Biphasic tissue Doppler waveforms during isovolumic phases are associated with asynchronous deformation of subendocardial and subepicardial layers

Characterizing collagen scaffold compliance with native myocardial strains using an ex-vivo cardiac model: The physio-mechanical influence of scaffold architecture and attachment method

Applied to the epicardium in-vivo, regenerative cardiac patches support the ventricular wall, reduce wall stresses, encourage ventricular wall thickening, and improve ventricular function. Scaffold engraftment, however, remains a challenge. After implantation, scaffolds are subject to the complex, time-varying, biomechanical environment of the myocardium. The mechanical capacity of engineered tissue to biomimetically deform and simultaneously support the damaged native tissue is crucial for its efficacy. To date, however, the biomechanical response of engineered tissue applied directly to live myocardium has not been characterized. In this paper, we utilize optical imaging of a Langendorff ex-vivo cardiac model to characterize the native deformation of the epicardium as well as that of attached engineered scaffolds. We utilize digital image correlation, linear strain, and 2D principal strain analysis to assess the mechanical compliance of acellular ice templated collagen scaffolds. Scaffolds had either aligned or isotropic porous architecture and were adhered directly to the live epicardial surface with either sutures or cyanoacrylate glue. We demonstrate that the biomechanical characteristics of native myocardial deformation on the epicardial surface can be reproduced by an ex-vivo cardiac model. Furthermore, we identified that scaffolds with unidirectionally aligned pores adhered with suture fixation most accurately recapitulated the deformation of the native epicardium. Our study contributes a translational characterization methodology to assess the physio-mechanical performance of engineered cardiac tissue and adds to the growing body of evidence showing that anisotropic scaffold architecture improves the functional biomimetic capacity of engineered cardiac tissue. STATEMENT OF SIGNIFICANCE: Engineered cardiac tissue offers potential for myocardial repair, but engraftment remains a challenge. In-vivo, engineered scaffolds are subject to complex biomechanical stresses and the mechanical capacity of scaffolds to biomimetically deform is critical. To date, the biomechanical response of engineered scaffolds applied to live myocardium has not been characterized. In this paper, we utilize optical imaging of an ex-vivo cardiac model to characterize the deformation of the native epicardium and scaffolds attached directly to the heart. Comparing scaffold architecture and fixation method, we demonstrate that sutured scaffolds with anisotropic pores aligned with the native alignment of the superficial myocardium best recapitulate native deformation. Our study contributes a physio-mechanical characterization methodology for cardiac tissue engineering scaffolds.

Usefulness of tissue Doppler-derived left ventricular isovolumic contraction velocity in patients with heart failure with preserved ejection fraction

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is a group of diseases classified by left ventricular (LV) EF, a measure of pump function. However, LVEF does not reflect LV contractility. Previous studies have shown that tissue Doppler-derived LV isovolumic contraction velocity (IVCv) correlates well with the LV peak dP/dt, an index of LV contractility. We explored whether LV IVCv is associated with 1-year post-discharge outcomes in HFpEF.

METHODS

We enrolled 113 patients (median age, 86 years, 45 male) with HFpEF (EF on admission ≥ 50%) who were admitted to our hospital for the treatment of acute HF. Clinical characteristics including echocardiographic data were obtained before discharge. IVCv was obtained from the tissue Doppler waveforms of both the septal and lateral mitral annulus of the apical 4-chamber view and averaged data were used. Primary outcomes were all-cause death or unplanned hospitalization due to HF within the first year.

RESULTS

Among all patients, median LVEF was 61%, left atrial diameter was 47 mm, E/e' was 17.5, and IVCv was 4.5 cm/sec; mean tricuspid regurgitation velocity was 2.6 m/sec. Regarding laboratory data, the median plasma B-type natriuretic peptide level was 185 pg/mL. Thirty-four events occurred (15 deaths, 19 unplanned hospitalizations due to HF) within the first year. In multivariate Cox proportional hazards analyses, IVCv was significantly associated with outcomes (hazard ratio .68, 95% confidence interval .50-.89, p = .0095), independent of general characteristics, echocardiographic measures and pertinent laboratory parameters.

CONCLUSION

LV IVCv was independently associated with 1-year outcomes in patients with HFpEF.

The relationship between myocardial microstructure and strain in chronic infarction using cardiovascular magnetic resonance diffusion tensor imaging and feature tracking

BACKGROUND

Cardiac diffusion tensor imaging (cDTI) using cardiovascular magnetic resonance (CMR) is a novel technique for the non-invasive assessment of myocardial microstructure. Previous studies have shown myocardial infarction to result in loss of sheetlet angularity, derived by reduced secondary eigenvector (E2A) and reduction in subendocardial cardiomyocytes, evidenced by loss of myocytes with right-handed orientation (RHM) on helix angle (HA) maps. Myocardial strain assessed using feature tracking-CMR (FT-CMR) is a sensitive marker of sub-clinical myocardial dysfunction. We sought to explore the relationship between these two techniques (strain and cDTI) in patients at 3 months following ST-elevation MI (STEMI).

METHODS

32 patients (F = 28, 60 ± 10 years) underwent 3T CMR three months after STEMI (mean interval 105 ± 17 days) with second order motion compensated (M2), free-breathing spin echo cDTI, cine gradient echo and late gadolinium enhancement (LGE) imaging. HA maps divided into left-handed HA (LHM, - 90 < HA < - 30), circumferential HA (CM, - 30° < HA < 30°), and right-handed HA (RHM, 30° < HA < 90°) were reported as relative proportions. Global and segmental analysis was undertaken.

