Paediatrics (RCH) - Theses

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Author: Kowalski, Remi Roch × End date: 2018 × Start date: 2018 × Subject: congenital heart disease ×

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    Non-invasive arterial wave analysis in congenital heart disease
    Kowalski, Remi Roch ( 2018)
    Elevated large arterial stiffness is an independent risk factor for adult cardiovascular and cerebrovascular disease. Arterial dysfunction may already be evident in childhood, and children born preterm, or with a history of congenital cardiac surgery, particularly coarctation of the aorta, have a high burden of adult cardiovascular disease and hypertension. Novel arterial wave analyses such as Wave Intensity (WI) and Wave Power (WP) assess the interaction between the heart and great vessels, providing insights into mechanisms of hypertension. Non-invasive WI/WP analyses rely on accurate acquisition of velocity (U), and diameter (D) with ultrasound. Although ultrasound methods are well suited to measuring peak U, WI/WP rely on mean U, which is difficult to obtain routinely. Local pulse-wave speed (c), a measure of arterial stiffness, can also be determined by constructing PU or ln(D)U loops, which also rely on mean U. Errors in c with PU and ln(D)U loop methods due to inaccurate U were determined using MRI-based verification and simulated virtual cohort. A novel method for acquiring local c, which accounts for errors in U and those related to proximal wave reflections, was developed. This technique allowed for scaling factors to be derived to convert peak U into mean U, enabling WI/WP analysis using widely available clinical equipment. In an animal model, invasive and non-invasive WI/WP analyses were compared. The correlations for WI and WP indices were good, but agreement was poor- with a majority of the bias accounted for by either inaccurate invasive U or non-invasive flow estimation, and to non-invasive underestimation of peak P rates of change. Agreement and correlation for wave-related pressure changes were acceptable, and non-invasive WI analysis detected similar relative changes in wave indices during haemodynamic perturbations. Ex-preterm adolescents born at <28 weeks gestation and largely at appropriate weight for gestational age were found to have elevated systolic blood pressure, with no difference in conventional vascular indices. They had a smaller ascending aorta and greater wave reflection on non-invasive WI assessed in the aorta, which was associated with systolic blood pressure on multivariable analysis. Non-invasive WI/WP was also applied in a study of young adults after coarctation repair. They had higher aortic stiffness, but despite higher carotid IMT, there was no increased carotid stiffness. They had higher aortic WI indices, but not WP. In contrast, in the carotid artery both WI and WP indices were greater. Aortic stiffness was related to forward carotid WP in the coarctation group, but not controls. These findings demonstrate that greater stiffness of the aorta leads to increased transmission of wave energy towards the brain. Non-invasive WI/WP analyses have the potential to be more widely deployed using the methods developed in this thesis, and may yield novel insights into the circulatory phenomena that are encountered in children and young people with congenital cardiac and vascular disease.