Management of transplant renal artery stenosis

Transplant renal artery stenosis: utilization of machine learning to identify ancillary sonographic and doppler parameters to predict stenosis in patients with graft dysfunction

PURPOSE

To determine if ancillary sonographic and Doppler parameters can be used to predict transplant renal artery stenosis in patients with renal graft dysfunction.

MATERIALS AND METHODS

IRB-approved, HIPAA-compliant retrospective study included 80 renal transplant patients who had renal US followed by renal angiogram between January 2018 and December 2019. A consensus read of two radiologists recorded these parameters: peak systolic velocity, persistence of elevated velocity, grayscale narrowing, parvus tardus, delayed systolic upstroke, angle of the systolic peak (SP angle), and aliasing. Univariate analysis using t-test or chi-square was performed to determine differences between patients with and without stenosis. P values under 0.05 were deemed statistically significant. We used machine learning algorithms to determine parameters that could better predict the presence of stenosis. The algorithms included logistic regression, random forest, imbalanced random forest, boosting, and CART. All 80 cases were split between training and testing using stratified sampling using a 75:25 split.

RESULTS

We found a statistically significant difference in grayscale narrowing (p = 0.0010), delayed systolic upstroke (p = 0.0002), SP angle (p = 0.0005), and aliasing (p = 0.0024) between the two groups. No significant difference was found for an elevated peak systolic velocity (p = 0.1684). The imbalanced random forest (IRF) model was selected for improved accuracy, sensitivity, and specificity. Specificity, sensitivity, AUC, and normalized Brier score for the IRF model using all parameters were 73%, 81%, 0.82, and 69 in the training set, and 78%, 58%, 0.78, and 80 in the testing set. VIMP assessment showed that the combination of variables that resulted in the most significant change of the training set performance was that of grayscale narrowing and SP angle.

CONCLUSION

Elevated peak systolic velocity did not discriminate between patients with and without TRAS. Adding ancillary parameters into the machine learning algorithm improved specificity and sensitivity similarly in the training and testing sets. The algorithm identified the combination of lumen narrowing coupled with the angle of the systolic peak as better predictor of TRAS. This model may improve the accuracy of ultrasound for transplant renal artery stenosis.

Role of hypertension in kidney transplant recipients

Cardiovascular events are one of the leading causes of mortality in kidney transplant recipients. Hypertension is the most common comorbidity accompanying chronic kidney disease, with prevalence remaining as high as 90% even after kidney transplantation. It is often poorly controlled. Abnormal blood pressure profiles, such as masked or white-coat hypertension, are also extremely common in these patients. The pathophysiology of blood pressure elevation in kidney transplant recipients is complex and includes transplantation-specific risk factors, which are added to the traditional or chronic kidney disease-related factors. Despite these observations, hypertension management has been an under-researched area in kidney transplantation. Thus, relevant evidence derives either from studies in the general population or from small trials in kidney transplant recipients. Based on the relevant guidelines in the general population, lifestyle modifications should probably be applied as the first step of hypertension management in kidney transplant recipients. The optimal pharmacological management of hypertension in kidney transplant recipients is also not clear. Dihydropyridine calcium channel blockers are commonly used as first line agents because of their lack of adverse effects on the kidney, while other antihypertensive drug classes are under-utilised due to fear of the possible haemodynamic consequences on renal function. This review summarizes the existing data on the pathophysiology, diagnosis, prognostic significance and management of hypertension in kidney transplantation.

Intra-Arterial Hemodynamics to Guide the Percutaneous Treatment of a Difficult-to-Engage Transplant Renal Artery Stenosis

Transplant renal artery stenosis (TRAS) is the most frequent vascular complication after renal transplantation. TRAS is associated with resistant hypertension and allograft dysfunction, early diagnosis and either endovascular or surgical treatment is crucial to preserve graft function. Noninvasive imaging can usually detect the underlying stenosis. In this report we present a novel technique for successful angioplasty and stent deployment in a difficult-to-engage transplant-renal artery.

Endovascular management of transplant renal artery stenosis: A single-center retrospective study

OBJECTIVES

The aim is to evaluate the efficacy and complications of percutaneous transluminal angioplasty (PTA)/stenting in the treatment of transplant renal artery stenosis (TRAS).

