Cardiac Shear Wave Elastography Research Articles

Cardiac shear wave elastography can detect myocardial remodelling in LBBB patients undergoing CRT

Abstract Funding Acknowledgements Type of funding sources: None. Background Cardiac shear wave elastography (SWE) allows for the non-invasive assessment of myocardial stiffness via the detection of shear waves travelling through the heart after e.g. mitral valve closure (MVC). The propagation speed of these waves is directly related to myocardial stiffness. Myocardial stiffness depends on the intrinsic properties of the myocardium. Therefore, processes that alter these intrinsic properties, such as cardiac remodelling, could influence shear wave speed. In this way, SWE could be an interesting tool to directly and non-invasively monitor cardiac remodelling over time. Purpose To evaluate the effect of reverse remodelling on myocardial stiffness in left bundle branch block (LBBB) patients undergoing cardiac resynchronization therapy (CRT). Methods Fourteen non-ischemic patients with LBBB undergoing CRT were included. SWE was performed 1 day after CRT implantation and repeated after 6 and 12 months. Eleven age-matched healthy volunteers served as controls. Volumetric response was defined as ≥15% decrease in end-systolic volume after 1 year of CRT. Echocardiographic images were taken during biventricular (BiV) pacing ON (resynchronized) and BiV pacing OFF (native LBBB conduction), both with a conventional ultrasound machine and an experimental high frame rate ultrasound scanner (999 ± 134 frames/s). For SWE, LV parasternal long-axis views were acquired. Shear waves were visualized in M-modes of the septum, colour coded for tissue acceleration. The slope of the shear waves in the M-mode represents their propagation speed (Figure 1A). Results All included patients were volumetric responders. LV ejection fraction and global longitudinal strain improved significantly over time. LV volumes decreased significantly in all patients during one year of CRT (Table 1), reflecting reverse remodelling. Shear wave speed was significantly higher immediately after implantation compared to healthy controls during BiV ON (5.9±1.5 vs 4.6±1.1 m/s; p = 0.02; Figure 1B), but not at 6 months (5.3±1.5 vs 4.6±1.1 m/s; p = 0.19) and 12 months (5.1±1.1 vs 4.6±1.1 m/s; p = 0.39) after implantation (Figure 1B), indicating that myocardial stiffness normalized over time due to reverse remodelling. Moreover, shear wave speed was significantly higher during BiV OFF compared to BiV ON immediately after implantation (5.9±1.5 vs 6.7±1.4 m/s; p = 0.022) and at 6 months (5.3±1.5 vs 6.1±1.4 m/s; p = 0.048), indicating that the reintroduction of dyssynchrony increases shear wave speed after MVC (Figure 1B). One year after implantation shear wave speed was not significantly different between BiV ON and OFF (5.1±1.1 vs 5.2±0.4 m/s; p = 0.78; Figure 1B). This could imply that dyssynchrony decreases over time as a result of reverse remodelling. Conclusion SWE can non-invasively detect changes in myocardial properties during reverse remodelling under CRT. Myocardial stiffness gradually decreases towards the range of age-matched healthy hearts after CRT.

Transmural Wave Speed Gradient May Distinguish Intrinsic Myocardial Stiffening From Preload-Induced Changes in Operational Stiffness in Shear Wave Elastography.

