Echocardiogram: what it shows and how to prepare

What the scan measures

An echocardiogram uses high-frequency sound waves to build a moving image of the heart. Because it shows the heart in motion, it answers questions that a still image cannot.

It measures the size of each chamber and the thickness of the muscle walls; how vigorously the muscle contracts, expressed as the ejection fraction; whether any region of muscle moves poorly, which can indicate previous damage; the structure and movement of the four valves, and whether any is narrowed or leaking; the pressure in the lung arteries, estimated from the flow across the valves; and the lining around the heart, including any fluid.

What happens during the test

You will be asked to undress to the waist and lie on your left side. Small electrodes are placed on the chest to record the heart rhythm during the scan. Gel is applied and the probe is moved across the chest, mostly between the ribs on the left side and beneath the breastbone. Firm pressure is sometimes needed to obtain a clear view, and you may be asked to hold your breath briefly.

No preparation is required for a standard scan. You can eat, drink and take your usual medication beforehand. It typically takes twenty to forty-five minutes.

The variations

A transthoracic echocardiogram is the standard scan described above, performed from the surface of the chest.

A stress echocardiogram images the heart before and immediately after exercise, or during an infusion of a medicine that increases the heart's workload. It is used to assess whether blood flow becomes inadequate under stress, or how a valve behaves under load.

A transoesophageal echocardiogram uses a probe passed into the oesophagus, which lies directly behind the heart, giving considerably more detail. It requires fasting and sedation with throat anaesthesia, and is used when precise views are needed, such as before certain valve procedures or to look for a clot in the upper chambers.

A bubble study involves injecting agitated saline into a vein to look for an abnormal connection between the two sides of the heart, such as a patent foramen ovale.

What it cannot tell you

The most common misunderstanding is that an echocardiogram shows the coronary arteries. It does not. It may show the consequences of coronary disease, such as an area of muscle that moves abnormally after a previous heart attack, but the arteries themselves require CT coronary angiography or invasive angiography.

A normal echocardiogram is genuinely reassuring about the structure and pumping function of the heart. It does not exclude coronary artery disease, and it does not exclude a rhythm disturbance that was not occurring during the scan.

Getting the results

Images are recorded and measurements taken during the scan, then reported. The findings are interpreted alongside your symptoms, examination and other tests. Measurements are reported against expected ranges adjusted for body size, and a value slightly outside a reference range is not automatically abnormal for you. Where the scan is repeated for surveillance, the trend over time is often more informative than any single result.