Showing papers on "Cardiac cycle published in 2010"

Cardiac conduction is required to preserve cardiac chamber morphology

Abstract: Electrical cardiac forces have been previously hypothesized to play a significant role in cardiac morphogenesis and remodeling. In response to electrical forces, cultured cardiomyocytes rearrange their cytoskeletal structure and modify their gene expression profile. To translate such in vitro data to the intact heart, we used a collection of zebrafish cardiac mutants and transgenics to investigate whether cardiac conduction could influence in vivo cardiac morphogenesis independent of contractile forces. We show that the cardiac mutant dcos226 develops heart failure and interrupted cardiac morphogenesis following uncoordinated ventricular contraction. Using in vivo optical mapping/calcium imaging, we determined that the dco cardiac phenotype was primarily due to aberrant ventricular conduction. Because cardiac contraction and intracardiac hemodynamic forces can also influence cardiac development, we further analyzed the dco phenotype in noncontractile hearts and observed that disorganized ventricular conduction could affect cardiomyocyte morphology and subsequent heart morphogenesis in the absence of contraction or flow. By positional cloning, we found that dco encodes Gja3/Cx46, a gap junction protein not previously implicated in heart formation or function. Detailed analysis of the mouse Cx46 mutant revealed the presence of cardiac conduction defects frequently associated with human heart failure. Overall, these in vivo studies indicate that cardiac electrical forces are required to preserve cardiac chamber morphology and may act as a key epigenetic factor in cardiac remodeling.

Magnetic resonance elastography as a method for the assessment of effective myocardial stiffness throughout the cardiac cycle.

Abstract: MR elastography (MRE) is a noninvasive technique in which images of externally generated waves propagating in tissue are used to measure stiffness. The first aim is to determine, from a range of driver configurations, the optimal driver for the purpose of generating waves within the heart in vivo. The second aim is to quantify the shear stiffness of normal myocardium throughout the cardiac cycle using MRE and to compare MRE stiffness to left ventricular chamber pressure in an in vivo pig model. MRE was performed in six pigs with six different driver setups, including no motion, three noninvasive drivers, and two invasive drivers. MRE wave displacement amplitudes were calculated for each driver. During the same MRI examination, left ventricular pressure and MRI-measured left ventricular volume were obtained, and MRE myocardial stiffness was calculated for 20 phases of the cardiac cycle. No discernible waves were imaged when no external motion was applied, and a single pneumatic drum driver produced higher amplitude waves than the other noninvasive drivers (P < 0.05). Pressure-volume loops overlaid onto stiffness-volume loops showed good visual agreement. Pressure and MRE-measured effective stiffness showed good correlation (R(2) = 0.84). MRE shows potential as a noninvasive method for estimating effective myocardial stiffness throughout the cardiac cycle.

High-Resolution Fluid–Structure Interaction Simulations of Flow Through a Bi-Leaflet Mechanical Heart Valve in an Anatomic Aorta

Abstract: We have performed high-resolution fluid–structure interaction simulations of physiologic pulsatile flow through a bi-leaflet mechanical heart valve (BMHV) in an anatomically realistic aorta. The results are compared with numerical simulations of the flow through an identical BMHV implanted in a straight aorta. The comparisons show that although some of the salient features of the flow remain the same, the aorta geometry can have a major effect on both the flow patterns and the motion of the valve leaflets. For the studied configuration, for instance, the BMHV leaflets in the anatomic aorta open much faster and undergo a greater rebound during closing than the same valve in the straight axisymmetric aorta. Even though the characteristic triple-jet structure does emerge downstream of the leaflets for both cases, for the anatomic case the leaflet jets spread laterally and diffuse much faster than in the straight aorta due to the aortic curvature and complex shape of the anatomic sinus. Consequently the leaflet shear layers in the anatomic case remain laminar and organized for a larger portion of the accelerating phase as compared to the shear layers in the straight aorta, which begin to undergo laminar instabilities well before peak systole is reached. For both cases, however, the flow undergoes a very similar explosive transition to the small-scale, turbulent-like state just prior to reaching peak systole. The local maximum shear stress is used as a metric to characterize the mechanical environment experienced by blood cells. Pockets of high local maximum shear are found to be significantly more widespread in the anatomic aorta than in the straight aorta throughout the cardiac cycle. Pockets of high local maximum shear were located near the leaflets and in the aortic arc region. This work clearly demonstrates the importance of the aortic geometry on the flow phenomena in a BMHV and demonstrates the potential of our computational method to carry out image-based patient-specific simulations for clinically relevant studies of heart valve hemodynamics.

