ECG (Electrocardiogram).

Overview:

ECG also is known as the EKG which is an abbreviation of the word of the electrocardiogram. ECG that stands for Electro Cardio Gram which is a diagnostic tool used for detecting & recording the electrical activity of the heart.

History:

Considering the history of this device, there are 3 important persons can be declared as follows.

1. Dr.Alexander Muirhead 

2. British Physiologist Dr.Augustus D.Waller 

3. Dutch Physiologist Dr.William Einthoven

In 1902 Dr.William Einthoven was able to publish the first electrocardiogram recorded on a string galvanometer.

Dr.William Einthoven

Einthoven was born in 1860 in Indonesia. Before his time, it’s known that Electric currents were produced by blows heart, but this phenomenon could not be quantified exactly without electrodes directly on it. Einthoven's heart completed a series of prototypes wired galvanometers in 1901. Between very strong electromagnets the machine used a thin conductive filament.

The electromagnetic field this would origin the sequence to move at the time the chain passed through the filament. This series would direct a shadow over the delicate role of photo paper when the light was shining. The innovative machine requires cooling water for advanced electromagnets. It took 5 people to manage and weighed about 600 lbs.

This machine has increased the sensitivity of the typical galvanometer to electrical activity of the heart can be measured despite the isolation of flesh and bones. Einthoven went on to describe the electrocardiographic characteristics of many of cardiovascular disease after developing the galvanometer with cords. Later Einthoven studied acoustics, especially the sounds of the heart that he had investigated with Dr.P Battaerd. After that, he died in Leiden and was buried in the reformed cemetery Haarlemmerstraatweg Church in Oegstgeest.

Introduction:

An electrocardiogram is a record of electrical impulses generated inside the heart. These impulses cause contraction of the heart muscle. The vector terminology is used to describe electrical impulses.

Vector is a schematic method that shows the strength and direction of electrical impulses. Vector

add them in the same direction and cancel if they point in the opposite direction. However, when they are at an angle to each other, they subtract or add the energy and thus, change the direction of flow.

Sensor devices are using to identify and detect the electrical elements producing by heart every time it hits. The machine is recording these signals and a doctor checks the ECG waveform. An ECG can be prescribed or requested by a cardiologist (s) or any physician who thinks you may have a heart problem. The analysis can be performed by a medical specialist at a hospital, a hospital or your general physician.

Uses Of ECG Machine:

ECG is an adhesive used by other diagnostic tests to help identify and monitor the cardiovascular disease.

Some heart problems, such as fixation, dizziness, dizziness and lips can be used for a symptom investigation.

• Allows detecting the abnormalities of conduction.

• Use to identify a prior heart attack.

• Important in non-cardiac diseases. Ex:- Hypothermia, Pericarditis, Chamber hypertrophy, Arrhythmias.

• Helps detect electrolyte disturbances.

• Measure heart rate and heart rhythm.

Types of the ECG Machine:

ECG machine consists of Unipolar & Bipolar electrodes, amplifiers, connecting wires, output /display.

And there are two types of ECG machines called:

• Single Channel which consists of one recording system and one amplifier. 
• Multi-Channel devices which have 12 standard leads configuration that detects heart signal using a microprocessor. 

Single Channel ECG Machine:                                                                Multi-Channel ECG Machine:

Accessories of the ECG machine:
They are as follows:
1. ECG Clamps

These clamps are connected as the limb leads to the patient’s right arm, left arm, right leg, left leg.










2. Patient Cable

This patient cable is connected to the ECG machine and the other ends of the cable are connecting to the leads. This cable is designed to measure the ECG and the impedance respiration of the patients.






3. Chest Electrodes

There are six chest electrodes/bulbs are used to detect primarily the heart’s frontal plane electrical activity.








4. ECG Gel

This ECG gel is used to improve the conductivity between the electrodes and the skin of the patient.










ECG Paper Roll

On this paper, the electrical activity of the heart is recorded and printed. These papers are made of as water-resistant. 

Preparation for the ECG Test:
There are diverse ways to perform an ECG. The test generally involves performing a number of sticky, small sensors, known as electrodes in the chest, arms and legs. They are attached to the ECG recording device. There is nothing special preparing for the patient for the test. You can usually drink and eat in advance.

At first, need to remove the topcoat, and breasts may need to be cleaned before going to attach the electrodes. Hospital clothing cover may be given as soon as the electrodes are placed.

The test takes a few seconds for recording and you must go home immediately or return to the hospital if you are already in a hospital.

Considering the procedure of preparing the Electro Cardio Graph, in the heart, it’s producing tiny electrical impulses which spread through the myocardium or the heart muscle to make the cardiac contract.  Therefore ECG device is important to represent in composite action of potential that is generated by depolarization and repolarization of all cardiac cells which have the following physiological properties:
• Automaticity – Ability to initiate an impulse
• Excitability – Ability to respond to a stimulus
• Conductivity – Ability to transmit an impulse
• Contractility – Ability to respond with pumping action of the heart

Types of ECG Tests:
There are three types of ECG Tests.

