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Showing papers on "Cardiac cycle published in 1999"


Journal ArticleDOI
TL;DR: The rest period for coronary arteries in the cardiac cycle varies substantially from patient to patient, which may cause quality to be inconsistent in current coronary MR angiography.
Abstract: PURPOSE: To measure the duration of the rest period in the cardiac cycle, a parameter vital to data acquisition in coronary magnetic resonance (MR) angiography. MATERIALS AND METHODS: Motion of coronary arteries was measured in 13 patients by using breath-hold, biplane, conventional angiography, with frontal and lateral projections of the left and right coronary arteries acquired at 30 frames per second. The time courses of the coordinates of bifurcations of proximal parts of the coronary arteries were measured, from which the rest period (motion < 1 mm in orthogonal axes), velocity, displacement range, motion correlation, and reproducibility from heartbeat to heartbeat were estimated. RESULTS: Both the motion pattern and the amplitude varied substantially from patient to patient. The rest period varied from 66 to 333 msec (mean, 161 msec) for the left coronary artery and from 66 to 200 msec (mean, 120 msec) for the right coronary artery. CONCLUSION: The rest period for coronary arteries in the cardiac cy...

286 citations


Journal ArticleDOI
TL;DR: Aortic valve repair techniques or methods of replacement using unstented autograft, allograft or xenograft tissue valves that best preserve this normal pattern of aortic root dynamics should translate into a lower risk of long-term cusp deterioration.
Abstract: Background —Current surgical methods for treating aortic valve and aortic root pathology vary widely, and the basis for selecting one repair or replacement alternative over another continues to evolve. More precise knowledge of the interaction between normal aortic root dynamics and aortic valve mechanics may clarify the implications of various surgical procedures on long-term valve function and durability. Methods and Results —To investigate the role of aortic root dynamics on valve function, we studied the deformation modes of the left, right, and noncoronary aortic root regions during isovolumic contraction, ejection, isovolumic relaxation, and diastole. Radiopaque markers were implanted at the top of the 3 commissures (sinotubular ridge) and at the annular base of the 3 sinuses in 6 adult sheep. After a 1-week recovery, ECG and left ventricular and aortic pressures were recorded in conscious, sedated animals, and the 3D marker coordinates were computed from biplane videofluorograms (60 Hz). Left ventricular preload, contractility, and afterload were independently manipulated to assess the effects of changing hemodynamics on aortic root 3D dynamic deformation. The ovine aortic root undergoes complex, asymmetric deformations during the various phases of the cardiac cycle, including aortoventricular and sinotubular junction strain and aortic root elongation, compression, shear, and torsional deformation. These deformations were not homogeneous among the left, right, and noncoronary regions. Furthermore, changes in left ventricular volume, pressure, and contractility affected the degree of deformation in a nonuniform manner in the 3 regions studied, and these effects varied during isovolumic contraction, ejection, isovolumic relaxation, and diastole. Conclusions —These complex 3D aortic root deformations probably minimize aortic cusp stresses by creating optimal cusp loading conditions and minimizing transvalvular turbulence. Aortic valve repair techniques or methods of replacement using unstented autograft, allograft, or xenograft tissue valves that best preserve this normal pattern of aortic root dynamics should translate into a lower risk of long-term cusp deterioration.

198 citations


Journal ArticleDOI
TL;DR: The proposed method provides flow measurements with correction for through‐plane motion perpendicular to the aortic root between the valvular annulus and the coronary ostia throughout the cardiac cycle.
Abstract: A method for magnetic resonance cine velocity mapping through heart valves with adaptation of both slice offset and angulation according to the motion of the valvular plane of the heart is presented. By means of a subtractive labeling technique, basal myocardial markers are obtained and automatically extracted for quantification of heart motion at the valvular level. The captured excursion of the basal plane is used to calculate the slice offset and angulation of each required time frame for cine velocity mapping. Through-plane velocity offsets are corrected by subtracting velocities introduced by basal plane motion from the measured velocities. For evaluation of the method, flow measurements downstream from the aortic valve were performed both with and without slice adaptation in 11 healthy volunteers and in four patients with aortic regurgitation. Maximum through-plane motion at the aortic root level as calculated from the labeled markers averaged 8.9 mm in the volunteers and 6.5 mm in the patients. The left coronary root was visible in 2–4 (mean: 2.2) time frames during early diastole when imaging with a spatially fixed slice. Time frames obtained with slice adaptation did not contain the coronary roots. Motion correction increased the apparent regurgitant volume by 5.7 ± 0.4 ml for patients with clinical aortic regurgitation, for an increase of approximately 50%. The proposed method provides flow measurements with correction for through-plane motion perpendicular to the aortic root between the valvular annulus and the coronary ostia throughout the cardiac cycle. Magn Reson Med 42:970–978, 1999. © 1999 Wiley-Liss, Inc.