Passing Strange Flow in the Failing Ventricle

Abstract: Heart failure is diverse in its manifestations and pathophysiology with changes in chamber size and volume, wall motion, valvular competence, intracardiac pressures, and electrical events. These are routinely measured with well-established methods. However, it is common to observe different degrees of compensation despite echocardiographically similar degrees of cardiac dysfunction. How can we explain this phenomenon? One persistent gap in our understanding of the failing heart is the global behavior of the intracardiac blood flow and its potential impact on pump efficiency and disease progression. The concepts that ventricular filling and ejection are separate events distinct in timing and location and that acceleration and ejection of the stroke volume are only events due to systolic myocardial contraction are familiar but likely oversimplified. It seems reasonable that rather than coming to a halt at end diastole, flowing blood would keep moving as filling transitions to ejection and that it would be efficient for blood in the end-diastolic left ventricle (LV) to already be moving toward the aortic valve for ejection. Until recently, there was a lack of measurement tools able to accurately resolve the complex in vivo 3D flow fields to investigate these and other flow-based questions. New tools that can measure 3D flow throughout the cardiac cycle noninvasively are becoming increasingly mature, and a more detailed perspective is emerging on the organization of intracardiac blood flow. It is now possible to investigate the routes, behaviors, and interactions of the blood transiting the ventricles in normal and failing hearts1–3 and to consider the possible impact of flow characteristics on the efficiency of ventricular function. A focus on the flow aspects of cardiac function allows us to address a new and complementary set of questions. How does the efficiency of flow through the heart change with chamber dimensions, shape, and wall properties, …

A depression in left ventricular diastolic filling following prolonged strenuous exercise is associated with changes in left atrial mechanics.

Abstract: Background Standard marathon running can result in a depression of left ventricular (LV) diastolic function during early recovery. Left atrial (LA) mechanics are integral in maintaining an early diastolic pressure gradient as well as being responsive to changes in LV diastolic function, and therefore the detailed assessment of LA mechanics may provide further insight. The aim of this study was to determine the impact of prolonged strenuous exercise on mechanics of the left atrium and the association with changes in LV diastolic function. Methods Myocardial speckle-tracking echocardiograms of the left atrium and left ventricle were obtained prior to, immediately after, and 6 hours after the completion of a marathon (42.2 km) in 17 healthy adult men. Speckle tracking was used to determine peak atrial deformation, early diastolic deformation rate, and contractile function, including atrial activation time. LA volumes throughout the cardiac cycle were also assessed to provide reservoir, conduit, and booster pump volumes. Diastolic assessment of the left ventricle included peak early diastolic strain rate, late diastolic strain rate, and standard indices. Temporal assessment of LV “twist” and “untwist” was also evaluated. Results All 17 subjects completed the marathon (mean finishing time, 209 ± 19 minutes; range, 173-241 minutes). Although contractile function was significantly increased, there was a reduction in early diastolic deformation rate that was correlated with reduced atrial deformation. Atrial activation time was significantly increased after the race. All LV indices of diastolic function were reduced in early diastole, whereas late diastolic function was increased after the race. LV torsion was significantly reduced at end-systole and significantly elevated in the isovolumic period and early diastole, after the race. All indices returned toward baseline at 6 hours after exercise. Conclusions This study demonstrates transient changes in LV diastolic relaxation following prolonged exercise that appear to have a direct impact on subsequent LA deformation. The impact of reduced LA preload on these findings and the delay in LA activation time requires further exploration.

Hemodynamic environments from opposing sides of human aortic valve leaflets evoke distinct endothelial phenotypes in vitro.

Abstract: The regulation of valvular endothelial phenotypes by the hemodynamic environments of the human aortic valve is poorly understood. The nodular lesions of calcific aortic stenosis (CAS) develop predominantly beneath the aortic surface of the valve leaflets in the valvular fibrosa layer. However, the mechanisms of this regional localization remain poorly characterized. In this study, we combine numerical simulation with in vitro experimentation to investigate the hypothesis that the previously documented differences between valve endothelial phenotypes are linked to distinct hemodynamic environments characteristic of these individual anatomical locations. A finite-element model of the aortic valve was created, describing the dynamic motion of the valve cusps and blood in the valve throughout the cardiac cycle. A fluid mesh with high resolution on the fluid boundary was used to allow accurate computation of the wall shear stresses. This model was used to compute two distinct shear stress waveforms, one for the ventricular surface and one for the aortic surface. These waveforms were then applied experimentally to cultured human endothelial cells and the expression of several pathophysiological relevant genes was assessed. Compared to endothelial cells subjected to shear stress waveforms representative of the aortic face, the endothelial cells subjected to the ventricular waveform showed significantly increased expression of the “atheroprotective” transcription factor Kruppel-like factor 2 (KLF2) and the matricellular protein Nephroblastoma overexpressed (NOV), and suppressed expression of chemokine Monocyte-chemotactic protein-1 (MCP-1). Our observations suggest that the difference in shear stress waveforms between the two sides of the aortic valve leaflet may contribute to the documented differential side-specific gene expression, and may be relevant for the development and progression of CAS and the potential role of endothelial mechanotransduction in this disease.

Biomechanics of the aortic valve in the continuous flow VAD-assisted heart.

