An interventional sheep model of severe aortic valve stenosis hemodynamics for the evaluation of alterations in coronary physiology and microvascular function

We aimed to develop a large animal model of subcoronary aortic stenosis (AS) to study intracoronary and microcirculatory hemodynamics. A total of three surgical techniques inducing AS were evaluated in 12 sheep. Suturing the leaflets together around a dilator (n = 2) did not result in severe AS. Suturing of a pericardial patch with a variable opening just below the aortic valve (n = 5) created an AS which was poorly tolerated if the aortic valve area (AVA) was too small (0.38-1.02 cm2), but was feasible with an AVA of 1.2 cm2. However, standardization of aortic regurgitation (AR) with this technique is difficult. Therefore, we opted for implantation of an undersized AV-bioprosthesis with narrowing sutures on the leaflets (n = 5). Overall, five sheep survived the immediate postoperative period of which three had severe AS (one patch and two bioprostheses). The surviving sheep with severe AS developed left ventricular hypertrophy and signs of increased filling-pressures. Intracoronary assessment of physiological indices in these AS sheep pointed toward the development of functional microvascular dysfunction, with a significant increase in coronary resting flow and hyperemic coronary resistance, resulting in a significantly higher index of microvascular resistance (IMR) and lower myocardial resistance reserve (MRR). Microscopic analysis showed myocardial hypertrophy and signs of fibrosis without evidence of capillary rarefaction. In a large animal model of AS, microvascular changes are characterized by increased resting coronary flow and hyperemic coronary resistance resulting in increased IMR and decreased MRR. These physiological changes can influence the interpretation of regularly used coronary indices.NEW & NOTEWORTHY In an animal model of aortic valve stenosis (AS), coronary physiological changes are characterized by increased resting coronary flow and hyperemic coronary resistance. These changes can impact coronary indices frequently used to assess concomitant coronary artery disease (CAD). At this point, the best way to assess and treat CAD in AS remains unclear. Our data suggest that fractional flow reserve may underestimate CAD, and nonhyperemic pressure ratios may overestimate CAD severity before aortic valve replacement.

Ultrasound Shear Wave Elastography in Cardiology

The advent of high-frame rate imaging in ultrasound allowed the development of shear wave elastography as a noninvasive alternative for myocardial stiffness assessment. It measures mechanical waves propagating along the cardiac wall with speeds that are related to stiffness. The use of cardiac shear wave elastography in clinical studies is increasing, but a proper understanding of the different factors that affect wave propagation is required to correctly interpret results because of the heart's thin-walled geometry and intricate material properties. The aims of this review are to give an overview of the general concepts in cardiac shear wave elastography and to discuss in depth the effects of age, hemodynamic loading, cardiac morphology, fiber architecture, contractility, viscoelasticity, and system-dependent factors on the measurements, with a focus on clinical application. It also describes how these factors should be considered during acquisition, analysis, and reporting to ensure an accurate, robust, and reproducible measurement of the shear wave.

Continuous shear wave measurements for dynamic cardiac stiffness evaluation in pigs

Ultrasound-based shear wave elastography is a promising technique to non-invasively assess the dynamic stiffness variations of the heart. The technique is based on tracking the propagation of acoustically induced shear waves in the myocardium of which the propagation speed is linked to tissue stiffness. This measurement is repeated multiple times across the cardiac cycle to assess the natural variations in wave propagation speed. The interpretation of these measurements remains however complex, as factors such as loading and contractility affect wave propagation. We therefore applied transthoracic shear wave elastography in 13 pigs to investigate the dependencies of wave speed on pressure-volume derived indices of loading, myocardial stiffness, and contractility, while altering loading and inducing myocardial ischemia/reperfusion injury. Our results show that diastolic wave speed correlates to a pressure-volume derived index of operational myocardial stiffness (R = 0.75, p < 0.001), suggesting that both loading and intrinsic properties can affect diastolic wave speed. Additionally, the wave speed ratio, i.e. the ratio of systolic and diastolic speed, correlates to a pressure-volume derived index of contractility, i.e. preload-recruitable stroke work (R = 0.67, p < 0.001). Measuring wave speed ratio might thus provide a non-invasive index of contractility during ischemia/reperfusion injury.

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.

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.

