Showing papers on "Cardiac cycle published in 2013"

Relationship of phasic left atrial volume and emptying function to left ventricular filling pressure: a cardiovascular magnetic resonance study

Abstract: Background Left atrial volume (LAV) and emptying fraction (LAEF) are phasic during cardiac cycle. Their relationships to left ventricular end diastolic pressure (LVEDP) have not been fully defined.

Real-time 3-dimensional dynamics of functional mitral regurgitation: a prospective quantitative and mechanistic study.

Abstract: Background Three-dimensional transthoracic echocardiography (3D-TTE) with dedicated software permits quantification of mitral annulus dynamics and papillary muscle motion throughout the cardiac cycle. Methods and Results Mitral apparatus 3D-TTE was acquired in controls (n=42), patients with left ventricle dysfunction and functional mitral regurgitation (LVD-FMR; n=43) or without FMR (LVD-noMR, n=35). Annulus in both normal and LVD-noMR subjects displayed saddle shape accentuation in early-systole (ratio of height to intercommissural diameter, 10.6±3.7 to 13.5±4.0 in normal and 9.1±4.3 to 12.6±3.6 in LVD-noMR; P <0.001 for diastole to early-systole motion, P =NS between those groups). In contrast, saddle shape was unchanged from diastole in FMR patients (10.0±6.4 to 8.0±5.2; P =NS, P <0.05 compared to both other groups). Papillary tips moved symmetrically towards to the midanterior annulus in control and LVD-noMR subjects, maintaining constant ratio of the distances between both tips to midannulus (PtAR) throughout systole. In LVD-FMR patients midsystolic posterior papillary tip to anterior annulus distance was increased, resulting in higher PtAR ( P =0.05 compared to both other groups). Mechanisms of early- and midsystolic FMR differed between different etiologies of LV dysfunction. In patients with anterior MI and global dysfunction annular function and dilatation were the dominant parameters, while papillary muscle motion was the predominant determinant of FMR in patients with inferior MI. Conclusions Inadequate early-systolic annular contraction and saddle-shape accentuation in patients with impaired LV contribute to early–mitral incompetency. Asymmetric papillary tip movement towards the midanterior annulus is a major determinant of mid- and late-systolic functional mitral regurgitation.

Moving Domain Computational Fluid Dynamics to Interface with an Embryonic Model of Cardiac Morphogenesis

Abstract: Peristaltic contraction of the embryonic heart tube produces time- and spatial-varying wall shear stress (WSS) and pressure gradients (∇P) across the atrioventricular (AV) canal. Zebrafish (Danio rerio) are a genetically tractable system to investigate cardiac morphogenesis. The use of Tg(fli1a:EGFP) (y1) transgenic embryos allowed for delineation and two-dimensional reconstruction of the endocardium. This time-varying wall motion was then prescribed in a two-dimensional moving domain computational fluid dynamics (CFD) model, providing new insights into spatial and temporal variations in WSS and ∇P during cardiac development. The CFD simulations were validated with particle image velocimetry (PIV) across the atrioventricular (AV) canal, revealing an increase in both velocities and heart rates, but a decrease in the duration of atrial systole from early to later stages. At 20-30 hours post fertilization (hpf), simulation results revealed bidirectional WSS across the AV canal in the heart tube in response to peristaltic motion of the wall. At 40-50 hpf, the tube structure undergoes cardiac looping, accompanied by a nearly 3-fold increase in WSS magnitude. At 110-120 hpf, distinct AV valve, atrium, ventricle, and bulbus arteriosus form, accompanied by incremental increases in both WSS magnitude and ∇P, but a decrease in bi-directional flow. Laminar flow develops across the AV canal at 20-30 hpf, and persists at 110-120 hpf. Reynolds numbers at the AV canal increase from 0.07±0.03 at 20-30 hpf to 0.23±0.07 at 110-120 hpf (p< 0.05, n=6), whereas Womersley numbers remain relatively unchanged from 0.11 to 0.13. Our moving domain simulations highlights hemodynamic changes in relation to cardiac morphogenesis; thereby, providing a 2-D quantitative approach to complement imaging analysis.