Abstract: The biomechanics of the aortic valve are altered in patients with ventricular assist devices (VADs). During high VAD flow and low cardiac function, transvalvular pressure is high, and the aortic valve remains closed throughout the cardiac cycle. This condition has been linked to the development of aortic valve fusion and incompetence during VAD use. Thus, physicians try to maintain pulsatile flow to assure periodic valve opening. The aim of this study was to determine the extent of aortic valve opening and alterations in valve leaflet strain before and during VAD support using a specially designed mock loop. The results showed that diastole is prolonged during VAD use. In addition, there is a reduction in valve opening area, producing a VAD-related functional stenosis. The average leaflet strain increased during VAD support, primarily due to an increase in the minimum strain, during systole, rather than the maximum strain during diastole. The findings support our hypothesis that altered biomechanics in the VAD-assisted heart results in increased strain in the aortic valve leaflets, which can stimulate soft tissue remodeling. The implication for clinical use is that valve opening during parallel VAD flow is reduced compared with normal flow conditions. Consequently, current clinical practice for VAD patients may not be achieving sufficient valve opening to prevent changes such as fusion and incompetence.

How the python heart separates pulmonary and systemic blood pressures and blood flows

Abstract: The multiple convergent evolution of high systemic blood pressure among terrestrial vertebrates has always been accompanied by lowered pulmonary pressure. In mammals, birds and crocodilians, this cardiac separation of pressures relies on the complete division of the right and left ventricles by a complete ventricular septum. However, the anatomy of the ventricle of most reptiles does not allow for complete anatomical division, but the hearts of pythons and varanid lizards can produce high systemic blood pressure while keeping the pulmonary blood pressure low. It is also known that these two groups of reptiles are characterised by low magnitudes of cardiac shunts. Little, however, is known about the mechanisms that allow for this pressure separation. Here we provide a description of cardiac structures and intracardiac events that have been revealed by ultrasonic measurements and angioscopy. Echocardiography revealed that the atrioventricular valves descend deep into the ventricle during ventricular filling and thereby greatly reduce the communication between the systemic (cavum arteriosum) and pulmonary (cavum pulmonale) ventricular chambers during diastole. Angioscopy and echocardiography showed how the two incomplete septa, the muscular ridge and the bulbuslamelle - ventricular structures common to all squamates - contract against each other in systole and provide functional division of the anatomically subdivided ventricle. Washout shunts are inevitable in the subdivided snake ventricle, but we show that the site of shunting, the cavum venosum, is very small throughout the cardiac cycle. It is concluded that the python ventricle is incapable of the pronounced and variable shunts of other snakes, because of its architecture and valvular mechanics.

Automatic detection of end-diastole and end-systole from echocardiography images using manifold learning.

Abstract: The automatic detection of end-diastole and end-systole frames of echocardiography images is the first step for calculation of the ejection fraction, stroke volume and some other features related to heart motion abnormalities. In this paper, the manifold learning algorithm is applied on 2D echocardiography images to find out the relationship between the frames of one cycle of heart motion. By this approach the nonlinear embedded information in sequential images is represented in a two-dimensional manifold by the LLE algorithm and each image is depicted by a point on reconstructed manifold. There are three dense regions on the manifold which correspond to the three phases of cardiac cycle ('isovolumetric contraction', 'isovolumetric relaxation', 'reduced filling'), wherein there is no prominent change in ventricular volume. By the fact that the end-systolic and end-diastolic frames are in isovolumic phases of the cardiac cycle, the dense regions can be used to find these frames. By calculating the distance between consecutive points in the manifold, the isovolumic frames are mapped on the three minimums of the distance diagrams which were used to select the corresponding images. The minimum correlation between these images leads to detection of end-systole and end-diastole frames. The results on six healthy volunteers have been validated by an experienced echo cardiologist and depict the usefulness of the presented method.

MR Image-Based Geometric and Hemodynamic Investigation of the Right Coronary Artery with Dynamic Vessel Motion

Abstract: The aim of this study was to develop a fully subject-specific model of the right coronary artery (RCA), including dynamic vessel motion, for computational analysis to assess the effects of cardiac-induced motion on hemodynamics and resulting wall shear stress (WSS). Vascular geometries were acquired in the right coronary artery (RCA) of a healthy volunteer using a navigator-gated interleaved spiral sequence at 14 time points during the cardiac cycle. A high temporal resolution velocity waveform was also acquired in the proximal region. Cardiac-induced dynamic vessel motion was calculated by interpolating the geometries with an active contour model and a computational fluid dynamic (CFD) simulation with fully subject-specific information was carried out using this model. The results showed the expected variation of vessel radius and curvature throughout the cardiac cycle, and also revealed that dynamic motion of the right coronary artery consequent to cardiac motion had significant effects on instantaneous WSS and oscillatory shear index. Subject-specific MRI-based CFD is feasible and, if scan duration could be shortened, this method may have potential as a non-invasive tool to investigate the physiological and pathological role of hemodynamics in human coronary arteries.

