Estimation of renal functional reserve in patients with preserved renal function and coronary microvascular dysfunction
Authors: Bora M , Sakalidis A , Dimitriadis K , Giannou P , Kapota A , Chalkia A , Kourniotis D , Alexakou Z , Koulouriotis A , Aggelis G , Stamboliou E , Stathopoulou E , Tsiachris D , Petras D , Tsioufis K 
Published: June 2024

Abstract

Introduction
Renal Functional Reserve (RFR) is a field of scientific debate and may be a valuable diagnostic tool for the early detection of subclinical renal disease. According to literature, chronic kidney disease is related to cardiovascular disease (CVD), however the available data on the association of early renal dysfunction and CVD are sparse.

Purpose
The aim of the present study is to evaluate RFR in patients with coronary microvascular dysfunction (CMD) and preserved renal function [eGFR≥ 60 ml/min/1.73m2 (CKD-EPI) and proteinuria&lt; 400mg/24h].

Methods
This is a single-center, prospective study enrolling patients with CMD. We are presenting preliminary resuts. In the absence of significant coronary artery stenosis, functional coronary circulation assessment was performed for all patients. Coronary flow reserve (CFR) and index of microvascular resistance (IMR) were measured invasively. In all participants, RFR was estimated by endogenous creatinine clearance after oral protein load (cooked meal, 1.2gr/kg). Normal RFR was defined as ≥30 ml/min/1.73m2. Also, patients with CMD were offered 24-hour Ambulatory Blood Pressure Monitoring (ABPM).

Results
A total of 25 participants have been enrolled so far in study: 11 without CMD - non-CMD group [7 female, 64%, mean age: 52.9±8.8 years) and 14 with INOCA – CMD group (11 female, 79%, mean age : 53.5±10,3 years). CMD patients were classified into 2 groups, structural & functional endotype (CFR&lt;2.5 & IMR≥25 considered abnormal). The RFR value for CMD group is 7.4±6.3 ml/min/1.73m2, while for control group 36.3±5.8 ml/min/1.73m2 (p&lt;0.005), This difference between groups was found to be statistically significant after controlling for confounding factors. It was found that RFR value for functional CMD endotype was 3.8±2.6 ml/min/1.73m2, while for patients with structural endotype 9.6±7,2 ml/min/1.73m2 (p=0.06). Furthermore, no statistical significance was found between RFR & IMR, CFR indices (p =0.35, p =0.23 respectively). According to data from 24hr ABPM , there ere no significant differences in ambulatory blood pressure (systolic & diastolic) between the 2 endotypes of CMD (p=NS for all), as well as no relationship with RFR (p = 0.6, p =0.6 respectively) was observed. However, the proportion of non-dippers (for both SBP and DBP) was significantly higher in functional CMD endotype (p&lt;0.05). It was not found correlation between RFR and non-dipping phenotype, for both SBP and DBP.

Conclusion
Abnormal RFR has been observed in all patients with microvascular dysfunction. In addition, patients with functional CMD show a lower RFR value compared to those with structural. RFR is not related to levels of BP or the non-dipping pattern. Given the hypothesis that the assessment of renal functional reserve is an early diagnostic tool for subclinical renal disease, the early identification of patients with specific phenotypes could contribute to the individualization of therapeutic interventions.