Modern applications of echocardiography

When Prof Inge Edler and his physicist friend Carl Hellmuth Hertz described the use of sound waves to create a moving picture of the heart in 1954, their discovery was pronounced “one of the truly groundbreaking and remarkable innovations of the 20th century”. 

This year marks the 100th anniversary of the Swedish cardiologist Edler’s birth and the 10-year anniversary of his death. His pioneering work on ultrasonic diagnosis in cardiology has earned him the honourable title, the ‘father of echocardiography’. 

In the near 60 years since he and Hertz recorded the first ‘ultrasound cardiogram’, this non-invasive technology has become one of the most rapidly growing medical imaging techniques available, and its ultimate capabilities are still being realised.

Ultrasound is the common denominator between warships, fishermen, obstetricians and cardiologists. High-frequency sound waves were used by the navy during World War II to detect submarines; fisherman use ultrasound to find choice fishing spots; obstetricians can evaluate the foetus of a pregnant woman; and cardiologists can observe the heart of a patient.

Echocardiography, or ‘echo’ for short, is a simple pain-free test that makes use of ultrasound to create multiple images of the heart’s valves and chambers. The picture is more detailed than an x-ray image and involves no radiation exposure. Echo is often combined with Doppler ultrasound to evaluate blood flow across the heart’s valves.

Dr Angie Brown, consultant cardiologist who is president of the Irish Cardiac Echo and Imaging Group, and medical director of the Irish Heart Foundation, said echocardiography is an effective and cost-efficient tool that provides a wealth of vital information, including the size and shape of the heart, its pumping strength, and the location and extent of any damage to its tissues.

It is also one of the most widely used diagnostic tests for heart disease in certain groups of patients. Heart disease is the number one cause of death in Ireland, with almost 10,000 people dying from cardiovascular disease annually – 34% of all deaths.

“Echo is very widely used to diagnose certain types of heart problems as well as to monitor the success of medical or surgical heart treatments. It’s performed mainly by cardiac physiologists and cardiologists, and sometimes anaesthetists or emergency specialists. Echo is a very important tool as it is relatively cheap, relatively quick to do a basic study, and a very mobile technology for assessing patients,” Dr Brown noted.

Basically, in echocardiography, a ‘transducer’ (a microphone-like object which both transmits and receives the ultrasonic waves) is held against the chest of the patient. The transducer transmits a fan-shaped wave of sound. When the sound reaches the heart, it is reflected back, first by one exterior wall, then by internal structures, and finally by the opposite exterior wall. The ‘bounce back’ signals received by the transducer create a cross-sectional picture of the heart. An echo examination generally lasts about 15-20 minutes, though will take longer for complex studies.

Dr Brown explained that an echo is most often ordered to evaluate abnormal heart sounds, such as murmurs, an enlarged heart, unexplained chest pains, shortness of breath, palpitations or strokes, which may be due to blood clots from the heart. 

She continued: “It is used to assess the left and right heart function – both systolic and diastolic – in breathless patients, and the heart valves in patients with murmurs or unexplained breathlessness. It can also be ordered if we think there might be fluid around the heart, called a pericardial effusion. If someone has very high blood pressure we might use an echo to see whether there is thickening of the heart muscles as a consequence of the blood pressure. If someone has a hereditary disease such as hypertrophic cardiomyopathy, which is a thickening of the heart muscle, echocardiograms play an important role in diagnosing this condition.

“In theatre, an echo can be used to guide valve repair or replacement and it can also be used to guide implantation of AICDs – defibrillators – and biventricular pacemakers.

“If patients have a stroke it will be used to see if there is a cardiac source of embolism, and in patients with murmurs and fevers to help exclude endocarditis,” Dr Brown added.

Due to its portability, versatility, relative ease of use, and ability to deliver immediate real-time structural and functional information, echocardiography has become a vital imaging tool in the emergency management of acute cardiovascular conditions. 

“In the emergency situation, echo can be used to exclude cardiac emergencies such as tamponade, aortic dissection, and papillary muscle rupture,” said Dr Brown.