RESULTS

Mean left ventricular ejection fraction (LVEF) was 44 ± 10% with a mean infarct size of 18 ± 12 g and a mean infarct segment LGE enhancement of 66 ± 21%. Mean global radial strain was 19 ± 6, mean global circumferential strain was - 13 ± - 3 and mean global longitudinal strain was - 10 ± - 3. Global and segmental radial strain correlated significantly with E2A in infarcted segments (p = 0.002, p = 0.011). Both global and segmental longitudinal strain correlated with RHM of infarcted segments on HA maps (p < 0.001, p = 0.003). Mean Diffusivity (MD) correlated significantly with the global infarct size (p < 0.008). When patients were categorised according to LVEF (reduced, mid-range and preserved), all cDTI parameters differed significantly between the three groups.

CONCLUSION

Change in sheetlet orientation assessed using E2A from cDTI correlates with impaired radial strain. Segments with fewer subendocardial cardiomyocytes, evidenced by a lower proportion of myocytes with right-handed orientation on HA maps, show impaired longitudinal strain. Infarct segment enhancement correlates significantly with E2A and RHM. Our data has demonstrated a link between myocardial microstructure and contractility following myocardial infarction, suggesting a potential role for CMR cDTI to clinically relevant functional impact.

The basic heart anatomy and physiology from the cardiologist's perspective: Toward a better understanding of left ventricular mechanics, systolic, and diastolic function

A comprehensive understanding of the cardiac structure-function relationship is essential for proper clinical cardiac imaging. This review summarizes the basic heart anatomy and physiology from the perspective of a heart imager focused on myocardial mechanics. The main issues analyzed are the left ventricular (LV) architecture, the LV myocardial deformation through the cardiac cycle, the LV diastolic function basic parameters and the basic parameters of the LV deformation used in clinical practice for the LV function assessment.

Tissue Doppler derived biphasic velocities during the pre and post-ejection phases: patterns, concordance and hemodynamic significance in health and disease

BACKGROUND

Pre-(PRE) and post-ejection (POE) velocities by mitral annular tissue Doppler (TD) are biphasic and may be related to myocardial deformations. We investigated the predominance and concordance of TD-PRE and POE velocities and their effect on myocardial functions in controls and in heart failure (HF) patients.

METHODS

Retrospectively, 84 HF patients [57.6 years, 28(33%) females, NYHA: 2.3 ± 0.6, EF: 55 ± 15%, 52(62%) preserved EF, and 32(38%) reduced EF], 42 normal young controls, and 26 asymptomatic age matched controls were included. Echocardiography was done and from mitral annular tissue Doppler recordings, the biphasic PRE and POE velocity signals were identified and compared between groups.

RESULTS

While controls had almost always predominantly positive PRE and negative POE, HF had more negative PRE and positive POE. Moreover, almost all controls exhibited normal concordance (positive PRE and negative POE). HF exhibited more abnormal concordance which was significantly associated with worse NYHA, and parameters of diastolic and systolic functions. Opposite PRE and POE velocities correlated significantly in all groups (PREp vs POEn: young:r = 0.52, p < 0.001, age controls:r = 0.79, p < 0.001, HFpEF: r = 0.56, p < 0.001, HFrEF: r = 0.42, p = 0.018; PREn vs POEp: young: r = 0.25,p = 0.1, age controls: r = 0.42, p = 0.04, HFpEF: r = 0.43, p = 0.004, HFrEF: r = 0.61, p < 0.001) and the ratios PRE-P/N and POE-N/P correlated significantly with E/e' in HF only.

CONCLUSIONS

In physiological state, TD signals are predominantly positive during PRE and negative during POE. Opposite PRE and POE velocities corelate, representing the PRE-generation and POE-reversal of shortening-stretch relationships, the attenuation of which in HF may be related to elevated LV filling pressures. In HF, partially or completely reversed concordance of PRE and POE is associated with progressive worsening of clinical and hemodynamic profiles.

Vector Flow Mapping Application in Local Cardiac Function in Hypertension Assessment

Objective

This study aims to investigate the clinical significance of vector flow mapping (VFM) by observing and quantifying energy loss (EL) during different phases and in different left ventricle (LV) segments.

Methods

42 healthy physical examination subjects and 89 patients with hypertension (HTN) were enrolled in the present study. The patients with HTN were divided into two groups: the left ventricular hypertrophy group (LVH) (n = 51) and the non-left ventricular hypertrophy group (NLVH) (n = 38), while the healthy patients were control group. VFM analysis software DSA-RS1 was used to calculate EL during the rapid filling phase (P1), slow filling phase (P2), atrial contraction phase (P3), and rapid ejection phase (P4). The energy loss of basal segment (EL-B), middle segment (EL-M) and apical segment (EL-A) of left ventricle in different phases was calculated and compared among the three groups.

Results

In controls, segmental EL showed a gradual increase from the apex to the base during diastole; however, the regularity was not found in the HTN patients. During both P1 and P2 EL-B, EL-M and EL-A were significantly higher in the NLVH group and the LVH group compared with the control group (P < 0.05). EL in LVH group was the highest among the three groups (P < 0.05). During P3, EL-B, EL-M and EL-A were increased in the NLVH group and LVH group compared with the control group. However, EL-M and EL-A in LVH group were significantly lower than the NLVH group (P < 0.05). During P4, EL of all segments was significantly higher in the NLVH group and LVH group compared with the control group (P < 0.05).

Conclusion

VFM can visually quantify hydrodynamic LV changes in healthy subjects. The EL levels in the different LV segments during different phases were significantly higher in the patients with HTN compared with the healthy subjects.

Alpha and beta myosin isoforms and human atrial and ventricular contraction

Human atrial and ventricular contractions have distinct mechanical characteristics including speed of contraction, volume of blood delivered and the range of pressure generated. Notably, the ventricle expresses predominantly β-cardiac myosin while the atrium expresses mostly the α-isoform. In recent years exploration of the properties of pure α- & β-myosin isoforms have been possible in solution, in isolated myocytes and myofibrils. This allows us to consider the extent to which the atrial vs ventricular mechanical characteristics are defined by the myosin isoform expressed, and how the isoform properties are matched to their physiological roles. To do this we Outline the essential feature of atrial and ventricular contraction; Explore the molecular structural and functional characteristics of the two myosin isoforms; Describe the contractile behaviour of myocytes and myofibrils expressing a single myosin isoform; Finally we outline the outstanding problems in defining the differences between the atria and ventricles. This allowed us consider what features of contraction can and cannot be ascribed to the myosin isoforms present in the atria and ventricles.

