Showing papers on "Cardiac cycle published in 2003"

A dynamic approach to identifying desired physiological phases for cardiac imaging using multislice spiral CT

Abstract: In this investigation, we describe a quantitative technique to measure coronary motion, which can be correlated with cardiac image quality using multislice computed tomography (MSCT) scanners. MSCT scanners, with subsecond scanning, thin-slice imaging (sub-millimeter) and volume scanning capabilities have paved the way for new clinical applications like noninvasive cardiac imaging. ECG-gated spiral CT using MSCT scanners has made it possible to scan the entire heart in a single breath-hold. The continuous data acquisition makes it possible for multiple phases to be reconstructed from a cardiac cycle. We measure the position and three-dimensional velocities of well-known landmarks along the proximal, mid, and distal regions of the major coronary arteries [left main (LM), left anterior descending (LAD), right coronary artery (RCA), and left circumflex (LCX)] during the cardiac cycle. A dynamic model (called the "delay algorithm") is described which enables us to capture the same physiological phase or "state" of the anatomy during the cardiac cycle as the instantaneous heart rate varies during the spiral scan. The coronary arteries are reconstructed from data obtained during different physiological cardiac phases and we correlate image quality of different parts of the coronary anatomy with phases at which minimum velocities occur. The motion characteristics varied depending on the artery, with the highest motion being observed for RCA. The phases with the lowest mean velocities provided the best visualization. Though more than one phase of relative minimum velocity was observed for each artery, the most consistent image quality was observed during mid-diastole ("diastasis") of the cardiac cycle and was judged to be superior to other reconstructed phases in 92% of the cases. In the process, we also investigated correlation between cardiac arterial states and other measures of motion, such as the left ventricular volume during a cardiac cycle, which earlier has been demonstrated as an example of how anatomic-specific information can be used in a knowledge-based cardiac CT algorithm. Using these estimates in characterizing cardiac motion also provides realistic simulation models for higher heart rates and also in optimizing volume reconstructions for individual segments of the cardiac anatomy.

Clinical assessment of left ventricular diastolic function

Abstract: Diastolic left ventricular disease is being increasingly incriminated as a cause of limitation of exercise tolerance, whether or not ejection fraction is normal,1,2 though the mechanisms by which it does so are far from clear. Indeed, it has been suggested that no diastolic abnormality at all need be demonstrated for a diagnosis of possible or probable diastolic heart failure to be made.3 Measurements can be made during diastole with many techniques, old or new, but can there be said to be as many impaired “functions” as there are abnormal measurements? Surely, the term “diastolic function” applies only to a small number of more basic mechanisms whose nature must be elucidated independently of the method used to detect them and whose number depends on rigorous use of Occam's razor. Difficulties in defining diastolic heart failure strongly suggest that agreement in this field has still to be achieved. Indeed, no simple definition of diastolic disease itself has emerged. “Increased resistance to filling” has been suggested. While the resistance of a valve orifice or circulation can readily be defined in terms of pressure drop and flow, resistance to filling involves neither and so is poorly defined. This lack of gold standards by which discrete mechanisms can be assessed in individual patients is a major impediment to identifying and quantifying disturbances in disease. Left ventricular diastole is traditionally defined as the period in the cardiac cycle from the end of aortic ejection until the onset of ventricular tension development of the succeeding beat.4 Even in the normal subject, several mechanisms are involved:

Assessment and consequences of the constant-volume attribute of the four-chambered heart

