From wave speed to cardiac stiffness

Diastolic heart failure is one of the principal causes of death in Western countries, and there is currently no treatment available; prevention, on the other hand, may be possible, provided an early enough diagnosis. The worsening of diastolic functionality is associated with increased values of cardiac stiffness, which could therefore provide a measurable quantification of the diastolic health of the heart. Ultrasound imaging technologies can be used to non-invasively record the propagation of small amplitude shear waves propagating in the cardiac muscle. In principle, since the propagation speed of a wave is proportional to the stiffness of the medium in which it travels, ultrasonic shear wave imaging could provide a measure of the stiffness of the heart. However, various features of the heart, such as shape and contractility, complicate the relation between wave speed and stiffness in unknown ways. This thesis aims at understanding how wave propagation is affected by the temporal behaviour and the varying thickness of the heartmuscle, and consequently howultrasonic images of the propagation should be analysed to correctly convertwave speed intomuscle stiffness.