Association between echocardiography-derived haemodynamic force parameters and left ventricular reverse remodelling after cardiac resynchronization therapy.

AIMS: Cardiac resynchronization therapy (CRT) may induce left ventricular (LV) reverse remodelling (=LV response) in patients with heart failure. Intraventricular pressure gradients can be quantified using echocardiography-derived haemodynamic forces (HDF). The aim was to evaluate the association between baseline HDF and LV response and to compare the change of HDF after CRT between LV responders and LV non-responders. METHODS AND RESULTS: The following HDF parameters were assessed: 1)apical-basal (AB) strength, 2)lateral-septal strength, 3)force vector angle, 4)systolic AB impulse, 5)systolic force vector angle. LV response was defined as a reduction of LV end-systolic volume ≥15% at six months. One hundred ninety-six patients were included (64±11 years, 122(62%) men), 136(69%) showed LV response. On multivariable logistic regression analysis, the force vector angle in the complete heart cycle (OR 1.083 (95%CI 1.018, 1.153), p=0.012) and the systolic force vector angle (OR 1.089 (95%CI 1.021, 1.161), p=0.009), both included in separate models, were independently associated with LV response. Six months after CRT, LV responders had greater AB strength, AB impulse and higher force vector angles, while LV non-responders only showed improvement in the force vector angle in the complete heart cycle. CONCLUSION: The orientation of HDF at baseline is associated with LV response to CRT. Six months after CRT, the orientation of HDF improves in LV responders and LV non-responders, while the magnitude of AB HDF only improves in LV responders.

Evolution of Echocardiography-Derived Hemodynamic Force Parameters After Cardiac Resynchronization Therapy.

Echocardiography-derived hemodynamic forces (HDF) allow calculation of intraventricular pressure gradients from routine transthoracic echocardiographic images. The evolution of HDF after cardiac resynchronization therapy (CRT) has not been investigated in large cohorts. The aim was to assess HDF in patients with heart failure implanted with CRT versus healthy controls. HDF were assessed before and 6 months after CRT. The following HDF parameters were calculated: (1) apical-basal strength, (2) lateral-septal strength, (3) the ratio of lateral-septal to apical-basal strength ratio, and (4) the force vector angle (1 and 2 representing the magnitude of HDF, 3 and 4 representing the orientation of HDF). In the propulsive phase of systole, the apical-basal impulse and the systolic force vector angle were measured. A total of 197 patients were included (age 64 ± 11 years, 62% male), with left ventricular ejection fraction ≤35%, QRS duration ≥130 ms and left bundle branch block. The magnitude of HDF was significantly lower and the orientation was significantly worse in patients with heart failure versus healthy controls. Immediately after CRT implantation, the apical-basal impulse and systolic force vector angle were significantly increased. Six months after CRT, improvement of apical-basal strength, lateral-septal to apical-basal strength ratio and the force vector angle occurred. When CRT was deactivated at 6 months, the increase in the magnitude of apical-basal HDF remained unchanged while the systolic force vector angle worsened significantly. In conclusion, HDF in CRT recipients reflect the acute effect of CRT and the effect of left ventricular reverse remodeling on intraventricular pressure gradients. Whether HDF analysis provides incremental value over established echocardiographic parameters, remains to be determined.

Haemodynamic forces predicting remodelling and outcome in patients with heart failure treated with sacubitril/valsartan.

