The Renal Arterial Resistance Index Predicts Worsening Renal Function in Chronic Heart Failure Patients

Renal resistive index in patients supported with a durable continuous flow left ventricular assist device

BACKGROUND

The impact of continuous flow resulting from contemporary left ventricular assist devices (LVAD) on renal vascular physiology is unknown. Renal resistive index (RRI) reflects arterial compliance, as well as renal vascular resistance, contributed by afferent and efferent arteriolar tone, the renal interstitium as well as renal venous pressures.

METHODS

Prospective, single center study with renal Doppler evaluation at baseline (pre-implant) and at 3-months support. Outcomes assessed include need for post-operative renal replacement therapy (RRT), worsening renal function (WRF) defined as persistent increase from pre-implant KDIGO chronic kidney disease stage, right ventricular (RV) failure, and survival to transplantation.

RESULTS

Pre-implant RRI did not predict cardiorenal outcomes including right heart failure, need for renal replacement therapy or worsening renal function. Post-implant RRI was significantly lower than pre-implant RRI, with a distinct Doppler waveform characteristic of continuous flow. Post-implant renal end-diastolic velocity, but not RRI, correlated strongly with LVAD flow (Spearman rho -0.99, p < 0.001), with trend toward correlation with mean arterial pressure (Spearman's rho 0.63, p = 0.129). There was a negative correlation between post-implant RRI and mean pulmonary artery pressure (Spearman's rho -0.81, p = 0.049), likely driven by elevated pulmonary capillary wedge pressure (Spearman's rho -0.83, p = 0.058).

CONCLUSION

The hemodynamic contributors to RRI in LVAD supported patients are complex. Higher mean pulmonary artery and pulmonary capillary wedge pressures seen in lower RRI may reflect a smaller difference in systolic and diastolic flow. Future simultaneous Doppler assessment of the LVAD outflow graft and RRI may help understand the hemodynamic interactions contributing to this index.

Intraoperative hypotension during critical phases of liver transplantation and its impact on acute kidney injury: a retrospective cohort study

INTRODUCTION

Acute Kidney Injury (AKI) following Liver Transplantation (LT) is associated with prolonged ICU and hospital stay, increased risk of chronic renal disease, and decreased graft survival. Intraoperative hypotension is a modifiable risk factor associated with postoperative AKI. We aimed to determine in which phase of LT hypotension has the strongest association with AKI: the anhepatic or neohepatic phase.

METHODS

This retrospective cohort study included adult patients undergoing LT between January 2010 and June 2022. Exclusion criteria were re-do or combined transplantations, preoperative dialysis, and early graft failure or death. Primary outcome was AKI as defined by KDIGO. Hypotension was Mean Arterial Pressure (MAP) below predefined thresholds in minutes. Risk adjusted logistic regression analysis considered hypotension in 3 periods: the total procedure, anhepatic phase, and neohepatic phase.

RESULTS

Our cohort included 1153 patients. The median MELD-NA score was 19 (IQR 11-28), and 412 (35.9%) were living-related donations. AKI occurred in 544 patients (47.2%). The unadjusted model showed an association with AKI for MAP < 60 mmHg (OR = 1.011 [1.0, 1.022], p = 0.047) and MAP < 55 mmHg (OR = 1.023 [1.002, 1.047], p = 0.040) in the anhepatic phase, and for MAP < 60 mmHg (OR = 1.032 [1.01, 1.056], p = 0.006) in the neohepatic phase. The adjusted model did not reach significance in the subgroups but did in the total procedure: MAP < 60 mmHg (OR = 1.005 [1.002, 1.008], p < 0.001) and MAP < 55 mmHg (OR = 1.008 [1.003-1.013], p = 0.004).

CONCLUSION

Intraoperative hypotension is independently associated with AKI following LT. This association is seen during the anhepatic phase. Maintaining MAP above 60 mmHg may improve kidney function after LT.

Acute Cardiorenal Syndrome: An Update

The complex dynamic pathophysiological interplay between the heart and kidney causes a vicious cycle of worsening renal and/or cardiovascular function. Acute decompensated heart failure causing worsening renal function defines Type 1 cardiorenal syndrome (CRS). Altered hemodynamics coupled with a multitude of nonhemodynamic factors namely pathological activation of the renin angiotensin aldosterone system and systemic inflammatory pathways mechanistically incite CRS type 1. A multipronged diagnostic approach utilizing laboratory markers, noninvasive and/or invasive modalities must be implemented to enable timely initiation of effective treatment strategies. In this review, we discuss the pathophysiology, diagnosis, and emerging treatment options for CRS type 1.