Inter-individual variance and cardiac cycle dependency of aortic root dimensions and shape as assessed by ECG-gated multi-slice computed tomography in patients with severe aortic stenosis prior to transcatheter aortic valve implantation: is it crucial for correct sizing?

Abstract: To evaluate the inter-individual variance and the variability of the aortic root dimensions during the cardiac cycle by computed tomography (CT) in patients with severe aortic stenosis prior to transcatheter aortic valve implantation (TAVI). Fifty-six patients (m/w = 16/40, 81 ± 6.8 years), scheduled for a transapical aortic valve implantation with available preprocedural ECG-gated CT were retrospectively included. The evaluation included sizing of the aortic annulus and the aortic sinus, measurements of the coronary topography, aortic valve planimetry and scoring of calcification. The new defined aortic annulus sphericity ratio revealed a mostly elliptical shape with increasing diastolic deformation. The calculated effective diameter (ED), determined from the annulus’ lumen area, turned out to be the parameter least affected from cardiac cycle changes while systolic and diastolic annulus dimensions and shape (diameter and area) differed significantly (p < 0.001). In about 70 % of the patients with relevant paravalvular leaks the finally implanted prosthesis was too small according to the CT based calculated ED. The ostial height of the coronaries showed a high variability with a critical minimum range <5 mm. The degree of the aortic calcification did not have an influence on the aortic annulus deformation during the cardiac cycle, but on the occurrence of paravalvular leaks. The aortic root anatomy demonstrated a high inter-individual variability and cardiac cycle dependency. These results must be strongly considered during the patient evaluation prior to TAVI to avoid complications. The systolic effective diameter, as measured by ECG-gated CT, represents an appropriate parameter for sizing the aortic annulus.

A Novel Left Heart Simulator for the Multi-modality Characterization of Native Mitral Valve Geometry and Fluid Mechanics

Abstract: Numerical models of the mitral valve have been used to elucidate mitral valve function and mechanics. These models have evolved from simple two-dimensional approximations to complex three-dimensional fully coupled fluid structure interaction models. However, to date these models lack direct one-to-one experimental validation. As computational solvers vary considerably, experimental benchmark data are critically important to ensure model accuracy. In this study, a novel left heart simulator was designed specifically for the validation of numerical mitral valve models. Several distinct experimental techniques were collectively performed to resolve mitral valve geometry and hemodynamics. In particular, micro-computed tomography was used to obtain accurate and high-resolution (39 μm voxel) native valvular anatomy, which included the mitral leaflets, chordae tendinae, and papillary muscles. Three-dimensional echocardiography was used to obtain systolic leaflet geometry. Stereoscopic digital particle image velocimetry provided all three components of fluid velocity through the mitral valve, resolved every 25 ms in the cardiac cycle. A strong central filling jet (V ~ 0.6 m/s) was observed during peak systole with minimal out-of-plane velocities. In addition, physiologic hemodynamic boundary conditions were defined and all data were synchronously acquired through a central trigger. Finally, the simulator is a precisely controlled environment, in which flow conditions and geometry can be systematically prescribed and resultant valvular function and hemodynamics assessed. Thus, this work represents the first comprehensive database of high fidelity experimental data, critical for extensive validation of mitral valve fluid structure interaction simulations.

Atrial aspiration from pulmonary and caval veins is caused by ventricular contraction and secures 70% of the total stroke volume independent of resting heart rate and heart size.

Abstract: Whereas ventricular filling has been extensively studied and debated, atrial filling is less well characterized. Therefore, the aim of this study was to quantify atrial filling secured during ventricular diastole and systole, and to investigate whether atrial filling depends on heart rate (HR) and total heart volume (THV).

Essential role of the m2R-RGS6-IKACh pathway in controlling intrinsic heart rate variability.