AIMS: A novel tool for the evaluation of left ventricular (LV) systo-diastolic function through echo-derived haemodynamic forces (HDFs) has been recently proposed. The present study aimed to assess the predictive value of HDFs on (i) 6 month treatment response to sacubitril/valsartan in heart failure with reduced ejection fraction (HFrEF) patients and (ii) cardiovascular events. METHODS AND RESULTS: Eighty-nine consecutive HFrEF patients [70% males, 65 ± 9 years, LV ejection fraction (LVEF) 27 ± 7%] initiating sacubitril/valsartan underwent clinical, laboratory, ultrasound and cardiopulmonary exercise testing evaluations. Patients experiencing no adverse events and showing ≥50% reduction in plasma N-terminal pro-B-type natriuretic peptide and/or ≥10% LVEF increase over 6 months were considered responders. Patients were followed up for the composite endpoint of HF-related hospitalisation, atrial fibrillation and cardiovascular death. Forty-five (51%) patients were responders. Among baseline variables, only HDF-derived whole cardiac cycle LV strength (wLVS) was higher in responders (4.4 ± 1.3 vs. 3.6 ± 1.2; p = 0.01). wLVS was also the only independent predictor of sacubitril/valsartan response at multivariable logistic regression analysis [odds ratio 1.36; 95% confidence interval (CI) 1.10-1.67], with good accuracy at receiver operating characteristic (ROC) analysis [optimal cutpoint: ≥3.7%; area under the curve (AUC) = 0.736]. During a 33 month (23-41) median follow-up, a wLVS increase after 6 months (ΔwLVS) showed a high discrimination ability at time-dependent ROC analysis (optimal cut-off: ≥0.5%; AUC = 0.811), stratified prognosis (log-rank p < 0.0001) and remained an independent predictor for the composite endpoint (hazard ratio 0.76; 95% CI 0.61-0.95; p < 0.01), after adjusting for clinical and instrumental variables. CONCLUSIONS: HDF analysis predicts sacubitril/valsartan response and might optimise decision-making in HFrEF patients.

Cardiac and Vascular Remodeling After 6 Months of Therapy With Sacubitril/Valsartan: Mechanistic Insights From Advanced Echocardiographic Analysis.

Background: Effects of Sacubitril/Valsartan (S/V) on left ventricular (LV) mechanics and ventricular-arterial coupling in patients with heart failure with reduced ejection fraction (HFrEF) are not completely understood. The aim of this study was to evaluate both cardiac and vascular remodeling in a group of HFrEF patients undergoing S/V therapy. Methods: Fifty HFrEF patients eligible to start a therapy with S/V were enrolled. Echocardiographic evaluation was performed at baseline and after 6 months of follow-up (FU). Beside standard evaluation, including global longitudinal strain (GLS), estimated hemodynamic forces (HDFs) and non-invasive pressure-volume curves (PV loop) were assessed using dedicated softwares. HDFs were evaluated over the entire cardiac cycle, in systole and diastole, both in apex to base (A-B) and latero-septal (L-S) directions. The distribution of LV HDFs was evaluated by L-S over A-B HDFs ratio (L-S/A-B HDFs ratio). Parameters derived from estimated PV loop curves were left ventricular end-systolic elastance (Ees), arterial elastance (Ea), and ventricular-arterial coupling (VAC). Results: At 6 months of FU indexed left ventricular end-diastolic and end-systolic volumes decreased (EDVi: 101 ± 28 mL vs. 86 ± 30 mL, p < 0.001; ESVi: 72 ± 23 mL vs. 55 ± 24 mL, p < 0.001), ejection fraction and GLS significantly improved (EF: 29 ± 6% vs. 37 ± 7%, p < 0.001; GLS: -9 ± 3% vs. -13 ± 4%, p < 0.001). A reduction of Ea (2.11 ± 0.91 mmHg/mL vs. 1.72 ± 0.44 mmHg/mL, p = 0.008) and an improvement of Ees (1.01 ± 0.37 mmHg/mL vs. 1.35 ± 0.6 mmHg/mL, p < 0.001) and VAC (2.3 ± 1.1 vs. 1.5 ± 0.7, p < 0.001) were observed. Re-alignment of HDFs occurred, with a reduction of diastolic L-S/A-B HDFs ratio [23 (20-35)% vs. 20 (11-28) %, p < 0.001]. Conclusion: S/V therapy leads to a complex phenomenon of reverse remodeling involving increased myocardial contractility, HDFs distribution improvement, and afterload reduction.

