Ultrasound velocity criteria for renal in-stent restenosis

Renal artery stent placement is a recognized treatment for patients with hemodynamically significant renal artery stenosis when medical therapy fails. Duplex ultrasound (DUS) is the primary method used for noninvasive assessment of renal artery patency. Arterial stents alter the compliance of the artery, which could make the standard reference values, based on native renal artery velocities, inaccurate. This study attempted to determine DUS criteria for renal artery in-stent restenosis (ISR).

We studied 67 consecutive patients with suspected renal artery ISR based on abnormal renal DUS results, defined as peak systolic velocity (PSV) >or=200 cm/s and renal/aortic velocity ratio (RAR) >or=3.5. The ISR patients were compared with 55 consecutive nonstented patients who underwent renal DUS evaluation and renal angiography. Those with >or=50% angiographic narrowing in each group were analyzed, and renal PSV and RAR were compared.

In the 67 patients with renal stents and 55 patients without renal stents, a statistically significant correlation was found for both PSV and RAR in detecting renal ISR and renal artery stenosis as defined by quantitative angiography (P = .02). For any level of angiographic stenosis >or=50%, the ISR group had relatively higher PSV and RAR compared with the nonstented group. Receiver operating characteristic curves indicated that PSV >or=395 cm/s or RAR >or=5.1 were the most predictive of angiographically significant ISR >or=70%.

The current DUS criteria for native renal arteries may overestimate the degree of angiographic ISR due to changes in compliance. We recommend that DUS laboratories make adjustments in PSV and RAR obtained by DUS when monitoring the patency of renal stents for ISR.