Shear wave elastography (SWE) is a promising technique to non-invasively assess myocardial stiffness based on the propagation speed of mechanical waves. However, a high wave propagation speed can either be attributed to an elevated intrinsic myocardial stiffness or to a preload-induced increase in operational stiffness. Our objective was to find a way to discriminate intrinsic myocardial stiffening from stiffening caused by an increased pressure in SWE. We used the finite element method to study the shear wave propagation patterns when stiffness and/or pressure is elevated, compared to normal stiffness and pressure. Numerical findings were verified in a few human subjects. The transmural wave speed gradient was able to distinguish changes in intrinsic stiffness from those induced by differing hemodynamic load (a speed of ±3.2 m/s in parasternal short-axis (PSAX) view was associated with a wave speed gradient of -0.17 ± 0.15 m/s/mm when pressure was elevated compared to 0.04 ± 0.05 m/s/mm when stiffness was elevated). The gradient however decreased when stiffness increased (decrease with a factor 3 in PSAX when stiffness doubled at 20 mmHg). The human data analysis confirmed the presence of a wave speed gradient in a patient with elevated ventricular pressure. Cardiac SWE modeling is a useful tool to gain additional insights into the complex wave physics and to guide post-processing. The transmural differences in wave speed may help to distinguish loading-induced stiffening from intrinsic stiffness changes. The transmural wave speed gradient has potential as a new diagnostic parameter for future clinical studies.

Cardiac shear wave elastography can detect the presence of a septal scar in patients with LBBB

Abstract Background In patients with heart failure and a left bundle branch block (LBBB), cardiac resynchronization therapy (CRT) is an established treatment. However, the rate of non-response to this costly therapy remains high. So far, CRT has proven to be less effective in patients with a septal scar. Detection of a septal scar before CRT implantation could therefore help to improve response rate to CRT. The gold standard to detect septal scarring, LGE MRI, is quite costly and not suited or available for all patients. Cardiac shear wave elastography (SWE) may be an alternative. It allows for the non-invasive assessment of myocardial stiffness based on the detection of shear waves, after for example mitral valve closure (MVC). SWE has shown to be capable to detect myocardial scar, however this has never been demonstrated in the presence of LBBB. Purpose To determine whether SWE is able to detect the presence of a septal scar in patients with LBBB. Methods To investigate this, 39 CRT patients with a LBBB were included with ischemic (n=10; age: 73±6 y; 70% males) or non-ischemic (n=29; 68±14 y; 52% males) cardiomyopathy and 9 age-matched healthy volunteers (68±4 y; 55% males) served as controls. In order to obtain native ventricular conduction biventricular (BiV) pacing was turned off. All ischemic patients had septal scar only, proven by MRI or scintigraphy. For SWE, left ventricular parasternal long-axis views were acquired with an experimental high frame rate ultrasound scanner (frame rate: 932±32 fps). Shear waves were visualized in M-modes of the septum, colour coded for tissue acceleration. The slope of the shear waves in the M-mode represents their propagation speed (Figure 1A). Results Patients characteristics and echocardiographic parameters are shown in Table 1. Shear wave speed after MVC was significantly higher in LBBB patients with and without a septal scar compared to healthy controls (7.8±1.2 m/s vs 4.5±1.1 m/s; p<0.001; 5.6±1.1 m/s vs 4.5±1.1 m/s; p=0.041; Figure 1B), indicating that the presence of LBBB increases myocardial stiffness. However, more importantly, shear wave speed was significantly higher in LBBB patients with a septal scar compared to LBBB patients without a septal scar (7.8±1.2 m/s vs 5.6±1.1 m/s; p<0.001; Figure 1B). This implies that the presence of a septal scar increases shear wave speed even more than LBBB alone. A ROC-curve analysis further showed that SWE is capable of distinguishing scarred from non-scarred septum in LBBB patients (AUC: 0.92; p<0.001; Figure 1C). A cut-off of 7.1 m/s could identify LBBB patients with a septal scar with a sensitivity of 80% and specificity of 93%. Conclusion Septal scarring results in a significant increase in myocardial stiffness, so that it reaches a clear pathological range. SWE seems therefore capable of detecting the presence of a septal scar in LBBB patients and could potentially be used as a novel approach for the assessment of septal scarring in CRT candidates. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Research foundation Flanders (FWO)

Can cardiac shear wave elastography detect the presence of septal scar in patients with left bundle branch block?