Impact of synchronous atrioventricular delay optimization on left ventricle flow force angle evaluated by echocardiographic particle image velocimetry.

PURPOSE: To evaluate the improvement in electrical synchrony and left ventricle (LV) hemodynamics provided by combining the dynamic atrioventricular delay (AVD) of SyncAVTM CRT and the multiple LV pacing sites of MultiPoint pacing (MPP). METHODS: Patients with LBBB and QRS duration (QRSd) > 140 ms implanted with a CRT-D or CRT-P device and quadripolar LV lead were enrolled in this prospective study. During a post-implant follow-up visit, QRSd was measured from 12-lead surface electrograms by experts blinded to pacing configurations. QRSd reduction relative to intrinsic rhythm was evaluated during biventricular pacing (BiV) and MPP for two AVDs: nominal (140/110 ms paced/sensed) and SyncAV (patient-optimized SyncAV offset [10-60 ms] minimizing QRSd). Echocardiography particle imaging velocimetry (Echo-PIV) analysis was performed for each configuration. The resulting hemodynamic force LV flow angle (φ) was analyzed, which ranges from 0o (predominantly base-apex forces) to 90o (predominantly transverse forces). Higher angles indicate more energy dissipation at lateral walls due to transverse flow; lower angles indicate healthier flow aligned with the longitudinal base-apex path of the pressure gradient. RESULTS: Twelve patients (58% male, 17% ischemic, 32±7% ejection fraction, 165 ± 18 ms intrinsic QRSd) completed QRSd and Echo-PIV assessment. Relative to intrinsic rhythm, BiV and MPP with nominal AVD reduced QRSd by 10 ± 9% and 12 ± 9%, respectively. BiV+SyncAV and MPP+SyncAV further reduced QRSd by 19 ± 8%, (p < 0.05 vs. BiV with nominal AVD) and 23 ± 9% (p < 0.05 vs BiV+SyncAV), respectively. Echo-PIV showed similar sequential hemodynamic improvements. LV flow angular orientation during intrinsic activation (46 ± 3o) reduced with BiV+SyncAV (37 ± 4o, p < 0.05 vs intrinsic) and further with MPP+SyncAV (34 ± 4o, p < 0.05 vs BiV+SyncAV). CONCLUSION: These results suggest that SyncAV may improve electrical synchrony and influence LV flow patterns in patients suffering from heart failure compared to conventional CRT with a fixed AVD, with further improvement observed by combining with MPP.

Impact of intraventricular haemodynamic forces misalignment on left ventricular remodelling after myocardial infarction.

AIMS: Altered left ventricular (LV) haemodynamic forces (HDFs) have been associated with positive and negative remodelling after pathogenic or therapeutic events. We aimed to identify LV HDFs patterns associated with adverse LV remodelling (aLVr) in reperfused segment elevation myocardial infarction (STEMI) patients. METHODS AND RESULTS: Forty-nine acute STEMI patients underwent cardiac magnetic resonance (CMR) at 1 week (baseline) and after 4 months (follow-up). LV HDFs were computed at baseline from cine CMR long axis data sets, using a novel technique based on endocardial boundary tracking, both in apex-base (A-B) and latero-septal (L-S) directions. HDFs distribution was evaluated by L-S over A-B HDFs ratio (L-S/A-B HDFs ratio %). HDFs parameters were computed over the entire heartbeat, in systole and diastole. At baseline, aLVr patients had lower systolic L-S HDF (2.7 ± 0.9 vs. 3.6 ± 1%; P = 0.027) and higher diastolic L-S/A-B HDF ratio (28 ± 14 vs. 19 ± 6%; P = 0.03). At univariate logistic regression analysis, higher infarct size [odds ratio (OR) 1.05; 95% confidence interval (CI) 1.01-1.1; P = 0.04], higher L-S/A-B HDFs ratio (OR 1.1; 95% CI 1.01-1.2; P = 0.05) and lower L-S HDFs (OR 0.41; 95% CI 0.2-0.9; P = 0.04) were associated with aLVr at follow-up. In the multivariable logistic regression analysis, diastolic L-S/A-B HDF ratio remained the only independent predictor of aLVr (OR 1.1; 95% CI 1.01-1.2; P = 0.04). CONCLUSIONS: Misalignment of diastolic haemodynamic forces after STEMI is associated with aLVr after 4 months.