143 citations


Journal ArticleDOI
TL;DR: It is concluded that the 3D mathematical cardiac torso (MCAT) phantom can be used to study the influence of various physical parameters on radionuclide perfusion imaging.
Abstract: This manuscript documents the alteration of the heart model of the three-dimensional (3D) mathematical cardiac torso (MCAT) phantom to represent cardiac motion. The objective of the inclusion of motion was to develop a digital simulation of the heart such that the impact of cardiac motion on single-photon emission computed tomography(SPECT)imaging could be assessed and methods of quantitating cardiac function could be investigated. The motion of the gated 3D MCAT's (gMCAT) heart is modeled using 128 separate and evenly spaced time samples from a blood volume curve approximating an average heart cycle. Sets of adjacent time samples can be grouped together to represent a single time interval within the heart cycle. Maximum and minimum chamber volumes were selected to be similar to those of a normal healthy person while the total heart volume stayed constant during the cardiac cycle. Myocardial mass was conserved during the cardiac cycle and the bases of the ventricles were modeled as moving towards the static apex. The orientation of the 3D MCAT heart was changed during contraction to rotate back and forth around the long axis through the center of the left ventricle (LV) using the end systolic time interval as the time point at which to reverse direction. Simple respiratory motion was also introduced by changing the orientation of the long axis of the heart to represent its variation with respiration.Heart models for 24 such orientations spanning the range of motion during the respiratory cycle were averaged together for each time sample to represent the blurring of the heart during the acquisition of multiple cardiac cycles. Finally, an option to model apical thinning of the myocardium was included. As an illustration of the application of the gMCAT phantom, the gated heart model was evaluated by measuring myocardial wall thickening. A linear relationship was obtained between maximum myocardial counts and myocardial thickness, similar to published results. Similar results were obtained for full width at half maximum (FWHM) measurements. With the presence of apical thinning, an apparent increase in counts in the apical region compared to the other heart walls in the absence of attenuation compensation turns into an apparent decrease in counts with attenuation compensation. The apical decrease was more prominent in end systole (ES) than end diastole (ED) due to the change in the partial volume effect. These observations agree with clinical trends. It is concluded that the gMCAT phantom can be used to study the influence of various physical parameters on radionuclide perfusion imaging.

105 citations


Patent
28 Sep 1999
TL;DR: In this paper, adaptive filtering techniques were used to drive a closed loop therapy system responsive to those physiologic conditions discernible from good cardiac cycle electrocardiogram (ECG) signals.
Abstract: In using electrogram signals to determine physiologic conditions like ischemia, the bad cardiac cycle information due to noise, axis shifts in the cardiac electrical axis, and the like must be removed if the electrogram signal can be made to be a good indicator. If this is accomplished through the adaptive filtering techniques shown here, the signal can be used to drive a closed loop therapy system responsive to those physiologic conditions discernible from good cardiac cycle electrocardiogram signals.

102 citations


Journal ArticleDOI
TL;DR: It is established that longitudinal movement of IVUS transducers within coronary vessels occurs during the cardiac cycle, and IVUS images are best obtained with electrocardiographic gating.

89 citations


Journal ArticleDOI
TL;DR: Fetal cardiac and hemodynamic development in the first trimester of pregnancy is described to describe fetal cardiac and blood flow during pregnancy.
Abstract: Objective To describe fetal cardiac and hemodynamic development in the first trimester of pregnancy. Subjects and methods Forty-eight pregnancies were prospectively studied with transvaginal ultrasound and color Doppler. Fetal heart rate and size were documented together with the presence of inflow and outflow waveforms and valve signals. Results Heart rate and size showed a positive correlation with gestational age. At 6 weeks of gestation, 20% of the cardiac cycle was occupied by the isovolumic contraction time (ICT); the isovolumic relaxation time (IRT) occupied 16% and remained unchanged, while the ICT progressively shortened and was not measurable after 12 weeks. The peak inflow velocities had changed from monophasic to biphasic by 10 weeks of gestation. At 7 weeks of gestation, semilunar valves were detected in 10% of examinations and the atrioventricular valves in 3%. The detection rate for both valves at 12 weeks was ≥ 90%. In pregnancies that miscarried, the detection rate for both was < 25%. Conclusions The Doppler signals that characterize the heart during the first trimester suggest effective heart compliance by 12 weeks. Normal valve development can be inferred from non-invasive Doppler recordings.

73 citations


Journal ArticleDOI
TL;DR: Regular aerobic exercise training appears to enhance left ventricular diastolic function and may benefit patients with clinically relevant "diastolic dysfunction," and some of the involved putative mechanisms are reviewed.
Abstract: There are several important links between aerobic exercise performance and the diastolic phase of the cardiac cycle. During acute exercise, diastolic function must be augmented in order for left ventricular filling to match increased left ventricular output, i.e., cardiac output. This challenges the myocardium because the shortened duration of diastole during exercise may compromise left ventricular filling, thereby limiting the stroke volume. Additionally, left ventricular filling must be accomplished at relatively low filling pressures, otherwise pulmonary vascular congestion may occur. Left ventricular diastolic function may be impaired in the elderly and/or in individuals with ischemic coronary syndromes. Regular aerobic exercise training appears to enhance left ventricular diastolic function and may benefit patients with clinically relevant "diastolic dysfunction." The purpose of this paper is to discuss the relative importance between diastole and exercise and to review some of the involved putative mechanisms.