Abstract: The constant-volume hypothesis regarding the four-chambered heart states that total pericardial volume remains invariant throughout the cardiac cycle. Previous canine studies have indicated that the pericardial volume remains constant within 5%; however, this hypothesis has not been validated in humans using state-of-the-art technology. The constant-volume hypothesis has several predictable functional consequences, including a relationship between atrial ejection fraction and chamber equilibrium volumes. Using cardiac magnetic resonance (MR) imaging (MRI), we measured the extent to which the constant-volume attribute of the heart is valid, and we tested the accuracy of the predicted relationship between atrial ejection fraction and chamber equilibrium volumes. Eleven normal volunteers and one volunteer with congenital absence of the pericardium were imaged using a 1.5-T MR scanner. A short-axis cine-loop stack covering the entire heart was acquired. The cardiac cycle was divided into 20 intervals. For each slice and interval, pericardial volumes were measured. The slices were stacked and summed, and total pericardial volume as a function of time was determined for each subject. In the normal subjects, chamber volumes at ventricular end diastole, end systole, and diastasis were measured. Pericardial volume remained invariant within 5 ± 1% in normal subjects; maximum variation occurred near end systole. In the subject with congenital absence of the pericardium, total heart volume, defined by the epicardial surface, varied by 12%. The predictions of the relationship between atrial ejection fraction and chamber equilibrium volumes were well fit by MRI data. In normal subjects, the four-chambered heart is a constant-volume pump within 5 ± 1%, and constant-volume-based modeling accurately predicts previously unreported physiological relationships.

Sarcomere length changes in a 3D mathematical model of the pig ventricles

Abstract: Measurements of the geometry and fibrous-sheet structure of the left and right ventricles of the pig heart are fitted with a finite element model. Mechanical changes during the heart cycle are computed by solving the equations of motion under specified ventricular boundary conditions and using experimentally defined constitutive laws for the active and passive material properties of myocardial tissue. The resulting patterns of deformation, such as axial torsion and changes in wall thickness and base-apex length, are consistent with experimental observations. The model can therefore be used to predict sarcomere length changes and other strain patterns throughout the myocardium and throughout the cardiac cycle. Here we present sarcomere length changes at a limited number of material points within the wall. Sarcomere length typically varies by 10% above and below the unloaded length; although under the boundary conditions imposed in the current model the midwall circumferentially oriented sarcomere lengths increased by up to 20% at end diastole. We provide web-access details for a downloadable software program designed to provide more extensive information on mechanical deformation, such as the principal strains and muscle fibre cross-sectional area changes during the cardiac cycle.

Torsion of the Left Ventricle During Pacing with MRI Tagging

Abstract: The effects of different pacing protocols on left ventricular (LV) torsion were evaluated over the full cardiac cycle. A systolic and diastolic series of magnetic resonance imaging (MRI) scans were combined and used to calculate the torsion of the LV in a canine model. The asynchronous activation resulting from ventricular pacing interferes with the temporal evolution of LV torsion. The torsion of the left ventricle was investigated under three different protocols: 1) right atrial pacing, 2) right ventricular pacing, and 3) simultaneous pacing from the right ventricular apex and LV base. The temporal evolution of torsion was determined from tagged MRI and evaluated over the cardiac cycle. The peak rotation for the atrially paced hearts was 11.1 degrees (+/- 3.5 degrees) compared to 6.1 degrees (+/- 1.7 degrees) and 6.1 degrees (+/- 0.7 degree) for those hearts paced from the right ventricle and from both ventricles, respectively. While biventricular pacing increases the synchrony of contraction, it significantly alters the pattern of LV torsion. From these experiments we have shown that measuring torsion is an extremely sensitive indicator of the existence of ectopic excitation.

Dynamic properties of stretch-activated K+ channels in adult rat atrial myocytes

Abstract: The effect of mechanical stress on the heart’s electrical activity has been termed mechanoelectric feedback. The response to stretch depends upon the magnitude and the waveform of the stimulus, and upon the timing relative to the cardiac cycle. Stretch-activated ion channels (SACs) have been regarded as the most likely candidates for serving as the primary transducers of mechanical stress. We explored the steady state and dynamic responses of single channels in adult rat atrial cells using the patch clamp with a pressure clamp. Surprisingly, we only observed K + -selective SACs, probably of the 2P domain family. The channels were weakly outward rectifying with flickery bursts. In cell attached mode, the mean conductance was 74714 and 65716 pS for +60 and � 60 mV, respectively (140 mM [K + ]out, 2 mM [Mg 2+ ]out and 0 mM [Ca 2+ ]out). The latency of the response to pressure steps was 50–100 ms and the time to peak B400 ms. About half of the channels in cell-attached patches showed adaptation/inactivation where channel activity declined to a plateau of 20–30% of peak in B1 s. The time dependent behavior of these SACs is generally consistent with whole-cell currents observed in chick and rat ventricular cells, although the net current was outward rather than inward. r 2003 Published by Elsevier Science Ltd.