How His bundle pacing prevents and reverses heart failure induced by right ventricular pacing

Ideal heart performance demands vigorous systolic contractions and rapid diastolic relaxation. These sequential events are precisely timed and interdependent and require the rapid synchronous electrical stimulation provided by the His-Purkinje system. Right ventricular (RV) pacing creates slow asynchronous electrical stimulation that disrupts the timing of the cardiac cycle and results in left ventricular (LV) mechanical asynchrony. Long-term mechanical asynchrony produces LV dysfunction, remodeling, and clinical heart failure. His bundle pacing preserves synchronous electrical and mechanical LV function, prevents or reverses RV pacemaker-induced remodeling, and reduces heart failure.

How myofilament strain and strain rate lead the dance of the cardiac cycle

Movement of the myocardium can modify organ-level cardiac function and its molecular (crossbridge) mechanisms. This motion, which is defined by myocardial strain and strain rate (muscle shortening, lengthening, and the speed of these movements), occurs throughout the cardiac cycle, including during isovolumic periods. This review highlights how the left ventricular myocardium moves throughout the cardiac cycle, how muscle mechanics experiments provide insight into the regulation of forces used to move blood in and out of the left ventricle, and its impact on (and regulation by) crossbridge and sarcomere kinetics. We specifically highlight how muscle mechanics experiments explain how myocardial relaxation is accelerated by lengthening (strain rate) during late systole and isovolumic relaxation, a lengthening which has been measured in human hearts. Advancing and refining both in vivo measurement and ex vivo protocols with physiologic strain and strain rates could reveal important insights into molecular (crossbridge) kinetics. These advances could provide an improvement in both diagnosis and precise treatment of cardiac dysfunction.

[The antagonistic function of the heart muscle sustains the autoregulation according to Frank and Starling : Part I: Structure and function of heart muscle]

In the tradition of Harvey and according to Otto Frank the heart muscle structure is arranged in a strictly tangential fashion hence all contractile forces act in the direction of ventricular ejection. In contrast, morphology confirms that the heart consists of a 3-dimensional network of muscle fibers with up to two fifths of the chains of aggregated myocytes deviating from a tangential alignment at variable angles. Accordingly, the myocardial systolic forces contain, in addition to a constrictive also a (albeit smaller) radially acting component. Using needle force probes we have correspondingly measured an unloading type of force in a tangential direction and an auxotonic type in dilatative transversal direction of the ventricular walls to show that the myocardial body contracts actively in a 3-dimensional pattern. This antagonism supports the autoregulation of heart muscle function according to Frank and Starling, preserving ventricular shape, enhances late systolic fast dilation and attenuates systolic constriction of the ventricle wall. Auxotonic dilating forces are particularly sensitive to inotropic medication. Low dose beta-blocker is able to attenuate the antagonistic activity. All myocardial components act against four components of afterload, the hemodynamic, the myostructural, the stromatogenic and the hydraulic component. This complex interplay critically complicates clinical diagnostics. Clinical implications are far-reaching (see Part II, https://doi.org/10.1007/s00059-018-4735-x).

Will the real ventricular architecture please stand up?

Ventricular twisting, essential for cardiac function, is attributed to the contraction of myocardial helical fibers. The exact relationship between ventricular anatomy and function remains to be determined, but one commonly used explanatory model is the helical ventricular myocardial band (HVMB) model of Torrent‐Guasp. This model has been successful in explaining many aspects of ventricular function, (Torrent‐Guasp et al. Eur. J. Cardiothorac. Surg., 25, 376, 2004; Buckberg et al. Eur. J. Cardiothorac. Surg., 47, 587, 2015; Buckberg et al. Eur. J. Cardiothorac. Surg. 47, 778, 2015) but the model ignores important aspects of ventricular anatomy and should probably be replaced. The purpose of this review is to compare the HVMB model with a different model (nested layers). A complication when interpreting experimental observations that relate anatomy to function is that, in the myocardium, shortening does not always imply activation and lengthening does not always imply inactivation.

A potentially new phase of the cardiac cycle: Pre-isovolumic contraction recognized by echocardiography

Clinically the isovolumic contraction time (IVCT) can be measured by 3 echocardiographic methods of M-mode, pulse-wave Doppler (PWD), and tissue Doppler imaging (TDI). But IVCT can be clinically different by the 3 methods. This study is to investigate whether there is a potentially unidentified phase causing the discrepancies by analyzing electric mechanical delay time (EMD), IVCT, and pre-ejection period (PEP).A total of 30 healthy subjects were recruited for the study. EMD, IVCT, and PEP were obtained by the 3 methods, respectively. MCT (the interval from the onset of the QRS wave to the closure point of the mitral valve measured by TDI) and ICMC (the interval from the onset of IVC wave S1 to the closure point of the mitral valve measured by TDI) were both measured by color TDI.IVCTt (IVCT measured by TDI) was significantly longer than IVCTm or IVCTd (IVCT measured by M-mode or PWD) (both P < .0001), while EMDt (EMD measured by TDI) was significantly shorter than EMDm or EMDd (EMD measured by M-mode or PWD) (both P < .0001). But MCT was not significantly different from EMDm or EMDd (P > .05) and ICMC did not differ significantly from EMDm or EMDd minus EMDt or IVCTt minus IVCTm or IVCTd (P > .05), in other words, ICMC almost equaled to (EMDm or EMDd minus EMDt) or (IVCTt minus IVCTm or IVCTd).There may be an unidentified phase between the end of atrial contraction and the closure of mitral valve causing the discrepancies in IVCT, which is named as the pre-isovolumic contraction phase. It is a non-isovolumic phase and is included in the traditional isovolumic contraction phase.