Abstract: Normal heart function requires generation of a regular rhythm by sinoatrial pacemaker cells and the alteration of this spontaneous heart rate by the autonomic input to match physiological demand. However, the molecular mechanisms that ensure consistent periodicity of cardiac contractions and fine tuning of this process by autonomic system are not completely understood. Here we examined the contribution of the m2R-I(KACh) intracellular signaling pathway, which mediates the negative chronotropic effect of parasympathetic stimulation, to the regulation of the cardiac pacemaking rhythm. Using isolated heart preparations and single-cell recordings we show that the m2R-I(KACh) signaling pathway controls the excitability and firing pattern of the sinoatrial cardiomyocytes and determines variability of cardiac rhythm in a manner independent from the autonomic input. Ablation of the major regulator of this pathway, Rgs6, in mice results in irregular cardiac rhythmicity and increases susceptibility to atrial fibrillation. We further identify several human subjects with variants in the RGS6 gene and show that the loss of function in RGS6 correlates with increased heart rate variability. These findings identify the essential role of the m2R-I(KACh) signaling pathway in the regulation of cardiac sinus rhythm and implicate RGS6 in arrhythmia pathogenesis.

Three-dimensional structure of the flow inside the left ventricle of the human heart

Abstract: The laboratory models of the human heart left ventricle developed in the last decades gave a valuable contribution to the comprehension of the role of the fluid dynamics in the cardiac function and to support the interpretation of the data obtained in vivo. Nevertheless, some questions are still opened and new ones stem from the continuous improvements in the diagnostic imaging techniques. Many of these unresolved issues are related to the three-dimensional structure of the left ventricular flow during the cardiac cycle. In this paper, we investigated in detail this aspect using a laboratory model. The ventricle was simulated by a flexible sack varying its volume in time according to a physiologically shaped law. Velocities measured during several cycles on series of parallel planes, taken from two orthogonal points of view, were combined together in order to reconstruct the phase-averaged, three-dimensional velocity field. During the diastole, three main steps are recognized in the evolution of the vortical structures: (1) straight propagation in the direction of the long axis of a vortex ring originated from the mitral orifice; (2) asymmetric development of the vortex ring on an inclined plane; and (3) single vortex formation. The analysis of three-dimensional data gives the experimental evidence of the reorganization of the flow in a single vortex persisting until the end of the diastole. This flow pattern seems to optimize the cardiac function since it directs velocity towards the aortic valve just before the systole and minimizes the fraction of blood residing within the ventricle for more cycles.

Alterations in pulse wave propagation reflect the degree of outflow tract banding in HH18 chicken embryos

Abstract: Hemodynamic conditions play a critical role in embryonic cardiovascular development, and altered blood flow leads to congenital heart defects. Chicken embryos are frequently used as models of cardiac development, with abnormal blood flow achieved through surgical interventions such as outflow tract (OFT) banding, in which a suture is tightened around the heart OFT to restrict blood flow. Banding in embryos increases blood pressure and alters blood flow dynamics, leading to cardiac malformations similar to those seen in human congenital heart disease. In studying these hemodynamic changes, synchronization of data to the cardiac cycle is challenging, and alterations in the timing of cardiovascular events after interventions are frequently lost. To overcome this difficulty, we used ECG signals from chicken embryos (Hamburger-Hamilton stage 18, ∼3 days of incubation) to synchronize blood pressure measurements and optical coherence tomography images. Our results revealed that, after 2 h of banding, blood pressure and pulse wave propagation strongly depend on band tightness. In particular, while pulse transit time in the heart OFT of control embryos is ∼10% of the cardiac cycle, after banding (35% to 50% band tightness) it becomes negligible, indicating a faster OFT pulse wave velocity. Pulse wave propagation in the circulation is likewise affected; however, pulse transit time between the ventricle and dorsal aorta (at the level of the heart) is unchanged, suggesting an overall preservation of cardiovascular function. Changes in cardiac pressure wave propagation are likely contributing to the extent of cardiac malformations observed in banded hearts.