High-Frame-Rate Speckle Tracking for Echocardiographic Stress Testing

Stress echocardiography helps to diagnose cardiac diseases that cannot easily be detected or do not even manifest at rest. In clinical practice, assessment of the stress test is usually performed visually and, therefore, in a qualitative and subjective way. Although speckle tracking echocardiography (STE) has been proposed for the quantification of function during stress, its time resolution is inadequate at high heart rates. Recently, high-frame-rate (HFR) imaging approaches have been proposed together with dedicated STE algorithms capable of handling small interframe displacements. The aim of this study was to determine if HFR STE is effective in assessing strain and strain rate parameters during echocardiographic stress testing. Specifically, stress echocardiography, at four different workload intensities, was performed in 25 healthy volunteers. At each stress level, HFR images from the apical four-chamber view were recorded using the ULA-OP 256 experimental scanner. Then, the myocardium was tracked with HFR STE, and strain and strain rate biomarkers were extracted to further analyze systolic and diastolic (early and late) peaks, as well as a short-lived isovolumic relaxation peak during stress testing. The global systolic strain response was monophasic, revealing a significant (p < 0.001) increase at low stress but then reaching a plateau. In contrast, all strain rate indices linearly increased (p < 0.001) with increasing stress level. These findings are in line with those reported using tissue Doppler imaging and, thus, indicate that HFR STE can be a useful tool in assessing cardiac function during stress echocardiography.

Right ventricular strain related to pulmonary artery pressure predicts clinical outcome in patients with pulmonary arterial hypertension

Aims

In pulmonary arterial hypertension (PAH), the right ventricle (RV) is exposed to an increased afterload. In response, RV mechanics are altered. Markers which would relate RV function and afterload could therefore aid to understand this complex response system and could be of prognostic value. The aim of our study was to (i) assess the RV-arterial coupling using ratio between RV strain and systolic pulmonary artery pressure (sPAP), in patients with PAH, and (ii) investigate the prognostic value of this new parameter over other echocardiographic parameters.

Methods and results

Echocardiograms of 65 pre-capillary PAH patients (45 females, age 61 ± 15 years) were retrospectively analysed. Fractional area change (FAC), sPAP, tricuspid annular plane systolic excursion, and RV free-wall (FW) longitudinal strain (LS) were measured. A primary endpoint of death or heart/lung transplantation described clinical endpoint. Patients who reached a clinical endpoint had worse functional capacity (New York Heart Association), reduced RV function, and higher sPAP. Left ventricle function was similar in both groups. Only RVFW LS/sPAP ratio was found as an independent predictor of clinical endpoint in multivariable analysis (hazard ratio 8.3, 95% confidence interval 3.2–21.6, P &lt; 0.001). The RWFW LS/sPAP (cut-off 0.19) demonstrated a good accuracy for the prediction of reaching the clinical endpoint, with a sensitivity of 92% and specificity of 82.5%.

Conclusion

RVFW LS/sPAP ratio significantly predicts all-cause mortality and heart–lung transplantation, and was superior to other well-established parameters, in patients with pre-capillary PAH. We therefore propose RVFW LS/sPAP as a new prognostic echocardiographic marker.

Inter-vendor variability in strain measurements depends on software rather than image characteristics

Despite standardization efforts, vendors still use specific proprietary software algorithms for echocardiographic strain measurements, which result in high inter-vendor variability. Using vendor-independent software could be one solution. Little is known, however, how vendor specific image characteristics can influence tracking results of such software. We therefore investigated the reproducibility, accuracy, and scar detection ability of strain measurements on images from different vendors by using a vendor-independent software. A vendor-independent software (TomTec Image Arena) was used to analyse datasets of 63 patients which were obtained on machines from four different ultrasound machine vendors (GE, Philips, Siemens, Toshiba). We measured the tracking feasibility, inter-vendor bias, the relative test-re-test variability and scar discrimination ability of strain measurements. Cardiac magnetic resonance delayed enhancement images were used as the reference standard of scar definition. Tracking feasibility on vendor datasets were significantly different (p < 0.001). Variability of global longitudinal strain (GLS) measurements was similar among the vendors whereas variability of segmental longitudinal strain (SLS) showed modest difference. Relative test-re-test variability of GLS and SLS showed no relevant differences. No significant difference in scar detection capability was observed. Average GLS and SLS values were similar among vendors. Reproducibility of GLS measurements showed no difference among vendors and was in acceptable range. SLS reproducibility was high but similar for all vendors. No relevant difference was found for identifying regional dysfunction. Tracking feasibility showed a substantial difference among images from different vendors. Our findings demonstrate that tracking results depend mainly on the software used and show little influence from vendor specific image characteristics.