61 citations


Patent
05 Aug 1999
TL;DR: In this paper, an implanting atrial cardioverter is described for delivering therapy to atria of a human heart if an atrial tachyarrhythmia is present.
Abstract: There is disclosed an implanting atrial cardioverter (30) for delivering therapy to atria of a human heart if an atrial tachyarrhythmia is present. The cardioverter includes a first sense channel (35) for sensing atrial heart activity within the right atrium of the heart for providing an atrial electrogram having a plurality of cardiac cycles, and a second sense channel (34) for sensing ventricular activity of the heart to provide a ventricular electrogram. The cardioverter further includes an atrial tachyarrhythmia detector including a detection window stage responsive to at least the ventricular electrogram to identify for each cardiac cycle of the atrial electrogram, a detection window period free of any heart activity other than spontaneous atrial heart activity, an A wave detector (65) for identifying A waves occurring during each detection window period means for determining atrial cycle lengths between the identified A waves, and a decision stage responsive to the determined atrial cycle lengths for determining if an atrial tachyarrythmia is present. A cardioverting stage delivers therapy to the atria if an atrial tachyarrythmia is present.

60 citations


Patent
15 Sep 1999
TL;DR: In this paper, the pacemaker determines atrial capture threshold by generating atrial stimulation pulses while maintaining the ventricular stimulation pulse amplitude at a level known to ensure ventricular capture.
Abstract: A pacemaker programmer and diagnostic system retrieves information stored within a pacemaker and analyzes the retrieved data in real time. The stored information can be retrieved by means of a telemetry communication link. The pacemaker automatically lengthens a post-ventricular atrial refractory period (PVARP). The pacemaker determines atrial capture threshold by generating atrial stimulation pulses while maintaining the ventricular stimulation pulse amplitude at a level known to ensure ventricular capture, and by detecting loss of atrial capture. In response to loss of atrial capture, a processor automatically triggers a premature ventricular contraction (PVC) response to prevent a retrograde P-wave from initiating a pacemaker-mediated tachycardia. Also in response to loss of atrial capture, the processor sets the atrial stimulation pulse amplitude to a value above the atrial capture threshold in a subsequent cardiac cycle, and restores the PVARP to its pre-test value.

53 citations


Journal ArticleDOI
TL;DR: Athletes, compared with those leading a sedentary lifestyle, have higher early diastolic performance, which is less affected by the physiologic aging process.
Abstract: Myocardial velocity gradient (MVG) derived from Doppler myocardial imaging and standard echocardiographic parameters were used to investigate whether age-related left ventricular (LV) functional and/or structural changes are different in long-term training athletes than in those leading a sedentary life style. Eighty-nine athletes (64 men, mean age 38 years, range 18 to 64) and 105 age-matched sedentary normal subjects were enrolled into the study. The MVG was analyzed in all patients throughout the cardiac cycle, and peak values were measured in systole and in diastole during both rapid ventricular filling and atrial contraction. No differences were found in LV systolic and late diastolic function between athletes and sedentary normal subjects. However, athletes had higher peak E waves in early diastole (73 ± 10 cm/s vs 68 ± 10 cm/s, p −1 vs 7.2 ± 2.8 s −1 , p

Journal ArticleDOI
TL;DR: Tissue Doppler echocardiography (TDE) is available in most modern cardiac ultrasound imaging systems and can be used to obtain regional myocardial velocities during isovolumic relaxation, early filling, and atrial systole with high spatial and temporal resolution.
Abstract: Doppler indices of left ventricular (LV) filling have been used traditionally for the assessment of LV diastolic function. In many circumstances, however, the interpretation of these indices is difficult because they respond to alterations of different physiological variables such as preload, relaxation, and heart rate. A typical example of their limitation is seen in patients with abnormal LV relaxation and increased preload compensation, who often present a "pseudonormal" LV filling pattern. Thus, there is a need for noninvasive indices of diastolic function capable of discriminating the effects of relaxation and preload. Tissue Doppler echocardiography (TDE) is available in most modern cardiac ultrasound imaging systems. TDE can be used to obtain regional myocardial velocities during isovolumic relaxation, early filling, and atrial systole with high spatial and temporal resolution. This article discusses the complementary role, limitations, and future challenges of TDE in the study of diastolic function.