Efficient and reproducible high resolution spiral myocardial phase velocity mapping of the entire cardiac cycle

Abstract: Three-directional phase velocity mapping (PVM) is capable of measuring longitudinal, radial and circumferential regional myocardial velocities. Current techniques use Cartesian k-space coverage and navigator-gated high spatial and high temporal resolution acquisitions are long. In addition, prospective ECG-gating means that analysis of the full cardiac cycle is not possible. The aim of this study is to develop a high temporal and high spatial resolution PVM technique using efficient spiral k-space coverage and retrospective ECG-gating. Detailed analysis of regional motion over the entire cardiac cycle, including atrial systole for the first time using MR, is presented in 10 healthy volunteers together with a comprehensive assessment of reproducibility. A navigator-gated high temporal (21 ms) and spatial (1.4 × 1.4 mm) resolution spiral PVM sequence was developed, acquiring three-directional velocities in 53 heartbeats (100% respiratory-gating efficiency). Basal, mid and apical short-axis slices were acquired in 10 healthy volunteers on two occasions. Regional and transmural early systolic, early diastolic and atrial systolic peak longitudinal, radial and circumferential velocities were measured, together with the times to those peaks (TTPs). Reproducibilities were determined as mean ± SD of the signed differences between measurements made from acquisitions performed on the two days. All slices were acquired in all volunteers on both occasions with good image quality. The high temporal resolution allowed consistent detection of fine features of motion, while the high spatial resolution allowed the detection of statistically significant regional and transmural differences in motion. Colour plots showing the regional variations in velocity over the entire cardiac cycle enable rapid interpretation of the regional motion within any given slice. The reproducibility of peak velocities was high with the reproducibility of early systolic, early diastolic and atrial systolic peak radial velocities in the mid slice (for example) being −0.01 ± 0.36, 0.20 ± 0.56 and 0.14 ± 0.42 cm/s respectively. Reproducibility of the corresponding TTP values, when normalised to a fixed systolic and diastolic length, was also high (−13.8 ± 27.4, 1.3 ± 21.3 and 3.0 ± 10.9 ms for early systolic, early diastolic and atrial systolic respectively). Retrospectively gated spiral PVM is an efficient and reproducible method of acquiring 3-directional, high resolution velocity data throughout the entire cardiac cycle, including atrial systole.

High frame rate retrospectively triggered Cine MRI for assessment of murine diastolic function

Abstract: To assess left ventricular (LV) diastolic function in mice with Cine MRI, a high frame rate (>60 frames per cardiac cycle) is required. For conventional electrocardiography-triggered Cine MRI, the frame rate is inversely proportional to the pulse repetition time (TR). However, TR cannot be lowered at will to increase the frame rate because of gradient hardware, spatial resolution, and signal-to-noise limitations. To overcome these limitations associated with electrocardiography-triggered Cine MRI, in this paper, we introduce a retrospectively triggered Cine MRI protocol capable of producing high-resolution high frame rate Cine MRI of the mouse heart for addressing left ventricular diastolic function. Simulations were performed to investigate the influence of MRI sequence parameters and the k-space filling trajectory in relation to the desired number of frames per cardiac cycle. An optimized protocol was applied in vivo and compared with electrocardiography-triggered Cine for which a high-frame rate could only be achieved by several interleaved acquisitions. Retrospective high frame rate Cine MRI proved superior to the interleaved electrocardiography-triggered protocols. High spatial-resolution Cine movies with frames rates up to 80 frames per cardiac cycle were obtained in 25 min. Analysis of left ventricular filling rate curves allowed accurate determination of early and late filling rates and revealed subtle impairments in left ventricular diastolic function of diabetic mice in comparison with nondiabetic mice. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

Towards patient-specific modeling of coronary hemodynamics in healthy and diseased state

Abstract: A model describing the primary relations between the cardiac muscle and coronary circulation might be useful for interpreting coronary hemodynamics in case multiple types of coronary circulatory disease are present. The main contribution of the present study is the coupling of a microstructure-based heart contraction model with a 1D wave propagation model. The 1D representation of the vessels enables patient-specific modeling of the arteries and/or can serve as boundary conditions for detailed 3D models, while the heart model enables the simulation of cardiac disease, with physiology-based parameter changes. Here, the different components of the model are explained and the ability of the model to describe coronary hemodynamics in health and disease is evaluated. Two disease types are modeled: coronary epicardial stenoses and left ventricular hypertrophy with an aortic valve stenosis. In all simulations (healthy and diseased), the dynamics of pressure and flow qualitatively agreed with observations described in literature. We conclude that the model adequately can predict coronary hemodynamics in both normal and diseased state based on patient-specific clinical data.

