LAUSR

Coronary angiography is still the gold standard in the diagnosis of coronary artery disease, although its limitations in the assessment of haemodynamic severity of epicardial stenosis are widely recognised [1, 2]. In the 1990s, these limitations of angiography led to the introduction of sensorequipped guidewires measuring pressure and flow to optimise the diagnostic workup during cardiac catheterisation. The most frequently used parameter is the fractional flow reserve (FFR), defined as the ratio of the pressure distal to a lesion relative to the aorta pressure during maximal hyperaemia. The concept of FFR assumes a minimal influence of the microvascular resistance during hyperaemic conditions, although a large variability of microvascular resistance exists even in patients with single vessel disease and a normal left ventricular function [3]. Moreover, this microvascular resistance is also influenced by numerous other factors like hypertension, diabetes, left ventricular hypertrophy and/or diffuse coronary artery disease. The assessment of coronary flow reserve, defined as the ratio of the distal hyperaemic flow relative to baseline flow, may serve as an alternative. However, an accurate assessment of flow velocity is more cumbersome than FFR measurement. Moreover, the use of coronary flow reserve has also been criticised as it is determined by the resistance of the epicardial narrowing as well as the distal microvascular resistance and is therefore considered to be less lesionspecific. The FAME trials have shown the usefulness of FFR and this parameter has emerged as a class I A indication for