Showing papers on "Cardiac cycle published in 2016"

Studying Dynamic Myofiber Aggregate Reorientation in Dilated Cardiomyopathy Using In Vivo Magnetic Resonance Diffusion Tensor Imaging

Abstract: Background— The objective of this study is to assess the dynamic alterations of myocardial microstructure and strain between diastole and systole in patients with dilated cardiomyopathy relative to healthy controls using the magnetic resonance diffusion tensor imaging, myocardial tagging, and biomechanical modeling. Methods and Results— Dual heart-phase diffusion tensor imaging was successfully performed in 9 patients and 9 controls. Tagging data were acquired for the diffusion tensor strain correction and cardiac motion analysis. Mean diffusivity, fractional anisotropy, and myocyte aggregate orientations were compared between both cohorts. Cardiac function was assessed by left ventricular ejection fraction, torsion, and strain. Computational modeling was used to study the impact of cardiac shape on fiber reorientation and how fiber orientations affect strain. In patients with dilated cardiomyopathy, a more longitudinal orientation of diastolic myofiber aggregates was measured compared with controls. Although a significant steepening of helix angles (HAs) during contraction was found in the controls, consistent change in HAs during contraction was absent in patients. Left ventricular ejection fraction, cardiac torsion, and strain were significantly lower in the patients compared with controls. Computational modeling revealed that the dilated heart results in reduced HA changes compared with a normal heart. Reduced torsion was found to be exacerbated by steeper HAs. Conclusions— Diffusion tensor imaging revealed reduced reorientation of myofiber aggregates during cardiac contraction in patients with dilated cardiomyopathy relative to controls. Left ventricular remodeling seems to be an important factor in the changes to myocyte orientation. Steeper HAs are coupled with a worsening in strain and torsion. Overall, the findings provide new insights into the structural alterations in patients with dilated cardiomyopathy.

Impact of Pulmonary Hemodynamics and Ventricular Interdependence on Left Ventricular Diastolic Function in Children With Pulmonary Hypertension

Abstract: Background— Through ventricular interdependence, pulmonary hypertension (PH) induces left ventricular (LV) dysfunction. We hypothesized that pediatric PH patients have LV diastolic dysfunction, related to adverse pulmonary hemodynamics, leftward septal shift, and prolonged right ventricular systole. Methods and Results— Echocardiography was prospectively performed at 2 institutions in 54 pediatric PH patients during cardiac catheterization and in 54 matched controls. Diastolic LV measures including myocardial deformation were assessed by echocardiography. PH patients had evidence of LV diastolic dysfunction, most consistent with impaired LV relaxation, though some features of reduced ventricular compliance were present. PH patients demonstrated the following: reduced mitral E velocity and inflow duration, mitral E′ and E′ / A′ , septal E′ and A′ , pulmonary vein S and D wave velocities, and LV basal global early diastolic circumferential strain rate and increased mitral E deceleration time, LV isovolumic relaxation time, mitral E / E′ , and pulmonary vein A wave duration. PH patients demonstrated leftward septal shift and prolonged right ventricular systole, both known to affect LV diastole. These changes were exacerbated in severe PH. There were no statistically significant differences in diastolic measures between patients with and without a shunt and minimal differences between patients with and without congenital heart disease. Multiple echocardiographic LV diastolic parameters demonstrated weak-to-moderate correlations with invasively determined PH severity, leftward septal shift, and prolonged right ventricular systole. Conclusions— Pediatric PH patients exhibit LV diastolic dysfunction most consistent with impaired relaxation and reduced myocardial deformation, related to invasive hemodynamics, leftward septal shift, and prolonged right ventricular systole.

Left ventricular function: time-varying elastance and left ventricular aortic coupling.

Abstract: Many aspects of left ventricular function are explained by considering ventricular pressure–volume characteristics. Contractility is best measured by the slope, Emax, of the end-systolic pressure–volume relationship. Ventricular systole is usefully characterized by a time-varying elastance (ΔP/ΔV). An extended area, the pressure–volume area, subtended by the ventricular pressure–volume loop (useful mechanical work) and the ESPVR (energy expended without mechanical work), is linearly related to myocardial oxygen consumption per beat. For energetically efficient systolic ejection ventricular elastance should be, and is, matched to aortic elastance. Without matching, the fraction of energy expended without mechanical work increases and energy is lost during ejection across the aortic valve. Ventricular function curves, derived from ventricular pressure–volume characteristics, interact with venous return curves to regulate cardiac output. Thus, consideration of ventricular pressure–volume relationships highlight features that allow the heart to efficiently respond to any demand for cardiac output and oxygen delivery.

