Evaluation of renal functional reserve in patients with preserved renal function and coronary microvascular disease
Authors: Bora M , Sakalidis A , Dimitriadis K , Giannou P , Damianaki A , Kapota A , Chalkia A , Kourniotis D , Alexakou Z , Dri I , Leontsinis I , Chrysohoou C , Aznaouridis K , Petras D , Tsioufis K 
Published: October 2024

Abstract

Background/introduction
Renal Functional Reserve (RFR) stands as a subject of significant scientific discussion,holding promise as a diagnostic tool for early detection of subclinical renal disorders. Literature establishes a link between chronic kidney disease & cardiovascular disease (CVD).

Purpose
This study aims to assess RFR in patients with coronary microvascular dysfunction (CMD), while maintaining preserved renal function (eGFR≥60ml/min/1.73m2 by CKD-EPI criteria)&proteinuria&lt;400mg/24hr. The investigation seeks to provide insights into the nuanced relationship between renal function&CMD, offering potential early indicators of CVD.

Methods
This is a single-center, prospective study enrolling patients with CMD. In the absence of significant coronary artery disease, functional coronary circulation assessment was performed. Coronary flow reserve (CFR) & index of microvascular resistance (IMR) were measured invasively with bolus thermodilution technique. 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 - control group [7 female, 64%, mean age: 52.9±8.8 years) & 14 with CMD – 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 were considered abnormal). The RFR value for CMD & control group is 7.4±6.3 vs 36.3±5.8 ml/min/1.73m2 respectively (p&lt;0.05). This difference between groups remained statistically significant after controlling for confounding factors. It was found that RFR value for functional & structural CMD endotype was 3.8±2.6 & 9.6±7,2 ml/min/1.73m2 respectively (p=0.06). Furthermore, no statistical significance was found between RFR and IMR, CFR indices. According to data from ABPM, there were no significant differences in ambulatory blood pressure (both systolic and diastolic) between the two endotypes of CMD, as well as no relationship with RFR was observed. However, the proportion of non-dipping BP pattern was significantly higher in functional CMD endotype (p&lt;0.05). It was not found correlation between RFR & non-dipping phenotype.

Conclusions
Impaired RFR is evident across all individuals experiencing microvascular angina. Furthermore, those with functional CMD exhibit a diminished RFR when compared with their counterparts with structural CMD. RFR does not exhibit a correlation with blood pressure levels or the absence of a nocturnal dipping pattern. In light of the hypothesis asserting that appraising renal functional reserve serves as an early diagnostic measure for subclinical renal disorders, promptly recognizing individuals with distinct phenotypes could facilitate tailoring therapeutic interventions on an individual basis.Functional Coronary AngiogramCMD group baseline characteristics