Mechanics of the Mitral Valve Strut Chordae Insertion Region

Abstract: Interest in developing durable mitral valve repair methods is growing, underscoring the need to better understand the native mitral valve mechanics. In this study, the authors investigate the dynamic deformation of the mitral valve strut chordae-to-anterior leaflet transition zone using a novel stretch mapping method and report the complex mechanics of this region for the first time. Eight structurally normal porcine mitral valves were studied in a pulsatile left heart simulator under physiological hemodynamic conditions 120 mm peak transvalvular pressure, 5 l/min cardiac output at 70 bpm. The chordal insertion region was marked with a structured array of 31 miniature markers, and their motions throughout the cardiac cycle were tracked using two high speed cameras. 3D marker coordinates were calculated using direct linear transformation, and a second order continuous surface was fit to the marker cloud at each time frame. Average areal stretch, principal stretch magnitudes and directions, and stretch rates were computed, and temporal changes in each parameter were mapped over the insertion region. Stretch distribution was heterogeneous over the entire strut chordae insertion region, with the highest magnitudes along the edges of the chordal insertion region and the least along the axis of the strut chordae. At early systole, radial stretch was predominant, but by mid systole, significant stretch was observed in both radial and circumferential directions. The compressive stretches measured during systole indicate a strong coupling between the two principal directions, explaining the small magnitude of the systolic areal stretch. This study for the first time provides the dynamic kinematics of the strut chordae insertion region in the functioning mitral valve. A heterogeneous stretch pattern was measured, with the mechanics of this region governed by the complex underlying collagen architecture. The insertion region seemed to be under stretch during both systole and diastole, indicating a transfer of forces from the leaflets to the chordae and vice versa throughout the cardiac cycle, and demonstrating its role in optimal valve function. DOI: 10.1115/1.4001682

Estimates of systolic and diastolic myocardial blood flow by dynamic contrast-enhanced MRI

Abstract: Myocardial blood flow varies during the cardiac cycle in response to pulsatile changes in epicardial circulation and cyclical variation in myocardial tension. First-pass assessment of myocardial perfusion by dynamic contrast-enhanced MRI is one of the most challenging applications of MRI because of the spatial and temporal constraints imposed by the cardiac physiology and the nature of dynamic contrast-enhanced MRI signal collection. Here, we describe a dynamic contrast-enhanced MRI method for simultaneous assessment of systolic and diastolic myocardial blood flow. The feasibility of this method was demonstrated in a study of 17 healthy volunteers at rest and under adenosine-induced vasodilatory stress. We found that myocardial blood flow was independent of the cardiac phase at rest. However, under adenosine-induced hyperemia, myocardial blood flow and myocardial perfusion reserve were significantly higher in diastole than in systole. Furthermore, the transmural distribution of myocardial blood flow and myocardial perfusion reserve was cardiac phase dependent, with a reversal of the typical subendocardial to subepicardial myocardial blood flow gradient in systole, but not diastole, under stress. The observed difference between systolic and diastolic myocardial blood flow must be taken into account when assessing myocardial blood flow using dynamic contrast-enhanced MRI. Furthermore, targeted assessment of systolic or diastolic perfusion using dynamic contrast-enhanced MRI may provide novel insights into the pathophysiology of ischemic and microvascular heart disease.

Longitudinally and circumferentially directed movements of the left ventricle studied by cardiovascular magnetic resonance phase contrast velocity mapping

Abstract: Using high resolution cardiovascular magnetic resonance (CMR), we aimed to detect new details of left ventricular (LV) systolic and diastolic function, to explain the twisting and longitudinal movements of the left ventricle. Using CMR phase contrast velocity mapping (also called Tissue Phase Mapping) regional wall motion patterns and longitudinally and circumferentially directed movements of the left ventricle were studied using a high temporal resolution technique in healthy male subjects (n = 14, age 23 ± 3 years). Previously undescribed systolic and diastolic motion patterns were obtained for left ventricular segments (based on the AHA segmental) and for basal, mid and apical segments. The summation of segmental motion results in a complex pattern of ventricular twisting and longitudinal motion in the normal human heart which underlies systolic and diastolic function. As viewed from the apex, the entire LV initially rotates in a counter-clockwise direction at the beginning of ventricular systole, followed by opposing clockwise rotation of the base and counter-clockwise rotation at the apex, resulting in ventricular torsion. Simultaneously, as the entire LV moves in an apical direction during systole, the base and apex move towards each other, with little net apical displacement. The reverse of these motion patterns occur in diastole. Left ventricular function may be a consequence of the relative orientations and moments of torque of the sub-epicardial relative to the sub-endocardial myocyte layers, with influence from tethering of the heart to adjacent structures and the directional forces associated with blood flow. Understanding the complex mechanics of the left ventricle is vital to enable these techniques to be used for the evaluation of cardiac pathology.

Cyclic and radial variation of the echogenicity of blood in human carotid arteries observed by harmonic imaging.

Abstract: To better understand the characteristics of erythrocyte aggregation in flowing blood, echogenicity variation in blood was observed both in vitro and in vivo. However, few noninvasive observations of blood echogenicity variation during the cardiac cycle in human arteries have been reported. In the present study, to reduce the dynamic range between the blood vessel lumen and the surrounding tissue, coded harmonic images were acquired from human carotid arteries using a GE LOGIQ 700 Expert system (GE, Milwaukee, WI, USA) with an M12L probe, which enabled the noninvasive detection of the cyclic and radial variation of echogenicity in arterial vessels. It was found that blood echogenicity increased during systole, reaching a maximum at peak systole and then decreased to a weak level during diastole. The echogenicity profiles of blood along the vessel diameter were found to be approximately parabolic in the cardiac cycle, except for the hypoechoic zone near the center of the vessel at peak systole. The present results for human carotid arteries corroborate previous in vitro observations that showed a cyclic and radial variation of blood echogenicity, which was thought to be caused by the enhancement of erythrocyte aggregation due to the combined effects of flow acceleration and shear rate during systole.

