ELECTROCARDIOGRAPHY điện não đồ

Is calculated by the Nernst equation: E =- 61.5log - Working voltage: when cells in the active state, the inside membrane surface positively charged, negatively charged outer surface -

(ECG-EKG)

Teacher: Dang Tran Huy Student: Nguyen Mai Chi

(ECG-EKG)

1, Overview

2, Clinical signification

3, Physiological basis

4, Block diagram ECG & software

1, Overview

 ECG (electrocardiography) is the process of recording the electrical activity

of the heart over a period of time using electrodes placed on the skin These electrodes detect the tiny electrical changes on the skin that arise from the heart muscle's electrophysiologic pattern of depolarizing during each

heartbeat It is a very commonly performed cardiology test

 In a conventional 12 lead ECG, ten electrodes are placed on the patient's limbs and on the surface of the chest The overall magnitude of the heart's electrical potential is then measured from twelve different leads and is

recorded over a period of time (usually 10 seconds) In this way, the overall magnitude and direction of the heart's electrical depolarization is captured

at each moment throughout the cardiac cycle The graph of voltage versus time produced by this noninvasive medical procedure is referred to as an electrocardiogram (abbreviated ECG or EKG)

 During each heartbeat, a healthy heart will have an orderly progression of depolarization that starts with pacemaker cells in the sinoatrial node,

spreads out through the atrium,

1, Overview

passes through the atrioventricular node down into the bundle of His and into the Purkinje fibers spreading down and to the left throughout the ventricles This

orderly pattern of depolarization gives rise to the characteristic ECG tracing To the trained clinician, an ECG conveys a large amount of information about the

structure of the heart and the function of its electrical conduction system

2, Clinical signification

 ECG is an important parameter of life

 Mission: ECG monitoring, monitoring of the ECG parameters and then analyze and provide timely warning of abnormal changes

 ECG monitoring allows us to identify the current state of the heart: heart activity; fast (>100

beats/min) or slow (<60 beats/min) heart rate and early detection of arrhythmias

 ECG monitoring allows to detect a number of

diseases related to the heart’s activity: myocardial infarction, pericarditis, ischemia,…

3, Physiological basis

a, Basis electrophysiological cell

- There is a difference (gradient) between the concentration of ions in and out of heart muscle cells The difference depends on the permeability of the cell

- Resting voltage: voltage between the inside and the outside of the cell

membrane when idle, the cell inside surface positively charged, negatively charged outer surface Is calculated by the Nernst equation:

E =- 61.5log

- Working voltage: when cells in the active state, the inside membrane surface

positively charged, negatively charged outer surface

- Depolarization : the phenomenon is lost the positively charged outer surface when working voltage

- Repolarization : after depolarization, cells gradually return to equilibrium ion (idle)

3, Physiological basis

 The P wave represents atrial

depolarization

 PR Interval represents impulse

from atria to ventricles

 The QRS complex represents

ventricular depolarization.

 ST segment = isoelectric – part

of repolarization

 The T wave represents ventricular

repolarization.

 QT interval = this interval spans the

onset of depolarization to the completion

of repolarization of the ventricles

 The U wave represents papillary

muscle repolarization

3, Physiological basis

b , The ECG leads and electrodes:

 An eletrode is a conductive pad in contact with

the body that makes an electrical circuit with the eletrocardiograph

 A lead is a slightly more abstract and is the source

of measurement of a vector

 Leads are broken down into three sets: limb,

augmented limd and precodial

 On a standard 12 leak ECG there are only 10

electrodes, which are listed in the table below:

Electrode name Electrode placement

RA On the right arm, avoiding thick muscle

LA In the same location where RA was placed, but on the left arm

RL On the right leg, lateral calf muscle

LL In the same location where RL was placed, but on the left leg

V1 In the fourth intercostal space (between ribs 4 and 5) just to the right of the sternum (breastbone) V2 In the fourth intercostal space (between ribs 4 and 5) just to the left of the sternum V3 Between leads V2 and V4

V4 In the fifth intercostal space (between ribs 5 and 6) in the mid-clavicular line. V5 Horizontally even with V4, in the left anterior axillary line

V6 Horizontally even with V4 and V5 in the midaxillary line

3, Physiological basis

3, Physiological basis

 Limb leads: Leads I, II, III are called the limd leads The electrodes that form these signals are located on the limbs- one on each arm and one on the left leg The limb leads form the points of what is known as Einthoven’s triangle

 Lead I is the voltage between the (positive) left arm (LA) electrode and right arm (RA) electrode: I= LA-RA

 Lead II is the voltage between the (positive) left leg (LL) electrode and the right arm (RA) electrode: II= LL-RA

 Lead III is the voltage between the (positive) left leg (LL) electrode and the left arm (LA) electrode: III= LL-LA

3, Physiological basis

 Augmented limb leads: Leads aVR, aVL, and aVF are augmented limb leads They are

derived from the same three electrodes as leads I, II and III, but they use Goldberger’s

central terminal as their negative pole which is a combination of inputs from other two limb electrodes:

 Lead augmented vector right (aVR) has the positive electrode on the right arm The negative pole is a combination of the left arm electrode and the left leg electrode: aVR =

RA-1/2(LA+LL)

 Lead augmented vector left (aVL) has the positive electrode on the left arm The negative pole is a combination of the right arm electrode and the left leg electrode: aVL =

LA-1/2(RA+LL)

 Lead augmented vector foot (aVF) has the positive electrode on the left leg The negative pole is a combination of the right arm electrode and the left arm electrode: aVF =

LL-1/2(RA+LA)

3, Physiological basis

 Precordial leads:

The Precodial leads lie in the transverse (horizontal) plane, perpendicular to the other six leads The six precordial electrodes act as the positive poles for the six corresponding precordial leads: V1, V2, V3, V4, V5 and V6 Wilson’s central terminal is used as the negative pole

4, Block diagram ECG & software

 Block diagram ECG:

Electrodes

Switch electrodes Filter Amplifier ADC

CPU Source

Data out

4, Block diagram ECG & software

 Switch electrodes: choose leads

 Filter: noise filtering from the inputs to not affect ECG.

 Amplifier: amplifier the ECG.

 ADC: Analog digital converse: convert analog signals into digital signals

 CPU: ECG signal processing to give other devices

 Source : Power supply for devices

4, Block diagram ECG & software

 Software

 Mission : signal processing in order to improve anti-interference ability, the reliability of the

measurements.

 Including automated program analysis measurements

to create favorable conditions for the monitoring of patients.

 Processing algorithms, calibration index ECG waves

is important and fundamental to significantly improve the reliability of the measurement by filter the noise mechanism in the ECG