Diastolic dysfunction is more apparent in STZ-induced diabetic female mice, despite less pronounced hyperglycemia

Diabetic cardiomyopathy is a distinct pathology characterized by early emergence of diastolic dysfunction. Increased cardiovascular risk associated with diabetes is more marked for women, but an understanding of the role of diastolic dysfunction in female susceptibility to diabetic cardiomyopathy is lacking. To investigate the sex-specific relationship between systemic diabetic status and in vivo occurrence of diastolic dysfunction, diabetes was induced in male and female mice by streptozotocin (5x daily i.p. 55 mg/kg). Echocardiography was performed at 7 weeks post-diabetes induction, cardiac collagen content assessed by picrosirius red staining, and gene expression measured using qPCR. The extent of diabetes-associated hyperglycemia was more marked in males than females (males: 25.8 ± 1.2 vs 9.1 ± 0.4 mM; females: 13.5 ± 1.5 vs 8.4 ± 0.4 mM, p < 0.05) yet in vivo diastolic dysfunction was evident in female (E/E' 54% increase, p < 0.05) but not male diabetic mice. Cardiac structural abnormalities (left ventricular wall thinning, collagen deposition) were similar in male and female diabetic mice. Female-specific gene expression changes in glucose metabolic and autophagy-related genes were evident. This study demonstrates that STZ-induced diabetic female mice exhibit a heightened susceptibility to diastolic dysfunction, despite exhibiting a lower extent of hyperglycemia than male mice. These findings highlight the importance of early echocardiographic screening of asymptomatic prediabetic at-risk patients.

The effects of load on transmural differences in contraction of isolated mouse ventricular cardiomyocytes

Mechanical properties of cardiomyocytes from different transmural regions are heterogeneous in the left ventricular wall. The cardiomyocyte mechanical environment affects this heterogeneity because of mechano-electric feedback mechanisms. In the present study, we investigated the effects of the mechanical load (preload and afterload) on transmural differences in contraction of subendocardial (ENDO) and subepicardial (EPI) single cells isolated from the murine left ventricle. Various preloads imposed via axial stretch and afterloads (unloaded and heavy loaded conditions) were applied to the cells using carbon fiber techniques for single myocytes. To simulate experimentally obtained results and to predict mechanisms underlying the cellular response to change in load, our mathematical models of the ENDO and EPI cells were used. Our major findings are the following. Our results show that ENDO and EPI cardiomyocytes have different mechanical responses to changes in preload to the cells. Under auxotonic contractions at low preload (unstretched cells), time to peak contraction (T_max) and the time constant of [Ca²⁺]_i transient decay were significantly longer in ENDO cells than in EPI cells. An increase in preload (stretched cells) prolonged T_max in both cell types; however, the prolongation was greater in EPI cells, resulting in a decrease in the transmural gradient in T_max at high preload. Comparing unloaded and heavy loaded (isometric) contractions of the cells we found that transmural gradient in the time course of contraction is independent of the loading conditions. Our mathematical cell models were able to reproduce the experimental results on the distinct cellular responses to changes in the mechanical load when we accounted for an ENDO/EPI difference in the parameters of cooperativity of calcium activation of myofilaments.

Effects of cellular electromechanical coupling on functional heterogeneity in a one-dimensional tissue model of the myocardium

Based on the experimental evidence, we developed a one-dimensional (1D) model of heterogeneous myocardial tissue consisting of in-series connected cardiomyocytes from distant transmural regions using mathematical models of subendocardial and subepicardial cells. The regional deformation patterns produced by our 1D model are consistent with the transmural regional strain patterns obtained experimentally in the normal heart in vivo. The modelling results suggest that the mechanical load may essentially affect the transmural gradients in the electrical and mechanical properties of interacting myocytes within a tissue, thereby regulating global myocardial output.

Tissue Doppler-Derived Myocardial Acceleration during Isovolumetric Contraction Predicts Pulmonary Capillary Wedge Pressure in Patients with Significant Mitral Regurgitation

The aim of this study was to determine whether isovolumic contraction velocity (IVV) and acceleration (IVA) predict pulmonary capillary wedge pressure (PCWP) in mitral regurgitation. Forty-four patients with mitral regurgitation were studied. PCWP was invasively measured. IVV, IVA and the ratio IVRT/Te'-E (where IVRT = isovolumic relaxation time, and Te'-E = time difference between the onset of mitral annular e' and mitral flow E waves) were measured. Mean age was 59.2 ± 13.3 y. Twenty-six patients had an ejection fraction ≥55%, and 18 patients had an ejection fraction <55%. IVRT/Te'-E was impossible in 11 patients because Te'-E = zero. PCWP correlated with IVV, IVA and IVRT/Te'-E; overall (r = -0.714, -0.892 and, -0.752, all p < 0.001), ejection fraction ≥55 (r = -0.467, -0.749, -0.639, p = 0.016, <0.001, 0.003) and ejection fraction <55% (r = -0.761, -0.911 and -0.833, all p < 0.001). Similar correlations were found for sinus and atrial fibrillation. Our study suggests that IVV and IVA correlate with PCWP in patients with mitral regurgitation irrespective of systolic function or rhythms and, thus, can be alternatives to the tedious IVRT/Te'-E, especially when impossible because Te'-E = 0.

