Assessment of Renal Artery Stenosis Severity by Pressure Gradient Measurements

ObjectivesThe purpose of this study was to define “significant” renal artery stenosis (i.e., a stenosis able to induce arterial hypertension).BackgroundThe degree of renal artery stenosis that justifies an attempt at revascularization is unknown.MethodsIn 15 patients, transstenotic pressure measurements were obtained before and after unilateral stenting. After stenting, graded stenoses were created in the stented segment by progressive inflation of a balloon catheter. Stenosis severity was expressed as the ratio of distal pressure (Pd) corrected for aortic pressure (Pa). Balloon inflation pressure was adjusted to create 6° of stenosis (Pd/Pafrom 1.0 to 0.5, each step during 10 min). Plasma renin concentration was measured at the end of each step in the aorta and in both renal veins.ResultsFor a Pd/Paratio >0.90, no significant change in plasma renin concentration was observed. However, when Pd/Pabecame <0.90, a significant increase in renin was observed in the renal vein of the stenotic kidney, finally reaching a maximal increase of 346 ± 145% for Pd/Paof 0.50 (p = 0.006). These values returned to baseline when the stenosis was relieved. In addition, plasma renin concentration increased significantly in the vein from the non-stenotic kidney (p = 0.02).ConclusionsIn renal artery stenoses, a Pd/Paratio of 0.90 can be considered a threshold value below which the stenosis is likely responsible for an up-regulation of renin production and, thus, for renovascular hypertension. These findings might contribute to better patient selection for renal angioplasty.