Renal Arterial and Venous Doppler in Cardiorenal Syndrome: Pathophysiological and Clinical Insights

In recent decades, there has been considerable effort in investigating the clinical utility of renal Doppler measurements in both cardiovascular and renal disorders. In particular, a measure of renal arterial resistance, the renal resistive index (RRI), has been demonstrated to predict chronic kidney disease progression and acute kidney injury in different clinical settings. Furthermore, it is linked to a poorer prognosis in individuals suffering from chronic heart failure. Examining the renal venous flow through pulsed Doppler can offer additional insights into renal congestion and cardiovascular outcomes for these patients. This review seeks to summarize the existing data concerning the clinical significance of arterial and venous renal Doppler measurements across various cardiovascular and renal disease contexts.

Changes in renal microcirculation in patients with nephrotic and nephritic syndrome: The role of resistive index

BACKGROUND

Renal Resistive Index (RRI) is an important and non-invasive parameter of renal damage and it is associated with abnormal microcirculation or to a parenchymal injury. The aim of our study was to compare the RRI in a cohort of patients with renal diseases categorized in three groups: nephrotic syndrome (NS), acute nephritic syndrome (ANS) and patients with urinary abnormalities (UA).

METHODS

Four hundred eighty-two patients with median age of 48 years (IQR 34-62) with indications for kidney disease were included in the study. Biochemical analyses, clinical assessment with detection of NS, ANS and UA and comorbidities were reported. Renal Doppler ultrasound with RRI was evaluated in all patients at the time of enrolment.

RESULTS

NS was present in 81 (16.8 %) patients while ANS in 81 (16.8 %) and UA in 228 (47.3 %) patients. Patients with ANS showed significant higher RRI compared to both patients with NS [0.71 (IQR 0.67-0.78) vs 0.68 (0.63-0.73), p < 0.001] and UA [0.71 (0.67-0.78) vs 0.65 (0.61-0.71), p < 0.001]; RRI was higher in NS patients than in patients with UA [0.68 (0.63-0.73) vs 0.65 (0.61-0.71), p < 0.001]. Patients with ANS had significantly lower median estimated glomerular filtration rate (eGFR) compared respectively to NS and UA patients [19.7 ml/min vs 54.8 ml/min and vs 72.3 ml/min, p < 0.001], while renal length was significantly higher in patients with NS compared to both patients with ANS and UA [111.88 mm vs 101.98 mm and vs 106.15, p < 0.001]. Patients with ANS had more frequently hematuria and RRI ≥ 0.70 (p < 0.001) compared to both patients with NS and patients with UA. The multiple regression analysis, weighted for age, showed that RRI inversely correlates with eGFR (β coefficient = -0.430, p < 0.001).

CONCLUSIONS

Higher and pathological RRI were found in ANS than NS and UA. Renal resistive index in ANS reflects changes in intrarenal perfusion and microvascular dysfunction related to disease characteristics.

Renal hemodynamic evaluation protocol based on the pathophysiological mechanism of acute kidney injury: Critical Care UltraSound Guided-A(KI)BCDE

The multiple etiological characteristics of acute kidney injury (AKI) have brought great challenges to its clinical diagnosis and treatment. Renal injury in critically ill patients always indicates hemodynamic injury. The Critical Care UltraSound Guided (CCUSG)-A(KI)BCDE protocol developed by the Chinese Critical Ultrasound Study Group (CCUSG), respectively, includes A(KI) diagnosis and risk assessment and uses B-mode ultrasound, Color doppler ultrasound, spectral Doppler ultrasound, and contrast Enhanced ultrasound to obtain the hemodynamic characteristics of the kidney so that the pathophysiological mechanism of the occurrence and progression of AKI can be captured and the prognosis of AKI can be predicted combined with other clinical information; therefore, the corresponding intervention and treatment strategies can be formulated to achieve targeted, protocolized, and individualized therapy.

The Incremental Role of Multiorgan Point-of-Care Ultrasounds in the Emergency Setting

Point-of-care ultrasonography (POCUS) represents a goal-directed ultrasound examination performed by clinicians directly involved in patient healthcare. POCUS has been widely used in emergency departments, where US exams allow physicians to make quick diagnoses and to recognize early life-threatening conditions which require prompt interventions. Although initially meant for the real-time evaluation of cardiovascular and respiratory pathologies, its use has been extended to a wide range of clinical applications, such as screening for deep-vein thrombosis and trauma, abdominal ultrasonography of the right upper quadrant and appendix, and guidance for invasive procedures. Moreover, recently, bedside ultrasounds have been used to evaluate the fluid balance and to guide decongestive therapy in acutely decompensated heart failure. The aim of the present review was to discuss the most common applications of POCUS in the emergency setting.