The R21C Mutation in Cardiac Troponin I Imposes Differences in Contractile Force Generation between the Left and Right Ventricles of Knock-In Mice

We investigated the effect of the hypertrophic cardiomyopathy-linked R21C (arginine to cysteine) mutation in human cardiac troponin I (cTnI) on the contractile properties and myofilament protein phosphorylation in papillary muscle preparations from left (LV) and right (RV) ventricles of homozygous R21C(+/+) knock-in mice. The maximal steady-state force was significantly reduced in skinned papillary muscle strips from the LV compared to RV, with the latter displaying the level of force observed in LV or RV from wild-type (WT) mice. There were no differences in the Ca(2+) sensitivity between the RV and LV of R21C(+/+) mice; however, the Ca(2+) sensitivity of force was higher in RV-R21C(+/+) compared with RV-WT and lower in LV- R21C(+/+) compared with LV-WT. We also observed partial loss of Ca(2+) regulation at low [Ca(2+)]. In addition, R21C(+/+)-KI hearts showed no Ser23/24-cTnI phosphorylation compared to LV or RV of WT mice. However, phosphorylation of the myosin regulatory light chain (RLC) was significantly higher in the RV versus LV of R21C(+/+) mice and versus LV and RV of WT mice. The difference in RLC phosphorylation between the ventricles of R21C(+/+) mice likely contributes to observed differences in contractile force and the lower tension monitored in the LV of HCM mice.

Normal left ventricular torsion mechanics in healthy children: age related changes of torsion parameters are closely related to changes in heart rate

Background and Objectives

This study was aimed at assessing left ventricular torsion (LVtor) mechanics using speckle tracking echocardiography (STE), establishing normal reference values of principal LVtor parameters, and analyzing the age-related changes in normal children.

Subjects and Methods

Eighty children (aged 3 months to 15 years) with normal cardiac function and rhythm were recruited. LVtor parameters including rotations, twist and untwist, torsion, and their rate indices were measured using STE. Age and heart rate related changes of the parameters were analyzed.

Results

Speckle tracking echocardiography analyses for LVtor parameters had excellent reliability in 64 of 80 subjects (80%) (intraclass correlation coefficients; 0.93-0.97). Early systolic twist (EST) motions (-8.4--0.1°) were observed in all subjects during an early 20±7% of systolic time intervals. The peak systolic twist and torsion were 17.0±6.5° and 2.9±1.3°/cm, respectively. The peak twist velocity was recorded at 51±13% of systolic time and the peak untwist velocity at 13.8±11.5% of diastolic time intervals. Multivariate analysis showed that heart rate change was an independent predictor of changes in torsion parameters; significantly decreasing LV length-normalized apical and basal rotation, torsion, and twist and untwist rate with increasing age. Isovolumetric recoil rate was independent of change in age and heart rate.

Conclusion

Left ventricle showed unique torsion mechanics in children with EST, torsion, and untwists. Heart rate was an independent predictor of the change in torsion parameters with aging.

Two-Dimensional Strain Imaging: Basic principles and Technical Consideration

Tissue Doppler Imaging (TDI) and TDI-derived strain provide considerably accurate information in the non-invasive assessment of local myocardial functions. Given its high temporal and spatial resolution, TDI allows assessment of local myocardial functions in each phase of cardiac cycle. However, the most important limitation of this method is its angle dependence. New techniques to measure myocardial deformation, such as speckle tracking echocardiography, overcome the angle-dependence limitation of TDI-derived strain. Moreover, these techniques provide more unique information about myocardial fiber orientation. This review examines the architectural structure and function of the myocardium and includes technical revisions of this information that will provide a basis for STE.

The tissue Doppler imaging derived post-systolic velocity notch originates at the aortic annulus

Background

A distinct velocity pattern represented by a "notch" is observed during the time interval between the end of the systolic and the onset of the early diastolic velocity wave on longitudinal myocardial velocity curve. The origin of the post-systolic velocity notch (PSN) has not been resolved.

Methods

The high frame rate color tissue Doppler imaging of the apical longitudinal axis was performed in 32 healthy subjects.

Results

The time delays of the PSN onset at the posterior aortic wall (AW), the mid anteroseptal wall (MAS) and the posterior mitral annulus (MA) relatively to the anterior aortic annulus (AA) were found to be significantly longer than zero (5.1 ± 2.2, 6.0 ± 2.3, 6.8 ± 2.8 ms; p < 0.001). The amplitude was the highest at the AA when compared to the AW, the MAS and the MA (4.77 ± 1.28 vs. 2.88 ± 1.11, 2.15 ± 0.73, 2.44 ± 1.17 cm/s; p < 0.001). A second PSN spike was identifiable in 10/32 (31%) of the studied subjects at the AA. Of these, 9 (28%) exhibited a second PSN spike at the AW, 3 (9%) at the MAS and no one at the MA.

Conclusion

The AA represents the site of the earliest onset and maximal amplitude of the PSN on the longitudinal velocity curve suggesting its mechanism to be that of an energy release at the instant of the aortic valve closure causing an apically directed acceleration of the myocardium. A substantial number of healthy subjects exhibit a second PSN spike predominantly at the level of the AA. Its mechanism remains to be elucidated.

Ultra-high frame rate tissue Doppler imaging

We describe a new tissue Doppler imaging (TDI) method, ultra-high frame rate tissue Doppler imaging (UFR-TDI). With two broad transmit beams covering only the ventricular walls, we achieve 1200 frames/s in a four-chamber apical view. We examined 10 healthy volunteers to study the feasibility of this method. Ultra-high-frame-rate TDI provided peak annular velocities and time to peak S' intervals in good agreement with those measured with conventional TDI. Moreover, UFR-TDI provided additional information in early and late systole: In all subjects, the method was able to separate the timing of electrical activation, start of mechanical contraction, mitral valve closure and start of ejection. The earliest mechanical activation was seen before mitral valve closure. The method was also able to measure the propagation speed of the mechanical wave created by aortic valve closure.

Fluid-structure interaction of an aortic heart valve prosthesis driven by an animated anatomic left ventricle

We develop a novel large-scale kinematic model for animating the left ventricle (LV) wall and use this model to drive the fluid-structure interaction (FSI) between the ensuing blood flow and a mechanical heart valve prosthesis implanted in the aortic position of an anatomic LV/aorta configuration. The kinematic model is of lumped type and employs a cell-based, FitzHugh-Nagumo framework to simulate the motion of the LV wall in response to an excitation wavefront propagating along the heart wall. The emerging large-scale LV wall motion exhibits complex contractile mechanisms that include contraction (twist) and expansion (untwist). The kinematic model is shown to yield global LV motion parameters that are well within the physiologic range throughout the cardiac cycle. The FSI between the leaflets of the mechanical heart valve and the blood flow driven by the dynamic LV wall motion and mitral inflow is simulated using the curvilinear immersed boundary (CURVIB) method [1, 2] implemented in conjunction with a domain decomposition approach. The computed results show that the simulated flow patterns are in good qualitative agreement with in vivo observations. The simulations also reveal complex kinematics of the valve leaflets, thus, underscoring the need for patient-specific simulations of heart valve prosthesis and other cardiac devices.

