A Clinical and Computational Study to Improve Brachiocephalic Fistula (BCF) Outcomes

METHOD Subject Population: Subjects for consideration in the study will be those referred from the out-patient nephrology clinic at the University of Chicago or a dialysis unit affiliated with DaVita Dialysis for a primary AVF. Eligible patients are those who are evaluated at the University of Chicago by a transplant or vascular surgeon. If the treating surgeon determines that the patient will have an attempted BCF, these patients will be eligible to participate in this study. The research team will be notified of a potential subject.

Clinical Protocol: After the patient is enrolled, pre-operative labs and work-up will be at the discretion of the surgeon. At the time of the OR, if a BCF is placed, labs will be drawn for viscosity, hematocrit, and ADMA. If it is determined at any time by the treating surgeon that a subject is not a suitable surgical candidate for a fistula due to underlying medical conditions, the subject will be withdrawn from the study. A venogram and Doppler of the cephalic arch will be obtained prior to anastomosis creation. A segment of the cephalic vein and arterial tissue will be collected from the excised amount and sent to the Human Tissue Research Center to be preserved for future assay for histology, cytokines, and growth factors as discussed below. The serum specimens for viscosity, Hct, and ADMA will be transported on ice to IIT for assay. The patient will then have follow up Doppler, venogram, and associated tests according to the same procedure following the schedule provided in table \ref{protocol} for the large-scale prospective study. The clinically obtained measurements of geometry, flow rate, and whole blood viscosity will be used as input to the CFD model that will be used to compute the WSS and other HDP throughout the arch. Patients who develop symptoms of stenosis between protocol measurements will have a venogram performed at the time of diagnosis. These venograms will be considered standard of care, although data may be used for study analysis. In addition, excised tissue samples of the cephalic vein and arterial tissue will be obtained when the access is placed and at each surgical revision and banked for future studies.

A subset of ten subjects from the large-scale study will be invited for a sub study that will involve: 1) more detailed three-dimensional imaging of the cephalic arch using IVUS, and 2) blood flow monitoring via Doppler during dialysis. Subjects who have not undergone previous dialysis treatment will be invited to participate in this optional sub-study. Participation in this sub-study will not affect participation in the main study. The IVUS imaging will provide a three-dimensional image of the vessel geometry and remodeling characteristics of the vein upon which the remodeling index (RI) will be computed [26,27]. Detailed CFD modeling will be carried out on these cephalic arch reconstructions, which will be performed at 0 and 24 months after fistula insertion. This will allow for a detailed prospective study of the evolution of IH, remodeling, and stenosis in the cephalic arch.

For the same ten subjects in the small-scale study, actual venous blood flow will be measured during hemodialysis treatment using a hand held Doppler device in the upper arm cephalic vein as close to the cephalic arch inlet as possible. The Doppler readings will be obtained at dialyzer blood flows of 300, 350, 400 and 450 mL/minute. Three measurements will be obtained at each of four blood flows, and the average at each blood flow calculated. These readings will be taken at 0, 6, 12, 18, and 24 months after fistula insertion. The Doppler data obtained during hemodialysis will be used along with recent clinical venograms and laboratory data outlined above to perform CFD modeling. This data during dialysis treatment will be used to 1) quantify the differences in the HDP for subjects pre-dialysis and while on dialysis, and 2) seek a correlation between the Doppler readings at the various dialyzer flow rates and the onset of CAS. It is expected that formation of stenosis would alter the resistance to blood flow through the arch, thereby altering the flow rate in such a way that a unique signature will be apparent in the Doppler data during the controlled dialysis process. If this is the case, then additional surveillance techniques could be developed for identifying the onset of CAS.

History and Physical: The history and physical will be focused on the dialysis access. The history will include type and problems with cannulation, pain score with cannulation, needle size used, and bleeding complications. The physical exam will include an extensive examination of the access including pulse, description of anastomosis, any evidence of aneurisms, hematoma, inflammation, edema, or swelling of the head and neck.