Ipsilateral Aorto-Iliac Calcification is Not Directly Associated With eGFR After Kidney Transplantation: A Prospective Cohort Study Analyzed Using a Linear Mixed Model

Aorto-iliac calcification (AIC) is a well-studied risk factor for post-transplant cardiovascular events and mortality. Its effect on graft function remains unknown. The primary aim of this prospective cohort study was to assess the association between AIC and estimated glomerular filtration rate (eGFR) in the first year post-transplant. Eligibility criteria were: ≥50 years of age or ≥30 years with at least one risk factor for vascular disease. A non-contrast-enhanced CT-scan was performed with quantification of AIC using the modified Agatston score. The association between AIC and eGFR was investigated with a linear mixed model adjusted for predefined variables. One-hundred-and-forty patients were included with a median of 31 (interquartile range 26-39) eGFR measurements per patient. No direct association between AIC and eGFR was found. We observed a significant interaction between follow-up time and ipsilateral AIC, indicating that patients with higher AIC scores had lower eGFR trajectory over time starting 100 days after transplant (p = 0.014). To conclude, severe AIC is not directly associated with lower post-transplant eGFR. The significant interaction indicates that patients with more severe AIC have a lower eGFR trajectory after 100 days in the first year post-transplant.

A CT-based pelvic calcification score in kidney transplant patients is a possible predictor of graft and overall survival

OBJECTIVES

Computerized tomography (CT) is the most accurate method for evaluating pelvic calcifications, which are of utmost importance for planning kidney transplantation (KT). The aim of our study was to evaluate the incidence and distribution of iliac artery calcifications and correlate the novel pelvic calcification score (PCS) with cardiovascular risk factors and graft and overall survival in KT patients.

METHODS

We retrospectively included 118 KT patients operated at our institution with pretransplant pelvic CT. Calcification morphology, circumference and length of both common and external iliac arteries were independently scored by two uroradiologists. PCS was calculated as the total score sum of all three calcification features in all vessels. PCS correlation with graft and patient survival was performed.

RESULTS

Calcification in at least one vascular segment was found in 79% of patients. PCS was significantly higher in male patients (p = 0.006), patients over 55 years (p < 0.001), and patients on haemodialysis (p = 0.016). Patients with a PCS >3 had significantly shorter graft and overall survival rates (p = 0.041 and p = 0.039, respectively).

CONCLUSIONS

The extent of iliac artery calcification in KT recipients quantified by PCS on pretransplant CT correlates with graft and overall patient survival. A PCS over three was associated with worse clinical outcomes and could become a possible prognostic factor.

ADVANCES IN KNOWLEDGE

Our novel PCS is a robust method for quantifying iliac artery calcification burden. Since higher a PCS correlates with worse patient and graft survival, PCS has the potential to become a prognostic factor in kidney transplant patients.

Utility of a Simplified Iliac Artery Calcium Scoring System to Guide Perioperative Management for Renal Transplantation