Nano-imaging of the beating mouse heart in vivo: Importance of sarcomere dynamics, as opposed to sarcomere length per se, in the regulation of cardiac function

Abstract: Sarcomeric contraction in cardiomyocytes serves as the basis for the heart’s pump functions in mammals. Although it plays a critical role in the circulatory system, myocardial sarcomere length (SL) change has not been directly measured in vivo under physiological conditions because of technical difficulties. In this study, we developed a high speed (100–frames per second), high resolution (20-nm) imaging system for myocardial sarcomeres in living mice. Using this system, we conducted three-dimensional analysis of sarcomere dynamics in left ventricular myocytes during the cardiac cycle, simultaneously with electrocardiogram and left ventricular pressure measurements. We found that (a) the working range of SL was on the shorter end of the resting distribution, and (b) the left ventricular–developed pressure was positively correlated with the SL change between diastole and systole. The present findings provide the first direct evidence for the tight coupling of sarcomere dynamics and ventricular pump functions in the physiology of the heart.

Three-dimensional left atrial blood flow characteristics in patients with atrial fibrillation assessed by 4D flow CMR

Abstract: Aims To apply 4D flow cardiac magnetic resonance (CMR) for the volumetric measurement of 3D left atrial (LA) blood flow to evaluate its potential to detect altered LA flow in patients with atrial fibrillation (AF) and to investigate associations of changes in systolic and diastolic LA flow with the current clinical risk score (CHA2DS2-VASc) used for the assessment of thromboembolic risk in AF. Methods and results 4D flow CMR was performed in 40 patients with a history of AF (in sinus rhythm during CMR scan, age = 61 ± 11 years), 20 age-appropriate controls (59 ± 7 years), and 10 young healthy volunteers (24 ± 2 years) to measure in vivo time-resolved 3D LA blood flow. LA velocities were characterized with respect to atrial function and timing by calculating normalized LA flow velocity histograms during ventricular systole, early diastole, mid-late diastole, and the entire cardiac cycle. Mean, median, and peak LA velocity steadily decreased when comparing young volunteers, age-appropriate controls, and AF patients by 10–44% and 8–26% for early diastole and the entire cardiac cycle, respectively ( P < 0.01 for all comparisons except median velocity for young vs. older volunteers and peak velocity for older volunteers and AF patients). There were moderate but significant inverse relationships between increased CHA2DS2-VASc score and reduced mean LA velocity (early diastole: r = −0.37, P < 0.001; entire RR-interval: r = −0.33, P = 0.005), median LA velocity ( r = −0.33, P = 0.003; r = −0.25, P = 0.017), and peak velocity ( r = −0.36, P = 0.001; r = −0.45, P < 0.001). LA flow indices also correlated significantly with age and LA volume ( R 2 = 0.44–0.62, P < 0.001), but not with left ventricular ejection fraction. Conclusion Left atrial 4D flow CMR demonstrated significantly reduced LA blood flow velocities in patients with AF. Further study is needed to determine whether these measures can improve upon the CHA2DS2-VASc score for stroke risk prediction and enhance individual decisions on anticoagulation in patients with AF.

Differences in Left Versus Right Ventricular Electrophysiological Properties in Cardiac Dysfunction and Arrhythmogenesis.

Abstract: A wide range of ion channels, transporters, signaling pathways and tissue structure at a microscopic and macroscopic scale regulate the electrophysiological activity of the heart. Each region of the heart has optimised these properties based on its specific role during the cardiac cycle, leading to well-established differences in electrophysiology, Ca(2+) handling and tissue structure between atria and ventricles and between different layers of the ventricular wall. Similarly, the right ventricle (RV) and left ventricle (LV) have different embryological, structural, metabolic and electrophysiological features, but whether interventricular differences promote differential remodeling leading to arrhythmias is not well understood. In this article, we will summarise the available data on intrinsic differences between LV and RV electrophysiology and indicate how these differences affect cardiac function. Furthermore, we will discuss the differential remodeling of both chambers in pathological conditions and its potential impact on arrhythmogenesis.

Mimicking the cardiac cycle in intact cardiomyocytes using diastolic and systolic force clamps; measuring power output

Abstract: Aims A single isolated cardiomyocyte is the smallest functional unit of the heart. Yet, all single isolated cardiomyocyte experiments have been limited by the lack of proper methods that could reproduce a physiological cardiac cycle. We aimed to investigate the contractile properties of a single cardiomyocyte that correctly mimic the cardiac cycle. Methods and results By adjusting the parameters of the feedback loop, using a suitably engineered feedback system and recording the developed force and the length of a single rat cardiomyocyte during contraction and relaxation, we were able to construct force-length relations analogous to the pressure-volume relations at the whole heart level. From the cardiac loop graphs, we obtained, for the first time, the power generated by one single cardiomyocyte. Conclusion Here, we introduce a new approach that by combining mechanics, electronics and a new type optical force transducer, can measure the force-length relationship of a single isolated cardiomyocyte undergoing a mechanical loop that mimics the pressure-volume cycle of a beating heart.