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): FWO: Fonds Wetenschappelijk Onderzoek (fund for scientific research Flanders) Background Cardiac resynchronization therapy (CRT) is an established treatment for heart failure patients with left bundle branch block (LBBB). Regardless, CRT has proven to be less effective in patients with ischemic cardiomyopathy, in particular when the septum is affected. The detection of septal scar prior to CRT implantation could therefore help to improve response rate. However, magnetic resonance imaging (MRI), the gold standard to assess myocardial scar, cannot be used in every patient due to already implanted devices or impaired renal function. Cardiac shear wave elastography (SWE) allows for the non-invasive assessment of myocardial stiffness via the detection of shear waves, for example induced by mitral valve closure (MVC), that travel through the myocardium. Shear wave speed is directly related to tissue stiffness. Recently, SWE has shown to be capable to detect myocardial scar, however this has never been demonstrated in the presence of LBBB. Purpose To evaluate whether SWE is able to detect the presence of septal scar in patients with LBBB. Methods We included 34 heart failure patients with LBBB (age: 69 ± 13 y; 56% males) and with ischemic (n = 9) or non-ischemic (n = 25) cardiomyopathy and 9 age-matched healthy volunteers (age: 68 ± 4 y; 66% males) as controls. In order to obtain native ventricular conduction biventricular (BiV) pacing was turned off. All ischemic patients had septal scar only, proven by MRI or scintigraphy. For SWE, left ventricular parasternal long-axis views were acquired with an experimental high frame rate ultrasound scanner (frame rate: 932 ± 32 fps). Shear waves were visualized in M-modes of the septum, colour coded for tissue acceleration. The slope of the shear waves in the M-mode represents their propagation speed (Figure A). Results Patient characteristics including echocardiographic parameters are shown in Table 1. Shear wave speed after MVC was significantly higher in patients with LBBB with or without septal scar compared to healthy controls (7.9 ± 1.2 m/s vs 4.5 ± 1.1 m/s; p = 0.044; 5.6 ± 1.2 m/s vs 4.5 ± 1.1 m/s: p < 0.001; figure B). This implies that the presence of LBBB alone increases myocardial stiffness. Most importantly, however, shear wave speed was significantly higher in LBBB patients with a septal scar compared to LBBB patients without a septal scar (7.9 ± 1.2 m/s vs 5.6 ± 1.2 m/s; p < 0.001; figure B), indicating that the presence of scar increases myocardial stiffness even more than LBBB alone. Conclusions LBBB causes a mild but significant increase in shear wave propagation speed in non-ischemic patients compared to controls. The presence of septal scarring leads to an additional and more significant increase. This indicates that SWE is capable of detecting stiffer scarred myocardium even in the presence of LBBB. Therefore, SWE could potentially be used as a novel method to detect septal scarring in LBBB patients before CRT implantation. Abstract Figure. Abstract Figure.

On the interplay of loading, myocardial stiffness and contractility in transthoracic acoustic radiation force-induced shear wave measurements in pigs