Journal ArticleDOI
TL;DR: A four-dimensional (x,y,z,t) composite superquadric-based object model of the human heart for Monte Carlo simulation of radiological imaging systems has been developed and no phantom discretization artifacts are involved.
Abstract: A four-dimensional (x,y,z,t) composite superquadric-based object model of the human heart for Monte Carlo simulation of radiological imaging systems has been developed. The phantom models the real temporal geometric conditions of a beating heart for frame rates up to 32 per cardiac cycle. Phantom objects are described by boolean combinations of superquadric ellipsoid sections. Moving spherical coordinate systems are chosen to model wall movement whereby points of the ventricle and atria walls are assumed to move towards a moving center-of-gravity point. Due to the non-static coordinate systems, the atrial/ventricular valve plane of the mathematical heart phantom moves up and down along the left ventricular long axis resulting in reciprocal emptying and filling of atria and ventricles. Compared to the base movement, the epicardial apex as well as the superior atria area are almost fixed in space. Since geometric parameters of the objects are directly applied on intersection calculations of the photon ray with object boundaries during Monte Carlo simulation, no phantom discretization artifacts are involved.

Journal ArticleDOI
TL;DR: This work investigated the blood flow through the ATS bileaflet valve during forward flow, with particular attention to the leaflet pivot regions, and found recirculating regions were found both within and downstream of the valve housing ring.
Abstract: Bileaflet heart valves are currently the most commonly implanted type of mechanical prosthetic valve, because of their low transvalvular pressure drop, centralised flow and durability. However, in common with all mechanical heart valves, implanted bileaflet valves show an inherent tendency for blood clot formation at the valve site. Fluid dynamical phenomena associated with blood clotting are elevated blood shear stresses and regions of persistent blood recirculation, particularly when both occur together. Using three-dimensional CFD modelling, combined with enlarged scale experimental modelling, we investigated the blood flow through the ATS bileaflet valve during forward flow, with particular attention to the leaflet pivot regions. Recirculating regions were found both within and downstream of the valve housing ring. Qualitative assessment of the entire cardiac cycle suggested that recirculating blood within the housing ring will be washed away whilst the valve is closed, but as with all bileaflet valve designs recirculating blood downstream of the valve may have a residence time much longer than one cardiac cycle.

Journal ArticleDOI
TL;DR: Coronary sinus narrowing occurs consistently during atrial contraction, but is always absent in atrial fibrillation; in patients with congestive heart failure and systemic venous congestion, this narrowing is significantly attenuated.
Abstract: M-mode echography of the coronary sinus in the apical 2-chamber view enabled us to measure coronary sinus caliber at specific phases of the cardiac cycle. Coronary sinus narrowing occurs consistently during atrial contraction, but is always absent in atrial fibrillation; in patients with congestive heart failure and systemic venous congestion, this narrowing is significantly attenuated.

Journal ArticleDOI
TL;DR: Left atrial filling volume and pulmonary vein flow give a reliable estimate of regurgitant volume in mitral regurgitation.

Journal ArticleDOI
TL;DR: The dynamic effect of left vagal stimulation on atrioventricular conduction was studied in six isofluorane-anesthetized dogs and the total effect was virtually over by 800–1000 ms.
Abstract: The dynamic effect of left vagal stimulation on atrioventricular conduction was studied in six isofluorane-anesthetized dogs ranging in weight from 22 to 29 kg. The cervical vagus nerve trunks were left intact and no beta-adrenergic blockade was produced so that any influences of the sympathetic nervous system and autonomic reflex activity could be observed. Atrial pacing was used to control the heart rate while single, short trains of left vagal stimulation were delivered and timed to occur at different instants during the cardiac cycle. The magnitude of the A—V delay depended on the instant of delivery of the train of vagal stimuli during the cardiac cycle. Vagal effect curves were constructed and fit to a mathematical equation which describes the pharmacokinetic behavior of a bolus injection of a drug whose onset time is of the same order as its half-life. The three parameters of this equation have physiologic significance and are related to nerve propagation time and synaptic delay, acetylcholine concentration rise, and the acetylcholineesterase mechanism. The maximum A—V delay occurred when the short train of left vagal stimuli was applied 200–300 ms after the atrial pacing stimulus and the total effect was virtually over by 800–1000 ms. © 1999 Biomedical Engineering Society.

Patent
05 Apr 1999
TL;DR: In this paper, a new ventricular assist device is provided, which enables the native heart to eject blood with very low ejection resistance and ensures sufficient ventricular relaxation and filling. But this device is not suitable for use in the case of stroke patients.
Abstract: A ventricular assist device 10 includes a blood conduit 14, which carries the blood ejected from the ventricle to the ventricular assist device, a one-way valve 22, which is provided in the blood conduit and can open only toward the ventricular assist device, an afterload-controlling chamber 11, which temporarily stores the blood ejected from the ventricle, a pressure sensor 23, which measures the pressure in the afterload-controlling chamber, a blood pump 25 and a control unit 26 thereof, a blood conduit 16 that carries the blood to an artery, and a probe 27 for measuring blood flow rate and a flowmeter 28, which control the flow rate of the blood pump 25. The pressure of the afterload-controlling chamber 11 is controlled so as to keep the one-way valve closed during ventricular diastole, and also controlled so as to direct all the blood ejected from the ventricle into the afterload-controlling chamber 11 during ventricular systole. Therefore, a new ventricular assist device can be provided, which enables the native heart to eject blood with very low ejection resistance and ensures sufficient ventricular relaxation and filling.