Ductus venosus Doppler in the assessment of fetal cardiovascular health: an updated practical approach

Abstract: The ductus venosus has a central role in the distribution of highly oxygenated umbilical venous blood to the heart. Its waveform is related to the pressure-volume changes in the cardiac atria and it is therefore important in the monitoring of any fetal condition that may affect forward cardiac function. The cardiovascular parameters that can influence forward cardiac function include afterload, myocardial performance and preload. Decreased forward flow during atrial systole (a-wave) is the most sensitive and ubiquitous finding when any of these parameters is affected. In contrast, decreased forward velocities during end-systolic relaxation (v-wave) are more specifically related to myocardial performance. The ductus venosus pulsatility index alone does not accurately reflect cardiac function, and in cases of suspected fetal cardiac dysfunction, echocardiography is required to identify the underlying mechanism. The role of ductus venosus Doppler in the assessment of fetal growth restriction, supraventricular tachycardia, fetal hydrops, complicated monochorionic twins and congenital heart disease is discussed with these considerations in mind.

Cardiac cycle time effects on selection efficiency in vision.

Abstract: The effect of cardiac cycle time on attentional selection was investigated in an experiment in which participants classified target letters in a visual selection task. Stimulus onsets were aligned to the R wave of the electrocardiogram and stimuli presented either during the ventricular systole or diastole. Selection efficiency was operationalized as difference in target selection performance under conditions of homogeneous and heterogeneous distractors. Differences in performance (i.e., the impact selection difficulty had on the ability to select the target) were attenuated for stimuli presented during the ventricular systole compared to the diastole. Increased baroafferent signal transmission during the systole appears to reduce interference of highly distracting stimuli on visual selection efficiency.

Hemodynamics in a Pediatric Ascending Aorta Using a Viscoelastic Pediatric Blood Model.

Abstract: Congenital heart disease is the leading cause of infant death in the United States with over 36,000 newborns affected each year. Despite this growing problem there are few mechanical circulatory support devices designed specifically for pediatric and neonate patients. Previous research has been done investigating pediatric ventricular assist devices (PVADs) assuming blood to be a Newtonian fluid in computational fluid dynamics (CFD) simulations, ignoring its viscoelastic and shear-thinning properties. In contrast to adult VADs, PVADs may be more susceptible to hemolysis and thrombosis due to altered flow into the aorta, and therefore, a more accurate blood model should be used. A CFD solver that incorporates a modified Oldroyd-B model designed specifically for pediatric blood is used to investigate important hemodynamic parameters in a pediatric aortic model under pulsatile flow conditions. These results are compared to Newtonian blood simulations at three physiological pediatric hematocrits. Minor differences are seen in both velocity and wall shear stress (WSS) during early stages of the cardiac cycle between the Newtonian and viscoelastic models. During diastole, significant differences are seen in the velocities in the descending aorta (up to 12%) and in the aortic branches (up to 30%) between the two models. Additionally, peak WSS differences are seen between the models throughout the cardiac cycle. At the onset of diastole, peak WSS differences of 43% are seen between the Newtonian and viscoelastic model and between the 20 and 60% hematocrit viscoelastic models at peak systole of 41%.

Beat-by-Beat Quantification of Cardiac Cycle Events Detected From Three-Dimensional Precordial Acceleration Signals

Abstract: The vibrations produced by the cardiovascular system that are coupled to the precordium can be noninvasively detected using accelerometers. This technique is called seismocardiography. Although clinical applications have been proposed for seismocardiography, the physiology underlying the signal is still not clear. The relationship of seismocardiograms of on the back-to-front axis and cardiac events is fairly well known. However, the 3-D seismocardiograms detectable with modern accelerometers have not been quantified in terms of cardiac cycle events. A major reason for this might be the degree of intersubject variability observed in 3-D seismocardiograms. We present a method to quantify 3-D seismocardiography in terms of cardiac cycle events. First, cardiac cycle events are identified from the seismocardiograms, and then, assigned a number based on the location in which the corresponding event was found. 396 cardiac cycle events from 9 healthy subjects and 120 cardiac cycle events from patients suffering from atrial flutter were analyzed. Despite the weak intersubject correlation of the waveforms (0.05, 0.27, and 0.15 for the x -, y -, and z -axes, respectively), the present method managed to find latent similarities in the seismocardiograms of healthy subjects. We observed that in healthy subjects the distribution of cardiac cycle event coordinates was centered on specific locations. These locations were different in patients with atrial flutter. The results suggest that spatial distribution of seismocardiographic cardiac cycle events might be used to discriminate healthy individuals and those with a failing heart.

