The Association of Aortic Valve Pathology With Renal Resistive Index as a Kidney Injury Biomarker

Abstract

Background: Acute kidney injury (AKI) is a common serious complication after cardiac surgery. Doppler-determined renal resistive index (RRI) is a promising early AKI biomarker in this population. However, the relationship between aortic valve pathology (insufficiency and/or stenosis) and RRI is unknown. This study aimed to investigate RRI variability related to aortic valve pathology.

Methods: In a retrospective review of cardiac surgery patients, RRI and aortic valve pathology were assessed prior to cardiopulmonary bypass using transesophageal echocardiography. Aortic valve status was categorized into four subgroups: normal (insufficiency and stenosis, none/trace/mild), insufficiency (insufficiency, moderate/severe; stenosis, none/trace/mild), combined insufficiency/stenosis (insufficiency and stenosis, moderate/severe), or stenosis (insufficiency, none/trace/mild; stenosis, moderate/severe). RRI and time-matched hemodynamic and Doppler measurements were compared among subgroups.

Results: Of 175 patients, 60 had aortic valve pathology (16 insufficiency, 18 insufficiency/stenosis, 26 stenosis). Compared with the normal subgroup, patients with aortic insufficiency had lower diastolic blood pressure and trough renal Doppler velocities, and higher RRI (0.77 versus 0.69; p < 0.001); patients with combined insufficiency/stenosis also had higher RRI (0.72 versus 0.69, p = 0.042).

Conclusions: Patients with aortic insufficiency and combined insufficiency/stenosis had higher median RRI values compared with normal patients. For these individuals, diastolic flow differences related to aortic insufficiency may explain why their presurgery RRI values often exceeded postoperative thresholds typically associated with AKI. Strategies to account for the potentially confounding effects of aortic insufficiency on renal flow patterns, independent of renal injury, may add to the value of RRI as an early AKI biomarker.