BACKGROUND

TRAS is a relatively rare condition, and currently, there is not enough study about interventional therapy for TRAS.

METHODS

Between April 2011 and July 2018, 33 patients with TRAS underwent interventional therapy. Analysis of parameters was as follows: technical success, pretreatment and posttreatment serum creatinine, and blood pressure, and vessel patency via ultrasound at 1, 6, and 12 months posttreatment and once a year thereafter.

RESULTS

One procedure failed. The success rate of PTA/stenting placement was 97.0%. Fourteen PTAs with 16 stents were primary interventions, with 2 stent procedures performed subsequently due to restenosis; the restenosis rate was 6.3%. During the follow-up period, two patients progressed to graft renal failure and three patients were lost to follow-up. The rest of the patients still had stable graft function and blood pressure. Compared with preoperative conditions, blood pressure and serum creatinine significantly decreased (p < .05). No treatment-related deaths or serious complications occurred.

CONCLUSIONS

PTA/stenting is a safe and effective treatment for TRAS. For selected TRAS patients, PTA or PTA with stent may achieve good therapeutic outcomes. Selecting appropriate puncture pathways may help improve the success rate and affect the operation results, and open surgery may be avoided.

Surgical Complications After Kidney Transplantation

Since the first successful organ transplant conducted between twins in 1954, kidney transplant has evolved considerably over the past 50 years. Kidney transplant plays an important role in the treatment of end-stage kidney disease to improve the quality of life and prolong the life of patients. Despite significant advances, postoperative medical and surgical complications still represent important causes of morbidity and mortality. Many problems can be avoided through prophylactic correction of abnormalities detected during the preoperative evaluation; however, it is critical that technical mishaps at all stages of the transplant process (donor nephrectomy, benchwork preparation, and implant) be prevented and that careful postoperative monitoring be carried out, including thorough examination by attending physicians. However, despite these advances, surgical complications still present serious problems in kidney transplant recipients.

Immediate Vascular Complications After Kidney Transplant: Experience from 2100 Recipients

OBJECTIVES

Vascular complications, especially immediate events during kidney transplant, are the major cause of graft loss, and prompt surgical intervention is important for salvage of the graft and recipient. In this study, our aim was to show our experiences with vascular interventions and their effects on graft outcomes in transplant patients with suspected immediate vascular events.

MATERIALS AND METHODS

Over 24 years (from 1990 to 2014), 2100 renal transplant procedures (1562 living and 538 deceased donors) were performed by one fixed team. We reviewed the recipients to find cases with immediate vascular complications, including artery or vein kinking or torsion, renal artery thrombosis, and renal vein thrombosis. Diagnosis of a vascular event was suspected when urinary output suddenly stopped and was confirmed by color Doppler ultrasonography or immediate exploration. Characteristics of the patients and events, surgical interventions for saving grafts, and graft outcomes were assessed.

RESULTS

Our study included 28 vascular accidents (1.3% of total renal transplants). Arterial kinking or torsion, venous kinking or torsion, renal artery thrombosis, and renal vein thrombosis occurred in 11 (0.52%), 2 (0.09%), 12 (0.57%), and 3 patients (0.14%). Nine of the 11 cases of arterial kinking occurred with use of internal iliac artery. Eleven of 13 grafts with vascular kinking or torsion were saved by immediate surgical intervention, but only 4 grafts in patients with renal artery thrombosis and only 1 graft in patients with renal vein thrombosis were saved by surgical intervention. Delayed graft function occurred in all cases of saved renal artery and renal vein thrombosis but only in 5 cases (4 arterial and 1 venous) of vascular kinking or torsion.

CONCLUSIONS

The incidence of immediate vascular complications was 1.3% in our study. Sudden cessation of urine after renal transplant is a warning sign, and immediate diagnosis of vascular events will help salvage the graft with proper intervention.

Artery Stenosis of the Renal Graft: Experience of a Center of Northeastern Brazil

BACKGROUND

Transplant renal artery stenosis (TRAS), the most common vascular complication after transplant (Tx), leads to resistant hypertension, impaired renal function, and even loss of the graft. The purpose of the study was to investigate the prevalence and factors associated with TRAS in northeastern Brazil.