Introduction to Hemodynamic Forces Analysis: Moving Into the New Frontier of Cardiac Deformation Analysis.

The potential relevance of blood flow for describing cardiac function has been known for the past 2 decades, but the association of clinical parameters with the complexity of fluid motion is still not well understood. Hemodynamic force (HDF) analysis represents a promising approach for the study of blood flow within the ventricular chambers through the exploration of intraventricular pressure gradients. Previous experimental studies reported the significance of invasively measured cardiac pressure gradients in patients with heart failure. Subsequently, advances in cardiovascular imaging allowed noninvasive assessment of pressure gradients during progression and resolution of ventricular dysfunction and in the setting of resynchronization therapy. The HDF analysis can amplify mechanical abnormalities, detect them earlier compared with conventional ejection fraction and strain analysis, and possibly predict the development of cardiac remodeling. Alterations in HDFs provide the earliest signs of impaired cardiac physiology and can therefore transform the existing paradigm of cardiac function analysis once implemented in routine clinical care. Until recently, the HDF investigation was possible only with contrast-enhanced echocardiography and magnetic resonance imaging, precluding its widespread clinical use. A mathematical model, based on the first principle of fluid dynamics and validated using 4-dimensional-flow-magnetic resonance imaging, has allowed HDF analysis through routine transthoracic echocardiography, making it more readily accessible for routine clinical use. This article describes the concept of HDF analysis and reviews the existing evidence supporting its application in several clinical settings. Future studies should address the prognostic importance of HDF assessment in asymptomatic patients and its incorporation into clinical decision pathways.

Comparative Analysis of Right Ventricle Fluid Dynamics.

The right and left sides of the human heart operate with a common timing and pump the same amount of blood. Therefore, the right ventricle (RV) presents a function that is comparable to the left ventricle (LV) in terms of flow generation; nevertheless, the RV operates against a much lower arterial pressure (afterload) and requires a lower muscular strength. This study compares the fluid dynamics of the normal right and left ventricles to better understand the role of the RV streamlined geometry and provide some physics-based ground for the construction of clinical indicators for the right side. The analysis is performed by image-based direct numerical simulation, using the immersed boundary technique including the simplified models of tricuspid and mitral valves. Results demonstrated that the vortex formation process during early diastole is similar in the two ventricles, then the RV vorticity rapidly dissipates in the subvalvular region while the LV sustains a weak circulatory pattern at the center of the chamber. Afterwards, during the systolic contraction, the RV geometry allows an efficient transfer of mechanical work to the propelled blood; differently from the LV, this work is non-negligible in the global energetic balance. The varying behavior of the RV, from reservoir to conduct, during the different phases of the heartbeat is briefly discussed in conjunction to the development of possible dysfunctions.

Assessment of right ventricular function in advanced heart failure with nonischemic dilated cardiomyopathy: insights of right ventricular elastance.

