A systems approach to assessment of left ventricular outflow tract anatomy and function: The aortoventricular interface in the era of transcatheter aortic valve replacement

Abstract

The aortoventricular interface describes the functional syncytium between the left ventricle and proximal aorta, necessary for normal central haemodynamic operation. Normal function would be considered as providing for optimal passage of oxygenated blood delivered from the left ventricle through the aortic valve to the systemic circulation. Non-­‐optimal function of the aortic valve through congenital malformation or degenerative processes is associated with a clear constellation of clinical signs and symptoms and with a well established natural history. These can all be understood on the basis of loss of normal function. Narrowing of the aortic orifice results in decreased systemic blood pressure, syncope, decreased exercise ability, left ventricular remodelling compensating for increased wall stress, secondary mitral and atrial dysfunction and increased pulmonary pressures. Aortic incompetence with its well known features of left ventricular dilatation, exertional fatigue, dyspnoea and palpitations is also explained by the deranged haemodynamic effects due to loss of hydraulic separation (temporal and spatial) between the low and high pressure components across the aortoventricular interface. The common connection between these clinical entities is the disruption of appropriate flow across the left ventricular outflow tract – aortic valve – proximal aorta anatomical continuum. In health the structure of this interface functions to provide optimally matched volume blood flow with appropriate direction and timing for optimal energy utilisation and supply. Disturbance in the normal anatomy and its associated clinical symptoms or signs are well described but the failure in underlying function not usually acknowledged. This thesis aims, in the first instance, to review and, thereafter, to investigate, the potential influence of anatomy and function on both sides of the aortoventricular interface in populations without aortic valve disease, with aortic valve stenosis and post-­‐ treatment. Assessment based on modern anatomical imaging technology provides a concrete structural representation of left ventricular – aortic mechanisms. This thesis will present work aimed at integrating structural assessment by computed tomography with assessment of clinical function in patients affected by stenosis of the aortic valve and following percutaneous aortic valve intervention.