Data will be collected via abstraction from central medical charts, physical examinations, and laboratory tests. Standardized instruments will be used. All data will be treated as protected health information and securely stored in a password-protected database.
The primary outcome is the diagnostic value of CEUS compared with CTA for low-grade (lumen reduced by <60%) and high-grade (lumen reduced by ≥60%) RAS, including (1) positive predictive value (PPV); (2) negative predictive value (NPV); (3) sensitivity; (4) specificity; (5) accuracy; and (6) area under the receiver operating characteristic curve.
The secondary outcome is the association between CEUS findings for RMP and GFR measured by a radionuclide imaging method. These variables will include PI, rise time (RT), TTP, MTT, AUC.
Safety end points are the risks of local or systemic adverse events associated with planned imaging methods, including the number (percentage) of patients having allergic reactions, palpitation, dizziness, and contrast-induced nephropathy (CIN). CIN will be diagnosed if all 4 of the following criteria are met: (1) exposure to contrast agent; (2) increase in serum creatinine concentration of 0.5 mg/dL or 25% greater than baseline; (3) increase in serum creatinine concentration occurring 48–72 h after administration of contrast agent and persisting for 2–5 d; and (4) exclusion of alternative major responsible factors. Any new condition (symptom, injury, or significant abnormal laboratory value) that is not present at the beginning of the study will be documented as an unexpected adverse event. Serious adverse events, including death, life-threatening events, hospitalization or prolongation of hospitalization, requirement of medical/surgical intervention, and CIN, will be reported to the Institutional Review Board (IRB) within 24 h.
In this diagnostic study, categorical variables will be compared. In accordance with the previous studies,[16,17] the hypothetical sensitivity is 0.85 and specificity is 0.9, and acceptable variations in sensitivity and specificity both is 0.05. With α as 0.05, 2-tailed test, and accuracy as 0.5, the minimal required sample size is 400. If the attrition rate can be kept at 1 higher than 0.1, a sample size of 440 should be adequate.
Results will be analyzed quantitatively with STATA 14.0 software (Stata, CA). Continuous variables will be expressed as mean ± standard deviation (SD), and categorical variables expressed as frequencies or percentages. Categorical variables will be compared using the χ2 or Fisher's exact test and quantitative variables using the paired samples t-test. The diagnostic value for RAS will be assessed by the receiver operating characteristic curve, including the accuracy, sensitivity, specificity, PPVs, NPVs, and AUC. Pearson correlation analysis will be performed to assess the association between CEUS findings for RMP and GFR measured by a radionuclide imaging method. Statistical significance will be set at 0.05.
This will be a single-center diagnostic study aimed at investigating the feasibility, safety, and accuracy of CEUS for 1-stop assessment of RAS and RMP in patients with suspected renovascular hypertension. The study will provide evidence as to whether CEUS can safely and reliably provide clinical benefits with respect to simultaneous evaluation of RAS and RMP, especially in patients with renal insufficiency.
The CEUS is a reliable imaging method to assess the functional significance of RAS. What extent a kidney is influenced depends on not only the degree of the stenosis, but also how acutely this happens, and the autoregulatory potential of the kidney. Real-time CEUS using microbubble-based contrast agents, which are well regarded for the renal safety, high tolerance, and lack of radiation, can visualize the perfused microvascular bed. Kogan et al  found that CEUS-derived parameters, such as PI, TTP, MTT, and area under the time-dependent intensity curve, were comparable to absolute measurements of blood flow in rat kidney. In humans, CEUS has already been used to the study of various kidney diseases, including acute kidney injury, CKD, and kidney transplantation. By assessing RMP, CEUS could not only evaluate renal dysfunction, but also predict early kidney injury. Furthermore, several clinical studies have showed that angioplasty with or without stenting could not decrease the level of systolic blood pressure, the rate of renal events and cardiovascular complications in patients with high-grade stenosis.[23–25] However, the included patients were with high-grade stenosis, had little viable kidney tissue left, and their chances to improve after revascularization were poor. Therefore, CEUS may be useful to guide the patient selection and efficacy evaluation in angioplasty procedure. Collectively, CEUS can provide real-time, non-invasive, and relative quantitative estimate of RMP and offers great potential in monitoring and predicting renal injury in acute and chronic renal disease. However, there is no international standard for assessing RMP. Hence, well-powered clinical studies are needed to establish the parameters that are optimal for clinical evaluation and the normal range in different patient groups.
This study could make several important contributions to expanding clinical applications of CEUS in patients with suspected renovascular hypertension. First, this study will provide preliminary evidence of the accuracy of CEUS for RAS in real-world practice, especially in patients with low-grade stenosis. Second, this study will provide evidence concerning the safety of CEUS, especially in patients with Stages 4 and 5 CKD. Third, this study will promote the clinical application of CEUS for assessment of renal RMP. Real-time CEUS using microbubble-based contrast agents, which are well regarded for their renal safety, high tolerance, and lack of radiation, enable visualization of the perfused microvascular bed. Thus, CEUS can provide real-time, non-invasive, and relative quantitative estimate of renal RMP and offers great potential for monitoring and prediction of renal injury in acute and chronic renal disease.
The present study has a few limitations. First, this study was a single-center design, therefore, it cannot represent the actual situation of the whole RAS population owing to geographical and regional differences. Second, there are inherent limitations to use an observational method owing to these unmeasured or undefined confounding factors. Third, there is no international standard for assessing RMP, and the normal range in different patient groups is also lacking. Fourth, CEUS is operator dependent. Previous study showed that imaging quality was correlated with the radiologist's experience, and it was markedly higher for radiologists who had performed more than 60 CEUS examination. Fifth, CEUS has an inherent relatively high variability, related to several factors, including the patient, contrast agent used, and machine settings. Stock et al  found that time-related parameters for the renal cortex showed a reasonable repeatability, whereas poor repeatability is present for intensitity-related parameters and those related to inflow and outflow of contrast agent. Furthermore, Lassau et al  showed that AUC and area under the washout are the 2 most reproducible CEUS parameters. Therefore, future studies will require larger numbers of patients, careful matching of key clinical and technical variables to definitively quantify the potential clinical value of one-stop evaluation of RAS and RMP by CEUS for patients with suspected RAS.
In summary, we have designed this study to evaluate the feasibility, safety, and accuracy of CEUS for 1-stop assessment of RAS and RMP in patients with resistant hypertension.
The authors acknowledge Dr. Yang Wang from National Center for Cardiovascular Diseases, Fuwai Hospital, Chinese Academy of Medical Sciences, for study design and sample size calculation. Meanwhile, they also thank Dr. Trish Reynolds, MBBS, FRACP, from Liwen Bianji, Edanz Group China (www.liwenbianji.cn/ac), for editing the English text of a draft of this manuscript.
This study was supported by grants from the Beijing Hospital Clinical Research 121 Project (No. BJ-2018-198) and the Scientific Research Project of Beijing Hospital (No. 2018-001).
There are no conflicts of interest.
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