Pulmonary blood volume variation decreases after myocardial infarction in pigs: a quantitative and noninvasive MR imaging measure of heart failure.

Abstract: MR imaging can be used to assess the variation of the pulmonary blood volume during the cardiac cycle as a marker of heart failure.

Quantitative analysis of exercise-induced enhancement of early- and late-systolic retrograde coronary blood flow.

Abstract: Coronary blood flow (CBF) is reduced and transiently reversed during systole via cardiac contraction. Cardiac contractility, coronary tone, and arterial pressure each influence systolic CBF (CBFSYS), particularly by modulating the retrograde component of CBFSYS. The effect of concurrent changes in these factors on CBFSYS during dynamic exercise has not been examined. Using chronically instrumented swine, we hypothesized that dynamic exercise enhances retrograde CBFSYS. Phasic CBF was examined at rest and during treadmill exercise [2–5 miles/h (mph)]. Absolute values of mean CBF over the cardiac cycle (CBFCYCLE) as well as mean CBF in diastole (CBFDIAS) and mean CBFSYS were increased by exercise, while relative CBFDIAS and CBFSYS expressed as percentage of mean CBFCYCLE were principally unchanged. Early retrograde CBFSYS was present at rest and increased in magnitude (−33 ± 4 ml/min) and as a percent of CBFCYCLE (−0.6 ± 0.1%) at 5 mph. This reversal was transient, comprising 3.7 ± 0.3% of cardiac cycle duration at 5 mph. Our results also reveal that moderately intense exercise (>3 mph) induced a second CBF reversal in late systole before aortic valve closure. At 5 mph, late retrograde CBFSYS amounted to −53 ± 11 ml/min (−3.1 ± 0.7% of CBFCYCLE) while occupying 11.1 ± 0.3% of cardiac cycle duration. Wave-intensity analysis revealed that the second flow reversal coincided with an enhanced aortic forward-going decompression wave (vs. rest). Therefore, our data demonstrate a predictable increase in early-systolic CBF reversal during exercise and additionally that exercise induces a late-systolic CBF reversal related to the hemodynamic effects of left ventricular relaxation that is not predictable using current models of phasic CBF.

Accessory left atrial diverticulae: contractile properties depicted with 64-slice cine-cardiac CT.

Abstract: To assess the contractility of accessory left atrial appendages (LAAs) using multiphasic cardiac CT. We retrospectively analyzed the presence, location, size and contractile properties of accessory LAAs using multiphasic cardiac 64-slice CT in 102 consecutive patients (63 males, 39 females, mean age 57). Multiplanar reformats were used to create image planes in axial oblique, sagittal oblique and coronal oblique planes. For all appendages with an orifice diameter ≥ 10 mm, axial and sagittal diameters and appendage volumes were recorded in atrial diastole and systole. Regression analysis was performed to assess which imaging appearances best predicted accessory appendage contractility. Twenty-three (23%) patients demonstrated an accessory LAA, all identified along the anterior LA wall. Dimensions for axial oblique (AOD) and sagittal oblique (SOD) diameters and sagittal oblique length (SOL) were 6.3–19, 3.4–20 and 5–21 mm, respectively. All appendages (≥10 mm) demonstrated significant contraction during atrial systole (greatest diameter reduction was AOD [3.8 mm, 27%]). Significant correlations were noted between AOD-contraction and AOD (R = 0.57, P < 0.05) and SOD-contraction and AOD, SOD and SOL (R = 0.6, P < 0.05). Mean diverticulum volume in atrial diastole was 468.4 ± 493 mm3 and in systole was 171.2 ± 122 mm3, indicating a mean change in volume of 297.2 ± 390 mm3, P < 0.0001. Stepwise multiple regression analysis revealed SOL to be the strongest independent predictor of appendage contractility (R2 = 0.86, P < 0.0001) followed by SOD (R2 = 0.91, P < 0.0001). Accessory LAAs show significant contractile properties on cardiac CT. Those accessory LAAs with a large sagittal height or depth should be evaluated for contractile properties, and if present should be examined for ectopic activity during electrophysiological studies.

Spatiotemporal image correlation using high-definition flow: a new method for assessing ovarian vascularization.