Reference values for fetal tissue velocity imaging and a new approach to evaluate fetal myocardial function

Abstract: Myocardial function can be evaluated using color-coded tissue velocity imaging (TVI) to analyze the longitudinal myocardial velocity profile, and by expressing the motion of the atrioventricular plane during a cardiac cycle as coordinated events in the cardiac state diagram (CSD). The objective of this study was to establish gestational age specific reference values for fetal TVI measurements and to introduce the CSD as a potential aid in fetal myocardial evaluation. TVI recordings from 125 healthy fetuses, at 18 to 42 weeks of gestation, were performed with the transducer perpendicular to the apex to provide a four-chamber view. The myocardial velocity data was extracted from the basal segment of septum as well as the left and right ventricular free wall for subsequent offline analysis. During a cardiac cycle the longitudinal peak velocities of septum increased with gestational age, as did the peak velocities of the left and right ventricular free wall, except for the peak velocity of post ejection. The duration of rapid filling and atrial contraction increased during pregnancy while the duration of post ejection decreased. The duration of pre ejection and ventricular ejection did not change significantly with gestational age. Evaluating fetal systolic and diastolic performance using TVI together with CSD could contribute to increase the knowledge and understanding of fetal myocardial function and dysfunction. The pre and post ejection phases are the variables most likely to indicate fetuses with abnormal myocardial function.

Mitral valve dynamics in severe aortic stenosis before and after aortic valve replacement.

Abstract: Background The aortic and mitral valves are anatomically linked through a fibrous continuity. The investigators hypothesized that severe aortic stenosis (AS) would alter this fibrous continuity, affecting both the mitral valve and left ventricular function, and that mitral valve function would be altered after aortic valve replacement (AVR). The aim of this study was to evaluate the impact of AS and its treatment with surgical AVR on the mitral valve. Methods Three-dimensional transesophageal echocardiography (using a Philips iE33 system) was performed on 49 patients: 20 controls with normal valves and left ventricular function, 20 with AS and normal left ventricular function studied before and after AVR, and nine with systolic heart failure and normal valves. Custom software tracked the aortic and mitral valves in three-dimensional space, allowing automated measurements of aortic and mitral annular (MA) morphology throughout the cardiac cycle. Results Patients with AS before AVR had reduced MA velocities. After AVR, aortic and MA areas were significantly smaller throughout the cardiac cycle compared with controls and pre-AVR values. MA displacement was reduced after AVR and in patients with systolic heart failure compared with those with AS and controls. Conclusions Dynamic MA function is changed with AS and after AVR through alterations in the aortic-mitral fibrous continuity. The prosthetic valve ring results in reduced aortic and MA areas, which could affect blood flow in and out of the left ventricle. These changes suggest that the design of future prosthetic aortic valves should be more flexible to preserve the function of the aortic-mitral fibrous continuity.

Identification of the in vivo elastic properties of common carotid arteries from MRI: a study on subjects with and without atherosclerosis.

Abstract: The stiffness of the arterial wall, which is modified by many cardiovascular diseases such as atherosclerosis, is known to be an indicator of vulnerability. This work focuses on the in vivo quantification of the stiffness of the common carotid artery (CCA) by applying the Magnitude Based Finite Element Model Updating (MB-FEMU) method to 13 healthy and diseased volunteers aged from 24 to 76 years old. The MB-FEMU method is based on the minimisation of the deviation between the image of a deformed artery and a registered image of this artery deformed by means of a finite elements analysis. Cross sections of the neck of each subject at different times of the cardiac cycle are recorded using a Phase Contrast cine-MRI. Applanation tonometry is then performed to obtain the blood pressure variations in the CCA throughout a heart beat. First, a time averaged elastic modulus of each CCA between diastole and systole is identified and a stiffening of the artery with age and disease is observed. Second, four elastic moduli are identified during a single heart beat for each artery, highlighting the nonlinear mechanical behaviour of the artery. A stiffening of the artery is observed and quantified at systole in comparison to diastole.

Estimation of the displacement of cardiac substructures and the motion of the coronary arteries using electrocardiographic gating.