Proceedings ArticleDOI
21 May 1999
TL;DR: Good image quality can be obtained even during systole with temporal resolution which even exceeds that provided by an Electron Beam Scanner in standard mode of operation, and freezing motion of the coronary arteries during enddiastole allows high quality 3D display of coronary anatomy.
Abstract: Functional cardiac imaging with 3rd generation CT scanners is challenging, because the temporal resolution seems to be limited to approximately 2/3 of the rotation time of the gantry. We propose a new method for high temporal resolution volume heart imaging with multirow detectors based on a retrospective electrocardiogram-gated rebinning procedure. The limited time resolution is overcome using time consistent projection data retrieved from more than one cardiac cycle. In principle the method provides volume heart imaging with adjustable time resolution at arbitrary cardiac phases. It can be applied both for spiral and axial scan imaging. The presented study is based on computer simulations incorporating a model of the human heart taking into account anatomy, motion and heart rate variability. For multirow detectors we were able to show that good image quality can be obtained even during systole with temporal resolution which even exceeds that provided by an Electron Beam Scanner in standard mode of operation. Using an area detector with detector height > 3 cm (center of rotation) the total measurement time is within one breathhold for complete volume imaging of the heart. Furthermore, freezing motion of the coronary arteries during enddiastole allows high quality 3D display of coronary anatomy.

Book ChapterDOI
01 Jan 1999
TL;DR: In this paper, the development of the vertebrate cardiac building plan encompasses the necessity of forming the cardiac conduction system, which involves the proper formation and arrangement of myocardial building blocks within the tubular heart that displays posteroanterior polarity of pacemaker activity.
Abstract: Publisher Summary To understand the development of the conduction system, one must first consider the anatomical arrangement of structures that are responsible for the coordinated contraction of the formed heart from apex to base. In the formed mammalian heart, the conduction system and working myocardium are generally considered as two separate entities. This is difficult to reconcile with the embryonic heart, in which no distinctive conduction system is present and yet coordinated contraction of atria and ventricles is achieved. Moreover, the mammalian condition has been overemphasized compared to that of lower vertebrates, in which a well-defined cardiac conduction system is also lacking, similar to the mammalian embryonic heart, and yet proper cardiac contraction is realized. The discussion presents that the formation of the vertebrate cardiac building plan encompasses the necessity of forming the cardiac conduction system. It involves the proper formation and arrangement of myocardial building blocks within the tubular heart that displays posteroanterior polarity of pacemaker activity. The myocardial building blocks represent disparate cardiomyocyte populations with distinct functional and transcriptional qualities. They allow for the sequential activation of atria and ventricles and for the activation of the ventricles from apex to base, irrespective of whether a histologically distinct conduction system is present (mammals) or not (lower vertebrates). How these building blocks are specified and remodeled, what the nature is of the interactions that occur between surrounding myocardialand nonmyocardial cells, and how some primary myocardial cells differentiate into nodal tissue instead of working myocardium is largely unknown.

Journal ArticleDOI
TL;DR: The measurements of Aw at the LVPW and MA can be used to noninvasively evaluate the hemodynamic relationship between the LA and LV during atrial systole in patients with LV failure.
Abstract: The objective of the present study was to evaluate the hemodynamic relationship between the left atrium (LA) and left ventricle (LV) during atrial systole in the presence of an elevated left ventricular end-diastolic pressure (LVEDP) and LV failure using pulsed tissue Doppler imaging (TDI). Fifty-three patients with LV systolic dysfunction and no regional LV asynergy were divided into 3 groups: relaxation failure group (RF, n=20) with a ratio of peak early diastolic to atrial systolic velocity of the transmitral flow (E/A) ≤ 1; pseudonormalization group (PN, n=19) with 1 < E/A < 2; and restrictive group (RS, n=14) with E/A ≥ 2. In addition, 20 normal patients (E/A ≥ 1) were studied as a control group. The transmitral and pulmonary venous flow velocities were recorded by transesophageal pulsed Doppler echocardiography. The wall motion velocity patterns were recorded at the middle portion of the LV posterior wall (LVPW) and at the mitral annulus (MA) of the LVPW site in the apical LV long-axis view by transthoracic pulsed TDI. The LVEDP was significantly greater in the PN and RS groups than in the RF and control groups. The mean pulmonary capillary wedge pressure was greatest in the RS group. The percent fractional change of the LA area during atrial systole determined by 2-dimensional echocardiography was significantly lower in the RS group than in the PN group. The peak atrial systolic pulmonary venous flow velocity was significantly greater in the PN group than in the RS group. The peak atrial systolic motion velocity (Aw) at the LVPW was significantly lower in the PN and RS groups than in the RF and control groups. The Aw at the MA was significantly lower in the RS group than in the other groups. There was no significant difference in Aw between the LVPW and MA in the RS group, whereas Aw at the MA was significantly greater than that at the LVPW in the PN group. In conclusion, the measurements of Aw at the LVPW and MA can be used to noninvasively evaluate the hemodynamic relationship between the LA and LV during atrial systole in patients with LV failure. (Jpn Circ J 1999; 63: 763 - 769)