Computational haemodynamic analysis of left pulmonary artery angulation effects on pulmonary blood flow

Abstract: OBJECTIVES: To study the effect of the angulation between the left pulmonary artery (LPA) and the main pulmonary artery on pulmonary haemodynamics METHODS: A 3D model of patient-specific pulmonary artery (PA) was reconstructed as an original model Four models with descendent LPA angulation equalled to 120°, 110°, 100° and 90°, were reconstructed by computer-aided design for the virtual simulation of the pulmonary flow under different surgical strategies Computational fluid dynamics was introduced to calculate the pulmonary blood flow in five models Streamlines, wall shear stress, energy loss and flow distribution ratio were calculated and compared to determine the better haemodynamics in the pulmonary artery RESULTS: Vortices were formed at the lower wall of the opening of right PA and LPA in models with LPA angles equal to or less than 100° (Models 3 and 4) Relative high wall shear stress areas at the lateral and lower wall of LPA opening had an ascendant tendency as the angle declined Decreased flow distribution ratio to left lung (original model: 058, Model 1: 063, Model 2: 0586, Model 3: 0564, Model 4: 055) and increased energy loss (original model: 3852 mV, Model 1: 2394 mV, Model 2: 3843 mV, Model 3: 4309 mV, Model 4: 4398 mV) in a cardiac cycle were noted as the angle reduced CONCLUSIONS: Acute LPA angulation is associated with adverse haemodynamic performance This should be particularly addressed during the reconstruction of pulmonary artery in the repair of tetralogy of Fallot

Simultaneous Longitudinal Strain in All 4 Cardiac Chambers: A Novel Method for Comprehensive Functional Assessment of the Heart.

Abstract: Background— Simultaneous assessment of longitudinal strain (LS) by 2D speckle-tracking echocardiography in all 4 cardiac chambers has not yet been explored. Our goal was to study LS curves obtained simultaneously from all 4 cardiac chambers in healthy subjects to gain insight into interchamber functional relationships. Methods and Results— We studied 259 healthy subjects (age 44±15; 118 men) in whom it was possible to obtain apical 4-chamber views that contained the entire left and right ventricles and both atria in the same sector. 2D speckle-tracking echocardiography was performed in all 4 chambers in the same cardiac cycle, while considering the interventricular septum as part of the left ventricle and including the interatrial septum in the LS measurements for both atria. LS was measured over time using vendor-independent software (Epsilon), resulting in peak LS and time-to-peak strain. Strain curves of the right ventricle and right atrium were larger in magnitude than those of the left ventricle and left atrium, whereas time-to-peak values were shorter. LS for the ventricles peaked earlier than the LS for the corresponding atria. Peak systolic LS values were larger in magnitude in women than in men. For both atria, LS declined with age and time-to-peak increased. Left ventricle LS declined minimally with age, but right ventricle free-wall LS augmented with age until the sixth decade. Conclusions— Simultaneous measurement of LS provides new insights into interchamber relationships. This new tool may prove useful in evaluating diseases that affect cardiac chambers differently.

4D subject-specific inverse modeling of the chick embryonic heart outflow tract hemodynamics

Abstract: Blood flow plays a critical role in regulating embryonic cardiac growth and development, with altered flow leading to congenital heart disease. Progress in the field, however, is hindered by a lack of quantification of hemodynamic conditions in the developing heart. In this study, we present a methodology to quantify blood flow dynamics in the embryonic heart using subject-specific computational fluid dynamics (CFD) models. While the methodology is general, we focused on a model of the chick embryonic heart outflow tract (OFT), which distally connects the heart to the arterial system, and is the region of origin of many congenital cardiac defects. Using structural and Doppler velocity data collected from optical coherence tomography, we generated 4D ( $$\hbox {3D}\,+\,\hbox {time}$$ ) embryo-specific CFD models of the heart OFT. To replicate the blood flow dynamics over time during the cardiac cycle, we developed an iterative inverse-method optimization algorithm, which determines the CFD model boundary conditions such that differences between computed velocities and measured velocities at one point within the OFT lumen are minimized. Results from our developed CFD model agree with previously measured hemodynamics in the OFT. Further, computed velocities and measured velocities differ by $$<$$ 15 % at locations that were not used in the optimization, validating the model. The presented methodology can be used in quantifications of embryonic cardiac hemodynamics under normal and altered blood flow conditions, enabling an in-depth quantitative study of how blood flow influences cardiac development.

Quantitative multi-slice computed tomography assessment of the mitral valvular complex for transcatheter mitral valve interventions part 2: geometrical measurements in patients with functional mitral regurgitation.

Abstract: Aims Transcatheter mitral valve replacement (TMVR) is an emerging technology with the potential to treat patients with mitral regurgitation at excessive risk for mitral valve surgery. Geometrical measurements of the mitral valvular complex may have implications for the design of TMVR devices and for patient selection. This study sought to quantify the dynamic geometry of the mitral valvular complex in patients with significant functional mitral regurgitation (FMR) using multi-slice computed tomography (MSCT). Methods and results MSCT images were acquired in 32 patients with symptomatic, significant FMR. Two independent observers analysed image sets using a dedicated software package and a standard measurement methodology. In patients with FMR, the mean mitral annulus intercommissural and aorto-mural diameters were, respectively, 41.5±5.2 mm and 38.7±5.9 mm in systole, and were 41.5±4.4 mm and 40.0±4.7 mm in diastole. In patients without MR, the diameters were, respectively, 33.6±5.1 mm and 28.8±8.0 mm in systole, and 36.2±4.5 mm and 31.6±7.9 mm in diastole. The obstacle-free zone below the mitral annulus averaged more than 20.0 mm and varied by less than 1 mm between systole and diastole, which is not statistically significant. The aorto-mitral angle was 129.7±10.5° in systole and 131.0±9.4° in diastole. Conclusions The mitral annulus is larger in dimension, more circular, and less dynamic in patients with FMR. The obstacle-free zone below the mitral annulus is relatively constant during the cardiac cycle. Measurements of the mitral valvular apparatus vary considerably between patients, which suggests that tridimensional imaging will play an important role in the sizing of TMVR devices.

