Inflammation is central to the development of atherosclerosis, and pathogenic lesions in arteries are reported from early childhood onward.1 Children with acute and chronic inflammatory diseases, including Kawasaki disease, inflammatory bowel disease, psoriasis and juvenile arthritis may have persistent adverse changes in their vascular structure and function, although the implications for later cardiovascular disease risk are largely unknown.2–4 Toxic shock syndrome (TSS) is a rare, acute, life-threatening toxin-mediated illness causing fulminant vascular inflammation and dysfunction, often resulting in multiorgan failure. It is unknown whether children with TSS have changes in either the macro- or microvasculature years after the acute illness and are at increased long-term cardiovascular risk.
We aimed to investigate whether participants with past TSS have quantitative subclinical changes in macro- and retinal microvascular parameters indicative of a possible increased in cardiovascular risk. The retinal and coronary vasculature share many similarities and respond to common metabolic risk factors.5 We hypothesized that, compared with control participants, TSS participants have a more adverse macrovascular profile [eg, increased carotid and aortic intima-media thickness (IMT), increased pulse wave velocity (PWV) and decreased carotid artery distensibility and compliance] and retinal microvascular profile (eg, wider venules, narrower arterioles, reduced fractal dimension and increased tortuosity).
PATIENTS AND METHODS
We performed a case-control study including participants aged 6–30 years who had TSS at least 2 years previously and control participants of similar age and sex, recruited from The Royal Children’s Hospital Melbourne and Monash Medical Centre, Melbourne, Australia. Cases fulfilled the Centers for Disease Control and Prevention case definition for either probable or definite TSS.6 Exclusion criteria were pregnancy, diabetes, known atherosclerotic cardiovascular disease, treatment for hypertension and/or hyperlipidemia and chronic auto-immune inflammatory conditions. The study was approved by the human research ethics committee of both hospitals, and written informed consent was obtained from the parents or adult participants.
All data were collected at a single visit after a minimum of 6 hours of fasting. Demographic data and anthropometric measurements (BC 418, Tanita, Tokyo, Japan) were obtained. Pubertal status was based on self-reported Tanner stage. The mean of 3 blood pressure measurements (SphygmoCor XCEL, AtCor Medical, NSW, Australia) was recorded. Blood was collected for measurement of high-sensitivity C-reactive protein (Abbott Architect, IL), glucose, triglycerides, total cholesterol, high density lipoprotein and low density lipoprotein cholesterol (Vitros 5600, Ortho-Clinical Diagnostics, NJ) during the study visit.
Carotid and Aortic Intima-Media Thickness
Ultrasound images of the carotid artery and the abdominal aorta were acquired using Vivid i (General Electronics Healthcare, Little Chalfont, UK) with simultaneous electrocardiogram (ECG) gating as previously described.7,8 Cine loops of at least 5 cardiac cycles focused on the intima-media complex of the posterior wall of the right common carotid artery 1 cm proximal to the carotid bulb were recorded for offline analysis. Imaging was focused on the distal 10–15 mm of the abdominal aorta.
The IMT of the far wall 1 cm from the carotid bulb was measured at end diastole using a semiautomated software, Carotid Analyzer for Research (Medical imaging applications LLC, Coralville, IA). The “mean IMT” refers to the average IMT in the selected area of measurement while the “maximum IMT” to the thickest IMT measurement within that segment.8 The mean of these “mean IMT” or “maximum IMT” measurements from 5 end-diastolic frames was used in analyses.8
The 5 best-quality frames of the abdominal aorta were selected from the recorded cine loops for analysis using the same procedure. All IMT measurements were performed by a single grader blinded to subject status. The intrarater reliability was assessed on 10 masked subjects. Intraclass correlation for carotid IMT and aortic IMT was 0.92 [95% confidence interval (CI): 0.69–0.98] and 0.89 (95% CI: 0.59–0.97), respectively.
Pulse Wave Velocity, Carotid Artery Distensibility and Compliance
Arterial stiffness was assessed by carotid femoral PWV using SphygmoCor XCEL (AtCor Medical), according to manufacturer’s protocol. Only results meeting the in-built quality control criteria were analyzed. The mean of 3 measurements was calculated.
The minimum carotid artery lumen diameter, distensibility [(maximum diameter−minimum diameter)/(minimum diameter) × 100%] and compliance [(maximum diameter−minimum diameter)/pulse pressure] were calculated by the Carotid Analyzer software once the borders were set. Because of the poor image quality of the proximal aortic wall, these parameters were not obtained for the aortic data.