Correlation Between Negative Near-Wall Shear Stress in Human Aorta and Various Stages of Congestive Heart Failure

Abstract: The critical effect of advanced congestive heart failure is reduced blood flow in descending aorta resulting from mild to severe reduction in cardiac output, usually accompanying low ejection fraction. In these patients the heart tries to compensate by beating faster, but reduced blood flow combined with increased heart rate can lead to retrograde flow and negative shear stress along the vessel walls during each cardiac cycle. Our studies show that near-wall negative shear stress can result from an entire-retrograde flow at normal heart rates or a Womersley-type phase delayed near-wall retrograde flow at high heart rate and low ejection fraction conditions. In our experiments, a compliant aortic loop with appropriate pressure and flow instrumentation was used, running on either various aqueous glycerin solutions or property filtered, anticoagulated diluted bovine blood. The flow field was mapped using a General Electric Vingmed System 5 platform. The resulting images were analyzed with Caltech's digital ultrasound speckle image velocimetry technique. We showed the occurrence of near-wall retrograde flow under certain aortic flow rates and frequencies, charted via an empirical relationship between Reynolds and Womersley numbers. Also, we demonstrated a strong correlation between retrograde flow level and transition from preliminary to advanced congestive heart failure patients.

Effect of atrial fibrillation on the dynamics of mitral annular area.

Abstract: BACKGROUND AND AIMS OF THE STUDY The mitral annulus shows dynamic changes in shape and size during the cardiac cycle. A smaller size in end-diastole is attributed to the sphincteric action of atrial systole, and this may be important for functional integrity of the mitral valve. However, the effect of atrial fibrillation (AF) on dynamic changes in mitral annular size in humans is not known. METHODS Mitral annular diameters in apical four- and two-chamber views were measured using echocardiography in 25 patients in atrial fibrillation, and in 37 subjects in normal sinus rhythm at mid-diastole, end-diastole and end-systole. Mitral annular area was computed assuming elliptical geometry. RESULTS Patients in sinus rhythm showed a significant increase in mitral annular area of 25.9 +/- 12.8% with ventricular systole compared to its area in end-diastole (p < 0.0001), and a 10.5 +/- 8.4% reduction with atrial systole compared to mid-diastole (p < 0.001). Patients in AF had larger mitral annuli which showed non-significant changes in size between these three phases of the cardiac cycle. Percent reduction in mitral annular area in the latter half of diastole correlated significantly with left atrial (LA) diameter (r = -0.54, p < 0.0001), LA volume (r = -0.50, p < 0.0001), left ventricular (LV) fractional shortening (r = 0.37, p = 0.0036), mitral annular area in mid-diastole (r = -0.41, p = 0.0011) and mitral annular area in end-diastole (r = -0.64, p < 0.0001). That is, atrial sphincteric action on the mitral annulus was less in the presence of larger left atrium or the mitral annulus. Stepwise multiple regression analysis showed rhythm and mitral annular size to be independent predictors of dynamic changes in mitral annular area. CONCLUSION It is concluded that AF blunts or eliminates the phasic changes in mitral annular size during the cardiac cycle with loss of its presystolic sphincteric action; this may have implications in the genesis and surgical correction of mitral regurgitation.

Transient event mapping in the heart

Abstract: A method for performing a medical procedure is provided, including recording geometric information at a plurality of time points in a plurality of cardiac cycles of a heart of a subject. Subsequently, a transient event is detected that is produced at a location on the heart during a cardiac cycle. A time of occurrence of the transient event is identified in the cardiac cycle during which the transient event occurred. A map of the heart is displayed responsive to the identified time of occurrence and the geometric information recorded at a time point in the cardiac cycle that corresponds to the time of occurrence of the transient event.