Patient-Specific MRI-Based Right Ventricle Models Using Different Zero-Load Diastole and Systole Geometries for Better Cardiac Stress and Strain Calculations and Pulmonary Valve Replacement Surgical Outcome Predictions.

Abstract: Background Accurate calculation of ventricular stress and strain is critical for cardiovascular investigations. Sarcomere shortening in active contraction leads to change of ventricular zero-stress configurations during the cardiac cycle. A new model using different zero-load diastole and systole geometries was introduced to provide more accurate cardiac stress/strain calculations with potential to predict post pulmonary valve replacement (PVR) surgical outcome. Methods Cardiac magnetic resonance (CMR) data were obtained from 16 patients with repaired tetralogy of Fallot prior to and 6 months after pulmonary valve replacement (8 male, 8 female, mean age 34.5 years). Patients were divided into Group 1 (n = 8) with better post PVR outcome and Group 2 (n = 8) with worse post PVR outcome based on their change in RV ejection fraction (EF). CMR-based patient-specific computational RV/LV models using one zero-load geometry (1G model) and two zero-load geometries (diastole and systole, 2G model) were constructed and RV wall thickness, volume, circumferential and longitudinal curvatures, mechanical stress and strain were obtained for analysis. Pairwise T-test and Linear Mixed Effect (LME) model were used to determine if the differences from the 1G and 2G models were statistically significant, with the dependence of the pair-wise observations and the patient-slice clustering effects being taken into consideration. For group comparisons, continuous variables (RV volumes, WT, C- and L- curvatures, and stress and strain values) were summarized as mean ± SD and compared between the outcome groups by using an unpaired Student t-test. Logistic regression analysis was used to identify potential morphological and mechanical predictors for post PVR surgical outcome. Results Based on results from the 16 patients, mean begin-ejection stress and strain from the 2G model were 28% and 40% higher than that from the 1G model, respectively. Using the 2G model results, RV EF changes correlated negatively with stress (r = -0.609, P = 0.012) and with pre-PVR RV end-diastole volume (r = -0.60, P = 0.015), but did not correlate with WT, C-curvature, L-curvature, or strain. At begin-ejection, mean RV stress of Group 2 was 57.4% higher than that of Group 1 (130.1±60.7 vs. 82.7±38.8 kPa, P = 0.0042). Stress was the only parameter that showed significant differences between the two groups. The combination of circumferential curvature, RV volume and the difference between begin-ejection stress and end-ejection stress was the best predictor for post PVR outcome with an area under the ROC curve of 0.855. The begin-ejection stress was the best single predictor among the 8 individual parameters with an area under the ROC curve of 0.782. Conclusion The new 2G model may be able to provide more accurate ventricular stress and strain calculations for potential clinical applications. Combining morphological and mechanical parameters may provide better predictions for post PVR outcome.

Tricuspid annulus: A spatial and temporal analysis.

Abstract: Background: Traditional two-dimensional (2D) echocardiographic evaluation of tricuspid annulus (TA) dilation is based on single-frame measurements of the septolateral (S-L) dimension. This may not represent either the axis or the extent of dynamism through the entire cardiac cycle. In this study, we used real-time 3D transesophageal echocardiography (TEE) to analyze geometric changes in multiple axes of the TA throughout the cardiac cycle in patients without right ventricular abnormalities. Materials and Methods: R-wave-gated 3D TEE images of the TA were acquired in 39 patients undergoing cardiovascular surgery. The patients with abnormal right ventricular/tricuspid structure or function were excluded from the study. For each patient, eight points along the TA were traced in the 3D dataset and used to reconstruct the TA at four stages of the cardiac cycle (end- and mid-systole, end- and mid-diastole). Statistical analyses were applied to determine whether TA area, perimeter, axes, and planarity changed significantly over each stage of the cardiac cycle. Results: TA area (P = 0.012) and perimeter (P = 0.024) both changed significantly over the cardiac cycle. Of all the axes, only the posterolateral-anteroseptal demonstrated significant dynamism (P < 0.001). There was also a significant displacement in the vertical axis between the points and the regression plane in end-systole (P < 0.001), mid-diastole (P = 0.014), and mid-systole (P < 0.001). Conclusions: The TA demonstrates selective dynamism over the cardiac cycle, and its axis of maximal dynamism is different from the axis (S-L) that is routinely measured with 2D TEE.

