Background: Coarctation of the aorta (CoA) can be treated using surgery, balloon angioplasty or stent implantation. Although short-term results are excellent with all three treatment modalities, long term cardiovascular (CV) morbidity and mortality remain high, likely due to persistently abnormal vascular function. The effects of treatment modality on long term vascular function remain uncharacterized. The goal of this study is to assess vascular function in this patient population for comparison among the treatment modalities. Methods: Vascular function in large and small arteries will be prospectively assessed fusing multiple non-invasive modalities, and the results will be compared among the three groups of CoA patients previously treated using surgery, balloon angioplasty or stent implantation after frequency matching for confounding variables. A comprehensive vascular function assessment protocol was created to be used in 7 centers. The primary outcome is arterial stiffness measured by arterial tonometry. Inclusion and exclusion criteria were carefully established after consideration of several potential confounders. Sample size was calculated for the primary outcome variable. Conclusions: Treatment modalities for CoA may have distinct impact on large and small arterial vascular function. The results of this study will help identify the treatment modality that is associated with the most optimal level of vascular function, which, in the long term may reduce CV risk.

Study overview. This cross-sectional prospective observational study of patients with CoA previously treated using one of three treatment modalities assesses if treatment type is associated with differences in vascular function. The three treatment groups will be frequency-matched for key confounding variables.

Study feasibility. The investigators assembled a multi-disciplinary team with proven expertise in epidemiology, clinical trial design, congenital heart disease, non-invasive imaging, interventional cardiology, vascular function assessment, preventive cardiology and statistical analysis. A multicenter design is used to ensure sufficient statistical power in evaluating the hypothesis.

Participating centers and study core laboratories. Patients are recruited at six large pediatric cardiac centers from Portugal and USA.

Screening procedures. The medical records of potentially eligible patients are screened by a local study investigator using a pre-specified screening form to ensure that they satisfy our selection criteria.

Overview of the study workflow. Study procedures will occur in a one- or two-day visit. Upon arrival for testing, formal consent for participation will be obtained. Assessment of arterial stiffness, endothelial function, and blood sampling for biomarkers will be done while fasting. Cardiopulmonary stress test will be performed on the same day. CMR and ambulatory blood pressure monitoring (ABMP) will be arranged for the same or for the following day. When the study tests cannot be completed at the first visit, they will be completed within 3 months of the first visit. The study protocol was approved by the Institutional Review Board or Institutional Ethics Committee at each participating center, and informed consent and assent will be obtained, depending on age, from patients and their parents/legal guardians before trial enrollment.

Recruitment. A review of the patient database at each participating institution will be performed to assemble a cohort of patients with CoA who have previously undergone treatment with balloon dilation, surgery or stenting. Study data will be collected and managed using REDCap electronic data capture tools hosted at Boston Children's Hospital.

Data collection. A retrospective chart review will be performed to collect demographic and clinical data including severity of coarctation, type and details of CoA treatment and presence of associated conditions.

Diagnostic procedures.

Arterial Stiffness Plan & Rationale:

Measurements: Carotid-femoral PWV (cfPWV) will be measured using applanation tonometry. Segmental PWV is measured using CMR. Segmental measures of arterial distensibility will be measured using CMR. Other parameters that describe arterial stiffness reflect the relationship of arterial change in diameter to change in pressure and include aortic strain (relative change in diameter), compliance (absolute change in diameter in response to a change in pressure), distensibility (relative change in diameter in response to a change in pressure), and the aortic stiffness β index (distensibility using the logarithmic conversion of the relative pressure). Applanation tonometry, which uses a probe or tonometer to record the pulse wave with a transducer, is the most widely accepted method for estimating PWV and both the NIHem (Cardiovascular Engineering, Inc., Norwood, MA USA) and the SphygmoCor (AtCor Medical, West Ryde, NSW, Australia) devices have been validated in large cohort trials. Both devices will be used, based on local availability.

Endothelial Function Measurements: Endothelium-dependent reactive hyperaemia index and augmentation index will be measured using the EndoPAT 2000 system (Itamar Medical, Caesarea, Israel). The protocol includes measures to minimize the influence of the autonomic nervous system.