Classifying tachyarrhythmia using time interval between ventricular depolarization and mitral valve closure

Abstract: A cardiac rhythm management system measures a time interval between a first fiducial marker indicative of a ventricular depolarization (eg, a Q-wave, an R-wave, etc) and a second fiducial marker indicative of a subsequent mitral valve closure (MVC) occurring during the same cardiac cycle Such time intervals are used for detecting atrioventricular (AV) dissociation The AV dissociation may, in turn, be used for discriminating between a supraventricular tachyarrhythmia (SVT) and a ventricular tachyarrhythmia (VT) or for any other diagnostic or therapeutic purpose The AV dissociation and/or SVT/VT discrimination information may be communicated from an implantable cardiac rhythm management device to an external interface and/or used to determine the nature of therapy delivered to the subject In a further example, amplitudes indicative of the MVCs are also used for determining whether AV dissociation exists

Device for determining a characteristic point in the cardiac cycle

Abstract: The present invention relates to a device for determining a characteristic point in the cardiac cycle that comprises means for calculating the curve of the blood flow rate D(t) in the aorta from the curve of the arterial blood pressure signal P(t) and determining from the curve of the blood flow rate D(t) in each cardiac cycle the time at which an incisura point lies. The device can be used for activating an intra-aortal balloon pump (IABP).

Methods and apparatus for determining cardiac output

Abstract: The present invention provides methods and apparatus for determining a dynamical property of the systemic or pulmonary arterial tree using long time scale information, i.e., information obtained from measurements over time scales greater than a single cardiac cycle. In one aspect, the invention provides a method and apparatus for monitoring cardiac output (CO) from a single blood pressure signal measurement obtained at any site in the systemic or pulmonary arterial tree or from any related measurement including, for example, fingertip photoplethysmography. According to the method the time constant of the arterial tree, defined to be the product of the total peripheral resistance (TPR) and the nearly constant arterial compliance, is determined by analyzing the long time scale variations (greater than a single cardiac cycle) in any of these blood pressure signals. Then, according to Ohm's law, a value proportional to CO may be determined from the ratio of the blood pressure signal to the estimated time constant

Colour tissue velocity imaging can show resynchronisation of longitudinal left ventricular contraction pattern by biventricular pacing in patients with severe heart failure

Abstract: Objective: To quantify ventricular resynchronisation by biventricular pacing using colour tissue Doppler velocity imaging (c-TVI). Design and patients: c-TVI shows regional tissue velocity profiles with a very high time resolution (10 ms). Eighteen patients were studied from an apical four chamber view at baseline and after a one month follow up of biventricular pacing. Regional left ventricular peak tissue velocities and regional time differences during the cardiac cycle were compared in the basal and mid interventricular septal segments of the left ventricle, and in the corresponding segments in the left ventricular free wall. Results: From baseline to follow up, mean peak tissue velocities changed only during isovolumic contraction in the basal interventricular septum and the left ventricular free wall. At baseline the peak main systolic tissue velocities in the left ventricular free wall were typically delayed by an average of 42 ms in the basal left ventricular site and by 14 ms in the mid left ventricular site compared with the corresponding sites in the interventricular septum. After resynchronisation by biventricular pacing those regional movements were separated by an average of only 7 ms at the basal site, but there was still a 21 ms earlier movement of the left ventricular free wall in the mid left ventricular site. The diastolic movement pattern remained unchanged from baseline to follow up. Conclusions: c-TVI showed a significant asynchronous regional longitudinal movement of basal left ventricular sites at baseline. A change to a more synchronous longitudinal left ventricular movement pattern during biventricular pacing was demonstrated.

Mitral mechanical heart valves: in vitro studies of their closure, vortex and microbubble formation with possible medical implications.