The cardiac torsion as a sensitive index of heart pathology: A model study

Abstract: The torsional behaviour of the heart (i.e. the mutual rotation of the cardiac base and apex) was proved to be sensitive to alterations of some cardiovascular parameters, i.e. preload, afterload and contractility. Moreover, pathologies which affect the fibers architecture and cardiac geometry were proved to alter the cardiac torsion pattern. For these reasons, cardiac torsion represents a sensitive index of ventricular performance. The aim of this work is to provide further insight into physiological and pathological alterations of the cardiac torsion by means of computational analyses, combining a structural model of the two ventricles with simple lumped parameter models of both the systemic and the pulmonary circulations. Starting from diagnostic images, a 3D anatomy based geometry of the two ventricles was reconstructed. The myocytes orientation in the ventricles was assigned according to literature data and the myocardium was modelled as an anisotropic hyperelastic material. Both the active and the passive phases of the cardiac cycle were modelled, and different clinical conditions were simulated. The results in terms of alterations of the cardiac torsion in the presence of pathologies are in agreement with experimental literature data. The use of a computational approach allowed the investigation of the stresses and strains in the ventricular wall as well as of the global hemodynamic parameters in the presence of the considered pathologies. Furthermore, the model outcomes highlight how for specific pathological conditions, an altered torsional pattern of the ventricles can be present, encouraging the use of the ventricular torsion in the clinical practice.

Cardiac MR elastography of the mouse: Initial results.

Abstract: PURPOSE Many cardiovascular diseases are associated with abnormal function of myocardial contractility or dilatability, which is related to elasticity changes of the myocardium over the cardiac cycle. The mouse is a common animal model in studies of the progression of various cardiomyopathies. We introduce a novel noninvasive approach using microscopic scale MR elastography (MRE) to measure the myocardium stiffness change during the cardiac cycle on a mouse model. METHODS A harmonic mechanical wave of 400 Hz was introduced into the mouse body. An electrocardiograph-gated and respiratory-gated fractional encoding cine-MRE pulse sequence was applied to encode the resulting oscillatory motion on a short-axis slice of the heart. Five healthy mice (age range, 3-13.5 mo) were examined. The weighted summation effective stiffness of the left ventricle wall during the cardiac cycle was estimated. RESULTS The ratio of stiffness at end diastole and end systole was 0.5-0.67. Additionally, variation in shear wave amplitude in the left ventricle wall throughout the cardiac cycle was measured and found to correlate with estimates of stiffness variation. CONCLUSION This study demonstrates the feasibility of implementing cardiac MRE on a mouse model. Magn Reson Med 76:1879-1886, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

Numerical analysis of the 3-dimensional aortic root morphology during the cardiac cycle.

Abstract: OBJECTIVES The aim was to define the 3-dimensional (3D) geometrical changes of the aortic root and to determine the local shear stress profile of aortic root elements during the cardiac cycle. METHODS Six sonomicrometric crystals (200 Hz) were implanted into the aortic root of five pigs at the commissures and at the aortic root base (AoB). 3D aortic root deformation including volume, torsion and tilt angle were determined. Geometrical data with measured local flow and pressure conditions was used for computed fluid dynamics modelling of the aortic root. RESULTS Compared with end-diastole, the sinotubular junction and AoB have maximal expansion at peak ejection: 16.42 ± 6.36 and 7.60 ± 2.52%, and minimal at isovolaemic relaxation: 2.87 ± 1.62 and 1.85 ± 1.79%. Aortic root tilt and rotation angle were maximal at the end of diastole: 17.7 ± 8.8 and 21.2 ± 2.09°, and decreased to 15.24 ± 8.14 and 18.3 ± 0.1.94° at peak ejection. High shear stress >20 Pa was registered at peak ejection at coaptations, and during diastole at the superior two-thirds of the leaflets and intervalvular triangles (IVTs). The leaflet body, inferior one-third of the IVTs and valve nadir were exposed to moderate shear stress (8-16 Pa) during the cardiac cycle. CONCLUSIONS Aortic root geometry demonstrates precise 3D changes of tilt and rotation angle. Reduction of angles during ejection results in a straight cylinder with low shear stress that facilitates the ejection; the increase during diastole results in a tilted frustum with elevated shear stress. Findings can be used for comparative analysis of native and synthetic structures with individual compliance.

Left Atrial Intrinsic Strain Rate Correcting for Pulmonary Wedge Pressure Is Accurate in Estimating Pulmonary Vascular Resistance in Breathless Patients.

Abstract: OBJECTIVES: We hypothesized that left atrial deformation during atrial systole (LASRa) correlates with pulmonary capillary wedge pressure (PCWP), thus enabling echo-derived pulmonary vascular resis ...