Pulse Waveform Analysis: Central aortic pressure and pulse pressure will be measured using applanation tonometry). Augmentation index will be measured using applanation tonometry and Endo-PAT. CAP, PP and AIx can be measured non-invasively using radial or carotid applanation tonometry (and Endo-PAT for AIx), calibrated by the peripheral diastolic and mean arterial pressure. Both the NIHem system and the SphygmoCor device were used.

Blood Pressure Phenotype will be measured using conventional standard techniques including auscultatory right arm BP measurement, measurement of BP gradient between arm and leg, BP response during treadmill exercise stress testing (ET) and ABPM. Based on the auscultatory BP and ABPM results, the appropriate children and adult guidelines will be used to classify patients. Patients currently on antihypertensive medication will be classified as hypertensive.

Biomarkers: The researchers will measure biomarkers of endothelial function (total oxides of nitrogen- NOx and ADMA), inflammation (hs-CRP), vascular wall function (VCAM-1 and IL-1β) and vascular remodeling (MMP-2; MMP-9 and TGF-beta1). NOx will be determined by chemiluminescence (Sievers NOAnalyzer 280i) and all remaining measurements will be performed with appropriate enzyme-linked immunosorbent assay (ELISA) kits: ADMA (Sunred Biological Technology, Shanghai, China); hs-CRP (BoosterBio, Pleasanton, USA); VCAM-1; IL-1β; MMP-9; MMP-2 and TGFβ-1 (RayBiotech, Inc. Norcross, USA).

Left Ventricular Mass Assessment by CMR. The altered blood pressure phenotype that persists after CoA treatment represents an increase in afterload that leads to LV hypertrophy. Our CMR protocol will include sequences that allow this quantification.

Cardiovascular Health Assessment: The researchers will assess health factors (blood pressure, total cholesterol, plasma glucose), behaviors (smoking, body mass index BMI, physical activity and diet) and family history of cardiovascular disease and risk factors. A questionnaire was implemented to assess family history of CV disease and ICVH according to the procedures and recommendations of the American Heart Association.

Statistical Considerations. The treatment groups will be frequency-matched for documented confounders. The confounding variables will include: (a) Age at treatment; (b) Current age; (c) Bicuspid aortic valve as it is associated with impaired aortic elasticity. Because of the relatively large number of matching variables and three treatment groups, matching individual subjects was not feasible. During analysis, the treatment groups will be compared for each of these confounding variables and appropriate adjustments made, if needed. Differences in the confounding variables across the three treatment groups will be evaluated using Fisher's exact test for severity of coarctation and the Kruskal-Wallis test for age at treatment, current age and bicuspid aortic valve. The primary outcome variable will be carotid-femoral PWV assessed by tonometry. Differences in cfPVW across groups will be explored using one-way analysis of variance. If differences in matching variables are detected among the groups, adjustment will be made using analysis of covariance. Post-hoc analyses will be performed as necessary.

Sample size estimates were obtained based on prior data that show that ascending- descending PWV measured by CMR is 3.3±0.6 m/s in normal subjects and 4.7±1.1 m/sec after CoA surgery.22, 70 Sample size estimates for comparison of PVW between three equal sized treatment groups (assuming overall significance level=0.05 and power=0.8) are shown in table 2. The investigators plan on recruiting 24 to 30 patients in each group for a total sample size of 72 to 90.

Inclusion Criteria:

• Diagnosis of isthmic coarctation of the aorta;
• Current age between 8 (to allow cooperation with study procedures) and 35 years (to avoid confounding by aging-related vascular dysfunction); and
• Treatment for CoA after 1994, after which all three modalities were in clinical use.

Exclusion Criteria:

• Residual CoA defined by a systolic upper-to-lower extremity BP gradient> 20mmHg;
• Co-morbidities that may independently affect vascular function, including associated significant congenital heart disease, history of known vasculopathy, genetic syndromes or other cardiovascular risk factors;
• History of two treatment types for CoA; and
• CoA types likely representing a different entity or patients amenable to one single treatment type (surgery), including atypical CoA site (such as mid-thoracic or abdominal), severe hypoplasia of the aortic arch, and an age of treatment <1 year of age.

Patients with isthmic coarctation of the aorta, treated after 1994, submitted to only one of either of the three procedures described above.