Abstract: Objective: The goal of the present work was to create the closest possible in vitro fluid dynamic environment in which prosthetic mitral valves in the patients’ hearts function, in order to demonstrate whether microbubbles are generated, and if yes, under what conditions and at which stage of the cardiac cycle. Microbubbles were observed in the blood of patients with mitral mechanical heart valves (MHV) by means of echocardiography. The phenomenon, often referred to as high-intensity transient signals (HITS), appears as bright, intense, high-velocity and persistent echoes detected by Doppler echocardiography at the instant of valve closure. The question is no longer whether microbubbles are being formed in patients with MHV. as an inherent aspect of their design, but rather how they evolve and when. The answer to this question was the objective of the present paper. Methods: Hemodynamic conditions in which microbubbles were observed in patients with mitral MHV were simulated in our laboratory. We were able to describe the bubble formation process, as one consisting of nucleation and microbubble growth. While mild growth of nuclei is governed by diffusion, extensive growth of microbubbles is controlled by pressure drop during deceleration of the leaflets on the housing on the atrial side of the mitral MHV. Results: The present study has shown that bubbles form in a fluid at the instant of closure of mechanical valves. The formation of vortices after valve closure, although clinically not yet observed, was also demonstrated in the present in vitro studies. We believe that impact of such vortices on the endothelial layer of the left atrial wall may have clinical significance. These two phenomena were not observed in bioprosthetic valves. Conclusions: As demonstrated, there exist two distinct phenomena characteristic of mechanical heart valves, which take place during valve closure, namely, that of vortex formation and that of microbubble growth. Both phenomena may have far reaching clinical implications. q 2003 Elsevier B.V. All rights reserved.

Remodeling of the cardiac extracellular matrix differs between volume- and pressure-overloaded ventricles and is specific for each heart valve lesion.

Abstract: Background and aim of the study Different patterns of fibroblast-mediated remodeling of the extracellular matrix (ECM) might be expected between patients with pressure- and volume-induced left ventricular hypertrophy. Methods Patients with chronic pressure-overload due to aortic stenosis (AS, n = 19) and chronic volume-overload due to either aortic regurgitation (AR, n = 9) or mitral regurgitation (MR, n = 10) were examined. The amount of interstitial collagen was quantified by using circular-polarization-microscopy in picrosirius red-stained biopsies. Biopsies from 10 patients with mild cardiomyopathy served as controls. In a subgroup, collagen type-I (Coll-I) and collagen type-III (Coll-III) gene expression was evaluated by quantitative RT-PCR. After immunohistological staining, procollagen-I/procollagen-III ratio and density of fibroblasts (FB) per vision-field were analyzed. Results The amount of interstitial cardiac fibrosis (ICF) was significantly higher in AS (5.7 +/- 4.1 g/m2), AR (8.8 +/- 4.9 g/m2) or MR (4.7 +/- 2.8 g/m2) than in controls (2.3 +/- 1.5 g/m2) (p = 0.003). The amount of thick collagen fibers was higher in AR than in AS, where-by density of fibroblasts did not differ. In volume-overloaded ventricles, the Coll-I/Coll-III ratio was shifted towards Coll-I, and in pressure-overloaded ventricles towards Coll-III. The severity of ECM remodeling was positively correlated with wall stress and impaired diastolic function, but not with systolic function or clinical symptoms. Conclusion Remodeling of the ECM is specific for left ventricular volume and pressure overload, and may serve as an early indicator for inadequate adaptation.

Blood flow gated mri

Abstract: A magnetic resonance imaging method and apparatus includes a navigator region defined within the subject by selective excitation. Blood flow is measured within the selected region using the principles of phase contrast MR angiography. A cardiac cycle plot is constructed from Fourier transformed data that represents measured velocity of blood flow through the navigator region as a function of time. On the basis of the cardiac cycle plot and the navigator measurements, data acquisition is synchronized or gated to portions of the cardiac cycle.

