Cardiac Shear Wave Velocity Detection in the Porcine Heart

Abstract

Cardiac muscle stiffness can potentially be estimated non-invasively with shear wave elastography. Shear waves are present on the septal wall after mitral and aortic valve closure, thus providing an opportunity to assess stiffness in early systole and early diastole. We report on the shear wave recordings of 22 minipigs with high-frame-rate echocardiography. The waves were captured with 4000 frames/s using a programmable commercial ultrasound machine. The wave pattern was extracted from the data through a local tissue velocity estimator based on one-lag autocorrelation. The wave propagation velocity was determined with a normalized Radon transform, resulting in median wave propagation velocities of 2.2 m/s after mitral valve closure and 4.2 m/s after aortic valve closure. Overall the velocities ranged between 0.8 and 6.3 m/s in a 95% confidence interval. By dispersion analysis we found that the propagation velocity only mildly increased with shear wave frequency.

Naturally Occurring Shear Waves in Healthy Volunteers and Hypertrophic Cardiomyopathy Patients

“…The propagation velocity of the aortic valve closure wave in our healthy patients is lower than that found in a group of 10 human patients by Brekke et al (2014) (5.41 § 1.28 m/s), or in animal studies (Hollender et al 2012;Vos et al 2017). We speculate that the difference is originating from the different detection method and probe positioning: parasternal in our study in agreement with Kanai (2005) as opposed to apical in the study by Brekke et al (2014).…”

“…In animal model studies, the propagation of the mitral valve shear wave has been found to be lower than the aortic (Vos et al 2017). The opposite finding in the human heart cannot be explained by differences in electromechanical activation (Konofagou and Provost 2012;Costet et al 2014).…”

“…Yet, the relatively low oscillation frequency (order 50À100 Hz) of the waves might reduce the effect of the fiber structure (Song et al 2016. Furthermore, viscous loss will introduce dispersion (Bercoff et al 2004), and the finite wall thickness may lead to dispersive Lamb waves (Kanai 2005), although a previous animal study has shown only a mild dispersion of the waves after aortic valve closure (Vos et al 2017). For simplicity, we have chosen the mid-wall position, presumably having the highest consistency in placement.…”

Measuring Intraventricular Pressure Using Ultrasound Elastography

“…Regarding the feasibility of noninvasive measurements of shear wave elastography, a number of studies have been performed and technical advancements are under development . It has been shown that shear wave measurements can be recorded transthoracically in human and porcine models . A number of researchers have reported feasibility of ARFI measurement transthoracically during the cardiac cycle in clinical subjects .…”

“…23 It has been shown that shear wave measurements can be recorded transthoracically in human and porcine models. 24,25 A number of researchers have reported feasibility of ARFI measurement transthoracically during the cardiac cycle in clinical subjects. 20,26 Moreover, transthoracic SWEI measurements have been demonstrated in the clinic.…”