Shear Wave Elastography Using High-Frame-Rate Imaging in the Follow-Up of Heart Transplantation Recipients

OBJECTIVES

The purpose of this study was to investigate whether propagation velocities of naturally occurring shear waves (SWs) at mitral valve closure (MVC) increase with the degree of diffuse myocardial injury (DMI) and with invasively determined LV filling pressures as a reflection of an increase in myocardial stiffness in heart transplantation (HTx) recipients.

BACKGROUND

After orthotopic HTx, allografts undergo DMI that contributes to functional impairment, especially to increased passive myocardial stiffness, which is an important pathophysiological determinant of left ventricular (LV) diastolic dysfunction. Echocardiographic SW elastography is an emerging approach for measuring myocardial stiffness in vivo. Natural SWs occur after mechanical excitation of the myocardium, for example, after MVC, and their propagation velocity is directly related to myocardial stiffness, thus providing an opportunity to assess myocardial stiffness at end-diastole.

METHODS

A total of 52 HTx recipients who underwent right heart catheterization (all) and cardiac magnetic resonance (CMR) (n = 23) during their annual check-up were prospectively enrolled. Echocardiographic SW elastography was performed in parasternal long axis views of the LV using an experimental scanner at 1,135 ± 270 frames per second. The degree of DMI was quantified with T1 mapping.

RESULTS

SW velocity at MVC correlated best with native myocardial T1 values (r = 0.75; p < 0.0001) and was the best noninvasive parameter that correlated with pulmonary capillary wedge pressures (PCWP) (r = 0.54; p < 0.001). Standard echocardiographic parameters of LV diastolic function correlated poorly with both native T1 and PCWP values.

CONCLUSIONS

End-diastolic SW propagation velocities, as measure of myocardial stiffness, showed a good correlation with CMR-defined diffuse myocardial injury and with invasively determined LV filling pressures in patients with HTx. Thus, these findings suggest that SW elastography has the potential to become a valuable noninvasive method for the assessment of diastolic myocardial properties in HTx recipients.

Acute redistribution of regional left ventricular work by cardiac resynchronization therapy determines long-term remodelling

Aims 

Investigating the acute impact of cardiac resynchronization therapy (CRT) on regional myocardial work distribution in the left ventricle (LV) and to which extent it is related to long-term reverse remodelling.

Methods and results 

One hundred and thirty heart failure patients, referred for CRT implantation, were recruited in our prospective multicentre study. Regional myocardial work was calculated from non-invasive segmental stress–strain loop area before and immediately after CRT. The magnitude of volumetric reverse remodelling was determined from the change in LV end-systolic volume, 11 ± 2 months after implantation. CRT caused acute redistribution of myocardial work across the LV, with an increase in septal work, and decrease in LV lateral wall work (all P &lt; 0.05). Amongst all LV walls, the acute change in work in the septum and lateral wall of the four-chamber view correlated best and significantly with volumetric reverse remodelling (r = 0.62, P &lt; 0.0001), with largest change seen in patients with most volumetric reverse remodelling. In multivariate linear regression analysis, including conventional parameters, such as pre-implant QRS morphology and duration, LV ejection fraction, ischaemic origin of cardiomyopathy, and the redistribution of work across the septal and lateral walls, the latter appeared as the strongest determinant of volumetric reverse remodelling after CRT (model R2 = 0.414, P &lt; 0.0001).

Conclusion 

The acute redistribution of regional myocardial work between the septal and lateral wall of the LV is an important determinant of reverse remodelling after CRT implantation. Our data suggest that the treatment of the loading imbalance should, therefore, be the main aim of CRT.

Interplay of cardiac remodelling and myocardial stiffness in hypertensive heart disease: a shear wave imaging study using high-frame rate echocardiography

Aims

To determine myocardial stiffness by means of measuring the velocity of naturally occurring myocardial shear waves (SWs) at mitral valve closure (MVC) and investigate their changes with myocardial remodelling in patients with hypertensive heart disease.