BACKGROUND: The right ventriculoarterial coupling (R-V/A), a measure of right ventricular systolic dysfunction (RVSD) adaptation/maladaptation to chronic overload, and consequent pulmonary hypertension, has been little investigated in nonischemic dilated cardiomyopathy (NIDCM). We examined the correlates of R-V/A and traditional echocardiographic indices of RVSD, over the spectrum of pulmonary hypertension and tertiles of mean pulmonary artery pressures (PAPm). METHODS: In 2016-2017, we studied 81 consecutive patients for heart transplant/advanced heart failure. Inclusion criteria were NIDCM, reduced ejection fraction (≤40%) and sinus rhythm. R-V/A was computed as the RV/pulmonary elastances ratio (R-Elv/P-Ea), derived from a combined right heart catheterization/transthoracic- echocardiographic assessment [right heart catheterization/transthoracic-echocardiographic (RHC/TTE)]. RESULTS: A total of 68 patients (mean age 64 ±â€Š7 years, 82% men) were eligible. After adjustments, R-Elv and P-Ea were higher in isolated postcapillary-pulmonary hypertension (Ipc-PH) than combined-pulmonary hypertension (Cpc-PH) (P = 0.004 and P = 0.002, respectively), whereas R-V/A progressively decreased over Ipc-PH and Cpc-PH (P = 0.006). According to PAPm increment, P-Ea congruently increased (P-Trend = 0.028), R-Elv progressively decreased (P-Trend<0.00)1, whereas R-V/A significantly worsened (P-Trend = 0.045). At the multivariable analysis, a reduced RV longitudinal function (TAPSE<17 mm) was positively associated with R-V/A impairment (<0.8) [odds ratio 1.41, 95% confidence interval (CI) (1.07--1.87), P = 0.015]. R-Elv and P-Ea showed good interobserver reliability [interclass correlation (ICC) 0.84, 95% CI (0.32--0.99), P = 0.012 and ICC 0.98, 95% CI (0.93--99), P < 0.001, respectively]. CONCLUSION: Among NIDCM HF patients, in a small cohort study, RHC/TTE-derived R-V/A assessment demonstrated good correlations with pulmonary hypertension types and RV functional status. These data suggest that R-V/A encloses comprehensive information of the whole cardiopulmonary efficiency, better clarifying the amount of RVSD, with good reliability.

Integration between volumetric change and strain for describing the global mechanical function of the left ventricle.

INTRODUCTION: Evaluations of left ventricular systolic function based on ejection fraction (EF) alone are unable to recognize impaired myocardial performance in some dysfunctional states, and strain parameters are often invoked for an improved description of cardiac contraction. A comprehensive framework integrating deformation measures with volumetric changes is therefore necessary. METHODS: This study presents a general mathematical background that confirms and generalizes a previously proposed framework relating volumetric changes and strain values. The model is then validated with 5450 data samples made of LV volume, global longitudinal strain (GLS) and global circumferential strain (GCS) from 109 heterogeneous subjects who underwent cardiac magnetic resonance imaging. The GCS was measured by either three short-axis slices or 3D LV geometry reconstructed from 3 long-axis slices. RESULTS: Results demonstrated the reliability of the relationship EF = 1 - (GLS + 1)(GCS + 1)2. Accuracy is higher (correlation coefficient r = 0.997) when GCS is obtained by 3D deformation, although it remains high (r = 0.98) when GCS is measured from short-axis slices. However, the latter may underestimate (about 10% in relative terms) the circumferential deformation due to through-plane motion. CONCLUSIONS: The accuracy of this relationship permits a unitary description of LV systolic function in terms of both EF and global strain values by its position on the strain plane (GLS, GCS). This also allows to monitor pathologic or healing changes, as a consequence of exercise, drugs, surgery or other therapeutic options, as trajectories on that plane.

Cardiac fluid dynamics meets deformation imaging.

Cardiac function is about creating and sustaining blood in motion. This is achieved through a proper sequence of myocardial deformation whose final goal is that of creating flow. Deformation imaging provided valuable contributions to understanding cardiac mechanics; more recently, several studies evidenced the existence of an intimate relationship between cardiac function and intra-ventricular fluid dynamics. This paper summarizes the recent advances in cardiac flow evaluations, highlighting its relationship with heart wall mechanics assessed through the newest techniques of deformation imaging and finally providing an opinion of the most promising clinical perspectives of this emerging field. It will be shown how fluid dynamics can integrate volumetric and deformation assessments to provide a further level of knowledge of cardiac mechanics.