Abstract: Objective. The purpose of this study was to describe a new method for assessing ovarian vascularization using spatiotemporal image correlation (STIC)-high-definition flow (HDF). Methods. Thirty healthy premenopausal fertile women were assessed in the follicular part of the menstrual cycle by transvaginal sonography. A 4-dimensional STIC-HDF volume was obtained from the nondominant ovary to assess 3-dimensional (3D) vascular indices (vascularization index [VI] and flow index [FI]) during one cardiac cycle in each women. Using 1-cm3 spherical sampling, we calculated the VI and FI from the most vascularized part of the ovarian stroma at two different moments of the cardiac cycle (systole and diastole). System settings were kept constant for all of the patients (pulse repetition frequency, 0.9 kHz; gain, 0.8; and depth, 40 mm). We calculated the VI and FI ratios between systole and diastole. Results. The mean VI during systole (11.485%; SD, 6.7%) was significantly higher than during diastole (8.653%; SD, 5.6%; P< .0001). The mean FI values during systole (47.799 [unitless]; SD, 5.8) and diastole (47.791; SD, 6.0) were nearly identical (P = .993). The VI ratio was 1.35 (95% confidence interval, 1.28-1.42), which means that the mean VI was 35% higher during systole compared to diastole, whereas the FI during systole and diastole remained constant (FI ratio, 1.00; 95% confidence interval, 0.96-1.04). There was a high correlation between VI values during systole and diastole (r 2 = 0.94), whereas this correlation was weaker for the FI (r 2 = 0.45). Condusions. The STIC-HDF method allows assessment of 3D vascular indices throughout the cardiac cycle. Vascularization index calculation is affected by the moment of the cardiac cycle during which the measurement is taken. However, it seems that FI calculation is not affected by the cardiac cycle in the normal nondominant ovary.

Semi-automatic algorithm for construction of the left ventricular area variation curve over a complete cardiac cycle

Abstract: Two-dimensional echocardiography (2D-echo) allows the evaluation of cardiac structures and their movements. A wide range of clinical diagnoses are based on the performance of the left ventricle. The evaluation of myocardial function is typically performed by manual segmentation of the ventricular cavity in a series of dynamic images. This process is laborious and operator dependent. The automatic segmentation of the left ventricle in 4-chamber long-axis images during diastole is troublesome, because of the opening of the mitral valve. This work presents a method for segmentation of the left ventricle in dynamic 2D-echo 4-chamber long-axis images over the complete cardiac cycle. The proposed algorithm is based on classic image processing techniques, including time-averaging and wavelet-based denoising, edge enhancement filtering, morphological operations, homotopy modification, and watershed segmentation. The proposed method is semi-automatic, requiring a single user intervention for identification of the position of the mitral valve in the first temporal frame of the video sequence. Image segmentation is performed on a set of dynamic 2D-echo images collected from an examination covering two consecutive cardiac cycles. The proposed method is demonstrated and evaluated on twelve healthy volunteers. The results are quantitatively evaluated using four different metrics, in a comparison with contours manually segmented by a specialist, and with four alternative methods from the literature. The method's intra- and inter-operator variabilities are also evaluated. The proposed method allows the automatic construction of the area variation curve of the left ventricle corresponding to a complete cardiac cycle. This may potentially be used for the identification of several clinical parameters, including the area variation fraction. This parameter could potentially be used for evaluating the global systolic function of the left ventricle.

Cardiac biplane strain imaging: initial in vivo experience.

Abstract: In this study, first we propose a biplane strain imaging method using a commercial ultrasound system, yielding estimation of the strain in three orthogonal directions. Secondly, an animal model of a child's heart was introduced that is suitable to simulate congenital heart disease and was used to test the method in vivo. The proposed approach can serve as a framework to monitor the development of cardiac hypertrophy and fibrosis. A 2D strain estimation technique using radio frequency (RF) ultrasound data was applied. Biplane image acquisition was performed at a relatively low frame rate (<100 Hz) using a commercial platform with an RF interface. For testing the method in vivo, biplane image sequences of the heart were recorded during the cardiac cycle in four dogs with an aortic stenosis. Initial results reveal the feasibility of measuring large radial, circumferential and longitudinal cumulative strain (up to 70%) at a frame rate of 100 Hz. Mean radial strain curves of a manually segmented region-of-interest in the infero-lateral wall show excellent correlation between the measured strain curves acquired in two perpendicular planes. Furthermore, the results show the feasibility and reproducibility of assessing radial, circumferential and longitudinal strains simultaneously. In this preliminary study, three beagles developed an elevated pressure gradient over the aortic valve (Deltap: 100-200 mmHg) and myocardial hypertrophy. One dog did not develop any sign of hypertrophy (Deltap = 20 mmHg). Initial strain (rate) results showed that the maximum strain (rate) decreased with increasing valvular stenosis (-50%), which is in accordance with previous studies. Histological findings corroborated these results and showed an increase in fibrotic tissue for the hearts with larger pressure gradients (100, 200 mmHg), as well as lower strain and strain rate values.

The Timing of Onset of Mechanical Systole and Diastole in Reference to the QRS-T Complex: a Study to Determine Performance Criteria for a Non-Invasive Diastolic Timed Vibration Massage System in Treatment of Potentially Unstable Cardiac Disorders