Renal resistance index independently predicts worsening of renal function after coronary angiography

The renal resistance index (RRI) has been demonstrated to be a useful parameter that can detect patients at a high risk of worsening of renal function (WRF). This study was designed to evaluate the role of the RRI in predicting WRF mediated by the intravascular administration of contrast media. We enrolled patients who were referred for coronary angiography. Renal arterial echo-color Doppler was performed to calculate the RRI. WRF was defined as an increase of > 0.3 mg/dL and at least 25% of the baseline value in creatinine concentration 24-48 h after coronary angiography. Among the 148 patients enrolled in this study, 18 (12%) had WRF. In the multivariate logistic analysis, the RRI was independently associated with WRF (odds ratio [OR]: 1.22; 95% confidence interval [CI]: 1.09-1.36; p = 0.001). After angiography, the RRI significantly increased in both patients with and without WRF. In the receiver operating characteristic curve analyses for WRF, the RRI at baseline and after angiography showed similar accuracy, and the best cutoff value for predicting WRF was 70%. In patients undergoing coronary angiography, the RRI is independently associated with WRF, probably because it provides more accurate information about cardiorenal pathophysiological factors and reflects kidney hemodynamic status and flow reserve.

Effects of Sacubitril/Valsartan on the Renal Resistance Index

Background: Sacubitril/valsartan plays a key role in improving left ventricular remodeling and prognosis in patients with heart failure with a reduced ejection fraction (HFrEF). Moreover, some data support its role in preserving renal function. In order to better clarify the effects of sacubitril/valsartan in cardiorenal syndrome, this study evaluated its effects on the renal resistance index (RRI). Methods: A group of patients with HFrEF was enrolled. The RRI was assessed with renal echo-color Doppler at enrollment and again after at least six months of sacubitril/valsartan treatment. In a subgroup of patients, the RRI was also evaluated at least six months before enrollment. The variations in echocardiographic parameters reflecting the left and right ventricular function, as well as creatinine and the estimated glomerular filtration rate, were also evaluated. Results: After treatment with sacubitril/valsartan, significant improvements in the left ventricular ejection fraction, and a decrease in the left atrial and ventricular volumes were observed. The RRI also showed a significant decrease. No relationship was found between the improvements in the parameters reflecting cardiac function and changes in the RRI. Conclusions: Treatment with sacubitril/valsartan is associated with improvements in both left ventricular function and renal perfusion, through decreasing the renal resistance. These data help to clarify the effects of the drug on cardiorenal syndrome progression.

Effects of Smoking on Diabetic Nephropathy

Diabetes is a systemic metabolic disease with serious complications that cause significant stress on the healthcare system. Diabetic kidney disease is the primary cause of end stage renal disease globally and its progression is accelerated by various factors. Another major healthcare hazard is tobacco consumption and smoking has deleterious effects on renal physiology. Prominent factors are defined as sympathetic activity, atherosclerosis, oxidative stress and dyslipidemia. This review aims to enlighten the mechanism underlying the cumulative negative effect of simultaneous exposure to hyperglycemia and nicotine.

Renal Hemodynamics and Renin-Angiotensin-Aldosterone System Profiles in Patients With Heart Failure

OBJECTIVE

Understanding cardiorenal pathophysiology in heart failure (HF) is of clinical importance. We sought to characterize the renal hemodynamic function and the transrenal gradient of the renin-angiotensin-aldosterone system (RAAS) markers in patients with HF and in controls without HF.

METHODS

In this post hoc analysis, the glomerular filtration rate (GFR_inulin), effective renal plasma flow (ERPF_PAH) and transrenal gradients (arterial-renal vein) of angiotensin converting enzyme (ACE), aldosterone, and plasma renin activity (PRA) were measured in 47 patients with HF and in 24 controls. Gomez equations were used to derive afferent (R_A) and efferent (R_E) arteriolar resistances. Transrenal RAAS gradients were also collected in patients treated with intravenous dobutamine (HF, n = 11; non-HF, n = 11) or nitroprusside (HF, n = 18; non-HF, n = 5).

RESULTS

The concentrations of PRA, aldosterone and ACE were higher in the renal vein vs the artery in patients with HF vs patients without HF (P < 0.01). In patients with HF, a greater ACE gradient was associated with greater renal vascular resistance (r = 0.42; P 0.007) and greater arteriolar resistances (R_A: r = 0.39; P = 0.012; R_E: r = 0.48; P = 0.002). Similarly, a greater aldosterone gradient was associated with lower GFR (r = -0.51; P = 0.0007) and renal blood flow (RBF), r = -0.32; P = 0.042) whereas greater PRA gradient with lower ERPF (r = -0.33; P = 0.040), GFR (r = -0.36; P = 0.024), and RBF (r = -0.33; P = 0.036). Dobutamine and nitroprusside treatment decreased the transrenal gradient of ACE (P = 0.012, P < 0.0001, respectively), aldosterone (P = 0.005, P = 0.030) and PRA (P = 0.014, P = 0.002) in patients with HF only.

