole, atrial diastole]


What does ECG record?These mechanical changes in the heart can be detected by the

monitoring the changes in the electrical impulses from the heart.Situated in the right atrium, is a group of cells

(the ‘SA node’) which generate the electrical impulses by complex change in ionic concentration.

A cell-to-cell propagation of these signals take place throughout the myocardium to bring about the mechanical changes, assisted by AV Node and His-Purkinje fibres.

Since body acts as a resistive medium, these impulses move to the body surface, which can be accurately recorded by ECG.

The strength of the ECG signal is thus, dependent on the mass of tissue excited by the signal.


Modern ECG RecorderIn a standard ECG, 9 electrodes are stationed at various parts

of the body. The differential reading between 2 points of the body is called

a “Lead”.Most commonly, 12 such leads are taken into consideration

and hence called “12-lead standard ECG”.Out of these 12, : 3 are limb leads ( I, II, III) 3 are augmented leads ( aVR, aVL, aVF) 6 are chest leads (V1, V2,V3,V4,V5,V6)The first six monitors heart’s activity in frontal plane, whilst

the last six monitors the heart’s activity in horizontal plane.


The Electrodes positioning The first three electrodes are places in right arm (RA), left arm (LA),

and the left leg (LL). There are also six chest electrodes positioned horizontally around the

left anterior hemi-thorax between the 4th and 5th interspaces.

Lead Position

V1,V2 Right ventricle

V3,V4 Ventricular septum; Anterior wall of the left ventricle

V5, V6 Leftt Ventricle

Lead Coordinate ( °)

I 0

II 60

III 120

aVR -150

aVL -30

aVF 90

Leads from electrodes RA, LA,LL span the entire frontal plane of the body


ECG limb and augmented leadsLeads I, II, III are bipolar while others are unipolar.

o Limb I, II, III are measured by differential reading between three electrodes.

o Leads aVR, aVF, aVL uses the same electrode but a different reference potential called Wilson’s Composite terminal (WCT)

(which approximates to zero)

o Note: 1. I + (-II) + III = 0 (Einthoven’s relation) 2. Lead I,II,III forms a network (Einthoven’s triangle)


The Chest leads Each of the chest leads, are unipolar, measured w.r.t to Wilson

Composite Terminal (WCT). Together with the limb leads and augmented leads, the chest

leads form two orthogonal planes which monitors the electrical signal.

Note: The 12-lead data are NOT orthogonal.


Modern ECG measurements

NOTE: Both the amplitude and the direction of signal is essential for ECG signal


ECG output layoutThe ECG Graph paper is a heat-sensitive substance coated paper in which the data is recorded by heated stylus.

Note: Usual rate of recording: 25 mm/s, but it is customisable.


A 12-lead ECG strip


A resting state ECGKey durations:1. Ventricular systole: 0.3 s2. Ventricular diastole: 0.5 s3. Entire cardiac cycle: 0.8 s

Isopotential line


Interpretation of ECG data

1. P wave: During normal atrial depolarization, the main electrical impulse from SA Node spreads from the right atrium to the left atrium, thus forming the P wave. (80 ms)

2. PR Interval: Measured from the beginning of the P wave to the beginning of the QRS complex. It reflects the time the electrical impulse takes to travel from the sinus node through the AV node and entering the ventricles.(120-200 ms).


3. QRS Complex: Rapid depolarization of the right and left ventricles. Much larger amplitude than P wave, due to large muscle mass of ventricles. ( 80-120 ms).

4. ST Segment: The ST segment connects the QRS complex and the T wave. The ST segment represents the period when the ventricles are depolarized. It is isoelectric. (80 – 120 ms)




5. T wave: Represents the repolarization of the ventricles. The interval from the beginning of the QRS complex to the apex of the T wave is referred to as the absolute refractory period. (160 ms)


ECG are useful…

To detect abnormal characteristics of the cardiac cycle , like:

1. Bradycardia.2. Tachycardia.3. Ischemia.4. Arythmmia.5. Heart Blockage.


Classical electricity and magnetism

Modern Hi-end electronics engineering

Physiology Einthoven’s brilliance

ECG: My Summary


Before concluding…

Modern 12 lead-ECG’s are more sophisticated, compact, easy-to-use….

BUT

They are only as much sensitive, if not more as the Einthoven’s 3 lead string galvanometer, with salt solution electrodes.

Why Einthoven was a genius?


Thank you

Sandipan Dasgupta (10MS12) 3 rd year UG, Department of Biological Sciences Electro Cardio Graphy Sandipan Dasgupta, Indian Institute of Science Education.

Documents

research kolkata slide

recording sandipan dasgupta

sandipan dasgupta 10ms12

research kolkata cardiac

atrial diastole slide

electrical activity

atrial systole

termed systole