Intravascular ultrasound (IVUS) provides direct imaging of the coronary arteries, using a miniature ultrasound probe that can be passed down the coronary arteries via a catheter. IVUS probes use very high frequency ultrasound (typically 20-50 MHz) to image the wall of the artery, revealing not just the diameter of the lumen but also the characteristics of any atherosclerotic plaques (Fig. 13.1).

Coronary angiography (p. 113) commonly underestimates the severity of coronary atherosclerosis, particularly when the atheroma is diffusely distributed. IVUS plays an important role in clarifying the extent of coronary atheroma and can help identify obstructive disease that might be overlooked by angiography alone. IVUS has also provided an insight into the phenomenon of coronary artery remodelling, in which arterial diameter can increase as plaque accumulates, preserving the diameter of the lumen (so the vessel looks unobstructed on angiography) even though significant atheroma is present (as revealed by IVUS).

IVUS can also be helpful in guiding coronary artery stenting in percutaneous coronary intervention procedures. Performing an IVUS study immediately after stent deployment allows an assessment of how well-deployed the stent is, i.e. whether it is fully expanded and well-apposed to the walls of the artery.

The use of TOE during surgical procedures has grown over recent years, not only in the assessment of structural heart disease during cardiac surgery but also in monitoring cardiac performance more generally. However, not all patients can undergo such an intraoperative TOE examination, and in these cases epicardial echo provides a useful alternative (Table 13.1).