Snorkel/Chimney Stent Morphology Predicts Renal Dysfunction after Complex Endovascular Aneurysm Repair

Despite the high technical success and midterm patency of snorkel stents, concerns remain about structural durability and its effect on long-term renal function. We sought to evaluate the luminal stability of renal snorkel stents to investigate morphologic predictive factors of renal dysfunction after snorkel/chimney endovascular aneurysm repair (sn-EVAR).

Patients with high quality computer tomography angiography after sn-EVAR between 2009 and 2013 were included for analysis. Luminal diameters of renal snorkel stents were measured on a 3-dimensional workstation at the proximal, main-body junction, and distal locations. Creatinine values and estimated glomerular filtration rates (eGFR) were recorded throughout the preoperative, perioperative, and postoperative course. Acute kidney injury (AKI) and chronic renal decline were evaluated using the risk, injury, failure, loss of function, end stage renal disease (RIFLE) criteria and chronic kidney disease (CKD) staging system, respectively.

52 patients underwent sn-EVAR (33 double renal, 19 single renal) with a 2-year primary patency of 95% at a mean follow-up of 21 months, of which 34 had suitable imaging protocols. In this subset, snorkel stents had mean deformations of -0.14 ± 0.52 (2.8%), -0.23 ± 0.52 (4.6%) and -0.04 ± 0.16 mm (1.8%) at the proximal, junction, and distal segments. Four cases of significant >50% stent collapse occurred during follow-up, all of which occurred at the junctional segment. In the total cohort, 17 (32.6%) and 16 (30.7%) patients developed AKI and chronic renal decline, respectively. Multivariate regression identified larger proximal luminal diameters at latest follow-up (odds ratio 0.67; confidence interval [CI] 0.006-0.740; P = 0.037) as the only protective morphologic risk factor for developing chronic renal decline. No independent predictor factors for AKI were found. Rates of renal decline were significantly worse with smaller measured proximal lumens with a 1-year freedom from renal decline of 50% vs. 77-83% for diameters measured less than 4 mm vs. greater than 4 mm (P = 0.010). Degree of oversizing also affected rates of decline with greater oversizing associated with improved freedom from renal decline at 1 year of 100% vs. 57% (P = 0.012). Using a multivariate Cox model, stent oversizing (hazard ratio [HR], 0.039; P = 0.018) and baseline CKD (HR 0.033, P = 0.004) were the only independent factors, both of which resulted in slower rates of renal decline during follow-up.

Renal snorkel stent grafts maintain a high degree of patency and luminal stability at 2-year follow-up. However, stent collapse remains a rare but concerning risk, with the junctional segment most prone to significant stent deformation. Renal snorkel stents must be critically sized relative to native renal anatomy, and we recommend using at least stents sized ≥6 mm to minimize the risk of renal dysfunction. Frequent and regular radiographic and laboratory follow-up remains important as we further optimize the approach to complex EVAR.