Haemodynamic response of normal aortic valves to stress using invasive, non-invasive, and computational techniques.

Abstract

Aims: The haemodynamic physiology of the aortic valve has attracted renewed attention after the introduction of transcatheter aortic valve implantation (TAVI). Understanding normal valve function, especially under stress conditions, permits identification of early pathology and quantification of the extent to which TAVI restores normalcy. We aimed to describe the haemodynamic behaviour of a normal aortic valve during stress via invasive, non-invasive, and computational techniques.

Methods and results: Our cohort included subjects already undergoing invasive coronary angiography for clinical indications. Haemodynamic measurements were made invasively and non-invasively along with dobutamine infusion. Additionally, patient-specific anatomy from computed tomographic imaging served as input to a computational fluid dynamics model using fluid-structure interaction analysis. We studied 10 subjects with simultaneous invasive sensors and non-invasive echocardiography during dobutamine administration. The majority of normal valves (7 of 10) demonstrated a fall in the invasive gradient during stress, in contrast to the increase noted by Doppler assessment. The stress aortic valve index, a relative measure of pressure loss over the valve during ejection, uniformly exceeded 0.90 with median value of 0.96 and interquartile range 0.94-1.00. Simulation of increased transvalvular flow via faster heart rates produced a highly linear relationship (coefficient of determination R ² equal to 0.95) with the mean transvalvular pressure gradient.

Conclusion: Normal aortic valves demonstrated minimal pressure loss even during the high transvalvular flow generated by dobutamine infusion. Computational simulation using anatomy from a normal aortic valve behaved like a resistor, since mean gradient scaled directly with transvalvular flow.