Number needed to treat: analyzing of the effectiveness of thoracoabdominal aortic repair.

BACKGROUND: Number needed to treat (NNT) is a method used to calculate the number of patients who need to be treated to prevent one adverse outcome. To analyze the effectiveness of thoracoabdominal and descending thoracic aortic aneurysm repair, we computed the NNT required to prevent one death. METHODS: Between Jan 1991 and Feb 2003, we repaired 1004 aneurysms of the descending thoracic and thoracoabdominal aorta. We followed the patients from surgery until death. Five-year actuarial survival in our population was computed by the Kaplan-Meier method. Natural history data for comparison were taken from the population-based work of Bickerstaff et al., 1982. NNT was calculated as the reciprocal of the risk difference at 5 years. 95% confidence intervals were computed by the method of Daly. RESULTS: Five-year mortality in the population-based cohort was 87 vs. 39% in our treated population, for a risk difference of 48%. 1/0.48=2, indicating that two patients need to be treated to prevent one death at 5 years (95% CI 1.8-2.5, p<0.0001). CONCLUSION: An NNT of two demonstrates the effectiveness of surgical repair of descending thoracic and thoracoabdominal aortic aneurysms when compared to the natural history. By comparison, carotid endarterectomy for symptomatic lesions >70% has an NNT of 15 to prevent a single stroke or death. NNT can also be applied to aneurysm size criteria to estimate the effort required to prevent death or rupture for a given aneurysm size.

Chronic aortic dissection not a risk factor for neurologic deficit in thoracoabdominal aortic aneurysm repair.

OBJECTIVE: chronic aortic dissection has long been considered a risk factor for neurologic deficit following thoracoabdominal aortic aneurysm (TAA) surgery. We reviewed our experience with regard to aneurysm extent and the use of adjunct, (distal aortic perfusion/cerebrospinal fluid drainage), and examined the impact of these factors on neurologic deficit among chronic dissection and non-dissection cases. METHODS: between February 1991 and March 2001, we repaired 800 aneurysms of the descending thoracic and thoracoabdominal aorta. Seven hundred and twenty-nine cases were elective; 196 chronic dissection, 533 non-dissection. 182/729 (24.9%) were TAA extent II. Among these, 61/182 (33%) involved chronic dissection. Adjunct was used in 507/729 (69.6%). We conducted detailed multivariate analyses to isolate the impact of chronic aortic dissection on neurologic morbidity, with other important risk factors taken into account. RESULTS: overall, 32/729 (4.4%) patients had neurologic deficit upon awakening; 7/196 (3.6%) in chronic dissections, and 25/533 (4.7%) in non-dissections. Adjunct had a major effect, reducing neurologic deficit in TAA extent II from 10/36 (27.8%) to 10/146 (6.9%) (p=0.001). However, in univariate and multivariate analysis, chronic dissection did not increase the risk of neurologic deficit, regardless of extent or mode of treatment. CONCLUSION: in contrast to previous reports, we determined that chronic aortic dissection is not a risk factor in TAA patients.