Impact of loading and myocardial mechanical properties on natural shear waves

Background: Shear wave elastography (SWE) has been proposed as a novel noninvasive method for the assessment of myocardial stiffness, a relevant determinant of diastolic function. It is based on tracking the propagation of shear waves, induced, for instance, by mitral valve closure (MVC), in the myocardium. The speed of propagation is directly related to myocardial stiffness, which is defined by the local slope of the nonlinear stress-strain relation. Therefore, the operating myocardial stiffness can be altered by both changes in loading and myocardial mechanical properties. Objectives: This study sought to evaluate the capability of SWE to quantify myocardial stiffness changes in vivo by varying loading and myocardial tissue properties and to compare SWE against pressure-volume loop analysis, a gold standard reference method. Methods: In 15 pigs, conventional and high–frame rate echocardiographic data sets were acquired simultaneously with pressure-volume loop data after acutely changing preload and afterload and after inducting an ischemia/reperfusion (I/R) injury. Results: Shear wave speed after MVC significantly increased by augmenting preload and afterload (3.2 ± 0.8 m/s vs 4.6 ± 1.2 m/s and 4.6 ± 1.0 m/s, respectively; P = 0.001). Preload reduction had no significant effect on shear wave speed compared to baseline (P = 0.118). I/R injury resulted in significantly higher shear wave speed after MVC (6.1 ± 1.2 m/s; P < 0.001). Shear wave speed after MVC had a strong correlation with the chamber stiffness constant β (r = 0.63; P < 0.001) and operating chamber stiffness dP/dV before induction of an I/R injury (r = 0.78; P < 0.001) and after (r = 0.83; P < 0.001). Conclusions: Shear wave speed after MVC was influenced by both acute changes in loading and myocardial mechanical properties, reflecting changes in operating myocardial stiffness, and was strongly related to chamber stiffness, invasively derived by pressure-volume loop analysis. SWE provides a novel noninvasive method for the assessment of left ventricular myocardial properties

Impact of Loading and Myocardial Mechanical Properties on Natural Shear Waves: Comparison to Pressure-Volume Loops

Background: Shear wave elastography (SWE) has been proposed as a novel noninvasive method for the assessment of myocardial stiffness, a relevant determinant of diastolic function. It is based on tracking the propagation of shear waves, induced, for instance, by mitral valve closure (MVC), in the myocardium. The speed of propagation is directly related to myocardial stiffness, which is defined by the local slope of the nonlinear stress-strain relation. Therefore, the operating myocardial stiffness can be altered by both changes in loading and myocardial mechanical properties. Objectives: This study sought to evaluate the capability of SWE to quantify myocardial stiffness changes in vivo by varying loading and myocardial tissue properties and to compare SWE against pressure-volume loop analysis, a gold standard reference method. Methods: In 15 pigs, conventional and high–frame rate echocardiographic data sets were acquired simultaneously with pressure-volume loop data after acutely changing preload and afterload and after inducting an ischemia/reperfusion (I/R) injury. Results: Shear wave speed after MVC significantly increased by augmenting preload and afterload (3.2 ± 0.8 m/s vs 4.6 ± 1.2 m/s and 4.6 ± 1.0 m/s, respectively; P = 0.001). Preload reduction had no significant effect on shear wave speed compared to baseline (P = 0.118). I/R injury resulted in significantly higher shear wave speed after MVC (6.1 ± 1.2 m/s; P < 0.001). Shear wave speed after MVC had a strong correlation with the chamber stiffness constant β (r = 0.63; P < 0.001) and operating chamber stiffness dP/dV before induction of an I/R injury (r = 0.78; P < 0.001) and after (r = 0.83; P < 0.001). Conclusions: Shear wave speed after MVC was influenced by both acute changes in loading and myocardial mechanical properties, reflecting changes in operating myocardial stiffness, and was strongly related to chamber stiffness, invasively derived by pressure-volume loop analysis. SWE provides a novel noninvasive method for the assessment of left ventricular myocardial properties

Mechanical Dyssynchrony Combined with Septal Scarring Reliably Identifies Responders to Cardiac Resynchronization Therapy

Background and aim: The presence of mechanical dyssynchrony on echocardiography is associated with reverse remodelling and decreased mortality after cardiac resynchronization therapy (CRT). Contrarily, myocardial scar reduces the effect of CRT. This study investigated how well a combined assessment of different markers of mechanical dyssynchrony and scarring identifies CRT responders. Methods: In a prospective multicentre study of 170 CRT recipients, septal flash (SF), apical rocking (ApRock), systolic stretch index (SSI), and lateral-to-septal (LW-S) work differences were assessed using echocardiography. Myocardial scarring was quantified using cardiac magnetic resonance imaging (CMR) or excluded based on a coronary angiogram and clinical history. The primary endpoint was a CRT response, defined as a ≥15% reduction in LV end-systolic volume 12 months after implantation. The secondary endpoint was time-to-death. Results: The combined assessment of mechanical dyssynchrony and septal scarring showed AUCs ranging between 0.81 (95%CI: 0.74–0.88) and 0.86 (95%CI: 0.79–0.91) for predicting a CRT response, without significant differences between the markers, but significantly higher than mechanical dyssynchrony alone. QRS morphology, QRS duration, and LV ejection fraction were not superior in their prediction. Predictive power was similar in the subgroups of patients with ischemic cardiomyopathy. The combined assessments significantly predicted all-cause mortality at 44 ± 13 months after CRT with a hazard ratio ranging from 0.28 (95%CI: 0.12–0.67) to 0.20 (95%CI: 0.08–0.49). Conclusions: The combined assessment of mechanical dyssynchrony and septal scarring identified CRT responders with high predictive power. Both visual and quantitative markers were highly feasible and demonstrated similar results. This work demonstrates the value of imaging LV mechanics and scarring in CRT candidates, which can already be achieved in a clinical routine