Left-ventricular shape determines intramyocardial mechanical heterogeneity

Left-ventricular remodeling is considered to be an important mechanism of disease progression leading to mechanical dysfunction of the heart. However, the interaction between the physiological changes in the remodeling process and the associated mechanical dysfunction is still poorly understood. Clinically, it has been observed that the left ventricle often undergoes large shape changes, but the importance of left-ventricular shape as a contributing factor to alterations in mechanical function has not been clearly determined. Therefore, the interaction between left-ventricular shape and systolic mechanical function was examined in a computational finite-element study. Hereto, finite-element models were constructed with varying shapes, ranging from an elongated ellipsoid to a sphere. A realistic transmural gradient in fiber orientation was considered. The passive myocardium was described by an incompressible hyperelastic material law with transverse isotropic symmetry. Activation was governed by the eikonal-diffusion equation. Contraction was incorporated using a Hill model. For each shape, simulations were performed in which passive filling was followed by isovolumic contraction and ejection. It was found that the intramyocardial distributions of fiber stress, strain, and stroke work density were shape dependent. Ejection performance was reduced with increasing sphericity, which was regionally related to a reduction in the active fiber stress development, fiber shortening, and stroke work in the midwall and subepicardial region at the midheight level in the left-ventricular wall. Based on these results, we conclude that a significant interaction exists between left-ventricular shape and regional myofiber mechanics, but the importance for left-ventricular remodeling requires further investigation.

Evaluation of left ventricular twist in acute myocardial infarction patients using speckle tracking imaging

The aim of this study is to evaluate the differences of left ventricular (LV) twist and untwisting rate in patients with acute myocardial infarction (AMI) as compared with healthy subjects by means of Speckle Tracking Imaging (STI). 45 AMI patients (AMI group) and 48 healthy subjects (NOR group) were studied. Two-dimensional STI was performed in all patients. Peak apical rotation, peak basal rotation, peak LV twist, peak basal untwisting rate, peak apical untwisting rate, peak LV untwisting rate, time to peak LV twist, and untwisting rate were measured. In comparison with the NOR group, peak LV rotational parameters were found to be decreased in the AMI group (P < 0.01). A strong correlation was found between the peak LV twist and LV ejection fraction in the overall study population (P < 0.001). The LV twist is strongly related to LV systolic function, and the impairment of LV function observed in patients with AMI is associated with a decrease of LV twist and untwist rate. The STI appears to accurately evaluate LV function.

Chasing the reflected wave back into the heart: a new hypothesis while the jury is still out

Background:

Arterial stiffness directly influences cardiac function and is independently associated with cardiovascular risk. However, the influence of the aortic reflected pulse pressure wave on left ventricular function has not been well characterized. The aim of this study was to obtain detailed information on regional ventricular wall motion patterns corresponding to the propagation of the reflected aortic wave on ventricular segments.

Methods:

Left ventricular wall motion was investigated in a group of healthy volunteers (n = 14, age 23 ± 3 years), using cardiac magnetic resonance navigator-gated tissue phase mapping. The left ventricle was divided into 16 segments and regional wall motion was studied in high temporal detail.

Results:

Corresponding to the expected timing of the reflected aortic wave reaching the left ventricle, a characteristic “notch” of regional myocardial motion was seen in all radial, circumferential, and longitudinal velocity graphs. This notch was particularly prominent in septal segments adjacent to the left ventricular outflow tract on radial velocity graphs and in anterior and posterior left ventricular segments on circumferential velocity graphs. Similarly, longitudinal velocity graphs demonstrated a brief deceleration in the upward recoil motion of the entire ventricle at the beginning of diastole.

Conclusion:

These results provide new insights into the possible influence of the reflected aortic waves on ventricular segments. Although the association with the reflected wave appears to us to be unambiguous, it represents a novel research concept, and further studies enabling the actual recording of the pulse wave are required.

Limitations of standard echocardiographic methods for quantification of right ventricular size and function in children and young adults

OBJECTIVES

The aim of this study was to evaluate correlation of 2-dimensional (2D) echocardiographic assessment of right ventricular (RV) and left ventricular (LV) size and function with magnetic resonance imaging (MRI) in children and young adults.

METHODS

Patients with repaired tetralogy of Fallot (n = 23) and those who had normal RV volumes (n = 13) and a normal ejection fraction (EF) by MRI constituted the study groups. Echocardiographic indices including the end-diastolic area (EDa), end-systolic area (ESa), fractional area change (FAC), tricuspid annular motion (TAM), RV basal diameter, and RV basal shortening fraction were compared with MRI ventricular volumes and the EF. Two echocardiographers qualitatively graded RV size and function.

RESULTS

In both groups, neither the RV EDa nor the ESa correlated with MRI RV volumes. Only TAM correlated with the RV EF. Qualitative assessment of the RV showed poor interobserver agreement. The LV area and FAC correlated well with MRI data.

CONCLUSIONS

In contrast to the LV, 2D echocardiographic indices of RV size and function, with the exception of TAM, do not correlate with MRI data.

Evaluation of left ventricular rotation by two-dimensional speckle tracking method and real-time three-dimensional echocardiography: comparison with MRI tagging method

BACKGROUND

Recently, it has become possible to evaluate left ventricular (LV) torsion by two-dimensional (2D) speckle tracking images. However, LV torsion is a three-dimensional (3D) performance, which per se cannot be assessed by the 2D speckle tracking method. The present study investigated the accuracy of the 2D speckle tracking method and real-time 3D echocardiography in measuring LV rotation, comparing with the MRI tagging method.