Update on Echocardiography of Coronary Sinus Anatomy and Physiology

Abstract: The coronary sinus (CS) can be imaged echocardiographically as a small tubular sonolucency in the posterior atrioventricular groove. To date, its importance to echocardiographers has been that CS dilatation usually signifies a persistent left superior vena cava. Recently, we developed a technique to image CS caliber over the duration of the cardiac cycle. CS contraction accompanies the P wave on the electrocardiogram, in sinus rhythm or in various arrhythmias. CS contraction is always absent in atrial fibrillation. In sinus rhythm, CS contraction may be attenuated or absent if congestive heart failure, with marked venous congestion, is present. Thus, this attenuation is a potentially valuable echocardiographic sign of elevated central venous pressure. We demonstrate the echo visualization of CS-related structures, such as tributary veins and the Thebesian valve. The potentially useful concept of the CS as a "miniventricle" is discussed. CS blood flow can be recorded by interrogation in the right heart inflow view. The pattern of CS antegrade flow and the exceptional situation of retrograde systolic CS flow from a posteriorly directed tricuspid regurgitant jet are demonstrated.

[Spatial and temporal resolution with 16-slice computed tomography for cardiac imaging].

Abstract: The use of the CT scanner for cardiac imaging is mainly influenced by the spatial and temporal resolution that can be achieved with the applied technologies and procedures. The data acquisition with 16 x 0.5 mm scan slice thickness and a special multisegment image reconstruction procedure are a new combination for accurate imaging of the cardiac morphology. A 0.5 mm slice thickness and an overlapping pitch < 0.35 generate an isotropic image voxel of 0.35 x 0.35 x 0.35 mm. The object size of a coronary artery with a diameter of 2.5 mm amounts to a relative spatial blurring factor K (d) of approximately 15 %. The segment reconstruction with 4 segments from 4 consecutive cardiac cycles requires the optimum acquisition time of 50 ms for one frame. The relative exposure factor K (t) with reference to the R-R interval is an appropriate measure to validate the influence of coronary artery movement on the image quality at different heart rates. This relative exposure varies between 10 % and 20 % for a heart rate of 40 to 140 beats per minutes (bpm) and its mean is approximated by a linear trend function with K (t) = 14 %. A constant value in this linear trend function means a constant "blurring" of the imaged coronary arteries, independent of the actual heart rate. Thus, computed tomographic examinations can be carried out for heart rates between 40 and 140 bpm without using beta-blocking medication. Case studies of the 3D reconstruction and curved reformatting of coronary arteries with stents and calcifications show the achievable image quality at different heart rates.

Comparison of permanent left ventricular and biventricular pacing in patients with heart failure and chronic atrial fibrillation: a prospective hemodynamic study.

Abstract: Background: Left ventricular pacing (LVP) and biventricular pacing (BVP) have been proposed as treatments for patients with advanced heart failure complicated by discoordinate contraction due to intraventricular conduction delay. For patients in sinus rhythm, BVP works in part by modulating the electronic atrial-ventricular time delay and thus optimizing contractile synchrony, the contribution of atrial systole, and reducing mitral regurgitation. However, little is known of the mechanisms of BVP in heart failure patients with drug-resistant chronic atrial fibrillation. Hypothesis and Methods: LVP differs from BVP because hemodynamic and clinical improvement occurs in association with prolongation rather than shortening of the QRS duration. We sought to determine if LVP or BVP improves mechanical synchronization in the presence of atrial fibrillation. Thirteen patients with chronic atrial fibrillation, severe heart failure and QRS ≥140 ms received (after His bundle ablation) a pacemaker providing both LVP and BVP. The mean age was 62 ± 6 years and left ventricular ejection fraction was 24 ± 8%. After a baseline phase of one month with right ventricular pacing, all patients underwent in random order 2 phases of 2 months (LVP and BVP). At the end of each phase, an echocardiogram, a hemodynamic analysis at rest and during a 6-minute walking test and a cardio-pulmonary exercise test were performed. Results: LVP and BVP provided similar performances at rest (p = ns). The 6-minute walking test revealed similar performances in both pacing modes but patients were significantly more symptomatic at the end of the test with LVP (p = 0.035). The cardio-pulmonary exercise test showed higher performances with BVP (92 ± 34 Watts) vs. LVP (77 ± 23; p = 0.03). LVP was associated with significantly more premature ventricular complexes recorded during the 6 minute walking test (49 ± 71) than BVP (10 ± 23; p = 0.04). Conclusions: In this small series of patients with atrial fibrillation, congestive heart failure and a prolonged QRS duration, LVP and BVP provided similar hemodynamic effects at rest whereas BVP was associated with better hemodyamic effects during exercise and fewer premature ventricular complexes. Although the mechanisms for the observed differences are uncertain, it is possible that there is worsening of right ventricular function due to a rise in left-to-right electromechanical delay during exercise. Increased catecholamines release might contribute to the lower exercise tolerance and greater number of premature ventricular complexes recorded during exercise observed during LVP compared to BVP. Recommendations: Patients with atrial fibrillation, heart failure and QRS prolongation who are candidates for His-bundle ablation and cardiac resynchronization therapy may respond better to BVP rather than to LVP.