The differences in left atrial function between ischemic and idiopathic dilated cardiomyopathy patients: A two-dimensional speckle tracking imaging study.

Abstract: Purpose To evaluate left atrial (LA) function in patients with ischemic (ICM) or idiopathic dilated (DCM) cardiomyopathy via two-dimensional speckle-tracking imaging. Methods We measured the LA maximum volume, minimum volume, and volume before the atrial systole, and calculated total emptying volume, expansion index, active emptying volume, and fraction. We measured strain and strain rate during systole and late diastole using two-dimensional speckle-tracking imaging, and analyzed correlations between variables. Results We found no significant differences in LA size, left ventricle (LV) end-diastole diameter, LV ejection fraction (EF), E/A, E/e′, deceleration time of the E wave, and effective mitral regurgitant orifice area between the DCM and the ICM group. However, the LA expansion index, active EF, systolic and late diastolic strain, and strain rate were lower in the ICM group (p < 0.05). The expansion index and active EF were positively correlated with the systolic strain rate and the absolute value of the late diastolic strain rate, respectively. Conclusions LA basic echocardiographic variables did not reflect the differences between ICM and DCM patients, but the systolic and late diastolic strain, as well as the strain rate, were lower in DCM patients. Two-dimensional speckle-tracking imaging is a promising method to differentiate these patients. © 2016 Wiley Periodicals, Inc. J Clin Ultrasound, 2016

Cardiovascular System I: The Heart

Abstract: In this chapter, we look at the human heart: how it is constructed, how it works as a pump and how this is controlled. We will then look at how we can measure how it is performing, both in mechanical and electrical terms. The cardiac cycle is explained in detail and, in the following chapter, the interaction between the heart and the vasculature will be examined.

A laboratory model of the aortic root flow including the coronary arteries

Abstract: Cardiovascular flows have been extensively investigated by means of in vitro models to assess the prosthetic valve performances and to provide insight into the fluid dynamics of the heart and proximal aorta. In particular, the models for the study of the flow past the aortic valve have been continuously improved by including, among other things, the compliance of the vessel and more realistic geometries. The flow within the sinuses of Valsalva is known to play a fundamental role in the dynamics of the aortic valve since they host a recirculation region that interacts with the leaflets. The coronary arteries originate from the ostia located within two of the three sinuses, and their presence may significantly affect the fluid dynamics of the aortic root. In spite of their importance, to the extent of the authors’ knowledge, coronary arteries were not included so far when modeling in vitro the transvalvular aortic flow. We present a pulse duplicator consisting of a passively pulsing ventricle, a compliant proximal aorta, and coronary arteries connected to the sinuses of Valsalva. The coronary flow is modulated by a self-regulating device mimicking the physiological mechanism, which is based on the contraction and relaxation of the heart muscle during the cardiac cycle. Results show that the model reproduces satisfyingly the coronary flow. The analysis of the time evolution of the velocity and vorticity fields within the aortic root reveals the main characteristics of the backflow generated through the aorta in order to feed the coronaries during the diastole. Experiments without coronary flow have been run for comparison. Interestingly, the lifetime of the vortex forming in the sinus of Valsalva during the systole is reduced by the presence of the coronaries. As a matter of fact, at the end of the systole, that vortex is washed out because of the suction generated by the coronary flow. Correspondingly, the valve closure is delayed and faster compared to the case with no coronary flow.

Dynamic changes in the ischemic mitral annulus: Implications for ring sizing.

Abstract: Objectives: Contrary to the rest of the mitral annulus, inter-trigonal distance is known to be relatively less dynamic during the cardiac cycle. Therefore, intertrigonal distance is considered a suitable benchmark for annuloplasty ring sizing during mitral valve (MV) surgery. The entire mitral annulus dilates and flattens in patients with ischemic mitral regurgitation (IMR). It is assumed that the fibrous trigone of the heart and the intertrigonal distance does not dilate. In this study, we sought to demonstrate the changes in mitral annular geometry in patients with IMR and specifically analyze the changes in intertrigonal distance during the cardiac cycle. Methods: Intraoperative three-dimensional transesophageal echocardiographic data obtained from 26 patients with normal MVs undergoing nonvalvular cardiac surgery and 36 patients with IMR undergoing valve repair were dynamically analyzed using Philips Qlab ® software. Results: Overall, regurgitant valves were larger in area and less dynamic than normal valves. Both normal and regurgitant groups displayed a significant change in annular area (AA) during the cardiac cycle (P 0.05). Conclusions: Annular dimensions in regurgitant valves are dynamic and can be measured feasibly and accurately using echocardiography. The echocardiographically identified inter-trigonal distance does not change significantly during the cardiac cycle.