Left ventricular pacing vector selection by novel echo-particle imaging velocimetry analysis for optimization of quadripolar cardiac resynchronization device: a case report.

BACKGROUND: The availability of pacing configurations offered by quadripolar left ventricular leads could improve patients' response to cardiac resynchronization therapy; however, the selection of an optimal setting remains a challenge. Echo-particle imaging velocimetry has shown that regional anomalies of synchrony/synergy of the left ventricle are related to the alteration, reduction, or suppression of the physiological intracavitary pressure gradients. These observations are also supported by several numerical models of the left ventricle that have shown the close relationship between wall motion abnormalities, change of intraventricular flow dynamics, and abnormal distribution of forces operating on the ventricular endocardium. CASE PRESENTATION: A 73-year-old white man in New York Heart Association III functional class with an ejection fraction of 27.5 % did not improve after 1 month of cardiac resynchronization therapy. Five configurations were tested and settings were defined by optimizing intraventricular flow. After 6 months, he became New York Heart Association II class with left ventricular ejection fraction of 53.2 %. CONCLUSIONS: The abnormal dynamic of pressure gradients during the cardiac cycle, through biohumoral endocrine, autocrine, and paracrine transduction, may lead to structural changes of the myocardial walls with subsequent left ventricular remodeling. The echo-particle imaging velocimetry technique may be useful for elucidating the favorable effects of cardiac resynchronization therapy on intraventricular fluid dynamics and it could be used to identify appropriate pacing setting during acute echocardiographic optimization of left pacing vector.

Changes in electrical activation modify the orientation of left ventricular flow momentum: novel observations using echocardiographic particle image velocimetry.

AIMS: Changes in electrical activation sequence are known to affect the timing of cardiac mechanical events. We aim to demonstrate that these also modify global properties of the intraventricular blood flow pattern. We also explore whether such global changes present a relationship with clinical outcome. METHODS AND RESULTS: We investigated 30 heart failure patients followed up after cardiac resynchronization therapy (CRT). All subjects underwent echocardiography before implant and at follow-up after 6+ months. Left ventricular mechanics was investigated at follow-up during active CRT and was repeated after a temporary interruption <5 min later. Strain analysis, performed by speckle tracking, was used to assess the entity of contraction (global longitudinal strain) and its synchronicity (standard deviation of time to peak of radial strain). Intraventricular fluid dynamics, by echographic particle image velocimetry, was used to evaluate the directional distribution of global momentum associated with blood motion. The discontinuation of CRT pacing reflects into a reduction of deformation synchrony and into the deviation of blood flow momentum from the base-apex orientation with the development of transversal flow-mediated haemodynamic forces. The deviation of flow momentum presents a significant correlation with the degree of volumetric reduction after CRT. CONCLUSION: Changes in electrical activation alter the orientation of blood flow momentum. The long-term CRT outcome correlates with the degree of re-alignment of haemodynamic forces. These preliminary results suggest that flow orientation could be used for optimizing the biventricular pacing setting. However, larger prospective studies are needed to confirm this hypothesis.

Cardiac fluid dynamics anticipates heart adaptation.

Hemodynamic forces represent an epigenetic factor during heart development and are supposed to influence the pathology of the grown heart. Cardiac blood motion is characterized by a vortical dynamics, and it is common belief that the cardiac vortex has a role in disease progressions or regression. Here we provide a preliminary demonstration about the relevance of maladaptive intra-cardiac vortex dynamics in the geometrical adaptation of the dysfunctional heart. We employed an in vivo model of patients who present a stable normal heart function in virtue of the cardiac resynchronization therapy (CRT, bi-ventricular pace-maker) and who are expected to develop left ventricle remodeling if pace-maker was switched off. Intra-ventricular fluid dynamics is analyzed by echocardiography (Echo-PIV). Under normal conditions, the flow presents a longitudinal alignment of the intraventricular hemodynamic forces. When pacing is temporarily switched off, flow forces develop a misalignment hammering onto lateral walls, despite no other electro-mechanical change is noticed. Hemodynamic forces result to be the first event that evokes a physiological activity anticipating cardiac changes and could help in the prediction of longer term heart adaptations.