Non-contrast computed tomography scans of the abdomen and pelvis (CTAP) are often obtained prior to renal transplant to evaluate the iliac arteries and help guide surgical implantation. The purpose of this study was to describe the association of iliac calcification scores with operative and clinical outcomes using a simplified scoring system. A retrospective review of 204 patients who underwent renal transplant from 1/2013 to 11/2014 and who had a CTAP within 3 years prior to transplant was performed. Data were collected from the electronic medical record. Common iliac artery (CIA) and external iliac artery (EIA) calcification on CTAP were assessed using a simple scoring system. Descriptive statistics, logistic regression, and survival analyses were performed. A total of 204 patients were included in the analysis. The mean age was 57.4 ± 11.2 years and 134/204 (66%) were men. Nineteen patients (9%) had a history of peripheral artery disease (PAD), 78 (38%) had coronary artery disease, and 22 (11%) had a previous cerebrovascular accident (CVA). Patients with severe right EIA plaque morphology were significantly more likely to require arterial reconstruction compared to those without severe plaque (3/14[21%] 4/153 [3%], p = 0.03). Eleven patients (5%) had one or more amputations (toe, foot, or transtibial) following transplant. In UV logistic regression, severe EIA plaque morphology (OR 8.1, CI 2.2–29.6, p = 0.002) and PAD (OR 10.7, CI 2.8–39.9, p = 0.0004) were associated with increased odds of amputation. In the MV model containing both variables, EIA plaque morphology (OR 4.4, CI 0.99–18.3, p = 0.04) and PAD (OR 6.3, CI 1.4–26.4, p = 0.01) remained independently associated with increased odds of amputation. Over a median follow up of 3.3 years (IQR 2.9–3.6), 21 patients (10%) had post-operative major adverse cardiac events (MACE, defined as myocardial infarction, coronary intervention, or CVA), and 23 patients died (11%). In unadjusted Kaplan Meier analysis, CIA plaque (p = 0.00081) and >75% CIA length calcification (p = 0.0015) were significantly associated with MACE. Plaque burden in the EIA is associated with increased need for intra-operative arterial reconstruction and post-operative lower extremity amputations, while CIA plaque is associated with post-operative MACE. Assessment of CIA and EIA calcification scores on pre-transplant CT scans in high risk patients may guide operative strategy and perioperative management to improve clinical outcomes.

Aorto-Iliac Artery Calcification Prior to Kidney Transplantation

As vascular calcification is common in kidney transplant candidates, aorto-iliac vessel imaging is performed for surgical planning. The aim of the present study was to investigate whether a novel non-contrast enhanced computed tomography-based quantification technique for aorto-iliac calcification can be used for cardiovascular risk stratification prior to kidney transplantation. In this dual-center cohort study, we measured the aorto-iliac calcium score (CaScore) of 547 patients within three years prior to transplantation (2005-2018). During a median (interquartile range) follow-up of 3.1 (1.4, 5.2) years after transplantation, 80 (14.7%) patients died, of which 32 (40.0%) died due to cardiovascular causes, and 84 (15.5%) patients had a cardiovascular event. Kaplan-Meier survival curves showed significant differences between the CaScore tertiles for cumulative overall-survival (Log-rank test p < 0.0001), cardiovascular survival (p < 0.0001), and cardiovascular event-free survival (p < 0.001). In multivariable Cox regression, the aorto-iliac CaScore was associated with all-cause mortality (hazard ratio 1.53, 95%CI 1.14-2.06, p = 0.005), cardiovascular mortality (2.04, 1.20-3.45, p = 0.008), and cardiovascular events (1.35, 1.01-1.80, p = 0.042). These independent associations of the aorto-iliac CaScore with the outcome measures can improve the identification of patients at risk for (cardiovascular) death and those who could potentially benefit from stringent cardiovascular monitoring to improve their prognosis after transplantation.

Impact of Aortoiliac Stenosis on Graft and Patient Survival in Kidney Transplant Recipients Using the TASC II Classification

BACKGROUND

Patients with end-stage renal disease and aortoiliac stenosis are often considered ineligible for kidney transplantation, although kidney transplantation has been acknowledged as the best therapy for end-stage renal disease. The clinical outcomes of kidney transplantation in patients with aortoiliac stenosis are not well-studied. This study aimed to assess the impact of aortoiliac stenosis on graft and patient survival.

METHODS

This retrospective, single-center study included kidney transplant recipients transplanted between January 1, 2000, and December 31, 2016, who received contrast-enhanced imaging. Patients with aortoiliac stenosis were classified using the Trans-Atlantic Inter-Society Consensus (TASC) II classification and categorized as having TASC II A/B lesions or having TASC II C/D lesions. Patients without aortoiliac stenosis were functioning as controls.

