Multimodality Investigation of Intermediate Culprit Lesion With Negative Fractional Flow Reserve in Patients With no ST-segment Elevation Acute Coronary Syndrome.

Acute coronary syndrome without ST-segment elevation (NSTE-ACS) is by far the most frequent acute coronary syndrome (ACS) in the western world. In most of the cases, it is caused by a clearly identifiable culprit lesion, configuring a significant angiographic stenosis (>70%), with flux limitation and typical aspects of unstable plaque (thrombosis). In these cases, the one and only treatment is stent implantation. In a small percentage of patients (10-15%), NSTE-ACS is caused by an angiographically intermediate lesion (40-70%). This lesion is identifiable as culprit, but without the typical signs of unstable plaque.

In patients with stable coronary artery disease (SCAD) presenting with this type of lesion, fractional flow reserve (FFR) is the actual gold-standard for ischemic burden evaluation. Several studies showed that if FFR value is ≤0.80, the treatment with percutaneous coronary intervention (PCI) is associated with a significant reduction of hard cardiovascular events. When FFR is negative (>0.80), optical medical therapy showed a better outcome when compared to percutaneous intervention. In NSTE-ACS, FFR evaluation of intermediate lesions is still mandatory, as a recent study showed a better outcome in patient with positive fractional flow reserve treated invasively with stenting compared to patients treated solely based on angiography (1). When FFR is negative, several authors and studies suggest that further imaging techniques are needed. In this subgroup of patients with intermediate stenosis without angiographic evidence of plaque rupture, European Guidelines (2) suggest utilization of intravascular ultrasound-near infrared spectroscopy (IVUS-NIRS) or optical coherence tomography (OCT) in order to better characterize the culprit plaque. At the same time, the therapeutic strategy is left to the operator's discretion: some implant a stent in order to reduce occurrence of future events, while some others leave the patient in optical medical therapy without stent implantation. Moreover, in these patients, it is still unclear the pathophysiology of the disease leading to ACS. In the last years, researchers focused their attention on plaque erosion, deemed to be responsible for most of these NSTE-ACS (3). An imaging study evaluated the incidence of plaque erosion in patients with ACS (4). This study enrolled an heterogeneous group of patients, evaluated with a single imaging technique (OCT).

Based on these background, the investigators hypothesized to perform a prospective single-center data registry on this highly selected subgroup of patients: NSTE-ACS with culprit intermediate lesion with negative FFR evaluation.

Investigators will enroll consecutive patients with NSTE-ACS with a culprit intermediate stenosis between 40 and 70% and in whom FFR evaluation will result negative (>0.80). In these patients, the operator will perform IVUS-NIRS and OCT and a blood sample to evaluate endothelial function as per our previous experience (5). The study has no control group. Endothelial function and inflammatory state will be evaluated in all patients and will be compared to those obtained by patients enrolled in the NATHAN NEVER study (NCT02519608, Study ID: 150497)(5).

Aim of the present study is to understand whether in this group of patient endothelial function is impaired and which information is given by intracoronary imaging (presence of plaque erosion). The present study is a prospective data collection. Thus, a formal sample size calculation is not applicable. Contemporaneously, for pilot studies, at least 30 patients are recommended (6).