TECHNICAL ASPECTS

The first cardiac ultrasound machines displayed an ultrasound pulse versus depth on an oscilloscope screen. Incorporation of time as a dimension in the late 1960s converted this to a single line M mode display. M mode echocardiography is still in use, but has largely been supplanted by two dimensional (2D) echocardiography,¹ which was developed in the 1970s. In the 1980s, spectral and colour Doppler were developed. The Doppler principle allows determination of the velocity and direction of blood flow, enabling assessment of valvar disease, shunts, and diastolic function. Transoesophageal echocardiography (TOE) was also introduced in the 1980s; initial probes were uniplane but multiplane probes are now routinely used, and there has been progressive transducer miniaturisation. TOE is very safe, with a mortality of less than 1/10 000,² but not completely risk free (table 1) and should be performed by experienced physicians. It is relatively contraindicated in patients with oesophageal disease—for example, varices, stricture, oesophagitis, scleroderma—and may be hazardous in patients with severe coagulopathy or poor respiratory function; it is essential that the performing physician be aware of such conditions. Transthoracic echocardiography (TTE) and TOE are complementary techniques. While TOE avoids image degradation related to the chest wall and lungs, TTE may visualise anterior structures and the cardiac apex better. More windows for Doppler …