Abstract: Our institution is in development of a low frequency, non-invasive Diastolic Timed Vibrator (DTV) for use in emergency treatment of ST Elevation Myocardial Infarction (STEMI) It is preferable to avoid vibration emissions during the IsoVolumetric Contraction Period (IVCP) and at least the majority of mechanical systole thereafter, as systolic vibration may cause a negative inotropic effect in the ischemic heart Furthermore diastolic vibration should preferably include the IsoVolumetric Relaxation Period (IVRP) which has been shown in clinical studies to improve cardiac performance and enhance coronary flow Electrocardiographic (ECG) monitoring can be used to enable diastolic tracking, however, the timing of the phases of the cardiac cycle in relation to the ECG waveform must first be verified The objective of this study was therefore to determine timing of onset of mechanical systole and diastole in reference to the QRS-T Complex One hundred and twenty-three adult echocardiographic studies were assessed for the point of mitral and aortic valve closure in relation to the QRS complex and T wave in a representative population We found that onset of mechanical systole occurred on and usually shortly after the peak of a first dominant QRS complex deflection, and onset of diastole occurred at the earliest on and most commonly beyond the peak or midpoint of the T wave A DTV should ideally be able to stop vibrating on or before the peak of the first dominant deflection of a QRS complex, and begin vibrating near the peak of the T wave Given early detection of ventricular depolarization can occur 10–20 ms prior to R wave peak, it is proposed that a DTV should preferably be able to stop vibrating within 10 ms of a triggered stop command Onset of vibration during peak of T wave could be approximated by a rate adapted Q-T interval regression equation, and then fine tuned by manual adjustment during therapy

Wolff-Parkinson-White Syndrome and Accessory Pathways

Abstract: The heart has 4 chambers that pump blood. The 2 upper chambers are the right and left atria, and the 2 lower chambers are the right and left ventricles. The heart also has an electric system that directs the coordinated beating of these 4 chambers. A schematic drawing of the normal heart structure and electric system (red arrows) is shown in Figure 1. A normal electric impulse originates in an area of the upper right atrium called the sinus (SA) node, and an ordinary electric activity of the heart is referred to as normal sinus rhythm. In normal sinus rhythm, an electric impulse is generated by the SA node, and that electricity spreads through the right and left atria, directing these chambers to beat. On an electrocardiogram (ECG; bottom of Figure 1), the electric activity from the atria is seen as a small rounded deflection called a P wave. The same electric impulse then passes through a small area of tissue between the atria and ventricles called the atrioventricular (AV) node and then down through the ventricles. On the ECG, the electric activity from the ventricles results in a larger deflection called the R wave or QRS complex. Because the AV node is small, there is not enough electric activity to cause a deflection in the ECG. Therefore, the time spent by the electric impulse traveling through the AV node is represented on the ECG by a flat interval called the PR interval. In a normal heart, the AV node is a gatekeeper of sorts in that it is the only pathway for electricity that communicates from the upper chambers (atria) to the lower chambers (ventricles). The combination of electric impulses from the SA node to the atria, then through …

Physiology of heartbeat reversal in adult Drosophila melanogaster (Diptera: Drosophilidae).

Abstract: Heartbeat patterns were monitored in the living bodies of decapitated adult flies using several electrocardiographic methods (pulse-light optocardiography, thermocardiography, strain-gauge cardiography). Unlike other insect species, in which there is a peristaltic segmental propagation of cardiac contractions, Drosophila uses extremely efficient synchronic cardiac contractions. The rate of synchronic cardiac pulsation, which is characterized by simultaneous propagation of anterograde systolic contractions along all the segments of the heart, is relatively fast (~ 4 Hz at room temperature). This pulsation is used mainly for the vigorous pumping of haemolymph into the head and thorax through a narrow elastic tube, the aorta (anterograde I heartbeat). In addition, this synchronic pulsation is also used to enhance the circulation of haemolymph throughout the abdominal body cavity (anterograde II heartbeat). The switch between thoracic (anterograde I) and abdominal (anterograde II) haemolymph circulation is regulated by peri- odically alternating, tetanic contractions and relaxations of the conical heart chamber (ventricle). In the latter there is a pair of slit- like apertures, which are closed or opened by contraction or relaxation of the organ, respectively. During contraction of the conical chamber, the apertures are tightly constricted for several seconds and haemolymph is pumped forwards into the aorta (anterograde I heartbeat). Conversely, during relaxation of the conical chamber, the apertures are wide open for a few seconds, haemolymph leaves the heart and leaks out through open apertures and circulates from the tail to the base of the abdomen. The backward oriented, retro- grade heartbeat recorded in other insects, has a lower frequency (1 to 2 Hz), occurs in Drosophila only sporadically and usually in the form of individual or twinned systolic peaks of large amplitude. Unlike the synchronic nature of the anterograde I and II cardiac contractions, propagation of the relatively slow retrograde heartbeat is by peristalsis. The newly discovered, compact ventricle with atrium and synchronic functioning of the insect heart shows structural and functional analogies with the functioning of the human heart.

Myocardial Motion Analysis for Determination of Tei-Index of Human Heart

Abstract: The Tei index, an important indicator of heart function, lacks a direct method to compute because it is difficult to directly evaluate the isovolumic contraction time (ICT) and isovolumic relaxation time (IRT) from which the Tei index can be obtained. In this paper, based on the proposed method of accurately measuring the cardiac cycle physical phase, a direct method of calculating the Tei index is presented. The experiments based on real heart medical images show the effectiveness of this method. Moreover, a new method of calculating left ventricular wall motion amplitude is proposed and the experiments show its satisfactory performance.

Letter to the editor: "Postulated functional advantages of a looped as opposed to a linearly arranged heart".

