Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved. Noninvasive assessment of haemodynamics in resistant hypertension: the role of the renal resistive index Konstantinos Kintis a , Costas Tsioufis a , Alexandros Kasiakogias a , Kyriakos Dimitriadis a , Dimitris Konstantinidis a , Eirini Andrikou a , Ioannis Andrikou a , Sotirios Patsilinakos b , Dimitris Petras c , Demetrios Vlahakos d , and Dimitris Tousoulis a Objective: The association of resistant hypertension (RHTN) with renal haemodynamics is unclear. Our aim was to evaluate differences in haemodynamic characteristics of patients with RHTN compared with patients with controlled hypertension (HTN) at the level of the heart, kidney and aorta. Methods: We studied 50 patients with RHTN confirmed by ambulatory blood pressure monitoring and 50 controlled hypertensive patients matched for age and sex. All participants underwent renal Doppler ultrasound to determine the renal resistive index (RRI), a complete echocardiographic study including measurements of diastolic function and evaluation of augmentation index. Results: Hypertensive patients with RHTN compared with those without RHTN had a significantly decreased E/A ratio (by 0.12, P ¼ 0.043), an increased E/e 0 ratio (by 3.1, P < 0.001), increased albumin-to-creatinine ratio levels (by 49 mg/g, P ¼ 0.023) and a significantly higher RRI (by 0.078, P < 0.001) but similar augmentation index values (P ¼ 0.79). Logistic regression revealed that presence of RHTN was the strongest predictor of an RRI more than 0.7 after controlling for other haemodynamic variables including blood pressure levels. Receiver-operator characteristic analysis revealed an area under the curve for prediction of RHTN by the RRI alone of 80.3% (95% confidence interval: 0.72–0.89, P < 0.001). An RRI cut- point of 0.648 has a sensitivity of 78% and a specificity of 72% for prediction of RHTN. Conclusion: In a well treated hypertensive population, patients with RHTN show more pronounced renal and cardiac haemodynamic dysfunction compared with patients with controlled HTN. A greater RRI seems to be associated with RHTN and may help identify such patients. Keywords: renal haemodynamics, renal resistive index, resistant hypertension Abbreviations: ACR, albumin-to-creatinine ratio; AIx, augmentation index; AUC, area under the curve; BP, blood pressure; DM, diabetes mellitus; GFR, glomerular filtration rate; HTN, hypertension; LV, left ventricular; LVH, left ventricular hypertrophy; MDRD, Modification of Diet in Renal Disease; RHTN, resistant hypertension; RRI, renal resistive index; V max , peak systolic velocity; V min , minimal diastolic velocity INTRODUCTION H ypertension (HTN), a leading independent risk factor for morbidity and mortality worldwide, has a well established bidirectional cause-and- effect relationship with kidney disease based on pathophy- siological and epidemiological data. Out of a series of clinical and laboratory markers of kidney dysfunction, there has been an increasing interest in studying renal haemody- namics by means of the renal resistive index (RRI) – a noninvasive and reproducible measure – in patients with cardiovascular diseases including HTN. The RRI is derived from intrarenal Doppler waveforms and seems to be a product of complex interaction between renal and systemic vascular haemodynamics. Although RRI has been used for diagnostic and prognostic assessment in renal vascular disease and chronic kidney disease including transplan- tation [1,2] and has been a marker of renal and extrarenal organ damage [3], a number of studies indicate that this index actually reflects systemic haemodynamics and depends on the aortic pulse pressure (PP) [4,5]. Research in hypertensive patients has shown that an increased RRI is associated with cardiovascular risk factors [6], target organ damage [3] as well as adverse cardiovascular and renal outcomes [7]. Despite the improvement in the pharmacological treat- ment of HTN, a huge number of patients remains with uncontrolled blood pressure (BP), and among them a portion (about 5% depending on the definition) suffer from resistant HTN (RHTN) [8]. The latter has a more complex pathophysiology and is accompanied by more pronounced subclinical target organ damage and a higher risk for cardiovascular and renal events [8]. In the present study, we investigate differences in the degree of subclinical target Journal of Hypertension 2017, 35:578–584 a First Cardiology Clinic, National and Kapodistrian University of Athens, Hippokration Hospital, b Department of Cardiology, Konstantopoulio General Hospital, c Nephrology Department, Hippokration Hospital and d Department of Internal Medicine, University of Athens, Attikon University Hospital, Athens, Greece Correspondence to Costas Tsioufis, MD, First Cardiology Clinic, University of Athens, Hippokration Hospital, 114 Vas. Sofias Ave, 11527 Athens, Greece. Tel: +30 2 106 131 393; fax: +30 2 132 089 522; e-mail: ktsioufis@hippocratio.gr Received 20 July 2016 Revised 2 November 2016 Accepted 5 November 2016 J Hypertens 35:578–584 Copyright ß 2017 Wolters Kluwer Health, Inc. All rights reserved. DOI:10.1097/HJH.0000000000001206 578 www.jhypertension.com Volume 35  Number 3  March 2017 Original Article