Correlation of hemodynamic impact and morphologic degree of renal artery stenosis in a canine model

In a noninvasive comprehensive magnetic resonance (MR) examination, the mor phologic degree of renal artery stenosis was correlated to corresponding ch anges in renal artery flow dynamics. Different degrees of stenosis were cre ated with the use of a chronically implanted inflatable arterial cuff in se ven dogs. For each degree of stenosis, an ultrafast three-dimensional gadol inium MR angiography with high spatial resolution was performed, followed b y cardiac-gated MR flow measurements with high temporal resolution for dete rmination of pulsatile flow profiles and mean flow. Flow was also measured by a chronically implanted flow probe. In three of the dogs, trans-stenotic pressure gradients (DeltaP) also were measured via implanted catheters. Fi ve different degrees of stenosis could be differentiated in the MR angiogra ms (0%, 30%, 50%, 80%, >90%). The MR flow data agreed with the flow probe w ithin +/-20%. Stenoses between 30 and 80% gradually reduced the early systo lic peak (Max(1)) of the flow profile but only minimally affected the midsy stolic peak (Max(2)) or mean flow. Stenoses of more than 90% significantly depressed mean flow by more than 50%. The ratio between Max(1) and Max(2) ( Rmax(1/2)) gradually fell with the degree of stenosis. The onset of signifi cant mean flow reduction and DeltaP was indicated by a drop of Rmax(1/2) be low 1 to 1.2. Thus, the analysis of high-resolution flow profiles allows de tection of early hemodynamic changes even at degrees of stenoses not associ ated with a reduction of mean flow. Rmax(1/2) allows differentiation of the grade of hemodynamic compronrise for a given morphologic stenosis independ ent of mean flow in a single comprehensive MR examination.