Abstract: to the editor: My attention has been drawn to an article titled “The looped heart does not save energy by maintaining the momentum of blood flowing in the ventricle” (4). The study questions previously postulated functional implications of cardiac looping (2). Watanabe et al. (4) used finite element numerical modeling to compare the hemodynamics of virtual left ventricles rather than whole hearts, with physiological and nonphysiological intraventricular flow paths. The differences of flow paths were induced by changes in the direction of inflow, tangential to the cavity in each case, but inclined either toward or away from the lateral wall. The geometries of the ventricles did not differ. Neither of them represented the ventricle of an unlooped heart if, as illustrated in Fig. 1, that were interpreted to mean a heart with an atrium, a ventricle, and an aorta lying in approximate alignment without a change of direction between ventricular inflow and outflow. In that sense, all hearts found in humans, and possibly all found in mature vertebrates, are looped, even in those with congenital malformations. A degree of direction change at the ventricular level and the inclusion of an atrial as well as a ventricular cavity within a pericardium seem to be fundamental features of the hearts of vertebrates. Fig. 1. Schematic illustration of the interactions between atrium, ventricle, and blood in a linearly arranged heart (top) contrasted with those of a looped heart (bottom), as described in the text (reprinted from Nature; see Ref. 2). Watanabe et al. (4) reasonably refuted the concept of conservation of inflow momentum, which prompts me to reformulate the postulated functional advantages of cardiac looping that were put forward in relation to magnetic resonance studies of human intracardiac flow (2) (see Fig. 1). Three factors are illustrated schematically in Fig. 1 [republished with permission from Nature (2)]. First, the tendency in a looped heart for inflows to be aligned tangential to a cavity predisposes to more stable intracavity flow. Second, the recirculation of inflowing streams in the atrial and ventricular cavities of a looped heart then tends to turn predominantly toward rather than away from the next cavity, which could facilitate an efficient onward passage (given the time relations at peak exercise, at least). Third, in a looped heart, the appropriate direction of the inertial recoil of a vigorously ejecting ventricle (black arrowheads pointing away from the direction of the acceleration of blood into the outflow tract) can enhance rather than suppress the structural coupling (indicated by the white arrowheads) of ventricular systole to atrial filling. All three of these factors, even if trivial at rest, are likely to gain significance during strenuous exertion, a state likely to have been relevant to vertebrate survival through the course of evolution, but not necessarily so important to patients with cardiovascular disease. The third factor, concerning ventriculo-atrial coupling, is probably the most potent of the three. Of note, the velocities, volumes, and time courses of inflowing and outflowing streams, and hence the rates of change of momentum and the associated directional exchanges of force, change greatly from rest to strenuous exercise in humans. The heart rate of a physically fit young adult can increase more than threefold with exertion, and the cardiac output of an endurance-trained athlete, more than sixfold (3). The two peaks of early and late left ventricular filling of the resting heart become one during exertion, when a single peak of rapid ventricular filling is followed by vigorous ejection with little or no intervening isovolumetric period (1). In this state, the minimization of the dissipation of the kinetic energy of inflow would be functionally advantageous, allowing efficient transfers of energy between inflowing blood, myocardium, outflowing blood, and arterial walls. Even on exercise, only part of the momentum of blood flowing into a chamber is likely to be conserved and redirected. There will also be an initial deceleration and decline of momentum as streamlines diverge, with an associated force field that may contribute to the expansion of the cavity, priming the myocardium for its subsequent contraction.

Supraventricular stimulation to control ventricular rate

Abstract: Various techniques for delivering atrial pacing and supraventricular stimulation to achieve a desired ventricular rate and/or cardiac output are described. One example method described includes delivering a pacing signal configured to cause an atrial depolarization to a heart of a patient, wherein the atrial depolarization results in an associated refractory period during the cardiac cycle, and delivering a signal to a supraventricular portion of the heart of the patient subsequent to the atrial refractory period and during a ventricular refractory period of the cardiac cycle.

Method And Device For Determination Of Efficacy Of Cardiac Resynchronization Pacing Utilizing Simultaneous RV And LV Electroanotomic Cardiac Phase Motion Mapping

Abstract: The current invention describes a method and system to measure and validate the efficacy of cardiac resynchronization therapy pacing using electroanatomical position and motion sensing during the various phases of the cardiac cycle. In this method, electroanatomical position and motion sensors are utilized with sensing from the tip of both right ventricular pacing lead and left ventricular pacing lead. An operator can therefore obtain data not currently available to an implanter with current technology. This data includes the physical distance between both leads and the relative motion of both leads during cardiac resynchronization therapy biventricular pacing. If good lead positioning for both the right ventricular lead and left ventricular lead has been obtained, then the operator will be able to demonstrate good synchronization of the cardiac cycle.

Assessment of cardiac wall motion using impedance measurements

Abstract: In general, this disclosure provides techniques for heart monitoring. In accordance with the techniques described in this disclosure, an implantable medical device (IMD) may assess cardiac wall motion using impedance measurements through cardiac leads. As an example, the IMD may calculate an amount or rate of change in impedance due to the motion of a wall of the heart during at least a portion of one cardiac cycle, e.g., systole, in order to assess the strength of systolic contraction.