METHODS

The study was conducted as a retrospective case-control study in a population of Tx recipients in a renal Tx center in northeastern Brazil. Demographic and clinical characteristics of the recipients and donors, data related to the surgery, laboratory data, and number of anti-hypertensive drugs were assessed. Statistical analysis was performed with the use of SPSS 17.0.

RESULTS

A total of 494 of 529 recipients were assessed, of which 24 had TRAS. The prevalence of TRAS was 4.8%. Twelve patients (50%) were men with a mean age of 46.7 ± 13.5 years. The mean time of diagnosis was 89.9 days after Tx. The risk factors associated with TRAS were number of anti-hypertensive drugs ≥2 (odds ratio, 17.0; confidence interval, 4.1 to 70.4; P = .001) and grafting with 2 or more arteries (odds ratio, 8.9; confidence interval, 1.4 to 56.6; P = .021). There was a significant reduction in mean systolic blood pressure (147.1 ± 23.7 to 127.8 ± 15.2 mm Hg, P = .001) and diastolic blood pressure (86.6 ± 13.0 to 77.6 ± 9.4 mm Hg, P = .001) after TRAS repair and in serum creatinine (2.8 ± 2.4 to 1.9 ± 1.8 mg/dL, P = .04).

CONCLUSIONS

Grafts with 2 or more arteries are associated with TRAS, as well as patients who use a higher number of anti-hypertensive drugs. TRAS repair was associated with improved blood pressure control and renal function.

MR Angiography of Renal Transplant Vasculature with Ferumoxytol:: Comparison of High-Resolution Steady-State and First-Pass Acquisitions

RATIONALE AND OBJECTIVES

This work aimed to quantify the differences in signal-to-noise ratio (SNR) and vessel sharpness between steady-state and first-pass magnetic resonance angiography (MRA) with ferumoxytol in renal transplant recipients.

MATERIALS AND METHODS

We performed a retrospective study of adult patients who underwent steady-state and first-pass MRA with ferumoxytol to evaluate renal transplant vasculature. SNR was calculated in the external iliac artery, and vessel sharpness was calculated in the external iliac and renal transplant arteries for both acquisitions. Data were compared using Student's t test.

RESULTS

Fifteen patients were included (mean age 56.9 years, 10 males). The mean SNR of the external iliac artery was 42.2 (SD, 11.9) for the first-pass MRA and 41.8 (SD, 9.7) for the steady-state MRA (p = 0.92). The mean vessel sharpness was significantly higher for the steady-state MRA compared to first-pass MRA for both external iliac (1.24 vs. 0.80 mm(-1), p < 0.01) and renal transplant arteries (1.26 vs. 0.79 mm(-1), p < 0.01).

CONCLUSION

Steady-state MRA using ferumoxytol improves vessel sharpness while maintaining equivalent SNR compared to conventional first-pass MRA in renal transplant patients.

Tailoring the endovascular management of transplant renal artery stenosis

In this study we analyze the different types of endovascular interventions (EVIs) in de novo transplant renal artery stenosis (TRAS) and its anatomical subtypes to examine any variation in recovery of allograft function, blood pressure control, EVI patency and allograft survival with respect to EVI type (DES: drug-eluting stent, BMS: bare-metal stent, PTA: percutaneous transluminal angioplasty). Forty-five patients underwent a total of 50 primary EVIs (DES: 18, BMS: 26, PTA: 6). Patients were stratified according to medical co-morbidities, graft characteristics, biopsy results, clinical presentation and TRAS anatomic subtypes (anastomotic: 26, postanastomotic: 17, bend-kink: 2). There was significant improvement in allograft function and mean arterial blood pressure (MAP) control across all interventions (pre-EVI-creatinine [CR]: 2.8 ± 1.4, post-EVI-Cr: 2.1 ± 0.7, p < 0.001; pre-EVI-MAP: 117 ± 16, post-EVI-MAP: 112 ± 17, p = 0.03) with no significant difference among EVI types. There was no significant difference in allograft survival with respect to EVI type. Patency was significantly higher in EVIs performed with DES and BMS compared to PTA (p = 0.001). In the postanastomotic TRAS subtype, patency rates were significantly higher in DES compared to BMS (p = 0.012) in vessels of comparable reference diameter (≤5 mm).