Methods and results

Thirty-three treated arterial hypertension (HT) patients with hypertrophic left ventricular (LV) remodelling (59 ± 14 years, 55% male) and 26 aged matched healthy controls (55±15 years, 77% male) were included. HT patients were further divided into a concentric remodelling (HT1) group (13 patients) and a concentric hypertrophy (HT2) group (20 patients). LV parasternal long-axis views were acquired with an experimental ultrasound scanner at 1266 ± 317 frames per seconds. The SW velocity induced by MVC was measured from myocardial acceleration maps. SW velocities differed significantly between HT patients and controls (5.83 ± 1.20 m/s vs. 4.04 ± 0.96 m/s; P &lt; 0.001). In addition, the HT2 group had the highest SW velocities (P &lt; 0.001), whereas values between controls and the HT1 group were comparable (P = 0.075). Significant positive correlations were found between SW velocity and LV remodelling (interventricular septum thickness: r = 0.786, P &lt; 0.001; LV mass index: r = 0.761, P &lt; 0.001). SW velocity normalized for wall stress indicated that myocardial stiffness in the HT2 group was twice as high as in controls (P &lt; 0.001), whereas values of the HT1 group overlapped with the controls (P = 1.00).

Conclusions

SW velocity as measure of myocardial stiffness is higher in HT patients compared with healthy controls, particularly in advanced hypertensive heart disease. Patients with concentric remodelling have still normal myocardial properties whereas patients with concentric hypertrophy show significant stiffening.

Impact of apical foreshortening on deformation measurements: a report from the EACVI-ASE Strain Standardization Task Force

Aims

Foreshortening of apical views is a common problem in echocardiography. It results in an abnormally thick false apex and a shortened left ventricular (LV) long axis. We sought to evaluate the impact of foreshortened (FS) on LV ejection fraction (LVEF) and layer-specific 2D speckle tracking based segmental (S) and global (G) longitudinal strain (LS) measurements.

Methods and results

We examined 72 participants using a GE Vivid E9 system. FS apical views were collected from an imaging window one rib-space higher than the optimal images. Ejection fraction as well as layer-specific GLS and SLS measurements were analysed by GE EchoPAC v201 and TomTec Image Arena 4.6 and compared between optimal and FS images. On average, LV long axis was 10% shorter in FS images than in optimal images. FS induced a relative change in LVEF of 3.3% and 6.9% for GE and TomTec, respectively (both, P < 0.001). Endocardial GLS was 9.0% higher with GE and 23.2% with TomTec (P < 0.001). Midwall GLS measurements were less affected (7.8% for GE and 14.1% for TomTec, respectively, both P < 0.001). Segmental strain analysis revealed that the mid-ventricular and apical segments were more affected by foreshortening, and endocardial measurements were more affected than midwall.

Conclusion

Optimal image geometry is crucial for accurate LV function assessment. Foreshorhening of apical views has a substantial impact on longitudinal strain measurements, predominantly in the apex and in the endocardial layer. Our data suggest that measuring midwall strain might therefore be the more robust approach for clinical routine use.

Comparison of Feasibility, Accuracy, and Reproducibility of Layer-Specific Global Longitudinal Strain Measurements Among Five Different Vendors: A Report from the EACVI-ASE Strain Standardization Task Force

BACKGROUND

Despite standardization efforts, vendors still use information from different myocardial layers to calculate global longitudinal strain (GLS). Little is known about potential advantages or disadvantages of using these different layers in clinical practice. The authors therefore investigated the reproducibility and accuracy of GLS measurements from different myocardial layers.

METHODS

Sixty-three subjects were prospectively enrolled, in whom the intervendor bias and test-retest variability of endocardial GLS (E-GLS) and midwall GLS (M-GLS) were calculated, using software packages from five vendors that allow layer-specific GLS calculation (GE, Hitachi, Siemens, Toshiba, and TomTec). The impact of tracking quality and the interdependence of strain values from different layers were assessed by comparing test-retest errors between layers.

RESULTS

For both E-GLS and M-GLS, significant bias was found among vendors. Relative test-retest variability of E-GLS values differed significantly among vendors, whereas M-GLS showed no significant difference (range, 5.4%-9.5% [P = .032] and 7.0%-11.2% [P = .200], respectively). Within-vendor test-retest variability was similar between E-GLS and M-GLS for all but one vendor. Absolute test-retest errors were highly correlated between E-GLS and M-GLS for all vendors.

CONCLUSIONS

E-GLS and M-GLS measurements showed no relevant differences in robustness among vendors, although intervendor bias was higher for M-GLS compared with E-GLS. These data provide no technical argument in favor of a certain myocardial layer for global left ventricular functional assessment. Currently, the choice of which layer to use should therefore be based on the available clinical evidence in the literature.