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): Research Foundation Flanders (FWO grant number 1211620N) & TTW-Dutch Heart Foundation partnership program "Early recognition of cardiovascular diseases" (project number 14740) Background Acoustic radiation force-based shear wave elastography (SWE) is a promising technique to non-invasively assess mechanical properties of the heart based on the propagation speed of acoustically induced shear waves. However, the interpretation of cardiac SWE measurements remains complex, and it is unclear how other factors such as loading affect shear wave propagation speed (SWS) measurements in diastole and systole. Purpose We applied transthoracic SWE in a pig model to investigate the dependencies of diastolic and systolic SWS on pressure-volume (PV) loop derived indices of loading, myocardial stiffness and contractility. Methods In 7 pigs, loading conditions were altered (increasing or decreasing preload; increasing afterload) and myocardial stiffness was changed (LAD occlusion for 60-100 minutes followed by 40 minutes of reperfusion). For each intervention, transthoracic SWE measurements were performed in a parasternal long-axis view with a high frame rate ultrasound system (> 6.2 kHz). Recordings of 28 ms were repeated at 34 Hz during 1.5 s to track shear waves throughout the cardiac cycle. To determine systolic and diastolic SWS in a robust manner, a piecewise linear model was fitted to the SWS data of each intervention representing multiple acquisitions, heartbeats and M-lines (fig. 1a). PV loops were recorded simultaneously with SWE measurements to estimate end-diastolic pressure (EDP), end-systolic pressure (ESP), end-diastolic pressure volume relation (EDPVR with exponential coefficient β in fig. 1b) and preload-recruitable stroke work (PRSW). Passive chamber stiffness was evaluated as the local slope of the EDPVR, i.e. β·EDP. Linear regressions and Pearson’s correlation coefficients were calculated. Results Diastolic SWS was significantly correlated to EDP when altering loading (blue in fig. 2a: R = 0.55; p < 0.01) and stiffness (orange in fig. 2a: R = 0.66; p < 0.01). A similar correlation is found between SWS and passive chamber stiffness β·EDP (fig. 2b). Diastolic SWS is more sensitive to changes in stiffness than in loading, as reflected by the larger slope of the regression line (0.79 vs. 0.28 in fig. 2b). Furthermore, systolic SWS significantly correlated with measures of contractility during loading alterations: ESP in fig. 2c (R = 0.69; p < 0.001) and PRSW in fig. 2d (R = 0.63; p = 0.02). However, no significant correlation was found between systolic SWS and contractility during infarct/reperfusion. Conclusion This study shows that diastolic SWS reflects the instantaneous stiffness of the myocardium, but is not a load-independent measure of the intrinsic passive mechanical properties of the heart. Instantaneous stiffness, and thus diastolic SWS, might be altered by loading (due to material non-linearity) or intrinsic mechanical changes. Furthermore, loading experiments suggest that systolic SWS is related to contractility. The relation between SWS and contractility in the presence of myocardial infarct deserves further study. Abstract Figure. Fig. 1: SWS and PV analysis. Abstract Figure. Fig. 2: SWS vs. PV-derived indices.

Cardiac shear wave elastography can distinguish healthy and scarred myocardium in patients with conduction delays

Abstract Background Cardiac resynchronization therapy (CRT) is an established therapy for patients suffering from heart failure and left bundle branch block (LBBB) conduction delays. Despite its proven beneficial effects, CRT is associated with a high percentage of non-response. Since CRT has shown to be less effective in patients with ischemic cardiomyopathy, determining the presence of myocardial scar before implantation could help to improve the response-rate. However, the gold standard to assess myocardial scar, magnetic resonance imaging (MRI), cannot be used in every patient, due to already implanted devices and/or reduced renal function. Recently introduced shear wave elastography (SWE) allows the non-invasive assessment of myocardial stiffness. Natural shear waves are excited by mitral valve closure (MVC) and travel through the heart with a speed directly related to tissue stiffness. SWE has previously been proven to be able to detect myocardial scar, however this has never been shown in the presence LBBB. Purpose The aim of this study was to evaluate the capability of SWE as a novel method to determine myocardial scar in patients with conduction delays. Methods We included 24 heart failure patients (age: 68±10; 50% males) with ischemic (n=8) and non-ischemic (n=16) cardiomyopathy. The CRT device was set to AAI mode in order to obtain native ventricular conduction. For patients with ischemic cardiomyopathy, the presence and location of scar was determined by MRI or scintigraphy. All ischemic patients had septal scar only. For SWE, left ventricular parasternal long-axis views were acquired with an experimental high frame rate ultrasound scanner (average frame rate: ±1200 Hz). Shear waves were visualized in M-modes of the septum, colour coded for tissue acceleration. The slope of the shear waves in the M-mode represents their propagation speed (Figure A). Results There was no significant difference between the ischemic and non-ischemic patients in QRS width after CRT (149±31 ms vs 144±26 ms), systolic blood pressure blood pressure (135±11 mmHg vs 135±23 mmHg), diastolic blood pressure (74±9 mmHg vs 70±11 mmHg) and heart rate (58±4 bpm vs 63±9 bpm) (all p>0.05). Ejection fraction (33±8% vs 45±10%), end-diastolic volume (196±34 ml vs 129±64 ml) and global longitudinal strain (−9.8±3.1% vs −14.1±4.1%) differed significantly between the groups (all p<0.05). Shear wave speed after MVC was significantly higher in patients with septal scar compared to non-ischemic patients (8.2±1.9 m/s vs 5.5±1.2 m/s; p<0.01) (Figure B). Conclusion In the presence of scar, we found markedly elevated shear wave propagation speed compared to non-ischemic patients. These results indicate that SWE is able to identify scarred myocardium even in patients with LBBB. We therefore believe that SWE could be a novel easy and non-invasive method to evaluate septal myocardial scarring in patients before CRT implantation. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): FWO - Research Foundation Flanders

