1. Introduction
Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by a wide range of clinical manifestations and an elevated risk of developing cardiovascular diseases (CVD) compared to the age- and sex-matched general population [
1]. CVD is the leading cause of mortality in SLE, attributed to accelerated atherosclerosis and altered vascular function, even at early, subclinical stages [
2].
Arterial stiffness reflects changes in the mechanical properties and function of large arteries either as an essential part of atherosclerosis-prone pathophysiological mechanisms or as a consequence of CVD [
3]. Its independent association with increased cardiovascular risk is widely known and its assay could assist the CVD stratification in a wide range of populations. Pulse wave velocity (PWV) constitutes a non-invasive, simple measurement of arterial stiffness, already measured, and validated in a plethora of studies. It has been recognized as a marker of vascular aging and has been found elevated in early stages of CVD development or in high-risk patients (e.g., diabetes) [
4]. Thereby, scientific societies recommend measuring of PWV as a screening test in the general population or as a surrogate index of CVDs, advocating its routine clinical application in cardiology daily practice [
5]. In the context of SLE, characterized by higher CV risk, a recent meta-analysis of 9 studies found significantly higher PWV in SLE patients compared to controls [
6].However, the measurement of PWV is notably susceptible to blood pressure variations, posing a significant limitation. To overcome it, another formula of PWV calculation, termed cardio-ankle vascular index (CAVI) has been proposed [
7]. Previous studies have demonstrated the discriminatory power of CAVI to stratify the CVD risk in patients without previous overt CVDs [
8]. Despite the increasing use of CAVI in other patient populations, its clinical application in SLE cohorts remains unexplored, indicating a significant gap in research.
The role of myocardial strain and the ventriculo-arterial coupling (VAC) in the pathophysiology of CVDs is well established [
9]. The former can detect even subtle myocardial dysfunction in a wide spectrum of cardiac and non-cardiac conditions. A previous study has reported a marked increase in global longitudinal strain (GLS), an index of myocardial strain, in SLE patients even without apparent cardiac disease [
10]. Besides this, the vascular injury and increased arterial stiffness in SLE patients seems to be a rational explanation of the frequent cardiovascular complications recorded in SLE patients [
11]. The interplay between cardiac dysfunction and increased afterload due to arterial stiffening is well-depicted by VAC estimation. Several parameters have been proposed for VAC calculation [
12]. Recently, the PWV/GLS ratio has been proposed as a reliable, feasible, easily performed, and reproducible index of VAC with prognostic value [
13]. However, very scarce data exist about the impact of SLE on VAC [
14]. From the clinical perspective the early identification of cardiovascular dysfunction with impaired VAC could stratify the cardiovascular risk and determine the therapeutic management of SLE.
The detection of biomarkers of myocardial injury, such as troponin, has raised as an additional way to assess the cardiac dysfunction in SLE patients. A recently published study demonstrated that women with SLE, normal kidney function and increased PWV, were more likely to have detectable levels of high-sensitivity troponin (hsTn) [
15]. This finding suggests hsTn could help stratify the risk of atherosclerotic lesions presence in SLE patients [
16]. Emerging evidence points to elevated troponin levels in SLE patients as indicative of subclinical cardiac involvement, occurring even in the absence of overt cardiac complications such as myocarditis or acute myocardial infarction [
17].
The objective of the present study was to conduct a comparative analysis of the CAVI, VAC, and hsTn between SLE patients and healthy controls. In addition, we assessed the relationship of CAVI and troponin with disease activity, and other clinical parameters.
4. Discussion
In the present study, we comparatively evaluated arterial stiffness, GLS, VAC and troponin levels between SLE patients and healthy subjects. We observed increased CAVI, GLS, and troponin and lower VAC levels in SLE patients compared to controls. Those significant differences remained after excluding from analysis patients with classical cardiovascular risk factors, such as hypertension or hyperlipidemia. Moreover, SLE patients with at least moderate disease activity had even greater CAVI and troponin levels than their counterparts with low disease activity. Notably, SELENA-SLEDAI ≥4, a measure of at least moderate disease activity was found to independently predict CAVI and troponin levels, emphasizing the direct impact of SLE activity on these cardiovascular markers.