METHODS

We assessed LV apical rotation using the 2D speckle tracking method, real-time 3D echocardiography, and MRI tagging method in 26 normal subjects, and compared the results of these three methods. LV apical rotation was measured just before the level in which the posterior papillary muscle was absorbed into the free wall.

RESULTS

The degree of LV apical rotation evaluated by the 2D speckle tracking method (Δθ 2D) was significantly smaller than that evaluated by 3D echocardiography (Δθ 3D) and the MRI tagging method (Δθ MRI) (Δθ 2D 7.3 ± 2.8°; Δθ 3D 8.8 ± 3.4°; Δθ MRI 9.0 ± 3.4°; Δθ 2D vs. Δθ 3D, p = 0.0001; Δθ 2D vs. Δθ MRI, p < 0.0001). There were good correlations among Δθ 2D, Δθ 3D, and Δθ MRI, but agreement between Δθ 3D and Δθ MRI (mean difference 0.14 ± 1.43°) was better than that between Δθ 2D and Δθ MRI (mean difference 1.68 ± 1.89°).

CONCLUSION

The degree of LV apical rotation was underestimated with the 2D speckle tracking method compared with the MRI tagging method, whereas it could be precisely measured by 3D echocardiography.

Lengthening-contractions in isolated myocardium impact force development and worsen cardiac contractile function in the mdx mouse model of muscular dystrophy

Lengthening-contractions exert eccentric stress on myofibers in normal myocardium. In congestive heart failure caused by a variety of diseases, the impact of lengthening-contractions of myocardium likely becomes more prevalent and severe. The present study introduces a method to investigate the role of stretching imposed by repetitive lengthening-contractions in myocardium under near-physiological conditions. By exerting various stretch-release ramps while the muscle is contracting, consecutive lengthening-contractions and their potential detrimental effect on cardiac function can be studied. We tested our model and hypothesis in age-matched (young and adult) mdx and wild-type mouse right ventricular trabeculae. These linear and ultrathin muscles possess all major cardiac cell types, and their contractile behavior very closely mimics that of the whole myocardium. In the first group of experiments, 10 lengthening-contractions at various magnitudes of stretch were performed in trabeculae from 10-wk-old mdx and wild-type mice. In the second group, 100 lengthening-contractions at various magnitudes were conducted in trabeculae from 10- and 20-wk-old mice. The peak isometric active developed tension (F(dev), in mN/mm(2)) and kinetic parameters time to peak tension (TTP, in ms) and time from peak tension to half-relaxation (RT50, in ms) were measured. Our results indicate lengthening-contractions significantly impact contractile behavior, and that dystrophin-deficient myocardium in mdx mice is significantly more susceptible to these damaging lengthening-contractions. The results indicate that lengthening-contractions in intact myocardium can be used in vitro to study this emerging contributor to cardiomyopathy.

Tissue Doppler image-derived measurements during isovolumic contraction predict exercise capacity in patients with reduced left ventricular ejection fraction

OBJECTIVES

We explored the incremental value of quantification of tissue Doppler (TD) velocity during the brief isovolumic contraction (IVC) phase of the cardiac cycle for the prediction of exercise performance in patients referred for cardiopulmonary exercise testing (CPET).

BACKGROUND

Experimental studies have shown that rapid left ventricular (LV) shape change during IVC is essential for optimal onset of LV ejection. However, the incremental value of measuring IVC velocities in clinical settings remains unclear.

METHODS

A total of 82 subjects (age 53+/-14 years, 56 men) were studied with echocardiography and CPET. Reduced LV ejection fraction (EF) (EF<50%) was present in 38 (46%) subjects. Pulsed-wave annular TD velocities were averaged from the LV lateral and septal annulus during isovolumic contraction (IVCa), ejection, isovolumic relaxation, and early and late diastole (Aa) and compared with peak oxygen consumption (VO2) and percentage of the predicted peak VO2 (% predicted peak VO2) obtained from CPET.

RESULTS

Patients with reduced EF had lower IVCa (6.3 vs. 4.5 cm/s, p=0.04), ejection (7.7 vs. 5.5 cm/s, p<0.001), and Aa velocities (7.9 vs. 6.6 cm/s, p=0.04). Similarly, % predicted peak VO2 was lower in patients with reduced EF (52.9% vs. 73.1%, p<0.001) and correlated with the variations in IVCa (r=0.7, p=0.001). Multivariate analysis of 2-dimensional and Doppler variables in the presence of reduced LV EF revealed only IVCa and Aa as independent predictors of % predicted peak VO2 (r2=0.612, p=0.02 for IVCa and p=0.009 for Aa). The overall performance of IVCa in the prediction of exercise capacity was good (area under the curve=0.86, p<0.001).

CONCLUSIONS

Assessment of TD-derived IVC and atrial stretch velocities provide independent prediction of exercise capacity in patients with reduced LV EF. Assessment of LV pre-ejectional stretch and shortening mechanics at rest may be useful for determining the myocardial functional reserve of patients with reduced EF.

Echocardiographic strain imaging and its use in the clinical setting

The use of echocardiography has grown tremendously over the past several years. It is used routinely for diagnosis, prognosis and monitoring changes of cardiac function in coronary artery disease, heart failure, pulmonary hypertension, arrhythmias, pericardial disease and valvular disease, as well as congenital conditions. In recent years, the advancing technology used to evaluate the heart by ultrasound has allowed physicians to understand the mechanics of the heart muscle and the contribution of abnormalities in myocardial movement to heart disease. This review will discuss novel echocardiographic strain imaging techniques, placing them in the context of myocardial mechanics and describing current and future applications.

Transmural myocardial mechanics during isovolumic contraction

OBJECTIVES

We sought to resolve the 3-dimensional transmural heterogeneity in myocardial mechanics observed during the isovolumic contraction (IC) phase.

