Assessment of coronary physiology - the evidence and implications.

Use of angiography for the assessment of coronary lesions is limited by its inability to provide information regarding the functional significance of stenoses. A number of studies have demonstrated the presence of ischaemia to be the most important determinant of the benefit associated with coronary revascularisation in stable coronary artery disease. Assessment of intra-coronary physiology can guide percutaneous coronary intervention, and is often used for angiographically borderline stenoses. There is now increasing evidence to suggest that more routine use can improve clinical outcomes. Fractional flow reserve (FFR) is the most established measure of intra-coronary physiology, but is currently under-utilised. The main drawback of FFR is the dependence on a pharmacological infusion to maintain hyperaemia. An alternative technique which measures flow at a specific point in the cardiac cycle (instantaneous wave-free ratio) has been developed which obviates the need for hyperaemia and may replace FFR as the default measure.