Renal artery stenosis (RAS) has been shown to cause a reduction in the index of maximal systolic acceleration (AImax: the maximal acceleration of flow waveform in early systole divided by the peak systolic velocity) of blood in the renal interlobar arteries, caused by local dampening of the pulse wave. In previous studies, AImax demonstrated diagnostic accuracy in terms of negative predictive value, which is useful for screening, but had a relatively low specificity. We hypothesized that an upstream focal resistance, such as an aortic stenosis or aneurysm, could act in the same way as RAS, thus generating false positives in non-stenotic kidneys. We studied 226 patients who underwent a complete protocol for RAS screening. AImax was 6.2 ± 2.9 s–1 and 13.4 ± 3.5 s–1 (mean ± standard deviation) in stenotic and non-stenotic kidneys, respectively. Diagnostic accuracy of ultrasonography with respect to the benchmark of renal computed tomography or magnetic resonance angiography (significant RAS cutoff ≥50%) resulted in 97% sensitivity, 94% specificity and a negative and positive predictive value of 99% and 55%, respectively. Using logistic regression for unexpectedly low AImax in non-stenotic kidneys (AImax cutoff ≤ 9.0 s–1), aortic pathology, such as aortic valve stenosis or aortic arch dilation (as assessed by echocardiography), was found to be the only significant predictor (Χ2 = 33.8, p < 0.0001) of false positive cases compared with clinical and hemodynamic variables. We concluded that the aortic valvular and non-valvular pathology can act as a proximal resistance that can attenuate the Doppler flowmetric parameters, which explore the flow waveform in the renal parenchymal arterial circulation, thus mimicking the presence of a focal resistance in the peripheral vascular region explored.
