Naturally Occurring Shear Waves in Healthy Volunteers and Hypertrophic Cardiomyopathy Patients

Abstract

We apply a high frame rate (over 500 Hz) tissue Doppler method to measure the propagation velocity of naturally occurring shear waves (SW) generated by aortic and mitral valves closure. The aim of this work is to demonstrate clinical relevance. We included 45 healthy volunteers and 43 patients with hypertrophic cardiomyopathy (HCM). The mitral SW (4.68 § 0.66 m/s) was consistently faster than the aortic (3.51 § 0.38 m/s) in all volunteers (p < 0.0001). In HCM patients, SW velocity correlated with E/e' ratio (r = 0.346, p = 0.04 for aortic SW and r = 0.667, p = 0.04 for mitral SW). A subgroup of 20 volunteers were matched for age and gender to 20 HCM patients. In HCM, the mean velocity of 5.1 § 0.7 m/s for the aortic SW (3.61 § 0.46 m/s in matched volunteers, p < 0.0001) and 6.88 § 1.12 m/s for the mitral SW(4.65 § 0.77 m/s in matched volunteers, p < 0.0001). A threshold of 4 m/s for the aortic SW correctly classified pathologic myocardium with a sensitivity of 95% and specificity of 90%. Naturally occurring SW can be used to assess differences between normal and pathologic myocardium.

A direct comparison of natural and acoustic-radiation-force-induced cardiac mechanical waves

“…3 for pig 3). A lower propagation speed for AVC was also found by Strachinaru et al 8 in 45 healthy volunteers (mean of 3.51 m/s for AVC vs. 4.68 m/s for MVC). Both observations might be related to a timing difference of valve closure between heartbeats, subjects or even species, but also to measurement inaccuracies (in wave speed estimation, echocardiographic view, and M-spline location) or to changes in the global cardiac dynamics affecting the pressure difference across the valve.…”

“…speed, wavelength, and wave magnitude) measured with natural and active SWE, and to discuss their clinical interpretation. Both SWE methods have yet demonstrated potential added value in various clinical cardiac studies 8 – 10 , 27 , however it was unsure whether the techniques assess a similar stiffness property of the heart. Systolic wave propagation speeds as well as wave speeds after AVC have both been proposed to be potentially related to myocardial contractility 23 , 47 .…”

“…It is only very recently that various clinical studies have shown the potential of natural and active SWE to distinguish SW properties of the myocardium in different patient groups from healthy volunteers. Higher propagation speeds were measured in hypertrophic cardiomyopathy patients than in healthy volunteers, using natural SWs after AVC 8 and actively induced SWs at end-diastole 27 . Also, higher propagation speeds were found in cardiac amyloidosis patients when analyzing natural SWs after AVC and MVC 9 .…”

“…The term ‘shear wave elastography’ is generally used in literature 8 , 9 , 19 , 27 when propagation speeds of transversal wave motion are measured to assess the material’s stiffness. However, it should be noted that the term ‘shear wave’ does probably not describe the complex wave phenomena in the myocardium from a physics point of view.…”

Local myocardial stiffness variations identified by high frame rate shear wave echocardiography

“…This approach is limited by the need for special equipment in order to induce and track these waves. Another technique, exploited in the current study, detects naturally occurring shear waves generated by the closing of the valves [3,5,[11][12][13][14].…”