The vortex--an early predictor of cardiovascular outcome?

Blood motion in the heart features vortices that accompany the redirection of jet flows towards the outlet tracks. Vortices have a crucial role in fluid dynamics. The stability of cardiac vorticity is vital to the dynamic balance between rotating blood and myocardial tissue and to the development of cardiac dysfunction. Moreover, vortex dynamics immediately reflect physiological changes to the surrounding system, and can provide early indications of long-term outcome. However, the pathophysiological relevance of cardiac fluid dynamics is still unknown. We postulate that maladaptive intracardiac vortex dynamics might modulate the progressive remodelling of the left ventricle towards heart failure. The evaluation of blood flow presents a new paradigm in cardiac function analysis, with the potential for sensitive risk identification of cardiac abnormalities. Description of cardiac flow patterns after surgery or device therapy provides an intrinsic qualitative evaluation of therapeutic procedures, and could enable early risk stratification of patients vulnerable to adverse cardiac remodelling.

On the geometrical relationship between global longitudinal strain and ejection fraction in the evaluation of cardiac contraction.

Ejection fraction (EF) and global longitudinal strain (GLS) provide measures of left ventricle (LV) contraction that are closely related and also reflect different aspects of systolic function. Their comparative analysis can be informative about additional physiological properties on how LV contraction is achieved. The mathematical underlying relationship between EF and the GLS has been exploited and verified through data collected from recent literature. It was demonstrated that GLS and EF are bi-univocally related in the case of a self-similar systolic contraction. The deviation from this relationship, which can be quantified in terms of a shape function, characterizes the change of LV shape during the contraction. This analysis provides a firm ground to highlight the incremental information carried by GLS in the clinical evaluation of cardiac function.

Functional strain-line pattern in the human left ventricle.

Analysis of deformations in terms of principal directions appears well suited for biological tissues that present an underlying anatomical structure of fiber arrangement. We applied this concept here to study deformation of the beating heart in vivo analyzing 30 subjects that underwent accurate three-dimensional echocardiographic recording of the left ventricle. Results show that strain develops predominantly along the principal direction with a much smaller transversal strain, indicating an underlying anisotropic, one-dimensional contractile activity. The strain-line pattern closely resembles the helical anatomical structure of the heart muscle. These findings demonstrate that cardiac contraction occurs along spatially variable paths and suggest a potential clinical significance of the principal strain concept for the assessment of mechanical cardiac function. The same concept can help in characterizing the relation between functional and anatomical properties of biological tissues, as well as fiber-reinforced engineered materials.

Emerging trends in CV flow visualization.

Blood flow patterns are closely linked to the morphology and function of the cardiovascular system. These patterns reflect the exceptional adaptability of the cardiovascular system to maintain normal blood circulation under a wide range of workloads. Accurate retrieval and display of flow-related information remains a challenge because of the processes involved in mapping the flow velocity fields within specific chambers of the heart. We review the potentials and pitfalls of current approaches for blood flow visualization, with an emphasis on acquisition, display, and analysis of multidirectional flow. This document is divided into 3 sections. First, we provide a descriptive outline of the relevant concepts in cardiac fluid mechanics, including the emergence of rotation in flow and the variables that delineate vortical structures. Second, we elaborate on the main methods developed to image and visualize multidirectional cardiovascular flow, which are mainly based on cardiac magnetic resonance, ultrasound Doppler, and contrast particle imaging velocimetry, with recommendations for developing dedicated imaging protocols. Finally, we discuss the potential clinical applications and technical challenges with suggestions for further investigations.