Читать книгу Interventional Cardiology - Группа авторов - Страница 171

“Normalization” of the pressure wire at the vessel ostium is an essential step and must be performed before the wire is passed into any vessel of interest. The process ensures that intracoronary pressure measurements are made in comparison to the aortic pressure. It provides the operator an opportunity to review the aortic pressure traces and ensure they are not damped in appearance; both anacrotic and dicrotic notch should be present (Figure 7.5). Normalization can be performed with the pressure‐sensor placed at the ostium of the vessel. It is recommended that normalization is formally documented under fluoroscopy to demonstrate wire position during this key step. Normalization should be performed with the introducer needle removed, since this can create an offset of 1–2 mmHg which may be important for borderline stenoses. Active normalization will not only ensure the pressure ratios are 1.0, but also ensure there is no time delay between proximal and distal pressure tracings. This is pertinent for phasic pressure analysis such as iFR, since time offsets will generate incorrect calculation. Operators should visually confirm normalization by assessing the pressure traces, and if a residual issue remains, the normalization should be repeated.

Figure 7.5 Active and Phasic Normalization. (a) The pressure wire sensor should be normalized at the ostium of the vessel. For most pressure wires the sensor is at the junction of the radio‐opaque marker. (b) There is a phase delay between proximal aortic pressure (Pa, red) and distal wire pressure (Pd, yellow); while the Pd/Pa ratio over the whole cycle is 1.0, during the wave‐free period in diastole, the ratio is an erroneous 1.08 at the ostium. Therefore, any measurements taken would be erroneous. (c) After the formal normalization process, the Pd and Pa are now aligned.