Abstract: Purpose: The aim of this study was to quantify the displacement of cardiac substructures, including the anterior myocardial territory (AMT), left ventricle, and coronary arteries during a normal cardiac cycle. Materials and methods: Computed tomography (CT) images with retrospective electrocardiographic gating of 17 eligible patients were obtained. All images were reconstructed automatically for the end-diastolic and end-systolic phases. CT scanning without contrast at a random phase and a selected vertebral body were used as references to measure three-dimensionaldisplacements of the cardiac substructures. Results: The displacement between the end-diastolic and end-systolic phases (D d-s ) was greater than that between the end-systolic and random phases and between the end-diastolic and random cardiac phases. The largest displacements for the heart were in the left, posterior, and inferior directions with an average D d-s of approximately 4–6 mm. The average D d-s for the AMT and left ventricle was 1.2–2.7 mm in the anterior and right directions, 4.3–7.8 mm in left and posterior directions, and 4.9–6.3 mm in superior and inferior directions. For the coronary arteries, the average D d-s was 2.8–5.9 mm in the anterior-posterior direction, 3.5–6.6 mm in left-right direction, and 3.8–5.3 mm in the superior-inferior direction. Inter-observer agreement was excellent for the heart, AMT, and left ventricle (kappa coefficient, .0.75 for all) and good for most coronary arteries in three dimensions (kappa coefficient, 0.511–0.687). The D d-s did not differ significantly between men and women. Conclusion: Most average displacements of the cardiac substructures and coronary arteries were 3–8 mm in three dimensions. These findings will be useful to accurately estimate the radiation dose to cardiac substructures during thoracic radiation and to evaluate the risk of radiation-related heart disease.

Intraventricular pressure gradients throughout the cardiac cycle: effects of ischaemia and modulation by afterload.

Abstract: New Findings • What is the central question of this study?The aim of the present study was to characterize the intraventricular pressure gradients (IVPGs) along the cardiac cycle, to correlate them with myocardial segmental asynchrony and to evaluate their response to regional myocardial ischaemia and ventricular afterload • What is the main finding and its importance?We showed the existence of diastolic and systolic IVPGs in the left ventricle (LV) and demonstrated for the first time that normal gradient pattern is related to physiological asynchrony between basal and apical myocardial segments Moreover, we showed that IVPG, a marker of normal left ventricular function, can be attenuated, lost entirely, or even reversed after regional acute ischaemia and afterload elevations The aim of the present study was to characterize the intraventricular pressure gradients (IVPGs) througout the cardiac cycle, to correlate them with myocardial segmental asynchrony and to evaluate the effects of ischaemia and modulation by afterload Open-chest anaesthetized rabbits (n= 6) were instrumented with pressure-tip micromanometers placed in the apex and outflow tract of the left ventricular (LV) cavity and with sonomicrometer crystals placed in the apex and base of the LV free wall to measure IVPGs and myocardial segment length changes during basal, afterloaded (aortic cross-clamping) and ischaemic conditions (left anterior descending coronary artery ligation) During early diastole (rapid filling), we recorded an IVPG (46 ± 07 mmHg) from the cardiac base towards the apex followed by an apex-to-outflow pressure gradient (36 ± 02 mmHg) During systole, we recorded an IVPG (06 ± 01 mmHg) from apex to outflow during early rapid ejection, which inverted during late slow ejection Interestingly, the maximal rate of LV pressure fall occurred earlier and relaxation rate was faster in the base than in the apex While shortening of basal segments was complete at the end of ejection, apical segments always showed a significant amount of postsystolic shortening The IVPGs were entirely lost during ischaemia and attenuated by afterload elevations During ischaemia, systolic shortening of the apical segment decreased, while postsystolic shortening increased The present study confirms the existence of diastolic and systolic IVPGs in the LV and demonstrates, for the first time, that this normal gradient pattern is related to physiological asynchrony between basal and apical myocardial segments Moreover, we show that the IVPG, a marker of normal left ventricular function, can be attenuated, lost entirely or even reversed after regional acute ischaemia and afterload elevations

Quantifying left ventricular trabeculae function - application of image-based fractal analysis.