The most common type of echocardiogram used is the transthoracic echo (TTE), which is performed by placing the probe on the outside of the chest wall with a gel-like substance to transmit sound waves into the body. These sound waves bounce off the heart structures, producing images and sounds that can be used by the doctor to detect heart damage and disease.

In addition to creating two-dimensional pictures of the cardiovascular system, an echocardiogram can also produce accurate assessment of the velocity of blood and cardiac tissue at any arbitrary point using pulsed or continuous wave Doppler ultrasound.

Doppler is usually performed along with the TTE and uses sounds and the difference in sounds to measure the speed and direction of the blood flow within the heart. This allows assessment of cardiac valve areas and function, any abnormal communications between the left and right side of the heart, any leaking of blood through the valves (valvular regurgitation), and calculation of the cardiac output as well as the ejection fraction (EF).

A normal EF is around 55-65%. Numbers below 45% usually represent some decrease in the pumping strength of the heart, while numbers below 30-35% are representative of a significant decrease. 

Tissue Doppler imaging (TDI) is a relatively new echocardiographic technique that uses conventional Doppler principles to measure the velocity of myocardial tissue motion. 

Transoesophageal echocardiography (TEE) is more detailed and is used when the transthoracic echocardiography is insufficient or when a doctor needs to get a closer look at the heart. In this type of echo test the ultrasound transducer, like an endoscope, is guided down the patient’s throat into the oesophagus. As the oesophagus is located close to the heart, this invasive procedure allows clear images of the heart structures to be obtained without the interference of the lungs and chest.

A stress echocardiogram is performed during physical activity, for example while the person exercises on a treadmill or stationary bicycle. This test can be used to visualise the motion of the heart’s walls and pumping action when the heart is stressed. It may reveal a lack of blood flow, which can indicate narrowing of the coronary arteries, which may not be apparent on other heart tests. The stress echo is performed just prior to and just after the exercise.

Dobutamine stress echo is another form of stress echocardiogram but instead of exercising to stress the heart, the stress is obtained by giving a medication that stimulates the heart and makes it ‘think’ it is exercising. This test is used to evaluate the heart and valve function when a patient is unable to physically exercise.

“Dobutamine stress echo is more sensitive and specific than standard exercise testing,” Dr Brown observed. “A few centres in Ireland do these tests, with a couple of centres using contrast which further improves the sensitivity and specificity.”

Intracardiac echocardiography (ICE) is a new ultrasound modality that is becoming increasingly available as an alternative to transoesophageal echo to guide percutaneous interventional procedures. ICE uses a catheter with a transducer to obtain safe, real-time images of the heart from within, allowing the heart to be easily viewed during, for example, electrophysiological mapping and ablation procedures. 

The main advantages of ICE over transoesophageal echocardiography include the elimination of the need for general anaesthesia, clearer imaging, shorter procedure times and therefore reduced radiation doses to the patient.

Dr Brown pointed out that ICE is expensive, as it requires a new catheter for each procedure. There are only a handful of places in Ireland where ICE is occasionally used.

“New developments in echocardiography include 3D echo, both transthoracic and transoesophageal, which provides more accurate assessment of complex cardiac anatomy and sophisticated functional mechanisms.” 

“There have also been improvements in image quality over the years and the more recent development of handheld devices that can be used in the field, from roadside to battle field, as well as in situations in hospital where limited information is needed with a portable device to exclude tamponade etc.”

Earlier this year, a team of Belgian researchers evaluated the imaging capabilities of these handheld scanners, comparing their results to high-end echocardiography. They found similar results in image quality, as well as for functional assessment, dimension measurements, and valve lesions.

Decades after Edler’s pioneering work, the cardiac echo has prolonged and improved the lives of many millions of patients. Technology in echocardiography has grown and has become an integral part of the practice of cardiology. 

“Echo has come a long way in the past few years with huge improvements in image quality, increasing portability, and new technologies such as 3D,” agreed Dr Brown. “Though other imaging modalities such as CMR and CT are now more widely available, I think it’s remarkable that we can rapidly take a machine to an acutely ill patient’s bedside and in seconds make a lifesaving diagnosis.”