PROJECT ABSTRACT Transesophageal echocardiography (TEE) is an ultrasound-based cardiac imaging procedure frequently used to facilitate informed surgical decision making and manage intraoperative complications during the quarter million cardiac surgeries performed in the US each year. And yet, there is no randomized evidence to support the use of intraoperative TEE in any type of cardiac surgery. This lack of randomized evidence is particularly problematic in isolated coronary artery bypass graft (CABG) surgery because observational comparative effectiveness studies are conflicted regarding the association between improved postoperative outcomes with (vs without) intraoperative TEE. Complicating matters, TEE is an invasive procedure where its unconfirmed clinical benefits may not outweigh its confirmed risks of gastroesophageal injury. The questions surrounding the unclear clinical efficacy, unknown real-world effectiveness, and undefined risk-benefit ratio of intraoperative TEE during isolated CABG surgery is a critical evidence gap with clinical equipoise that has resulted in widespread practice pattern variability and a near 50/50 split in TEE (vs no TEE) intraoperatively. Thus, the overall objectives of this K23 research will leverage this existing clinical equipoise and practice pattern variability to generate the required foundational data necessary to inform a future, multicenter, randomized controlled trial (RCT) that could resolve the questions surrounding the clinical efficacy, effectiveness, and risk- benefit ratio of intraoperative TEE use (vs lack of use) during isolated CABG surgery. To that end, three aims will test the central hypothesis that among a routine isolated CABG surgery population (i.e. a population suitable for randomization given the absence of valve disease), the treatment effects of intraoperative TEE on postoperative clinical outcomes after isolated CABG surgery will vary among subgroups (aim 1) and that randomizing routine isolated CABG surgery patients to either default (i.e. obligatory) or as-needed (i.e. backup) intraoperative TEE will garner adequate participation by stakeholders (aim 2), and demonstrate enough practical feasibility in a single-center, pilot RCT conducted at the Candidate’s institution (aim 3), to accomplish on a larger scale in a future, multicenter RCT. The information gained from completion of these three aims will provide the preliminary data required to inform subsequent, multicenter clinical trial(s) comparing perioperative clinical outcomes among routine isolated CABG surgery patients randomized to default vs as-needed intraoperative TEE. In combination with a structured course of mentoring, and a research training plan heavily focused on the how to plan, design, and conduct randomized clinical trials, this K23 will be the foundation for the Candidate’s progression toward becoming a leading clinical trialist and comparative effectiveness researcher dedicated to improving clinical outcomes...