Abstract: The ventricular-blood interface is geometrically complex due to the presence of ventricular trabeculae carneae (VTC). We introduce a new image-based framework to quantify VTC function using high-resolution computed tomography (CT) imaging and offer new insights into the active role of VTCs during ejection. High-resolution Cine CT scans of a patient with normal cardiac function were acquired at a resolution of 0.77 mm per pixel at 10 phases of the cardiac cycle. The images were segmented and the VTC surface was obtained by triangulating the segmented data. Fractal dimension of the VTC surface was calculated for each cardiac phase as a function of scale size using the box-counting algorithm. The fractal dimension, D corresponding to VTCs ranged between 2.05 and 2.2 and varied as a function of time during the cardiac cycle. Fractal dimension is highest at diastole and lowest at peak systole with the change being significantly different (P < 0.003). This variation of D when plotted against stroke volume (i.e., D-V loop) revealed an active VTC role due to hysteresis in the loop. Physically the hysteresis in the D-V loop indicates a new mechanical function of VTCs as structures that provide mechanical leverage during early systolic ejection through contraction. VTC relaxation is noted to occur during late diastole at larger ventricular volume. D-V loop of VTCs quantifies VTC function. A new dynamic physical role of VTCs is suggested by way of mechanical leverage, as opposed to the traditionally accepted passive role.

Thoracic aorta cardiac-cycle related dynamic changes assessed with a 256-slice CT scanner.

Abstract: Objective: The aim of our study was to demonstrate whether the dynamic changes previously documented at the ascending and abdominal aorta are replicated at the thoracic aorta. Methods and results: A consecutive series of thirty patients referred to our institution to undergo CT angiography of the thoracic aorta (CTA) constituted the study population. Patients with diffuse aortic atherosclerosis were excluded from the analysis. All studies were acquired with a 256-MDCT scanner and ECG-gating was performed in all cases. Two orthogonal imaging planes (maximal and minimal diameters) were obtained at three different levels of the descending thoracic aorta, using the distance from the left subclavian artery as proximal landmark: 10, 40, and 80 mm distance. The mean age was 58.9±15.7 years and 16 (53%) patients were male. Descending aorta measurements at 10, 40, and 80 mm distance from the left subclavian artery were all significantly larger within the systolic window (P<0.01 for all comparisons). Measurements of the maximal diameter were systematically larger than the minimal diameters among all aortic positions including ungated, systolic, and diastolic measurements (P<0.05 for all comparisons). Conclusions: The main finding of our pilot investigation was that the thoracic descending aorta undergoes significant conformational changes during the cardiac cycle, irrespective from the distance from the left subclavian artery.

Elliptical subject-specific model of respiratory motion for cardiac MRI

Abstract: Respiratory motion is a major problem in cardiac MRI. In this work, the displacement of the heart relative to the diaphragm was investigated. A subject-specific nonlinear elliptical affine model has been developed to incorporate the effect of hysteresis in motion correction. Nine healthy volunteers participated in a study in which the diaphragm position and an image of the heart were acquired during each cardiac cycle, while breathing freely. The elliptical model was compared to a linear affine model, and the results show that the elliptical model performed significantly (P < 0.05) better than the linear model. Further, it has been established that the model can be constructed from 25 s of prescan data, which makes it feasible to perform a short prescan to construct the model, so that subject-specific prospective motion correction of the heart can be integrated into structural cardiac MRI sequences.

Regional analysis of left ventricle function using a cardiac-specific polyaffine motion model

Abstract: Given the complex dynamics of cardiac motion, understanding the motion for both normal and pathological cases can aid in understanding how different pathological conditions effect, and are affected by cardiac motion. Naturally, different regions of the left ventricle of the heart move in different ways depending on the location, with significantly different dynamics between the septal and free wall, and basal and apical regions. Therefore, studying the motion at a regional level can provide further information towards identifying abnormal regions for example. The 4D left ventricular motion of a given case was characterised by a low number of parameters at a region level using a cardiac specific polyaffine motion model. The motion was then studied at a regional level by analysing the computed affine transformation matrix of each region. This was used to examine the regional evolution of normal and pathological subjects over the cardiac cycle. The method was tested on 15 healthy volunteers with 4D ground truth landmarks and 5 pathological patients, all candidates for Cardiac Resynchronisation Therapy. Visually significant differences between normal and pathological subjects in terms of synchrony between the regions were obtained, which enables us to distinguish between healthy and unhealthy subjects. The results indicate that the method may be promising for analysing cardiac function.