BACKGROUND

Although myocardial deformation during IC is expected to be little, recent tissue Doppler imaging studies suggest dynamic myocardial motions during this phase with biphasic longitudinal tissue velocities in left ventricular (LV) long-axis views. A unifying understanding of myocardial mechanics that would account for these dynamic aspects of IC is lacking.

METHODS

We determined the time course of 3-dimensional finite strains in the anterior LV of 14 adult mongrel dogs in vivo during IC and ejection with biplane cineradiography of implanted transmural markers. Transmural fiber orientations were histologically measured in the heart tissue postmortem. The strain time course was determined in the subepicardial, midwall, and subendocardial layers referenced to the end-diastolic configuration.

RESULTS

During IC, there was circumferential stretch in the subepicardial layer, whereas circumferential shortening was observed in the midwall and the subendocardial layer. There was significant longitudinal shortening and wall thickening across the wall. Although longitudinal tissue velocity showed a biphasic profile; tissue deformation in the longitudinal as well as other directions was almost linear during IC. Subendocardial fibers shortened, whereas subepicardial fibers lengthened. During ejection, all strain components showed a significant change over time that was greater in magnitude than that of IC. Significant transmural gradient was observed in all normal strains.

CONCLUSIONS

IC is a dynamic phase characterized by deformation in circumferential, longitudinal, and radial directions. Tissue mechanics during IC, including fiber shortening, appear uninterrupted by rapid longitudinal motion created by mitral valve closure. This study is the first to report layer-dependent deformation of circumferential strain, which results from layer-dependent deformation of myofibers during IC. Complex myofiber mechanics provide the mechanism of brief clockwise LV rotation (untwisting) and significant wall thickening during IC within the isovolumic constraint.

Feasibility of a three-axis epicardial accelerometer in detecting myocardial ischemia in cardiac surgical patients

OBJECTIVE

We investigated the feasibility of continuous detection of myocardial ischemia during cardiac surgery with a 3-axis accelerometer.

METHODS

Ten patients with significant left anterior descending coronary artery stenosis underwent off-pump coronary artery bypass grafting. A 3-axis accelerometer (11 x 14 x 5 mm) was sutured onto the left anterior descending coronary artery-perfused region of left ventricle. Twenty episodes of ischemia were studied, with 3-minute occlusion of left anterior descending coronary artery at start of surgery and 3-minute occlusion of left internal thoracic artery at end of surgery. Longitudinal, circumferential, and radial accelerations were continuously measured, with epicardial velocities calculated from the signals. During occlusion, accelerometer velocities were compared with anterior left ventricular longitudinal, circumferential, and radial strains obtained by echocardiography. Ischemia was defined by change in strain greater than 30%.

RESULTS

Ischemia was observed echocardiographically during 7 of 10 left anterior descending coronary artery occlusions but not during left internal thoracic artery occlusion. During ischemia, there were no significant electrocardiographic or hemodynamic changes, whereas large and significant changes in accelerometer circumferential peak systolic (P < .01) and isovolumic (P < .01) velocities were observed. During 13 occlusions, no ischemia was demonstrated by strain, nor was any change demonstrated by the accelerometer. A strong correlation was found between circumferential strain and accelerometer circumferential peak systolic velocity during occlusion (r = -0.76, P < .001).

CONCLUSIONS

The epicardial accelerometer detects myocardial ischemia with great accuracy. This novel technique has potential to improve monitoring of myocardial ischemia during cardiac surgery.

New Echocardiographic Techniques for Evaluating Left Ventricular Myocardial Function

Ultrasound imaging of the heart continues to play an important role in diagnosis and management of patients with cardiovascular diseases. Recent advances in ultrasound technology and introduction of newer imaging modalities have enabled improved assessment of left ventricular myocardial function. Tissue Doppler imaging and 2-dimensional speckle tracking allow more objective quantification of myocardial function in the form of tissue velocities, displacement, strain, and strain rate. Similarly, contrast-enhanced echocardiography and 3-dimensional echocardiography have provided a unique insight into left ventricular form and function that was not possible by unenhanced 2-dimensional echocardiography. In this review, the authors discuss the clinical application of these new imaging techniques in the assessment of left ventricular myocardial function.

Age-related changes in the biomechanics of left ventricular twist measured by speckle tracking echocardiography

The increasing number and proportion of aged individuals in the population warrants knowledge of normal physiological changes of left ventricular (LV) biomechanics with advancing age. LV twist describes the instantaneous circumferential motion of the apex with respect to the base of the heart and has an important role in LV ejection and filling. This study sought to investigate the biomechanics behind age-related changes in LV twist by determining a broad spectrum of LV rotation parameters in different age groups, using speckle tracking echocardiography (STE). The final study population consisted of 61 healthy volunteers (16–35 yr, n = 25; 36–55 yr, n = 23; 56–75 yr, n = 13; 31 men). LV peak systolic rotation during the isovolumic contraction phase (Rotearly), LV peak systolic rotation during ejection (Rotmax), instantaneous LV peak systolic twist (Twistmax), the time to Rotearly, Rotmax, and Twistmax, and rotational deformation delay (defined as the difference of time to basal Rotmax and apical Rotmax) were determined by STE using QLAB Advanced Quantification Software (version 6.0; Philips, Best, The Netherlands). With increasing age, apical Rotmax ( P < 0.05), time to apical Rotmax ( P < 0.01), and Twistmax ( P < 0.01) increased, whereas basal Rotearly ( P < 0.001), time to basal Rotearly ( P < 0.01), and rotational deformation delay ( P < 0.05) decreased. Rotational deformation delay was significantly correlated to Twistmax ( R2 = 0.20, P < 0.05). In conclusion, Twistmax increased with aging, resulting from both increased apical Rotmax and decreased rotational deformation delay between the apex and the base of the LV. This may explain the preservation of LV ejection fraction in the elderly.