Читать книгу Interventional Cardiology - Группа авторов - Страница 220

Coronary angiography may underestimate stenosis severity most markedly in arteries with a 50–75% plaque burden and in patients with multivessel disease [6]. In patients with stable coronary artery disease, fractional flow reserve (FFR) or instantaneous flow reserve (iFR) is the well‐established physiologic index to assess the functional significance of a coronary stenosis. Studies have used FFR ≤0.80 as the optimal cut‐off point to guide revascularization [29,30], and have reported correlation between FFR values and anatomic parameters (especially minimum lumen area; MLA) derived from IVUS or optical coherence tomography (OCT) [31]. Of the IVUS‐derived measurements, MLA cut‐off values to predict FFR had been widely reported. The correlation between MLA cut‐off points and ischemic FFR threshold ranged from 2.0 to 3.9 mm² in non‐left main coronary artery (LMCA) intermediate stenosis and from 4.5 to 5.9 mm² in LMCA stenosis [4–5,32]. The FIRST (Fractional Flow Reserve and Intravascular Ultrasound Relationship) study, based on a multicenter, prospective registry in the USA and Europe proposed 3.07 mm² as a best cut‐off value to define the presence of myocardial ischemia [33]. In the largest sample‐size and international multicenter study with 822 patients (881 lesions), Han et al. [31] found that best cut‐off value of IVUS‐MLA to define the functional significance (FFR <0.8) to be 2.75 mm². A meta‐analysis of 11 studies comparing IVUS‐MLA with FFR for assessment of intermediate lesions showed that the weighted overall mean MLA cut‐off was 2.61 mm² in non‐LMCA and 5.35 mm² in LMCA to predict a functional stenosis [34].

Atherosclerotic obstruction of the LMCA is present in approximately 4% of all coronary angiograms [35] and is often underestimated by coronary angiography. The main reasons for the discrepancy between angiography and IVUS are the following: (i) diffuse atherosclerotic plaque involvement may lead to a lack of a “true normal” reference segment, (ii) a short LMCA makes identification of a normal reference segment difficult, (iii) the presence of arterial remodeling, (iv) the correlation between angiography and necropsy or IVUS appears to be better in non‐LMCA lesions possibly because of unique geometric and angulation issues in the LMCA [66], and (v) significant inter‐ and intraobserver variability in the angiographic assessment of LMCA disease, especially in ostium location [4–6]. Hence, comparable to LMCA limitations of FFR, IVUS interrogation of the LMCA has multiple shortcomings. Imaging pullback from 2 directions (i.e. from each of its 2 branch arteries) can be helpful.