Journal ArticleDOI
TL;DR: In eight elderly human subjects with atrial fibrillation, breathing spontaneously during general anaesthesia, data support a model of cardioventilatory coupling in which a heart beat triggers the onset of inspiration, rather than modulation of cardiac timing by ventilation or a phase relationship between the two systems.
Abstract: Cardioventilatory coupling is an entrainment phenomena, distinct from respiratory sinus arrhythmia, whereby heart and breathing rhythms show temporal coherence. Coupling is commonly observed during rest, sleep and anaesthesia. Five graphical methods, each with different underlying mechanistic assumptions, have been suggested for studying this entrainment relationship: (a) time relationship between inspiration and a preceding heart beat, (b) time relationship between inspiration and a following heart beat, (c) phase of the cardiac cycle at which inspiration occurs, (d) phases of the ventilatory cycle at which heart beats occur and (e) 'relative phases' over multiple ventilatory cycles at which heart beats occur. In eight elderly human subjects with atrial fibrillation, breathing spontaneously during general anaesthesia, we recorded heart period and ventilatory time series and compared each of the graphical methods used for demonstration of coupling. We observed cardioventilatory coupling in seven of eight subjects. In each of these seven subjects, coupling was best described, both qualitatively and quantitatively, in terms of the relationship between inspiration and a preceding heart beat. The variation of the interval between inspiration and a preceding heart beat was less than for any other phase or time relationship. These data support a model of cardioventilatory coupling in which a heart beat triggers the onset of inspiration, rather than modulation of cardiac timing by ventilation or a phase relationship between the two systems.

Journal Article
TL;DR: Doppler echocardiography is a simple, noninvasive and safe technique that can be used for measurement of diastolic filling and, therefore, for assessment of diastsolic function.
Abstract: Introduction Clinical studies have shown that approximately 40% of patients with congestive heart failure have predominantly diastolic left ventricular dysfunction. Doppler echocardiography is a simple, noninvasive and safe technique that can be used for measurement of diastolic filling and, therefore for assessment of diastolic function. Physiology of diastole Diastole is divided into four phases: isovolumetric relaxation, rapid filling, slow filling (diastasis) and atrial contraction. Diastolic filling can be defined as the period from the onset of mitral valve opening to mitral valve closure. Determinants of diastolic filling The two major determinants of diastolic filling are ventricular relaxation (characterized by the rate and duration of the decrease of left ventricular pressure after systole) and compliance (defined by volume changes over the change in pressure during diastolic filling). Normal transmitral flow pattern When pulsed Doppler sample volume is placed at the tips of mitral leaflets, recorded transmitral velocity pattern is composed of two principal deflections: the E wave, occurring during the rapid filling phase, and the lower A wave, arising from atrial contraction. These two waves are usually separated with relatively low velocity signal during diastasis. Numerous indices derived from this pattern have been proposed as markers of diastolic function (peak and integrated velocities of the E and A waves, their ratio, and acceleration and deceleration times of the E wave). However, it should be noted that these indices, in fact, measure diastolic filling, rather than function. Even in healthy individuals, numerous factors may have impact on transmitral flow pattern, including age, heart rate, loading conditions and filling pressures. Normal pulmonary venous flow pattern Analysis of pulmonary venous flow pattern (obtained by pulsed Doppler sample volume placed in pulmonary vein) gives additional information and may help in the assessment of left ventricular filling. Usually, three distinct velocity waves can be observed: S wave, occurring during ventricular systole; 1) wave, diastolic wave that begins after mitral wave opening: and finally, AR wave, reversal velocity during atrial contraction. When diastolic filling is altered, typically there is an inverse relationship between transmitral E and pulmonary venous S wave, as well as transmitral A and pulmonary venous D wave. Pathologic filling patterns There are three different pathologic filling patterns: 1) delayed (prolonged, impaired) relaxation pattern, characterized by prolonged isovolumetric relaxation time and deceleration time, low E and high A wave velocities with an E/A wave ratio typically 1; 2) restrictive pattern, associated with shortened isovolumetric relaxation time, increased peak E wave velocity with very short deceleration time, and small (or even absent) A wave, leading to an E/A wave ratio 2; and 3) pseudonormal pattern, usually an intermediate stage between delayed relaxation and restrictive filling, as a consequence of disease progression; it may be unmasked by Valsalva maneuver and is characteristically associated with atrial dilatation and prominent pulmonary venous AR reversal. Clinical applications Impaired diastolic function is frequently the first detectable abnormality in many of cardiac diseases. With serial recordings, changing of filling patterns, from delayed relaxation, through pseudonormalization, and, finally, to restrictive filling pattern can be observed. These changes have been demonstrated to correspond well with progression of cardiac diseases. According to the severity of symptoms and transmitral filling pattern, four-grade model of diastolic dysfunction has been proposed. It has been shown that the E/A ratio 2 and deceleration time 150 ms indicate poor prognosis in patients with dilated cardiomyopathy, cardiac amyloidosis and old myocardial infarction, independently of the severity of systolic dysfunction. (ABS