Disc-centered retinal photographs of both eyes were obtained using nonmydriatic retinal camera (CR6-45NM, Canon, Tokyo, Japan or model VX 10i KOWA, Tokyo, Japan). Retinal images were analyzed at Singapore Eye Research Institute using a semiautomated computer-assisted program [Singapore I Vessel Assessment (SIVA), version 4.0, Singapore Eye Research Institute, Singapore] by trained graders blinded to subject status. Using a standardized protocol, the following parameters were measured in the region 0.5–2.0 disc diameters from the disc margin: retinal microvascular caliber, branching angle, fractal dimension and tortuosity of both arterioles and venules. Intra/intergrader reliability of the SIVA-derived retinal microvasculature data has been reported previously.9
Measures of arterial structure and function were analyzed as continuous variables and expressed as mean and standard deviation or median and interquartile range for normally distributed or skewed data, respectively. Arteriolar and venular tortuosities were log-transformed because of skewed distributions and expressed as geometric mean and geometric mean ratios. Multivariable linear regression was applied to analyze the association between TSS status and macro/microvascular parameters, after adjusting for age, sex, mean arterial blood pressure, body mass index, pubertal status, waist–hip ratio and total cholesterol. To investigate whether the macro- and microvascular parameters between cases and controls differ if the participants were children and adolescents (younger than 18 years) or adults (18 years and older), the effect modification by age group was investigated using multivariable linear regression. All analyses were performed using Stata 13.0 (Stata Corporation, College Station, TX).
A total of 22 TSS cases and 60 controls were studied. Other than a higher mean waist–hip ratio in the control (0.78 ± 0.06) compared with TSS participants (0.74 ± 0.06), there were no differences between the groups, including age, sex, anthropometry, systolic and diastolic blood pressure, triglycerides, total cholesterol, low density lipoprotein cholesterol, high density lipoprotein cholesterol, glucose, high-sensitivity C-reactive protein or pubertal status.
The mean age ± standard deviation at TSS diagnosis was 8.7 ± 4.5 years, and the mean time since the acute illness was 5.9 ± 3.1 years. TSS was due to Staphylococcus aureus in 17 cases (77.3%) and Streptococcus pyogenes in 5 (22.7%). Ten (45.5%) of the TSS cases were admitted to the intensive care unit during their acute illness, 19 (86.4%) were treated with clindamycin and 9 (40.9%) received intravenous immunoglobulin. Four (18.2%) had residual morbidity at discharge, predominantly neurologic or movement limitations from either joint or muscular involvement, or general deconditioning. None had long-term renal impairment.
There were no differences in carotid and aortic IMT between TSS and control participants (Table 1). Compared with controls, TSS participants had reduced PWV (Table 1). There was some evidence of differences in retinal vascular parameters, in particular, TSS participants had wider arteriolar caliber, reduced total fractal dimension and venular tortuosity (Table 1).
The effect modification by age group (child/adolescents versus adults) on the outcomes for all macro- and microvascular parameters was statistically insignificant; therefore, analysis was not stratified by age group.
Apart from a decrease in total retinal fractal dimension in individuals after TSS, we found no other adverse vascular changes. The fractal dimension is a mathematical measure that quantifies the geometric complexity of the retinal circulation.10 Fractal dimensions outside the optimum range in adult studies are associated with cardiovascular risk factors (age, hypertension, diabetes and chronic kidney disease), cardiovascular disease (stroke and coronary heart disease) and ocular risk factors (cataracts, refractive error).10 A smaller fractal dimension reflecting rarefaction of the retinal vasculature is associated with higher blood pressure in children, although the clinical implications in those with normal blood pressure after TSS are unknown.11
We found healthier vascular function as measured by PWV in individuals after TSS. This finding is consistent with the changes in retinal arteriolar caliber and venular tortuosity, which are associated with less adverse cardiovascular outcomes and risk profiles in adult studies.12
Our study is the first to describe quantitatively measured macro- and retinal microvascular parameters after TSS. Limitations of our study include the small sample size, which was unavoidable for a rare condition and limited the statistical power. The wide age range of TSS participants was necessary to maximize sample size, but this introduces challenges in interpretation of vascular parameters, which differ between children, adolescents and adults. We adjusted for this by frequency matching by age and sex with control participants, including age and pubertal status in the multivariable regression model and by exploring effect modification by age groups.
In summary, we found no evidence of adverse vascular changes after TSS except a reduction in retinal total fractal dimension. The rarefaction of the retinal microvasculature found in our study requires validation in further studies to understand possible clinical implications for TSS patients.
The authors thank Jane Koleff from Murdoch Children’s Research Institute for training and providing technical support for the research staff and the assistance of Greta Goldsmith, BBiomedSc, and Meg Kaegi, BSc, from the same institution in study logistics and data acquisition.
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