1. INTRODUCTION
Patients with chronic kidney disease (CKD) are at a higher risk for cardiovascular disease (CVD) compared to the general population; CVD is responsible for about 50% of deaths in CKD patients [1]. The interrelation between kidney and heart function has long been recognized and current research effort is focused in delineating the exact mechanisms behind this complex pathophysiology. Increased cardiovascular risk in individuals with CKD is due partly to the high prevalence of traditional risk factors, such as hypertension and diabetes, but also to non-traditional cardiac risk factors that are particularly relevant to patients with chronic kidney disease, including decreased glomerular filtration and albuminuria. Early atherosclerosis progression and endothelial cell dysfunction, uraemia and kidney failure, neurohormonal dysregulation, anaemia and iron disorders, mineral metabolic derangements and inflammatory pathways may all contribute to the phenotype of cardio-renal syndrome [2-6].
Non-invasive and widely available diagnostic methods that may detect preclinical functional and structural myocardial abnormalities are needed in order to identify CKD patients at higher risk for CVD [7-9]. Echocardiography is an essential tool for the assessment of cardiac structure and function in several patient groups, including CKD patients, while various echocardiographic indices have been shown to predict adverse CVD outcomes. Classic echocardiographic indices of left ventricular (LV) systolic and diastolic function may not be sensitive enough in detecting early myocardial deterioration in CKD patients [10, 11]. Two-dimensional speckle tracking echocardiography (2DSTE) is a semi-automated modality for quantification of LV systolic as well as diastolic function in an operator-independent manner. LV myocardial deformation may be assessed in the longitudinal, radial and circumferential plane but peak global longitudinal strain (GLS) has been shown to be the most important load-independent index that gives an efficient and rather objective measurement of LV systolic and diastolic function with many prognostic implications [10, 12-17].
Dipyridamole stress echocardiography (DIPSE) is mostly used to measure coronary flow reserve (CFR) in a non-invasive way. CFR is used for evaluating both the presence of significant epicardial stenosis and the microcirculatory function in the left anterior descending artery (LAD) territory; a CFR value <2 is correlated to significant microvascular dysfunction and is proposed to be a strong predictor of epicardial coronary artery disease (CAD) [18]. Impaired CFR has been also advocated as an adverse prognosticator for CVD [19, 20].
The aim of the current study was to investigate differences in classic, 2DSTE-related indices, CFR and other DIPSE-induced changes in various echocardiographic parameters between: 1) healthy controls and age-matched younger CKD patients, 2) younger versus older CKD patients with similar clinical characteristics.