RESULTS

A total number of 374 patients was included in this study (n = 88 with TASC II lesions, n = 286 as controls). Death-censored graft survival was similar to the controls. Patient and uncensored graft survival was decreased in patients with TASC II C/D lesions (log-rank test P < 0.001). Patients with TASC II C/D lesions had a higher risk of 90-day mortality (hazard ratio, 3.96; 95% confidence interval, 1.12-14.04). In multivariable analysis, having a TASC II C/D lesion was an independent risk factor for mortality (hazard ratio, 3.25; 95% confidence interval, 1.87-5.67; P < 0.001). Having any TASC II lesion was not a risk factor for graft loss (overall P = 0.282).

CONCLUSIONS

Kidney transplantation in patients with TASC II A/B is feasible and safe without increased risk of perioperative mortality. TASC II C/D decreases patient survival. Death-censored graft survival is unaffected.

The prognosis of kidney transplant recipients with aorto-iliac calcification: a systematic review and meta-analysis

The prognosis of kidney transplant recipients (KTR) with vascular calcification (VC) in the aorto-iliac arteries is unclear. We performed a systematic review and meta-analysis to investigate their survival outcomes. Studies from January 1st, 2000 until March 5th, 2019 were included. Outcomes for meta-analysis were patient survival, (death-censored) graft survival and delayed graft function (DGF). Twenty-one studies were identified, eight provided data for meta-analysis. KTR with VC had a significantly increased mortality risk [1-year: risk ratio (RR) 2.19 (1.39-3.44), 5-year: RR 2.28 (1.86-2.79)]. The risk of 1-year graft loss was three times higher in recipients with VC [RR 3.15 (1.30-7.64)]. The risk of graft loss censored for death [1-year: RR 2.26 (0.58-2.73), 3-year: RR 2.19 (0.49-9.82)] and the risk of DGF (RR 1.24, 95% CI 0.98-1.58) were not statistically different. The quality of the evidence was rated as very low. To conclude, the presence of VC was associated with an increased mortality risk and risk of graft loss. In this small sample size, no statistical significant association between VC and DGF or risk of death-censored graft loss could be demonstrated. For interpretation of the outcomes, the quality and sample size of the evidence should be taken into consideration.

Classification of Computed Tomography Images in Different Slice Positions Using Deep Learning

This study aimed at elucidating the relationship between the number of computed tomography (CT) images, including data concerning the accuracy of models and contrast enhancement for classifying the images. We enrolled 1539 patients who underwent contrast or noncontrast CT imaging, followed by dividing the CT imaging dataset for creating classification models into 10 classes for brain, neck, chest, abdomen, and pelvis with contrast-enhanced and plain imaging. The number of images prepared in each class were 100, 500, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, and 10,000. Accordingly, the names of datasets were defined as 0.1K, 0.5K, 1K, 2K, 3K, 4K, 5K, 6K, 7K, 8K, 9K, and 10K, respectively. We subsequently created and evaluated the models and compared the convolutional neural network (CNN) architecture between AlexNet and GoogLeNet. The time required for training models of AlexNet was lesser than that for GoogLeNet. The best overall accuracy for the classification of 10 classes was 0.721 with the 10K dataset of GoogLeNet. Furthermore, the best overall accuracy for the classification of the slice position without contrast media was 0.862 with the 2K dataset of AlexNet.

Aortic calcifications and arterial stiffness as predictors of cardiovascular events in incident renal transplant recipients

