INTRODUCTION:

Sound is present in the Earth from its beginning. But people were not aware about its importance in the medicinal field, they considered it as a natural phenomenon that occur in the world like the sounds of a bird, thunder storm, river streams and so on. The ancestors also used this sound to call others or for giving signals to others. As the years goes they came to know about the natural sound reflection that happen in certain regions or the localities of landscape like in the mountain caves, banks of lakes and so on .With the fast going time period peoples also come up with the idea that sound waves get reflected especially in water. This tremendous achievement in the field of acoustics lead to a large invention in the field of clinical diagnosis.

The scientist introduce an echo probe to detect the refluxed sound wave and its interpretation to determine the change in the internal organs .Initially the effect was understood in diagnosis of abdominal problems but latter it’s used in the diagnosis of urological and cardiological problems .The test which usually check the abdomen and pelvis is named as USG.

In a normal individual the hearing limit is 20,000 cycles/second (20KiloHertz) .Yet in an echocardiographic diagnosis commonly use sonic frequency of one to ten million cycles/second (1-10 mHz).The young ones required higher frequency with reference from 3.5-10 mHz. While, it is only 2-5 mHz in the matured ones .The resolution (in an another way the clarity) increases with increasing in sonic frequency.

Definition

Echocardiography is a type of ultrasound test that uses high pitched sound waves to produce an image of the heart(1)

Common parts of echo machine

There are 5 basic components of an ultrasound scanner that are required for generation, display and storage of an ultrasound image. (2)

1. Pulse generator - applies high amplitude voltage to energize the crystals

2. Transducer - converts electrical energy to mechanical (ultrasound) energy and vice versa

3. Receiver - detects and amplifies weak signals

4. Display - displays ultrasound signals in a variety of modes

5. Memory - stores video display

Principles behind the magic

The principle behind echo is same as that of the USG (3)

· Piezoelectric effect – it happens when the transducer is provided with the electrical energy. The piezoelectrical elements in the transducer quiver so fastly to produce the high frequency sound waves.

· Sound waves travels in a linear fashion. Once they reach an area with different sound response, they behave in relation to the law of reflection and refraction.

· The quality of reflected sound waves get varies in response to its travel through different density mediums. The quantity of reflected wave is directly proportionate to the variation in acoustic impedance of the area that it hits

· With the help of piezoelectrical effect the reflected sound is changed into the primitive electrical form and its displayed in the monitor with the help of computer technology.

Modes of an Echo

There are mainly four modes in an Echo analysis

1. M-Mode

The transducer probe is placed directly over the left sternal border. Echo reflection varies in its colour, high reflection is white in , less reflection is gray and no reflection is black. The moving parts appear as wavy signals, while the stationary parts depicts by horizontal lines. However, the blood filled chambers are comparatively free from the effect of Echo.(1)

In the graphical tracing of this mode time is on the horizontal axis and Echo tracing in the vertical axis continuously. It also helps to identify the cardiac dimensions and motion patterns.

2. 2D – Mode

In this mode the waves moves in a sector so that a pie-shaped picture of heart is obtained.This is also called as brightness image mode (B-Mode). The sound waves in B- Mode is produced in three ways .Firstly, multiple crystals are mounded in the same line to develop a curtain of sound. Since it cannot image all the views in a clear way, its use is limited to cardiology. It commonly uses to find out pericardial abnormality and also detection of large vegetations.(2)

Secondly, the mechanical sector scanner in which the sound is created by oscillating the crystals in the transducer that produces Echo in the form of an arc.(1)

Lastly, the sound can also produced by electrically stimulating a group of crystals in an orderly manner. This method is known as phased away transducer .Good picture quality is a hurdle in this mode, thus it necessitate the examiner to place the probe in a place for long time.(2)

3. Doppler Echo

It utilizes the sound waves to identify the blood flow in the cardiovascular system

Basics

Ø In case of stationary object –the transmitted frequency and reflected frequency will be equal

Ø If target moves towards the transducer – the reflected frequency will be greater than transmitted frequency

Ø If target moves away from the transducer –transmitted frequency will be greater than reflected frequency

In case of medical field the moving object is red blood cells. Blood velocity can also be calculated from the difference in frequency of emitted and reflected sound waves. In order to monitor the velocity continuously two transducers are used in the same probe, i.e. One will emit the sound other will detect the reflected sound.(1)

4. Colour Doppler Echo

It is same like Doppler in addition colour code is given in response to the movement of the target