• Resting ECG –  while you're lying down in a comfortable position

• Stress or Exercise ECG – while you're using an exercise bike or treadmill

• Ambulatory ECG – the electrodes are connected to a small portable machine worn at your waist so your heart can be monitored at home for 1 or more days

How ECG Machine Works:

Switch on the ECG machine and check the ECG display/monitor parameters and all the accessories are cleaned and ready to connect to the patient. When the electrical signals are generating through the heart, by the connected ECG electrodes, it’s recorded the timing and the potential of the signal in a graph on the ECG display/ monitor. Therefore after connecting the machine to the patient leave 1-2 minutes and then start to record the ECG trace of the heart

Einthoven's Triangle and this theory applied in ECG device. This Einthovans triangle uses in the Electrocardiography as imaginary triangle using three limb leads to check whether there is incorrect placement of the leads of the patient. According to Einthoven's law, the ECG machine records the activity which is taken the three limb leads simultaneously.  And the following relationship equations of these three bipolar limb leads can be declared as given below.
1) I+II+III=0
2) I+(-II)+III=0
3) I+III=II

Therefore the summation of the electric potential of any two bipolar limb leads out of the three limb leads is equal to the value of the other third bipolar limb lead.

Einthoven’s Triangle

Block Diagram of the ECG Machine:

This is a block diagram of a basic single-channel ECG machine and the dotted line of the diagram shows the separation of the circuit for patient’s protection between the operation circuit from isolated supply and the main power supply.

Anatomy of the Heart:

Anatomy of the heart can be pointed out as follows-

Anterior view of the human heart.

• It’s a  muscular organ & it looks cone shape .
• Base is located above and apex is located below.
• The inclination of the heart at the left side
• Approx weight of it is 300gms
• Consists of two atriums & two ventricles separated by valves

Conduction Physiology of the Heart:
Location of the SA (Sinoatrial) node and AV (Atrioventricular) node in the right atrium of the heart is important to generating electric impulses of the heart.

Conduction system of the heart.

Therefore the system of the electrical conduction of the heart is beginning by generating electric impulses in the SA node also acknowledged as the pacemaker of the heart. Then it spreads throughout the internodal routes to the AV node.  This AV node is conscientious for transmission of the impulse as of the atria to the ventricles. There is a delay while the depolarization and this impulse continuous throughout the AV bundle & behind the left and right bunch of branches of the ‘Purkinje fibers’. This bundle conduct the impulsion to ventricles covering all parts of myocardium cells causing contraction due to action potential. 

The most popular cardiac controller  or the pacemaker is the SA node. Atrial cell, AV node, its node, ligaments, Purkinje fibers and myocardial cells are other objects of cardiac stimulation. When the SA node fails, they can start the pulse slowly.

ECG Leads:

ECG device consists of 12 Leads. They are six limb leads and six chest leads.

Limb leads consist of unipolar three leads and bipolar three leads.

• V1- fourth intercostal space at the right sternal border
• V2- fourth intercostal space at the left sternal border
• V4- fifth intercostal space at the midclavicular line
• V3- midway between V2 and V4
• V5- at the same horizontal level as V4 in the anterior axillary line
• V6- at the same horizontal level as V4 in the midaxillary line.

The limb leads I, II and III are the bipolar limb leads and the other three leads are the limb electrodes those are the unipolar limb leads. 

The pair of electrodes, which consists of a neutral conductor and an extremity electrode. "Reference line" that was created by connecting the additional two limb positions of the ECG amplifier to the negative electrode. 

Or else in other side, Each line has the positive end on the consequent limb line and runs straight to heart, the place of its "negative" end involving between the other two limbs. These are considered to be as guide augmented unipolar limbs. 

The voltage recorded linking the left arm is the limb lead and the neutral reference lead is called Lead aVL; The right arm limb guide is also aVR and the left Leg guide is aVF.

The following diagram shows the ECG electrodes placement of the human body and the relevant recordings of each and every electrode’s configurations.

Anatomical representation of the placement of the electrodes

Measuring ECG:

Normally the ECG is measured from the skin surface, what can be done by placing two electrodes directly on the skin and read the possible difference between them. This is possible because these signals are sent throughout the body. 

Again, as noted above, the characteristics of the detected waveform depend not only in the amount of heart tissue involved, but also further orientation of the electrodes relative to the dipole. That is, the ECG waveform appears small different when measured from different electrode positions, and ECG is usually obtained using different electrodes locations or settings, which is lucky standardized by the general application of certain conventions.

Components of the ECG trace: 

Typical ECG wave form as follows-

ECG waveform

• P Wave – Depolarization of atriums. Time taken 0.08s - 0.1s

• QRS Complex – Depolarization of ventricles. Time taken 0.06s – 0.1s

• T Wave – Repolarization of ventricles. 

Safety and Precautions for the Machine:

Before going to connect the device to the patient following points should be considered to get an accurate electrocardiograph.

• Always keep the device in a dust-free environment avoiding moisture.

• Should isolate the device from electronic devices, mobile phones, radiography equipment.

• Use 3 prong power supply cable with the machine.

• Make sure always the ECG Patient cable is not tied prevent damaging.

• Properly cleaned the gel of the ECG electrodes and ECG bulbs.

• Always check whether there is sufficient paper roll.

• Clean the thermal printer head.

• Check the display whether it’s showing the measurements of the parameters including speed, date, patient details, etc...

Taking into account the above points as Preventive Maintenance for  the device and now it is totally ready to be functioned. In order to get the betterment result, should advise the patient not to tremble the body and not to talk. 

Then apply enough gel on the cleaned limb and chest electrodes, and place on the body properly. 

Before going to print the paper let give few minutes to reduce disturbances affecting from noises and diagnose the chest leads readings and record it on the ECG thermal paper.

Troubleshooting:

There are some troubleshooting techniques that can be considered as follows-

Article Contributed By:-

👉 Darika Nirujani Nanayakkara