Fundamental modeling of wave propagation in temporally relaxing media with applications to cardiac shear wave elastography.

Shear wave elastography (SWE) might allow non-invasive assessment of cardiac stiffness by relating shear wave propagation speed to material properties. However, after aortic valve closure, when natural shear waves occur in the septal wall, the stiffness of the muscle decreases significantly, and the effects of such temporal variation of medium properties on shear wave propagation have not been investigated yet. The goal of this work is to fundamentally investigate these effects. To this aim, qualitative results were first obtained experimentally using a mechanical setup, and were then combined with quantitative results from finite difference simulations. The results show that the amplitude and period of the waves increase during propagation, proportional to the relaxation of the medium, and that reflected waves can originate from the temporal stiffness variation. These general results, applied to literature data on cardiac stiffness throughout the heart cycle, predict as a major effect a period increase of 20% in waves propagating during a healthy diastolic phase, whereas only a 10% increase would result from the impaired relaxation of an infarcted heart. Therefore, cardiac relaxation can affect the propagation of waves used for SWE measurements and might even provide direct information on the correct relaxation of a heart.

556 Shear wave imaging using ultra-high frame rate echocardiography for the assessment of structural changes in cardiac transplant recipients

Abstract Background Cardiac allografts undergo characteristic alterations of the extracellular matrix, including myocardial fibrosis, that contribute to functional changes, particularly diastolic dysfunction due to increased myocardial stiffness(MS). Histological examination is the gold standard for myocardial fibrosis quantification, however, it requires endomyocardial biopsies which are invasive and not without risk. Increased native T1 and extracellular volume(ECV) using CMR T1 mapping have shown good correlation with biopsy evidence of myocardial interstitial fibrosis in heart transplant(HTx) recipients. Echocardiographic shear wave(SW) elastography is an emerging approach for measuring MS in vivo. SWs occur after mechanical excitation of the myocardium, e.g. after mitral(MVC) and aortic valve closure(AVC), and their propagation velocity is directly related to MS, thus providing an opportunity to assess stiffness at end-diastole(ED) and end-systole(ES). Purpose The aim was to investigate if natural shear wave velocities increase with the degree of diffuse myocardial fibrosis in HTx recipients. Methods We prospectively enrolled 22 HTx patients (8.8 ± 5.9 years post-HTx) that underwent CMR during their annual check-up. We performed SW elastography in parasternal long axis views of the left ventricle(LV) using an experimental scanner (HD-PULSE) equipped with a clinical phased array transducer (Samsung Medison P2-5AC) at 1100 ± 250 frames per second. Tissue acceleration maps were extracted from an anatomical M-mode line along the midline of the LV septum. The SW propagation velocity at MVC and AVC was measured as the slope on the M-mode acceleration map(FigureA). All patients underwent right heart catheterization on the same day for the measurement of pulmonary capillary wedge pressure(PCWP), as surrogate for LV filling pressure. The CMR protocol consisted of standard sequences including native and post-contrast T1 mapping. To evaluate diffuse myocardial fibrosis, native T1 and ECV were measured in the anteroseptal wall over all available short-axis slices. Results We found good correlations between SW velocities at ED and both myocardial T1 (r = 0.8,p < 0.001,FigureB) and ECV (r = 0.6,p < 0.05,FigureC) measured with CMR. Similarly, we found significant correlations between SW velocities at ES and T1 (r = 0.7,p < 0.005) and ECV (r = 0.5,p < 0.05), respectively. Furthermore, we observed a significant correlation between SW velocities at ED and PCWP (r = 0.6,p < 0.05). Conclusions Both end-diastolic and end-systolic shear wave velocities showed a good correlation with CMR defined myocardial fibrosis in cardiac transplant patients. Shear wave velocities at end-diastole correlated with invasively-determined left ventricular filling pressure, reflecting the impact of the fibrous changes on the left ventricular diastolic function. These results suggest the potential of cardiac shear wave elastography for the assessment of structural changes in cardiac transplant recipients. Abstract 556 Figure.

