Assessment of Renal Artery Stenosis Severity by Pressure Gradient Measurements

Objectives: The purpose of this study was to define "significant" renal artery stenosis (i.e., a stenosis able to induce arterial hypertension). Background: The degree of renal artery stenosis that justifies an attempt at revascularization is unknown. Methods: In 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 (P d ) corrected for aortic pressure (P a ). Balloon inflation pressure was adjusted to create 6° of stenosis (P d /P a from 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. Results: For a P d /P a ratio >0.90, no significant change in plasma renin concentration was observed. However, when P d /P a became <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 P d /P a of 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). Conclusions: In renal artery stenoses, a P d /P a ratio 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.