Renal transplant recipients have an increased risk of cardiovascular (CV) disease. Arterial stiffness (AS) and aortic calcifications (ACs) are well-known CV risk factors in patients with chronic kidney disease. We aimed to determine the prognostic value of AS and AC in incident renal transplant recipients (RTRs). We conducted a prospective study in 253 single RTR. AC were scored by means of lumbar X-ray. Carotid-femoral pulse wave velocity (PWV) was assessed in a subgroup of 115 patients. AC were present in 61% of patients. After a mean follow-up of 36 months, 32 CV events occurred in the overall group and 13 events in the PWV subgroup. When we accounted for age, gender, and CV history, AC score (HR, hazard ratio 1.09 per 1 unit increase; 95% CI 1.02-1.17) and PWV (HR 1.45 per 1 m/s; 95% CI 1.16-1.8) remained an independent predictor of CV events in Cox-regression analyses. Using receiver operating characteristics, the area under the curve for predicting CV events amounted to 0.80 and 0.72 for sum AC and PWV, respectively. Both AS and AC are strong predictors of future CV events in an incident RTR population. These vascular assessments are readily available and easy to perform, making them ideal tools for further risk stratification. (ClinicalTrials.gov number: NCT00547040).

The prognostic significance of iliac vessel calcification in renal transplantation

BACKGROUND

Peripheral vascular disease and major extremity amputation are common in patients with established renal failure and are associated with considerable morbidity. Several studies have shown high rates of amputation following simultaneous pancreas-kidney transplantation, but there is minimal literature on the incidence of amputation following renal transplantation. Furthermore, there is little evidence regarding the best method of predicting which patients might be at risk of developing peripheral vascular complications after transplantation.

METHODS

We undertook a 5 year follow-up on the cohort of patients who were on our renal transplant waiting list 5 years ago (January 2007). At this time, it was standard practice within our unit for all patients to have routine pelvic x-rays to assess for vascular calcification of the iliac vessels at the time of activation onto the transplant waiting list. Any patients with moderate/severe calcification on x-ray, which may complicate transplantation, were referred for computed tomography angiogram (CTA) of their aorto-iliac vessels. Mortality, transplantation outcomes, and amputation rates at 5 years were correlated with the severity of calcification on preoperative imaging.

RESULTS

One hundred eighty-seven patients were on the waiting list for renal transplantation in January 2007 (92 men; mean age, 58.3 +/- 6.2 years). Ninety-three patients received a transplant during the subsequent 5 years. By January 2012, 82 patients had a functioning transplant, 45 remained on the waiting list (5 suspended), 40 patients had died, and 20 were alive but no longer on the waiting list. Seventy-three (39.5%) had moderate or severe calcification on plain x-ray and went on to have CTA. Of these patients, 16 (21.9%) had extensive calcification affecting all the iliac vessels and were removed from the waiting list as a result. Preoperative imaging was useful in determining the side for surgery in a further 18 patients (24.3%). Twenty-two patients developed vascular complications. Nineteen (86.4%) had moderate-severe vascular calcification on imaging. Four of the patients with vascular complications (18.2%) underwent transplantation (2 had below knee amputation (BKA) prior to transplantation; 1 developed distal ischemia on the same side as the transplantation 2 years postoperatively; 1 had bilateral above knee amputation (AKA) approximately 2 years after transplantation). Eleven (50%) of the patients with vascular complications were dead at 5 years of follow-up. Mortality and amputation rates were higher in patients with moderate-severe calcification than minimal calcification (30.1% vs 16.6%; P = .02 and 10.9% vs 1.8%; P = .003, respectively). There was no difference in rates of delayed graft function (DGF), biopsy-proven acute rejection (BPAR), or creatinine at 1 year between patients who underwent transplantation with moderate-severe calcification and those without, however, intraoperative vascular complications (26.7% vs 3%; P < .001), graft loss (28.1% vs 3.4%; P = .01), and death with a functioning transplant (9.7% vs 1.6%; P = .04) rates were higher in patients with extensive calcification compared with those without.

CONCLUSIONS

Plain x-ray of the pelvis is a useful screening tool to identify those patients who may require further detailed vascular imaging prior to transplantation. Amputation rates following renal transplantation are low and peripheral vascular disease (PVD) in isolation should not preclude transplantation. Nevertheless, significant vascular calcification is predictive of mortality both with and without transplantation and graft loss in patients with a renal transplant.