P2476Non-invasive left ventricular stiffness measurements for assessing diastolic myocardial properties after orthotopic heart transplantation

Abstract Background After orthotopic heart transplantation (HTx), allografts undergo characteristic alterations including myocardial fibrosis. These histologic changes contribute to functional impairment, especially to increased passive myocardial stiffness (MS), which is an important pathophysiological determinant of left ventricular diastolic dysfunction (DF). However, the transplanted heart is affected by many factors that make the interpretation of diastolic echocardiographic parameters difficult. Echocardiographic shear wave (SW) elastography is an emerging approach for measuring MS in vivo. Natural SWs occur after mechanical excitation of the myocardium, e.g. after mitral (MVC), and their propagation velocity is directly related to MS, thus providing an opportunity to assess stiffness at end-diastole (ED). Purpose The aim was to evaluate the relationship between MS and diffuse myocardial fibrosis as mechanism of DF in HTx patients. Methods We prospectively enrolled 33 patients (10.3±6.3 years after HTx) that underwent right heart catheterization (all) and CMR (n=18) during their annual check-up. We performed SW elastography in parasternal long axis views of the LV using a fully programmable experimental scanner (HD-PULSE) equipped with a clinical phased array transducer (Samsung Medison P2–5AC) at 1100±250 frames per second. Tissue acceleration maps were extracted from an anatomical M-mode line along the midline of the LV septum. The ED SW propagation velocity was measured as the slope in the M-mode image (Figure A). Right heart catheterization was performed on the same day. HTx patients were assumed to have diastolic dysfunction (DDF) if the pulmonary capillary wedge pressure (PCWP) exceeded 18mmHg (n=9). All other patients were assumed to have normal diastolic function (NDF, n=24). Native T1 and extracellular volume (ECV) were measured to evaluate diffuse myocardial fibrosis. Results Positive correlations were found between SW velocities at ED and PCWP (r=0.61, p<0.001; Figure B), between SW velocities at ED and T1 (r=0.80, p<0.001; Figure D), and between SW velocities at ED and ECV (r=0.66, p=0.004). SW propagation velocities at ED were significantly higher in DDF than in NDF (8.05±1.85 vs. 3.77±1.02 m/s; p<0.001; Figure C), and corresponded to the T1 values (as illustrated in Figure D). Conclusions End-diastolic shear wave velocity – as a measurement of passive myocardial stiffness – showed a good correlation with CMR defined myocardial fibrosis. High PCWPs were consistent with the increase in SW velocities, reflecting the fibrous changes in the ventricle. These findings thus suggest that cardiac shear wave elastography has the potential to become a powerful tool for the assessment of diastolic myocardial properties in cardiac transplant recipients.