Characterization of tissue by ultrasound echography

Abstract: Various embodiments concern sensing a first signal indicative of a plurality of different phases of a cardiac cycle with a sensor and sensing a second signal with an ultrasound sensor within the heart over different phases, the second signal indicative of the density of a section of cardiac tissue. Each phase can be associated with an indication of the density of the section of cardiac tissue during the phase based on the second signal. It can be determined whether the section of cardiac tissue compressed during the cardiac cycle based on a change in the indication of density of the cardiac tissue over the plurality of different phases. The efficacy of ablation therapy can be evaluated based on the compressibility of the section of cardiac tissue.

Comparison of aortic root dimension changes during cardiac cycle between the patients with and without aortic valve calcification using ECG-gated 64-slice and dual-source 256-slice computed tomography scanners: results of a multicenter study

Abstract: With advent of transcatheter aortic valve implantation, using multislice computed tomography (MSCT) to provide detailed data about aortic root has become more crucial. We compared aortic dimension changes during cardiac cycle in patients with and without aortic valve calcification and evaluated its correlation with aortic valve calcium score in former group. Fifty-two patients with and 52 subjects without aortic valve calcification underwent coronary MSCT using two 64-slice and a dual-source 256-slice CT scanners. Aortic root dimensions were measured in both systolic and diastolic phases. Changes in annular maximum diameter (D(max)), minimum diameter (D(min)), cross sectional area and perimeter, three diameters of sinuses of Valsalva (V(a), V(b) and V(c)), sinotubular junction maximum (STJ(max)) and minimum (STJ(min)) diameters between systolic and diastolic phases (systole minus diastole) were -0.59 mm, -0.05 mm, -2.53 mm(2), -1.48 mm, +0.91 mm, +1.08 mm, +0.42 mm, +0.63 mm, +0.40 mm and in those without aortic calcification -0.33 mm, 0.00 mm, -6.92 mm(2), -0.41 mm, +0.30 mm, +0.38 mm, +0.61 mm, +0.33 mm, +0.20 mm in patients with aortic calcification, respectively. Apart from two diameters in sinuses of Valsalva (V(a) and V(b)), changes in all other diameters of aortic root during cardiac cycle were not significantly different between the two groups. Furthermore, in patients with aortic calcification, no significant correlation was detected between changes in nearly all aortic root dimensions during cardiac cycle and aortic valve calcium score or location of calcification (annular, commissural or both).

Hemodynamics of the Boston Scientific Lotus™ Valve: An In Vitro Study

Abstract: Transcatheter Aortic Valve Replacement (TAVR) is currently used for patients with aortic valve disease at high risk for surgical intervention. The Lotus™ Valve system (Boston Scientific) is a novel repositionable TAVR with bovine pericardial leaflets and a Nitinol® frame, including miniature buckles for repositioning. A detailed characterization of the fluid flow environment in the vicinity of the buckles and the sinus regions will help identify regions of potential flow stagnation and thrombosis. A Lotus Valve was deployed in an in vitro left heart simulator, and the fluid flow through the valve was quantitatively characterized using particle image velocimetry. Three planes of high spatial resolution velocity data were obtained across the valve through the entire cardiac cycle at three stroke volumes (SV). The resulting velocity fields were processed to obtain Reynolds shear stresses (RSS), viscous shear stresses (VSS) and turbulent kinetic energy (TKE) fields. The Lotus Valve showed a central systolic jet at all three SV in the central plane. This jet caused a strong sinus vortex, which persisted through entire systole for all three SV. The location of the vortex was dependent on the SV through the valve. High VSS, RSS and TKE regions were observed at the edge of the systolic jet distal to the valve, however high velocities in these regions caused washout of fluid, which may prevent thrombus formation. The buckle region did not appear to significantly increase the potential for hemolysis of this valve. The Lotus Valve showed very good hemodynamic performance and no regions of stagnation were observed in the vicinity of the valve. These results compare favorably with flow characteristics through bioprosthetic aortic valve replacements, and suggest good clinical performance with this valve system.