Functional assessment of coronary stenosis: it does make sense, but why don't I do it more often?

and at 6 months follow-up. As in other studies, there was only moderate correlation between coronary flow velocity reserve and diameter stenosis in lesions of moderate severity and the cut-off of coronary flow velocity reserve was 1·9 for patients with intermediate lesions. There are some known limitations with the use of Doppler coronary flow velocity reserve determinations. To obtain a good signal of the instantaneous blood flow velocity it is necessary to achieve optimal placement of the Doppler wire in the vessel axis. Blood flow velocity can be influenced by the severity of the stenosis and by changes in vessel diameter. Coronary flow velocity reserve, although quite reproducible, is very sensitive to haemodynamic changes and microvascular function, and therefore able to give variable threshold values, particularly in moderate stenosis. However, a coronary flow velocity reserve <2·0 usually corresponds to reversible myocardial ischaemia. The main DEBATE study has defined, as optimal cut-off criteria for predictors of clinical events (symptoms, need for target vessel revascularization and angiographic restenosis) after balloon angioplasty, a diameter stenosis of 35% and coronary flow velocity reserve of 2·5. Because of these limitations, fractional flow reserve with the advantage of only measurements of mean distal coronary pressure and mean aortic pressure performed during maximal hyperaemia, seems to be a more attractive method. It is independent of driving pressure and other loading conditions, applicable in three-vessel disease, incorporates the contribution of the collateral blood supply to maximal myocardial perfusion, is highly reproducible and independent of the position of the wire tip. By definition, its normal value is equal to 1 (or 100%) for any vessel and several studies have established that a functionally significant stenosis has a fractional flow reserve 0·75. The problem of which is the better method to assess the functional significance of a moderate stenosis is, however, not yet solved. Both seemed to be complementary, as fractional flow reserve is specific for epicardial stenosis and coronary flow velocity reserve incorporates both the artery and the microvascular circulation, and neither takes into account stress-induced vasoconstriction that may occur in coronary atherosclerosis. Also, as many studies including the present work of Piek et al. have See page 466 for the article to which this Editorial refers