An in silico framework to analyze the anisotropic shear wave mechanics in cardiac shear wave elastography

Shear wave elastography (SWE) is a potential tool to non-invasively assess cardiac muscle stiffness. This study focused on the effect of the orthotropic material properties and mechanical loading on the performance of cardiac SWE, as it is known that these factors contribute to complex 3D anisotropic shear wave propagation. To investigate the specific impact of these complexities, we constructed a finite element model with an orthotropic material law subjected to different uniaxial stretches to simulate SWE in the stressed cardiac wall. Group and phase speed were analyzed in function of tissue thickness and virtual probe rotation angle. Tissue stretching increased the group and phase speed of the simulated shear wave, especially in the direction of the muscle fiber. As the model provided access to the true fiber orientation and material properties, we assessed the accuracy of two fiber orientation extraction methods based on SWE. We found a higher accuracy (but lower robustness) when extracting fiber orientations based on the location of maximal shear wave speed instead of the angle of the major axis of the ellipsoidal group speed surface. Both methods had a comparable performance for the center region of the cardiac wall, and performed less well towards the edges. Lastly, we also assessed the (theoretical) impact of pathology on shear wave physics and characterization in the model. It was found that SWE was able to detect changes in fiber orientation and material characteristics, potentially associated with cardiac pathologies such as myocardial fibrosis. Furthermore, the model showed clearly altered shear wave patterns for the fibrotic myocardium compared to the healthy myocardium, which forms an initial but promising outcome of this modeling study.

Cardiac Shear Wave Elastography Using a Clinical Ultrasound System

The propagation velocity of shear waves relates to tissue stiffness. We prove that a regular clinical cardiac ultrasound system can determine shear wave velocity with a conventional unmodified tissue Doppler imaging (TDI) application. The investigation was performed on five tissue phantoms with different stiffness using a research platform capable of inducing and tracking shear waves and a clinical cardiac system (Philips iE33, achieving frame rates of 400–700 Hz in TDI by tuning the normal system settings). We also tested the technique in vivo on a normal individual and on typical pathologies modifying the consistency of the left ventricular wall. The research platform scanner was used as reference. Shear wave velocities measured with TDI on the clinical cardiac system were very close to those measured by the research platform scanner. The mean difference between the clinical and research systems was 0.18 ± 0.22 m/s, and the limits of agreement, from −0.27 to +0.63 m/s. In vivo, the velocity of the wave induced by aortic valve closure in the interventricular septum increased in patients with expected increased wall stiffness.

Pediatric Cardiac Shear Wave Elastography for Quantitative Assessment of Myocardial Stiffness: A Pilot Study in Healthy Controls

The long-term goal of this study is to assess chemotherapy-induced cardiotoxicity for pediatric cancer patients using cardiac ultrasound shear wave (SW) elastography. This pilot study aimed to systematically investigate the feasibility of using cardiac SW elastography in children and provide myocardial stiffness control data for cancer patients. Twenty healthy volunteers (ages 5–18) were recruited. A novel cardiac SW elastography sequence with pulse-inversion harmonic imaging and time-aligned sequential tracking was developed for this study. Cardiac SW elastography produces and detects transient SWs propagating in the myocardium in late-diastole, which can be used to quantify myocardial stiffness. The parasternal long-axis (L-A) and short-axis (S-A) views of the interventricular septum (IVS) were feasible for pediatric cardiac SW elastography. The L-A and S-A views of the basal and mid IVS provided better success rates than those of the apical IVS. Success rates decreased with increased body mass index (BMI), but did not differ with age or gender. Two-dimensional SW speed measurements were 1.26, 1.22, 1.71 and 1.67 m/s for L-A base, L-A mid, S-A base and S-A mid IVS, respectively. All S-A SW speed values were significantly higher (p < 0.01) than L-A values due to myocardial anisotropy. No SW speed difference was observed for different ages and genders. This pilot study demonstrated, for the first time, the feasibility of using cardiac SW elastography to measure quantitative myocardial stiffness in children, and established control SW speed values for using SW elastography to assess chemo-induced cardiotoxicity for pediatric cancer patients. The results showed that the myocardial anisotropy needs to be accounted for when comparing SW speed from different imaging axes.