Journal ArticleDOI
TL;DR: The results showed the presence of a neuronal circuit that modulates the cardiac pacemaker activity depending on the timing of muscle contraction in the cardiac cycle.
Abstract: The influence of cardiac phase on the response of the cardiac pacemaker to dynamic hand contraction in eight healthy young men was studied to determine whether heart rate response to muscle contraction varied as a function of timing within the cardiac cycle. Changes in R-R interval (RRI) in response to muscle contraction were measured at various cardiac phases during heartbeat-synchronized handgrip at a rate of one contraction per two heartbeats. To extract the direct effect of the muscle contraction on the RRI, spontaneous slow variations and respiratory sinus arrhythmia were removed from the total RRI fluctuations in the frequency domain. Cross-correlograms between the extracted RRI fluctuations and muscle contraction showed that the coupling was strong when the muscle contraction occurred at the middle phase of the cardiac cycle. Muscle contraction at the systolic phase of the cardiac cycle had a tendency to produce a phase advance (shortening of RRI), whereas muscle contraction at the middle phase or later had a tendency to produce a phase delay (prolongation of RRI). The results showed the presence of a neuronal circuit that modulates the cardiac pacemaker activity depending on the timing of muscle contraction in the cardiac cycle.

Journal ArticleDOI
TL;DR: Both MVG assessment procedures enabled objective interpretation of dobutamine effects on left ventricular wall motion and the time-velocity plot method provided automatic detection of peak velocity, timing, and duration of wall velocity changes over time.
Abstract: Myocardial velocity gradient (MVG) has been shown to be the best quantitative parameter for the detection of ischemic myocardium during dobutamine infusion with the use of Doppler myocardial imaging. MVG has been previously assessed by velocity measurements across the thickness of the myocardium at the time of visually selected maximal color brightness (thickness-velocity plot method). We hypothesized that MVG could be assessed by velocity measurements throughout the cardiac cycle in the subendocardium parallel to the endocardial boundary to the left ventricular cavity and in the subepicardium parallel to the epicardial boundary (time-velocity plot method). This study was designed to compare MVG obtained from the thickness-velocity plot method and from the time-velocity plot method in quantifying dobutamine-induced changes in myocardial wall motion in 8 phases of the cardiac cycle on color M-mode Doppler myocardial imaging recordings of the left ventricular posterior wall performed in 8 conscious dogs at baseline and at steady state during dobutamine infusion (10 microg/kg per minute). For both methods, MVG was considered present if its mean value was significantly different from zero and if endocardial and epicardial velocities were significantly different. There was close agreement between the 2 methods. MVG was present during the preejection period, systole, rapid ventricular filling, and atrial contraction. Dobutamine induced a significant increase in MVG during the preejection period (from 2.64 +/- 0.83 to 4.05 +/- 0.81 seconds-1 ), systole (from 2.14 +/- 0.59 to 6.08 +/- 2.20 seconds-1 in early systole, from 1.90 +/- 1.06 to 5.31 +/- 2.95 seconds-1 in mid systole, from 1.37 +/- 0.57 to 2.44 +/- 0.53 seconds-1 in end systole), and rapid ventricular filling (from 3.06 +/- 1.12 to 7.82 +/- 2.58 seconds-1 ), related to a greater rise in endocardial than in epicardial velocities. The time-velocity plot method showed that ejection and diastole were 11% and 28% decreased during dobutamine infusion, respectively, as heart rate was 31% increased. Thus according to our quantitative criteria, both MVG assessment procedures enabled objective interpretation of dobutamine effects on left ventricular wall motion. In addition, the time-velocity plot method provided automatic detection of peak velocity, timing, and duration of wall velocity changes over time.