Analysis and processing of laser Doppler perfusion monitoring signals recorded from the beating heart.

Abstract: Laser Doppler perfusion monitoring (LDPM) can be used for monitoring myocardial perfusion in the non-beating heart. However, the movement of the beating heart generates large artifacts. Therefore the aim of the study was to develop an LDPM system capable of correlating the laser Doppler signals to the cardiac cycle and to process the signals to reduce the movement artifacts. Measurements were performed on three calves, both on the normal beating heart and during occlusion of the left anterior descending coronary artery (LAD). The recorded LDPM signals were digitally processed and correlated to the sampled ECG. Large variations in the output (perfusion) and DC signals during the cardiac cycle were found, with average coefficients of variation of 0.36 and 0.14 (n = 14), respectively. However, sections with a relatively low, stable output signal were found in late diastole, where the movement of the heart is at a minimum. Occlusion of the LAD showed the importance of recording the laser Doppler signals at an appropriate point in the cardiac cycle, in this case late systole, to minimise movement artifacts. It is possible to further reduce movement artifacts by increasing the lower cutoff frequency when calculating the output signal.

Inflow effect in first-pass cardiac and renal MRI

Abstract: Purpose To estimate the effect of the inflow effect on the arterial input function in vivo in cardiac and renal MR perfusion imaging using fast gradient echo (GRE) sequences and contrast media. Materials and Methods The MR exam protocol was designed to acquire images at different phases of the cardiac cycle. The arterial input was thus influenced by various blood flow velocities. Results It was found that the inflow effect was negligible in the left ventricle of the heart, while it was significantly higher in the aorta for the kidney perfusion measurement. This was principally due to the higher through-the-plane component of the blood flow velocity in the aorta than in the left ventricle. Conclusion The inflow effect can be neglected in the heart cavity, but should be taken into account in renal perfusion. J. Magn. Reson. Imaging 2003;18:372–376. © 2003 Wiley-Liss, Inc.

Determination of an average hemodynamic index for an active implantable medical device such as cardiac pacemaker, defibrillator, cardiovertor and/or multisite device

Abstract: An active implantable medical device such as a cardiac pacemaker, defibrillator, cardiovertor and/or multisite device that is able to determine and average a hemodynamic index parameter. The intracardiac impedance signal is correlated to the instantaneous blood flow, and is used to determine periodically an average hemodynamic index (D ave ) evaluated over several cardiac cycles under certain preset measurement conditions. For example, the preset conditions include checking that the state of the patient and of the device satisfies, the criteria (stages 12 - 20 ) defining predetermined measurement conditions, and inhibiting the determination of the aforesaid hemodynamic index if these criteria are not satisfied. A plurality of samples (Z ij ) of the measured impedance signal are collected over a length of time (T i ) of the systole of one cardiac cycle. Using the aforesaid samples, a value (D i ) representative of the blood volume ejected throughout this systole is determined by integrating the samples over the time period. Then, average hemodynamic index (D ave ) is calculated from a plurality of such integrated sample values successively determined over a plurality (N 2 ) of cardiac cycles.

Normal patterns of flow in the superior caval, hepatic and pulmonary veins as measured using Doppler echocardiography during childhood.