CONCLUSIONS

A larger transrenal RAAS marker gradient in patients with HF suggests a renal origin for neurohormonal activation associated with a vasoconstrictive renal profile.

New renal haemodynamic indices can predict worsening of renal function in acute decompensated heart failure

AIMS

Worsening of renal function (WRF) is a common complication in patients with acute decompensated heart failure (ADHF). We aimed to evaluate the role of intrarenal Doppler ultrasound (IRD) in the early prediction of WRF in this patient group.

METHODS AND RESULTS

Among 90 patients (age: 57.5 ± 11.1 years; 62% male) hospitalized with ADHF, resistivity index (RI), acceleration time (AT), and pulsatility index (PI) were measured on admission and at 24 and 72 h. WRF was defined as increased serum creatinine ≥0.3 mg/dL from baseline. Adverse clinical outcomes were defined as the composite of death, use of vasopressors, and need for ultrafiltration for refractory oedema. WRF developed in 40% of patients. Mean values of renal AT, RI, and PI on admission were 59.7 ± 15, 0.717 ± 0.08, and 1.5 ± 0.48 ms, respectively. At 24 h, there was significant decrease in AT (to 56.7 ± 10 ms, P = 0.02) and renal RI (to 0.732 ± 0.07; P < 0.001); these changes were maintained up to 72 h. Renal PI showed no significant changes. Independent predictors of WRF were renal AT at 24 h and admission values of renal RI, left ventricular ejection fraction, and plasma cystatin C. Renal AT at 24 h ≥ 57.8 ms had 89% sensitivity and 70% specificity for the prediction of WRF. Independent predictors for adverse clinical outcomes were left ventricular end systolic dimension and WRF.

CONCLUSIONS

Among ADHF patients receiving diuretic therapy, measurement of renal AT and RI by IRD can help identify patients at increased risk for WRF.

Intraoperative Renal Resistive Index as an Acute Kidney Injury Biomarker: Development and Validation of an Automated Analysis Algorithm

OBJECTIVE

Intraoperative Doppler-determined renal resistive index (RRI) is a promising early acute kidney injury (AKI) biomarker. As RRI continues to be studied, its clinical usefulness and robustness in research settings will be linked to the ease, efficiency, and precision with which it can be interpreted. Therefore, the authors assessed the usefulness of computer vision technology as an approach to developing an automated RRI-estimating algorithm with equivalent reliability and reproducibility to human experts.

DESIGN

Retrospective.

SETTING

Single-center, university hospital.

PARTICIPANTS

Adult cardiac surgery patients from 7/1/2013 to 7/10/2014 with intraoperative transesophageal echocardiography-determined renal blood flow measurements.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Renal Doppler waveforms were obtained retrospectively and assessed by blinded human expert raters. Images (430) were divided evenly into development and validation cohorts. An algorithm for automated RRI analysis was built using computer vision techniques and tuned for alignment with experts using bootstrap resampling in the development cohort. This algorithm then was applied to the validation cohort for an unbiased assessment of agreement with human experts. Waveform analysis time per image averaged 0.144 seconds. Agreement was excellent by intraclass correlation coefficient (0.939; 95% confidence interval [CI] 0.921 to 0.953) and in Bland-Altman analysis (mean difference [human-algorithm] -0.0015; 95% CI -0.0054 to 0.0024), without evidence of systematic bias.

CONCLUSION

The authors confirmed the value of computer vision technology to develop an algorithm for RRI estimation from automatically processed intraoperative renal Doppler waveforms. This simple-to-use and efficient tool further adds to the clinical and research value of RRI, already the "earliest" among several early AKI biomarkers being assessed.

Heart Failure and Kidney Disease

Kidney disease is commonly found in heart failure (HF) patients. They share many risk factors and common pathophysiological pathways which often lead to mutual dysfunction. Both haemodynamic and non-haemodynamic mechanisms are involved in the development of renal impairment in heart failure patients. Moreover, the presence of a chronic kidney disease is a significant independent predictor of worse outcome in chronic as well as in acute decompensated HF. As a consequence, an accurate evaluation of renal function plays a key role in the management of HF patients. Serum creatinine levels and glomerular filtration rate (GFR) estimates are the corner stones of renal function evaluation in clinical practice. However, to overcome their limits, several emerging glomerular and tubular biomarkers have been proposed over the last years. Alongside the renal biomarkers, imaging techniques could complement the laboratory data exploring different pathophysiological pathways. In particular, Doppler evaluation of renal circulation is a highly feasible technique that can effectively identify HF patients prone to develop renal dysfunction and with a worse outcome. Finally, some classes of drugs currently used in heart failure treatment can affect renal function and their use can be influenced by the presence of chronic kidney disease.