Journal ArticleDOI
TL;DR: The model successfully characterized both the dynamic changes in the shape of the left ventricle through the cardiac cycle and the pathological alterations resulting from spontaneous hypertension.
Abstract: This study develops a quantitative analysis and model for the differences in left ventricular dynamics in normal and spontaneously hypertensive rats, as determined using non-invasive magnetic resonance imaging (MRI). We emerge with a characterization of the geometrical changes in the left ventricle resulting from hypertension. In addition, the techniques we have adopted are potentially applicable to the study of other disease models for important human cardiac pathologies. A gradient-echo multislice imaging sequence (echo time 4.3 ms) achieved complete image coverage of the heart at high time resolution (13 ms) through the cardiac cycle. Cardiac anatomy in two age-matched groups of young adult (8 and 12 weeks old) normal Wistar-Kyoto (WKY, n = 8) and spontaneously hypertensive rats (SHR, n = 8) was imaged in synchrony with the electrocardiographic R wave in defined planes both parallel and perpendicular to the principal cardiac axis. The transverse left ventricular image sections were circularly symmetrical; this permitted application of different analytical models for the three-dimensional geometry of the epi- and endocardial borders. An ellipsoidal figure of revolution offered an effective description of the three-dimensional left ventricular geometry throughout the cardiac cycle in both normal WKY and SHR animals. The model successfully characterized both the dynamic changes in the shape of the left ventricle through the cardiac cycle and the pathological alterations resulting from spontaneous hypertension. The elliptical model also formed the basis of a simple stress distribution analysis. Such parametric descriptions thus provided a useful alternative to more complex finite element analyses of cardiac function. The eccentricity of the ventricle was characterized by an ellipticity factor a, where a = 1 for a sphere and a<1 for a prolate ellipsoid. At end systole, the endocardial surface of the left ventricle gave a = 0.43±0.02 and 0.49±0.02 for the WKY and SHR animals respectively (probability, P<0.05). At end diastole, the endocardial surface of the left ventricle gave a = 0.58±0.02 and 0.63±0.02 for the WKY and SHR animals respectively (P<0.05). Such a difference in ventricular shape was a potential adaptation to increased blood pressure. Hypertension thus altered the left ventricular ellipticity to give a more spherical geometry compared with the normal rats.

Journal ArticleDOI
Patrick W. O'Leary1
TL;DR: Atrioventricular valve flow signals must be interpreted in conjunction with the flow patterns seen in the proximal venous system in order to provide a complete Doppler assessment of diastolic function.

Journal ArticleDOI
TL;DR: To establish the nature and gestational age dependency of the pulmonary venous flow velocity pattern into the left atrium relative to systolic and diastolic phases of the cardiac cycle.
Abstract: Objective To establish the nature and gestational age dependency of the pulmonary venous flow velocity pattern into the left atrium relative to systolic and diastolic phases of the cardiac cycle. Design This was a cross-sectional study of Doppler measurements of fetal pulmonary venous inflow velocities, which were correlated with simultaneous recordings of transmitral and aortic flow velocity waveforms based on an equal cardiac cycle length (±5%). Results Successful recordings were obtained in 28 out of 60 (47%) normal singleton pregnancies at 20–36 weeks of gestation. Reproducibility of waveform analysis of the various phases of the cardiac cycle was satisfactory, within-patient variance ranging between 1.7% and 6.5%. A statistically significant increase (p < 0.05) in pulmonary venous time average velocity and velocity integral with advancing gestational age was established. A statistically significant increase (p < 0.05) of the pulmonary flow velocity integral was also found when related to each of the systolic and diastolic segments of the cardiac cycle, with the exception of isovolemic relaxation time. The duration of each of the diastolic and systolic segments of the cardiac cycle, as well as the pulmonary venous velocity integral expressed as a percentage of the cardiac cycle, remained constant with advancing gestational age. Conclusions The second half of pregnancy is characterized by pulmonary venous inflow into the left atrium throughout the cardiac cycle. Pulmonary venous inflow into the left atrium occurs predominantly during the filling and ejection phases of the cardiac cycle. Absolute cardiac diastolic and systolic time intervals as well as the percentage distribution of pulmonary venous flow velocity integrals between these cardiac time intervals remain unchanged with advancing gestational age. Copyright © 1999 International Society of Ultrasound in Obstetrics and Gynecology

Journal ArticleDOI
TL;DR: A reduction of reflection timing, reduces, on a pure mechanical basis, cardiac output and external ventricular work and has a negative effect on coronary driving pressure.

Patent
20 Aug 1999
TL;DR: In this article, a cardiac gated scan of a moving coronary artery using preparatory pulse sequences and two-dimensional EPI (echo planar imaging) pulse sequences was performed. But the coronary artery was not moved.
Abstract: An MRI system performs a cardiac gated scan of a moving coronary artery using preparatory pulse sequences and two-dimensional EPI (echo planar imaging) pulse sequences. The preparatory pulse sequence saturates spin magnetization in regions surrounding a slice which contains the coronary artery at one point in time during each cardiac cycle. The EPI imaging pulse sequence is performed later in the cardiac cycle after the coronary artery has moved and a two-dimensional image is reconstructed by projecting NMR signals from a volume within which the coronary artery moves during the cardiac cycle.