Abstract: To date, no reference values have been provided for right and left atrial filling in normal children The aim of our study, therefore, was to characterize measurements of superior caval, hepatic, and pulmonary venous flow using Doppler echocardiography in a large group of normal children to reflect the effects of age, body mass index, sex, heart rate and respiration Doppler echocardiographic examinations of the superior caval, hepatic and pulmonary veins were performed during inspiration and expiration in 72 healthy children with a mean age of 673 +/- 510 years The subjects were segregated into four age groups, namely infants 005) Except for the systolic pulmonary venous velocities, these parameters were not influenced by respiration (p > 005) The diastolic time, the interval between reverse atrial flow and ventricular systole reflected by the R wave on the electrocardiogram, and the interval between ventricular systole and diastolic flow, were negatively correlated with heart rate (p < 005; r = -035, -085, and -08 respectively), and positively correlated with age (p < 005; r = 03, 08, and 07 respectively) They were not influenced by respiration Our study provides data of the patterns and the normal ranges of velocities of superior caval, hepatic, and pulmonary venous flow in a series of normal children The results can now be used for comparison with the patterns found in the setting of disease

Is left ventricular postsystolic long-axis shortening a marker for severity of hypertensive heart disease?

Abstract: The complex myocardial fiber architecture of the left ventricle (LV) enables long-axis motion (annular excursion), short-axis motion and also a small torsional deformation throughout the cardiac cycle. The contribution of the long-axis motion has proven to be important in generating ventricular filling and emptying, and the analysis of annular excursion has become a well established diagnostic tool for the assessment of ventricular function. Cardiac motion can be accurately described with modem non-invasive imaging teclmiques, and this is important ground for deeper understanding and more reliable diagnosis of cardiovascular disease. The focus of this thesis was to provide new insights into cardiac pump function using variables originating from the annular excursion and dynamic changes in shape, applying both established and novel echocardiographic imaging approaches.The traditional method of evaluating systolic ventricular fimction according to the total annular excursion overestimates the excursion amplitude in relation to true systolic fimction. A novel method presented here, measurement of the systolic annular excursion, more accurately reflects the timing of true systole, and was applied both in patients with heart disease and in healthy subjects. To date, the form of asynchronous myocardial motion called postsystolic shortening (PSS) has mainly been observed in the setting of myocardial ischemia. The significance of PSS in hypertensive heart disease remains incompletely described. We found that a subgroup of hypertensive patients with PSS along the LV long-axis had signs of more severe cardiac involvement unrelated to the level of blood pressure. Endurance trained subjects showed a larger LV long-axis motion as compared to strength trained and untrained controls. Mitral annular (MA) excursion correlated strongly to LV stroke volume, end-diastolic volume and maximal oxygen consumption per body weight, but weakly to LV ejection fraction. These findings provide further evidence of the importance of annular excursion to normal cardiac performance. In order to assess the contribution of MA excursion and shape dynamics to total LV volume change in humans, a novel 4-dimensional transesophageal echocardiography teclmique was developed. The excursion of the annulus accounted for an important portion (19±3%) of the total LV filling and emptying in healthy human subjects. Furthermore, our findings elucidate an atrial influence on MA physiology in humans, as well as a sphincter-like action of the MA. These temporal changes may facilitate ventricular filling by annular expansion during early and mid diastole, and aid competent valve closure during the marked decrease in annular area during late diastole and early systole.

Analysis of Four-Dimensional Cardiac Data Sets Using Skeleton-Based Segmentation

Abstract: Computer-aided analysis of four-dimensional tomography data has become an important tool in modern cardiology. In order to examine the capability and health of a patient’s cardiac system, scans are taken at a number of time points evenly distributed over one cardiac cycle. A key task for understanding the dynamics involved within a recorded cardiac cycle is to segment the acquired data to identify objects of interest in each volume of the sequence. This paper presents an algorithm to segment the heart muscle and the left ventricle from a sequence of cardiac CT images using only a minimum of user interaction. Furthermore, the paper introduces methods to process the segmentation result for extraction of important properties of the cardiac cycle, which are helpful for diagnosis.