Ultrasound is sound beyond the hearing range of the human ear which normally can detect sounds of frequency between 20 to 25,000 cycles per second. Echocardiography or cardiac ultrasound utilises high frequency sounds of 2 to 7 million cycles per second or megaHertz per second to image the heart.

Echocardiography or Echo for short, is an extremely useful diagnostic tool to investigate non-invasively and in real-time, the structure and function of the heart. It is relatively simple to use, painless, fairly inexpensive, safe, does not use radiation and yields extremely useful information.

The Development of Echocardiography
Rudimentary echocardiography was first introduced in 1954 by Elder and Hertz with M-Mode echocardiography which provided an ice-pick view of the heart recording the movement of cardiac structures, in particular the mitral valve. It was very useful in diagnosing mitral valve stenosis (or blockage) at that time.

This was followed by 2-D or 2 Dimensional Echo in the mid-1970's where slices of the heart could be displayed on the monitor allowing the doctor to look inside the heart to study the heart valves, the heart muscles, the cardiac chambers and the surrounding structures in real-time.

Doppler Ultrasound soon followed. Using the physics of Doppler, blood flow velocities in the cardiac chambers or blood vessels, pressure gradients across narrowed valves or pressures in various cardiac chambers could be measured with accuracy. Cardiac output, valve areas, severity of valve stenosis or regurgitation or shunts could be derived from these Doppler measurements. All these hemodynamic data previously only obtainable through cardiac catheterisation could now be obtained non-invasively using echocardiography. This was a tremendous advance for Cardiology.

In the mid-1980's the flow of blood could be depicted in colour on the Echo machine. This was called Colour Flow Imaging. Blood flow within the blood vessels, across the valves and heart chambers could be visualised. Abnormal flows such as those produced by leaking or blocked heart valves and shunting of blood could be seen using Colour Flow Imaging and the severity assessed.

How Cardiac Ultrasound is Produced
The images and the Doppler information are acquired using the transducer or probe. The tip of the probe houses the piezo-electric crystals that generate the ultrasound when stimulated by electricity. The returning sound waves that bounced back from the various structures of the heart are processed by the computer and the images are created on the monitor, thus allowing a dynamic study of the heart.

Types of Echocardiographic Study

1) Transthoracic Echocardiography (TTE)
This is the most frequently and routinely used. In TTE the probe is placed on certain standardized areas of the chest wall called windows and pointed in certain directions so that standard views are obtained and recorded. Views that are routinely acquired are the LONG AXIS VIEWS and the SHORT AXIS VIEWS.

2) Transoesophageal Echocardiography (TEE)
In patients who are obese or have hyperinflated lungs or chest wall deformities, the images produced can be very poor because air bone and fat are poor conductor of sound. As a result, Trans-Oesophageal Echo (TEE) was introduced. TEE uses a flexible endoscope with a ultrasound probe at the end. The procedure is much like in Gastroscopy and is conducted under light or no sedation. The probe is introduced into the oesophagus and the stomach and images are obtained from the back of the heart. The images produced are far superior to that obtained through the trans-thoracic windows. The disadvantages are that the procedure is more difficult, is invasive, is relatively unpleasant, has a slight risk, is more expensive and less time is available to study the heart as it is dependent on the patientÕs tolerance of the endoscope.

3) Stress Echocardiography
This procedure studies the wall motion and contractility of the heart muscles at rest and after stressing the heart using drugs like Dobutamine or exercising on a treadmill or the bicycle. The images are compared side-by side. This is an accurate non-invasive way to detect coronary artery disease when treadmill stress tests cannot be done for various reasons or is likely to produce false positive or un-interpretable results. The accuracy of the test in the detection of coronary artery disease is between 80 - 95%.

Uses of Echocardiography
Echocardiography is extremely useful in the diagnosis and evaluation of:

1. Valvular Heart Disease
2. Congenital Heart Disease like 'hole in the heart'
3. Coronary Heart Disease
4. Cardiomyopathy or diseases of heart muscles
5. Pericardial Disease or diseases of the heart covering
6. Left ventricular function or how well the left ventricle is functioning

Echocardiography is also performed on the foetus in-utero to detect congenital heart disease allowing timely surgical intervention in cases of severe cardiac abnormality. Besides the Echo Lab, the Echo machines are being used in the Operating Theatres to monitor cardiac procedures like percutaneous widening of narrowed valves, closure of holes in the heart, valve repair, etc. It is often used in the Emergency Room or Intensive Care to diagnose cardiac emergencies such as ruptured aneurysms, dissecting aneurysms, cardiac tamponade, etc.

With rapid technological advances, more and more clinical applications are being introduced including 3 -Dimensional imaging, Intra-vascular imaging, Intra-operative imaging, Tissue imaging and Tissue Doppler. Normah has an advanced Echo machine with the capability to do 2- D, M-Mode, Doppler studies and Colour flow imaging as well as Stress Echo, Transoesophageal Echo and Paediatric Echo.

DR POK YANG HANG
Consultant Physician