Learning Curve for Endovascular Abdominal Aortic Aneurysm Repair: Evaluation of a 277-Patient Single-Center Experience

Abstract

Purpose: To determine the minimum number of stent-graft deployments that an interventional team with endovascular skills must do to be considered well trained in endovascular abdominal aortic aneurysm (AAA) exclusion. Methods: The records of 277 consecutive patients (236 men; median age 73 years, range 49–91) undergoing endovascular AAA repair at a single institution between 1994 and 1998 were reviewed. Information was collected on procedural success, conversion, time interval between procedures, operative complications, operative mortality, contrast volume, blood loss, intensive care unit (ICU) length of stay (LOS), and hospital LOS. A first-order differential equation was used to calculate a learning curve based on the success rate. Patients were subsequently divided into 5 sequential groups of 55 patients (the last group had 57 patients). Results: Analyzing the pattern of procedural success to failures, a sharp change in the slope was observed between 50 and 65 trials. The number 55 was arbitrarily chosen to represent the point after which the incremental change in the success rate never exceeded 0.01 (<1 failure per 100 attempts). In the intergroup comparisons, success rate (p<0.04), conversion rate (p<0.0001), and procedural frequency (p<0.0001) were statistically significant when the first 55-patient group was compared to the others. Operative complications (p=0.08) and operative mortality (p=0.16) were numerically but not significantly different. Contrast volume was significantly reduced for the last group (p<0.0001). A Cox regression model identified only procedural frequency (p=0.03) and procedural volume (p=0.04) as predictive of technical success. Performing endovascular AAA repairs at a ≤10-day interval was associated with a >80% success rate. Conclusions: This study shows that not only is the number of procedures important to outcome, but also the frequency with which they are performed. Based on our team's performance data, 55 cases would appear to be the minimum volume and 1 case every 10 days the minimum frequency to obtain good operative results with aortic endografting.