The effect of a central arteriovenous anastomosis on circulatory haemodynamics during a 2-minute active stand

Abstract

Orthostasis induces a rapid and large gravity-related shift of 500–1000 ml of blood volume from the thorax to the vasculature below the diaphragm. The bulk of the shift in fluid is achieved in the first 10 seconds and is complete by 2 to 3 minutes [1]. It has been shown that the fall in central blood volume and subsequent reduction in cardiac output is the dominant hypotensive mechanism which may lead to orthostatic intolerance [1–3]. The ROX Coupler is a novel device indicated for the treatment of resistant hypertension. The device is inserted percutaneously and creates an arteriovenous anastomosis at the iliac level, leading to a shunt of approximately 1000 ml/ min. The anastomosis has been shown to have significant effects on resting cardiovascular haemodynamics including a reduction in systemic vascular resistance, reduced activation of the renin–angiotensin system and increased cardiac output [4]. Herein, we present novel data assessing the effect of the anastomosis during orthostasis. In this pilot study we investigated ten subjects who had previously undergone implantation of the ROX Coupler and compared them to ten age-matched control subjects without a central arteriovenous anastomosis. The study was approved by the local National Health Service (NHS) research ethics committee (REC 19/LO/0964). The full inclusion and exclusion criteria are detailed in the supplementary material. Participants were attached to a digital non-invasive beatto-beat blood pressure monitor and patches for impedance monitoring using the Task Force® Monitor system (TFM, CNSystems, Graz, Austria). Once the Task Force® Monitor was attached, subjects lay supine for 15 minutes to allow for stabilisation. Baseline circulatory haemodynamics were then recorded. All subjects were in normal sinus rhythm during the testing. Subjects were then instructed to undergo an active stand. Subjects remained standing for 2 minutes. Haemodynamic variables were recorded every 10 s. Subjects were then returned to the supine position. There was no significant difference in age (68 ± 7 vs. 69 ± 11, P = 0.813) or BMI (29.1 ± 4.52 vs. 27.7 ± 4.83, P = 0.560) between the anastomosis and control groups. There was a significantly higher proportion of patients with hypertension in the anastomosis group than in the control group (supplementary material Table 1). Subjects with an anastomosis had a significantly higher heart rate at baseline when compared to control subjects (P = 0.006). Two-way ANOVA revealed no significant difference in heart rate, systolic blood pressure or diastolic blood pressure response between the two groups during orthostasis (group × time interaction P = 0.347, P = 0.583 and P = 0.435) (Supplementary material Fig. 2, Fig. 1a and b). Similarly, there was no significant difference in the response to orthostasis in stroke and cardiac index between the two groups (group × time interaction, P = 0.078 and P = 0.630). (Supplementary material Fig. 3 and Fig. 1c). There was also no significant difference in the response to orthostasis in thoracic fluid content or indexed total peripheral resistance between the anastomosis and control groups (group × time interaction, P = 0.337 and P = 0.167) (Supplementary material Figs. 4 and 5). This study reports that a central arteriovenous anastomosis does not negatively affect the haemodynamic response during orthostasis. This is an important finding considering that the central arteriovenous anastomosis increases venous return and subsequent cardiac index in these subjects, which maintains blood pressure during orthostasis. Further studies are required to assess whether reversing the gravitation fall in blood volume, via an anastomosis, leads to improved symptoms in subjects with orthostatic intolerance. * Rajdip Dulai [email protected]