Echocardiography

What is an echocardiography?

Echocardiography allows visualisation of cardiac structures, cardiac walls and the velocity of blood flow at certain points in the heart. The technique is an extension of ultrasound examination, using beams of sound at frequencies of 2.5-5 MHz, some of which is reflected at interfaces between tissues of different acoustic impedance.

There are three main echocardiogram techniques

• Cross-sectional - is two-dimensional and gives the impression of a moving picture.

• M-mode - uses a single static beam and appears as horizontal lines with superficial structures at the top and deep structures at the bottom.

• Doppler - uses pulsed wave (useful for low-velocity flow - eg, mitral valve flow), continuous wave (useful for high-velocity flow - eg, aortic stenosis) and colour. Colour Doppler allows the velocity and direction of movement of blood within a heart to be shown and this can be demonstrated as a colour display. Movement towards the transducer is coded red and away from the transducer is coded blue, with turbulent flow shown as a mosaic pattern.

In practice, varying amounts of all three methods are usually used.

Structures visualised with echocardiography

• Valves.

• Four chambers of the heart.

• Wall thickness.

• Amount of muscle contraction.

• Pericardium.

• Intracardiac masses.

• Ascending aorta.

Uses of echocardiography¹

These include:

• Valvular heart disease - valve dysfunction, follow-up of prosthetic valves.

• Abnormal left ventricular function - used to assess any underlying cause and to estimate left ventricular ejection fraction (LVEF).

• Atrial fibrillation- assess structural cause, risk of thromboembolism and likely response to direct current (DC) cardioversion.

• Congenital heart disease.

• Cardiomyopathy.

• Infective endocarditis - including assessment of valvular lesions and their haemodynamic severity.

• After embolic stroke - assess possible cardiac source.

• Pericardial disease - presence of fluid and allows guided (and therefore safe) drainage of pericardial fluid in cardiac tamponade.²

• Thoracic aortic disease - aneurysm, dissection (although CT is an alternative).

Types of echocardiography¹

Transthoracic echocardiogram (TTE)

• TTE is performed with the patient lying on their left side with their left arm behind their head and the transducer placed in the intercostal spaces to the left of the sternum and in the anterior axillary line.

• TTE is the preferred investigation in valvular heart disease because all four cardiac valves can be seen and tested by Doppler, and other abnormalities in ventricular performance can also be assessed.

Trans-oesophageal echocardiogram (TOE)

• TOE is performed under sedation (usually with midazolam) and with facilities for resuscitation. Local anaesthetic spray is used for the upper pharynx and an ultrasound probe is passed into the oesophagus behind the heart to give high levels of resolution of cardiac structures.

• It provides much better views of the posterior structures of the heart - eg, the left atrium, left atrial appendage and descending aorta. It is the investigation of choice for the diagnosis of infective endocarditis (especially of prosthetic heart valves), management of a hypotensive patient in the intensive care unit (not responding to filling) and in the search for a potential cardiac source of thromboembolism.³

• This procedure is invasive and requires patient consent.

Stress echocardiogram

• Can be used during or soon after exercise but an intravenous infusion of dobutamine is often used to induce stress similar to exercise. This is a relatively safe and non-invasive method for the evaluation of patients with coronary heart disease.

• Rest and stress images are obtained and compared.

• It has benefits over standard treadmill exercise testing for detecting myocardial ischaemia.

• Appearance of reversible systolic regional wall motion abnormalities is typical of coronary artery disease.

How to interpret results of the echocardiogram⁴

Some elements of echocardiogram results

Other points to note

• Right ventricle - some laboratories will not comment on the right ventricle if it is normal or unless indicated.

• Diastolic dysfunction - a possible cause of heart failure but not routinely looked for on echocardiogram (if suspect, specify it on the form).⁵

• Strokes and transient ischaemic attacks - there may be a cardiac cause of emboli (eg, patent foramen ovale) and echocardiography may help to detect this (TOE being superior to TTE).³