Wirelessly Powered Micro-Implantable Stimulation System for Intravascular Implantation Over one million cardiac pacemakers are implanted every year worldwide, of which approximately 200,000 are implanted in the United States (9). In the face of an aging population and increasing pacing indications, these numbers continue to rise. Implantable pacemaker technologies have rapidly advanced since their initial inception in the 1950s with the reduction in the generator size, increase in battery longevity, lead quality, and optimization in pacing algorithms. Despite these advances, most of the pacemaker technologies rely on the transvenous implanted leads for rhythm-control therapy. The potential complications and technical failures involving the lead and the subcutaneous pocket, including lead displacement, cardiac tamponade, pneumothorax, lead fracture and infection have remained (2). For these reasons, Medtronic released the first Food and Drug Administration (FDA)-approved leadless cardiac stimulation device via a minimally invasive delivery to the right ventricle (5, 6). Despite the recent dual chamber implantation (7), the integrated battery introduces new clinical challenges such as device implantation, perforation through the myocardium, and dislodgement. During the last funding cycle, we ameliorated these potential complications by demonstrating the leadless and batter-free micro-pacer that was implanted to the anterior cardiac vein (ACV) for restoring heart beats in the Yorkshire pigs (8). For the next funding cycle, we seek to develop the smallest (2 mm x 10 mm), lightweight (5 mg), and flexible bioelectronics that can be navigated in the tortuous cardiovascular anatomy to the ostium of coronary sinus for implantation into ACV. We hereby propose to develop a soft battery-free and leadless microtubular pacer with enhanced power transfer efficiency for intravascular deployment and implantation to the anterior vein. To test our hypothesis, we have three aims: In Aim 1, we seek to demonstrate an integrated soft tubular pacer via the radiofrequency (RF) receiving unit for myocardial stimulation. We plan to fabricate a tiny pacer harboring soft mechanical properties and microtubular structure with the capacity to convert RF energy into electrical DC pulses for cardiac stimulation. In Aim 2, we seek to demonstrate biocompatibility, flexibility, and stability at the electrical- tissue interface. We will test the biocompatibility of the soft materials with human peripheral blood mononuclear cells (PBMC), and we will evaluate the impedance of the vascular-electrode interface and power transfer efficiency (PTE). In Aim 3, we seek to demonstrate a catheter-assisted deployment of the flexible microtubular pacer to the anterior cardiac vein in a swine model for optimal inductive power transfer from the external transmitter to the internal receiver at RF of 1 MHz. Overall, advances in micro-electronics hold promises for the smallest volume and light-weight ...