Читать книгу Interventional Cardiology - Группа авторов - Страница 193

A key advantage of the NHPRs is that there is less flow interaction between stenoses. Under hyperemia, a significant distal stenosis can cause under‐estimation of a proximal lesion. Alternatively, a significant proximal stenosis can cause over‐estimation of a distal stenosis. As each stenosis alters hyperemic flow conditions it means a pressure gradient measured between two lesions does not predict the pressure gradient after a stenosis is removed. Under resting conditions, this interaction between stenoses occurs much less. Resting coronary flow velocity is preserved despite the presence of even severe stenoses up to 90%. The result is that the transtenotic pressure drop observed distal to a stenosis is resultant only due stenoses proximal to the pressure sensor. In the context of a resting pressure wire pullback, the gradient observed at a given point will be valid for all the disease proximal to that location. If a given stenosis is removed, then resting flow velocity does not change significantly meaning residual pressure gradients are preserved. Therefore it becomes possible to predict the physiology after PCI [22,43]. The expected iFR or other NHPR value is computed under the assumption that the intervention is ideal without any residual gradient in the treated segment. In that regard, it can provide a target physiological value for the real‐world intervention (Figure 7.8). It can also permit multiple different stenting strategies to evaluate their potential physiological benefit. In some cases, a limited interventional approach may be sufficient to achieve a good result, while in others more extensive stenting may be required.