SLE may lead to subtle changes in cardiac function, where early detection could substantially mitigate the irreversible cardiovascular system damage. The measurement of arterial stiffness in SLE population is associated with higher cardiovascular risk [
24]. Most but not all observational studies have reported higher arterial stiffness than controls [
25,
26], using the classical carotid-femoral probes for PWV calculation, with its inherent limitations. To our knowledge, this is the first study evaluating arterial stiffness in SLE patients using the CAVI technique. Our study showed that SLE patients had significantly higher CAVI levels than controls, demonstrating CAVI’s utility in assessing arterial stiffness without the influence of blood pressure on those measurements. Prior research has highlighted the role of age, mean arterial pressure, renal function, and various comorbidities on PWV among SLE patients [6, 27]. SLE is usually complicated with CVD and therefore increased arterial stiffness may be the late consequence of previous complications and/or co-existing CVD. In our study, SLE patients were CVD-free, while previous nephritis or pericarditis did not confer overt changes in kidney and cardiac function, respectively. Despite the absence of obvious cardiovascular complications, our findings further emphasize that active SLE disease is associated with CAVI elevation, and their interplay seems independent of cardiovascular complications. This is of clinical importance outlining that a high cardiovascular risk persists even in our CVD-free SLE population, which has been reported in previous studies [24, 28]. Regarding the prognostic utility of CAVI in SLE patients, its employment for cardiovascular risk stratification could revolutionize patients’ management by endorsing more aggressive therapeutic approaches in otherwise uncomplicated SLE patients. Numerous studies have demonstrated the association of CAVI with the development of cardiovascular events in patients with established atherosclerotic CVDs (ASCVDs) [
29,
30] or those at high risk for ASCVDs [
31]. No data are available for the prognostic value of CAVI in SLE population and this remains to be proved.
In agreement with previous studies, we confirmed the significant elevation of GLS in our SLE patients. Number of studies have previously reported the association of GLS with SLE, even in the absence of overt cardiac dysfunction [
32]. Such an observation has convinced some investigators to recommend the application of speckle tracking technique for the diagnosis of cardiac complications (e.g. myocarditis) or cardiac involvement of SLE patients at an early stage [
33]. Regarding the complex interplay between cardiac and vascular function in SLE patients, we hypothesized that VAC assessment may be superior to GLS or arterial stiffness solely measurement [
34]. While most related studies have focused on the diagnostic and prognostic value of VAC in hypertensive patients [
35], the role of VAC in evaluating the effects of novel anti-hypertensive and anti-diabetic treatments has been also noted [
36]. In our cohort, the calculated CAVI/GLS ratio, as a measure of VAC showed significantly lower values in SLE than controls, mainly driven by the elevated CAVI levels. The presence of at least moderate active disease was associated with further decline in VAC. Up to now, very scarce data exist about the impact of autoimmune diseases on VAC [
37]. A brief report of a small group of female patients with SLE showed considerably increased PWV/GLS ratio compared to controls [
10]. This is the second study in SLE population reporting a declined VAC which could of clinical relevance, since VAC has the potential to detect early organ damage in SLE and evaluate medication efficacy is promising. This is further supported by the independent association of VAC with hsTn levels. Finally, prospective studies are needed to confirm this hypothesis and the the formula of CAVI/GLS ratio for VAC assessment requires further validation.
HsTn is a well-known biomarker of myocardial injury. After excluding obvious acute, subacute or chronic cardiac complications, like myocarditis or myocardial infarction, hsTn may be found elevated in SLE implicating cardiac involvement [
14]. In agreement with recent research, our study verified increased hsTn levels in SLE patients characterized by lack of apparent kidney or cardiac dysfunction and a low CV risk profile [
12]. Compared to that study, which utilized PWV and categorized hsTn and PWV as dichotomous variables, our study employed CAVI to assess arterial stiffness and analyzed both hsTn and CAVI as continuous variables. This approach revealed a significant, independent association between hsTn levels, CAVI and VAC, suggesting a link between subtle myocardial injury in SLE and functional alterations in cardiovascular function including large arteries. Although our study could not establish a direct causal link, the significant impact of SELENA-SLEDAI on hsTn levels highlights a complex relationship between inflammatory processes, myocardial injury, and arterial stiffness in SLE patients. Wineau L et al (2018) reported inflammatory interstitial remodeling and oedema as the possible causes of hsTn elevation and subclinical myocardial injury, detectable by cardiac magnetic resonance (CMR) [
38]. The clinical significance of even a slight rise in hsTn is well-recognized across various diseases, emphasizing its utility as a highly sensitive marker for cardiac diseases [
39,
40]. Therefore, the elevated values and the interplay of those two potent CV predictors (CAVI and hsTn), in the SLE population predispose patients to an adverse prognosis. In a recent large, randomized, double-blind, placebo-controlled, multicenter trial, hsTn predicted the incidence of CV events during a follow-up period of over 20 months among SLE patients without a history of CVD [
41]. However, more data are required to confirm this hypothesis and implement the regular use of hsTn in SLE population, especially in those without overt CVD.
There are several limitations in the current study. The relatively small sample size of SLE patients without CVD, with mostly low or moderate disease activity and the limited number of CV risk factors might have impeded our ability to detect differences in GLS or identify independent associations with demographic and clinical variables in patients with more active disease. Moreover, the cross-sectional design of our study did not allow us to draw firm conclusions about the predictive value of CAVI for cardiovascular events in SLE patients, as well as the potential role of treatment in modifying CAVI measurements. The addition of CMR examination in our study would have provided more comprehensive information about cardiac involvement. Additionally, the possibility of mild chronic myocarditis cannot be definitively ruled out. Lastly, as our study was conducted at a single center and predominantly included female and Caucasian patients, the generalizability of the findings to broader populations remains uncertain.