Blue- target moves away from the transducer

Red –target moves towards the transducer

Green or mosaic – when turbulent flow occurs(4)

Verities of Echocardiography

1. Non-invasive technique

This is the usual techniques practiced in the hospitals. This is achieved by placing transducer on different axis over the pectoral region. The axis and the chamber views are explained latter in this article.(2)

2. Invasive technique

a) Transesophageal

This is achieved by placing a 2D echo probe at the distal end of a flexible endoscope .The visuals are archived in various axis. It is helpful in situations where the epi-cardial evaluation is not possible like open heart surgery, prosthetic valve, aortic disorders and intra-cardial mass. Also used as a guidance for invasive procedures like pericardiocentesis or diagnostic catheterization (endocardial biopsy).(4)

b) Intravascular

Transducer (micro) is placed in small catheter so that vessels can be clearly visualise .It is mainly done to image the atherosclerotic plaques adhere to the intimal layer of blood vessel .This technique rarely used to envisage heart from its chambers.(4)

3. Special echo techniques

a) contrast echocardiography

Primarily used to find out right to left shunting of blood in the atria .Agitated saline with small amount of air is injected into the IV line initially. As the bubble reaches the atria, images are taken which gives a clear picture of intra-atrial blood shift .At present commercial dies are using instead of agitated saline since it get easily absorbed into the pulmonary capillaries .(3)

b) Fetal Echo

Used for the evaluation of the fetal heart when it is in mother’s womb. It is used to detect any congenital heart problem in the fetus. The main disadvantage is that it require highly sophisticated instruments.(3)

c) 3D Echo

Technology has improved to image cardiac structures in a three dimensional way. But it requires a lot of commitment by the technologist and electrocardiographer. (3)

Various views in Echo

1. Parasternal Long-Axis View (PLAX)

This is the first view commonly used in an examination. Transducer is placed in the left sternal edge. i .e.2^nd – 4^th intercostal space. Many structures can be seen from this view.(1)

Fig:1 Parasternal Long-Axis View (PLAX)

2. Parasternal Short Axis View (PSAX)

Transducer is placed in the same left sternal edge; 2^nd – 4^th intercostal space. This can be achieved by placing the transducer on an axis between the left hip and right shoulder. Short axis views are obtained at different levels, from the aorta to the LV apex.(1)

Fig :2 Parasternal Short Axis View (PSAX)

3. Apical 4-Chamber View (AP4CH)

Transducer is placed in the apex of the heart. The Apical-5-Chamber view is obtained by slight anterior angulations of the transducer towards the chest wall. The LVOT can then be visualised(2)

Fig : 3Apical 4-Chamber View (AP4CH)

4. Apical 2-Chamber View (AP2CH)

Transducer is placed in the apex of the heart .Good for assessment of Left Ventricle anterior wall and inferior wall(1)

Fig: 4 Apical 2-Chamber View (AP2CH)

5. Sub–Costal 4 Chamber View(SC4CH)

Under the xiphisternum the transducer is placed. The subject lies supine with his head slightly low with feet on the bed and knees are slightly elevated Images can be gained with the abdomen relaxed and during inspiration.(1)

Fig :5 Sub–Costal 4 Chamber View (SC4CH)

6. Suprasternal View

Transducer is placed in the suprasternal notch. The subject is instructed to lie down in the supine position with his head hyperextended. Head should be lightly turned towards the left side. Mainly used to assess the aorta.(5)

Fig:6 Suprasternal View

Fig :7 parts of aorta visualized in suprasternal view

REFERENCES:

1. Braunwald E. Heart disease, a text book of cardiovascular medicine.5^th edition. Saunders publications .1997

2. Mansi A I. Echocardiography.[online].Available from: http://emedicine.medscape.com/article/1820912-overview

3. Garbi M. The general principles of echocardiography.[online]. DOI:10.1093/med/9780199599639.003.0001

4. Stoylen A. Basic ultrasound, echocardiography and Doppler for clinicians.[Online].Available from. http://folk.ntnu.no/stoylen/strainrate/Ultrasound/

5. Foster E. Echocardiographic evaluation of the aortic valve.[online].Available from: http://www.uptodate.com /contents/echocardiographic-evaluation-of-the-aortic-valve picture courtesy http://image.google.coms

Received on 12.05.2015 Modified on 27.06.2015

Int. J. Adv. Nur. Management 3(3): July- Sept. 2015; Page 289-293

DOI: 10.5958/2454-2652.2015.00018.9