Pilot Study of the α Prototype NIMBLE System: Feasibility, Safety, and Initial Performance in Non-Invasive Detection of Coronary In-Stent Restenosis

The NIMBLE-I study is a prospective, unicentric, single arm, feasibility clinical trial designed to evaluate a novel medical device for the non-invasive monitoring of coronary stents. The study is being conducted at the Hospital Germans Trias i Pujol in Badalona, Spain, under the supervision of Dr. Oriol Rodríguez Leor, an experienced interventional cardiologist. It is sponsored by NIMBLE Diagnostics, a company developing the NIMBLE system-a non-ionizing, non-invasive prototype based on microwave interferometry (MWI). The motivation behind the study stems from the clinical challenge of detecting in-stent restenosis (ISR), a common complication following stent implantation that affects up to 10% of patients. Current diagnostic methods typically rely on invasive procedures such as coronary angiography or intravascular imaging, which are resource-intensive and carry procedural risks. The NIMBLE system has the potential to address this need by providing a safe, fast, and non-invasive alternative capable of detecting structural changes around coronary stents. The primary objective of the NIMBLE-I study is to assess the technical feasibility of the NIMBLE device in a real-world clinical setting. Secondary objectives include evaluating the safety of the device, generating preliminary data on its effectiveness by comparing its measurements with those obtained from invasive coronary angiography-the reference standard for diagnosing ISR-and collecting usability data to inform improvements in future versions of the device. The study is designed to enroll up to 120 patients of whom 30 will undergo an OCT examination to evaluate the ability of the α prototype to measure ISR. Participants must be adults with previously implanted coronary stents who present with symptoms suggestive of ISR-such as chest pain or ischemic changes on an electrocardiogram-and are already scheduled for diagnostic angiography. Patients with contraindications such as pregnancy, implanted electronic devices (like pacemakers), or anatomical limitations that preclude correct device positioning will be excluded. The procedure begins with obtaining informed consent from eligible patients. Prior to the scheduled angiographic procedure, the NIMBLE system is used to perform a non-invasive scan. The device, which includes biocompatible transducers, is placed externally over the patient's chest at the level of the coronary stent. Data acquisition does not interfere with standard clinical care. After the NIMBLE scan, patients proceed with their routine coronary angiography as per standard of care. Importantly, operators performing the angiography remain blinded to the results of the NIMBLE device. Data analysis will focus on two main areas. The primary endpoint is the successful completion of NIMBLE measurements without device-related adverse events. Secondary endpoints include the agreement between NIMBLE output-specifically, a calculated metric called %RIS (percent restenosis intrastent)-and angiographic findings. Statistical methods will be applied to assess sensitivity, specificity, correlation, and agreement between modalities. Usability feedback from clinical operators will also be collected to inform future device iterations. The study complies with all applicable regulatory and ethical guidelines, including ISO 14155 and the European Medical Device Regulation (MDR 2017/745). It has been approved by the relevant ethics committee and competent authority before its launch. Each patient's data will be anonymized and handled according to Good Clinical Practice (GCP) standards. Expected outcomes from the NIMBLE-I study include confirmation that the device can be safely and effectively used in a clinical context and that its diagnostic output correlates with invasive imaging findings. Positive results will lay the groundwork for a pivotal clinical trial and advance the development of a tool that could significantly improve the follow-up of patients with coronary stents. Ultimately, this technology could reduce the need for invasive procedures and enable earlier detection of stent-related complications in an outpatient setting.