Duration of Systole and Diastole for Hydrodynamic Testing of Prosthetic Heart Valves: Comparison Between ISO 5840 Standards and in vivo Studies

Abstract: Objective: To complement the ISO 5840 standards concerning the duration of left ventricular systole and diastole as a function of changes in heart rates according to in vivo studies from the physiologic literature review. Methods: The systolic and diastolic durations from three in vivo studies were compared with the durations of systole proposed by the ISO 5840:2010 and ISO 5840-2:2015 for hydrodynamic performance assessment of prosthetic heart valves. Results: Based on the in vivo studies analyzed, the systolic durations proposed by the ISO 5840 standard seemed consistent for 45 and 120 beats per minute (bpm), and showed diverse results for the 70 bpm condition. Conclusion: Information on the realistic validation of the

Acoustic indices of cardiac functionality

Abstract: The mechanical processes of the cardiac cycle generate vibratory and acoustic signals that are received on the chest wall. We describe signal processing and feature extraction methods utilizing these signals for continuous non-invasive monitoring of cardiac systolic function. Vibro-acoustic heart signals were acquired from eleven subjects during a routine pharmacological stress echocardiography test. Principal component analysis, applied to the joint time-frequency distribution of the first heart sound (S1), revealed a pattern of an increase in the spectral energy and the frequency bandwidth of the signal associated with the increase of cardiac contractility during the stress test. Novel acoustic indices of S1 that compactly describe this pattern showed good linear correlation with reference indices of systolic functionality estimated by strainechocardiography. The acoustic indices may therefore be used to improve monitoring and diagnosis of cardiac systolic dysfunctions.

Analysis of Pulmonary Vein Antrums Motion with Cardiac Contraction Using Dual-Source Computed Tomography.

Abstract: Purpose The purpose of the study was to determine the extent of displacement of the pulmonary vein antrums resulting from the intrinsic motion of the heart using 4D cardiac dual-source computed tomography (DSCT). Methods Ten consecutive female patients were enrolled in this prospective planning study. In breath-hold, a contrast-injected cardiac 4-dimensional (4D) computed tomography (CT) synchronized to the electrocardiogram was obtained using a prospective sequential acquisition method including the extreme phases of systole and diastole. Right and left atrial fibrillation target volumes (CTVR and CTVL) were defined, with each target volume containing the antral regions of the superior and inferior pulmonary veins. Four points of interest were used as surrogates for the right superior and inferior pulmonary vein antrum (RSPVA and RIPVA) and the left superior and inferior pulmonary vein antrum (LSPVA and LIPVA). On our 4D post-processing workstation (MIM Maestro™, MIM Software Inc.), maximum displacement of each point of interest from diastole to systole was measured in the mediolateral (ML), anteroposterior (AP), and superoinferior (SI) directions. Results Median age of the enrolled patients was 60 years (range, 56-71 years). Within the CTVR, the mean displacements of the superior and inferior surrogates were 3 mm vs. 1 mm (p=0.002), 2 mm vs. 0 mm (p= 0.001), and 3 mm vs. 0 mm (p=0.00001), in the ML, AP, and SI directions, respectively. On the left, mean absolute displacements of the LSPVA vs. LIPVA were similar at 4 mm vs. 1 mm (p=0.0008), 2 mm vs. 0 mm (p= 0.001), and 3 mm vs. 1 mm (p=0.00001) in the ML, AP, and SI directions. Conclusion When isolated from breathing, cardiac contraction is associated with minimal inferior pulmonary veins motion and modest (1-6 mm) motion of the superior veins. Target deformation was thus of a magnitude similar or greater than target motion, limiting the potential gains of cardiac tracking. Optimal strategies for cardiac radiosurgery should thus either incorporate the generation of an internal target or cardiac gating. In either case, cardiac 4D DSCT would allow for personalized margin definition.

Fetal colour tissue Doppler imaging (cTDI): biventricular reference ranges for the time segments of the cardiac cycle in second and third trimesters of gestation

Abstract: To construct biventricular reference ranges for isovolumic time intervals (isovolumic contraction time, ICT; isovolumic relaxation time, IRT) and ejection time (ET) for colour tissue Doppler imaging (cTDI) between 15 and 37 weeks’ in healthy fetuses. This was a prospective multicentre cross-sectional study involving 160 singleton pregnancies between 15 and 37 weeks of gestation, using cTDI. ICT, ET, IRT and myocardial performance index (MPI) were analysed offline using a small region of interest (ROI) within the basal part of the right and left ventricular wall immediately distal to the annulus. Regression analysis was used to determine gestational age-adjusted reference ranges and to construct nomograms for cTDI parameters. Right and left ventricular ICT (p = 0.004 and p < 0.001) and ET (p = 0.011 and p = 0.050) increased, whereas IRT (p = 0.862 and p = 0.067) and MPI (p = 0.476 and p = 0.777) remained constant with gestational age. This is the first study to evaluate fetal isovolumic time intervals in the second and third trimesters of gestation using cTDI. Normal data for fetal isovolumic time intervals and biventricular MPI by colour tissue Doppler imaging are provided. The reference ranges may be useful in research or clinical studies and can be used in fetuses with compromised cardiac function.