Elevated red cell distribution width level is associated with oxidative stress and inflammation in a canine model of rapid atrial pacing

Abstract

Atrial fibrillation (AF) is the most common clinically significant cardiac arrhythmia. The prevalence of AF has been increasing for the past few decades with the aging population [1]. The pathogenesis underlying AF is multi-factorial. Accumulating evidences suggest that oxidative stress and inflammation may play an important role in the pathogenesis and perpetuation of AF [2–6]. The red blood cell distributionwidth (RDW) reflects variability in the size of circulating red blood cells (RBCs) and is mostly used in the differential diagnosis of anemia. Recently, several studies showed the potential association of increased RDW levels with adverse cardiovascular events. Elevated RDW levels may also have been correlated with nonvalvular AF [7]. However, the potential mechanisms between elevated RDW and the development of AF are still unclear. In the present study, we aimed to assess whether elevated levels of RDW are associated with oxidative stress and inflammation markers in a canine model of rapid atrial pacing (RAP). In the present study, all animals were cared for and used in compliance with the Experimental Animal Administration Committee of Tianjin Medical University and the Tianjin Municipal Commission for ‘Experimental Animal Control’. For this study, 20 mongrel dogs of either gender were randomly divided into two groups: sham group and paced group, 10 dogs in each group. We used a previously described approach to induce and maintain sustained AF in our experimental animals [8]. The dogs were anesthetized with intravenous 3% sodium pentobarbital (30 mg · kg−1). After mechanical ventilation, under aseptic condition, a modified unipolar J pacing lead (St. Jude Medical, USA) was inserted via the right jugular vein and the distal end of the lead was positioned in the right atrium or right auricular appendage under fluoroscopy. The proximal end of the pacing lead was connected to a programmable pacemaker (Fudan University, China), which was implanted into a subcutaneous pocket in the neck. The dogs in the paced group were paced at 500 bpm (120-ms cycle length) with the 0.2-ms square-wave pulses at twice the threshold current for 2 weeks. The dogs in the sham group were also instrumented but without pacing. Electrocardiogram (ECG) was verified after 24 h in awake dogs to ensure continuous 1:1 atrial capture. Hemodynamics parameters were monitored by a multi-channel electrophysiological recorder (Hongtong TOP2001, China) at baseline and after 2 weeks of rapid atrial pacing (RAP). After the above treatment for 2 weeks, venous blood samples were obtained from the two groups of dogs, and RDW levels were analyzed using an automated hematology analyzer (Mindray BC6800, China). The serum levels of superoxide dismutase (SOD), malondialdehyde (MDA), Toll-like receptor 4 (TRL4) and interleukin-18 (IL-18) were measured by ELISA kit (Nanjing Jiancheng Bioengineering Institute, China). All animals were survived to the end of the experiment. There was no difference in gender, body weight, ventricular rate and blood pressure between the two groups whether at baseline and after 2 weeks of RAP (P N 0.05) (Table 1). Our study showed that the RDW level was increased apparently by RAP from 12.37% ± 1.48% to 14.83% ± 2.24% (P b 0.05). We investigated the circulating serum levels of SOD, MDA, TLR4 and IL-18 in the two groups and found that the levels of SOD, MDA, TLR4 and IL-18 were higher in the paced group compared to the sham group (P b 0.01) (Table 1). The serum levels of SOD, MDA, TLR4 and IL-18 had no correlation to RDW in the sham group (r = 0.014, P = 0.976; r = 0.479, P =0.276; r = 0.101, P = 0.830; r = 0.032, P = 0.946, respectively), whereas they were correlated to RDW levels (P b 0.05 or P b 0.01) in the paced group (Fig. 1). Several studies have shown that RDW, a laboratory measure of the variability of red blood cell sizes, is a strong independent predictor of increased morbidity and mortality in patients with cardiovascular disease [9–14]. Our recent study [15] indicated that RDWmay serve as a promising and useful marker for paroxysmal AF. Adamsson et al. [16] also showed that RDW was associated with incidence of AF independently of several cardiovascular, nutritional and hematological factors in a recent study of middle-aged subjects from the general population. However, there are limited data regarding the potential mechanisms between RDW and AF in animal models. The potential mechanism behind their relationship may result from a direct effect of changes in erythrocyte volume and function on the heart, or may reflect other pathophysiological processes acting