Showing papers on "Cardiac cycle published in 1998"

Non-invasive assessment of the atrial cycle length during atrial fibrillation in man: introducing, validating and illustrating a new ECG method

Abstract: Objectives: Atrial fibrillation (AF) in man has previously been shown to include a wide variety of atrial activity. Assessment of the characteristics of this arrhythmia with a commonly applicable tool may therefore be important in the choice and evaluation of different therapeutic strategies. As the AF cycle length has been shown to correlate locally with atrial refractoriness and globally with the degree of atrial organization, with, in general, shorter cycle length during apparently random AF compared to more organized AF, we have developed a new method for non-invasive assessment of the AF cycle length using the surface and the esophagus (ESO) ECG. Methods and Results: From the frequency spectrum of the residual ECG, created by suppression of the QRST complexes, the dominant atrial cycle length (DACL) was derived. By comparison with multiple intracardiac simultaneously acquired right and left AF cycle lengths in patients with paroxysmal AF, we found that the DACL in lead V1, ranging from 130 to 185 ms, well represented a spatial average of the right AF cycle lengths, whereas the DACL in the ESO ECG, ranging from 140 to 185 ms, reflected both the right and the left AF cycle length, where the influence from each structure depended on the atrial anatomy of the individual, as determined by MRI. In patients with chronic AF, the method was capable of following changes in the AF cycle length due to administration of d,l-sotalol and 5 min of ECG recording was sufficient for the DACL to be reproducible. Conclusions: We conclude that this new non-invasive method, named ‘Frequency Analysis of Fibrillatory ECG’ (FAF-ECG), is capable of assessing both the magnitude and the dynamics of the atrial fibrillation cycle length in man.

Quantification of in-plane motion of the coronary arteries during the cardiac cycle: implications for acquisition window duration for MR flow quantification.

Abstract: Motion of the coronary arteries during the heart cycle can result in image blurring and inaccurate flow quantification by MR. This condition applies particularly for longer acquisition windows that are typical of breath-hold coronary flow measurements. To determine the sensitivity of the technique to in-plane motion of different coronary arteries, the temporal variation in coronary position was measured in a plane perpendicular to the proximal portion of the vessel. The results indicated the presence of substantial displacement of the coronary arteries within the cardiac cycle, with a magnitude of motion approximately twice as large for the right as for the left coronary arteries. An estimation of the resulting vessel blurring was calculated, showing that the duration of the acquisition window for high spatial resolution coronary flow acquisitions should be less than 25 to 120 msec, depending on the specific coronary artery studied. In addition, these data specify optimal acquisition window placement for high resolution coronary angiography.

Method and apparatus for the assessment and display of variability in mechanical activity of the heart, and enhancement of ultrasound contrast imaging by variability analysis

Abstract: This invention is a method of evaluating the mechanical variability of the heart activity by assessment of the variability of cardiologic echo Doppler images, and of enhancing contrast ultrasound imaging by variability imaging of two-dimensional echo images through the application of finite memory, ECG gated or ungated processing of the acquired images. For cardiac imaging and blood perfusion studies of non-cardiac structures, the acquired images are time-gated by the cardiac cycle to account for cardiac deformation due to contraction, relaxing and filling. To compare blood perfusion characteristics in normal tissue and abnormal tissue, a non-gated version, or gating to another physiologic cycle (e.g. breathing) can be used. The gated scans are either recursive processed in real time or are recorded and processed off-line to get estimation of the mean image and the variability of the image. The resulting images of the mean and variance are displayed for user interpretation.

Electromechanical Characterization of Chronic Myocardial Infarction in the Canine Coronary Occlusion Model

Abstract: Background—Defining the presence, extent, and nature of the dysfunctional myocardial tissue remains a cornerstone in diagnostic cardiology. A nonfluoroscopic, catheter-based mapping technique that can spatially associate endocardial mechanical and electrical data was used to quantify electromechanical changes in the canine chronic infarction model. Methods and Results—We mapped the left ventricular (LV) electromechanical regional properties in 11 dogs with chronic infarction (4 weeks after LAD ligation) and 6 controls. By sampling the location of a special catheter throughout the cardiac cycle at multiple endocardial sites and simultaneously recording local electrograms from the catheter tip, the dynamic 3-dimensional electromechanical map of the LV was reconstructed. Average endocardial local shortening (LS, measured at end systole and normalized to end diastole) and intracardiac bipolar electrogram amplitude were quantified at 13 LV regions. Endocardial LS was significantly lower at the infarcted area (...

Assessment of left-ventricular function.

Abstract: There are three distinct phases of the cardiac cycle (contraction, active relaxation, and passive relaxation) which should be examined in order to perform a thorough assessment of global left-ventricular function. Accurate measurements of left-ventricular pressure and volume are necessary to assess these phases of the cardiac cycle. The ideal index of contractility is sensitive to the intropic state of the heart, but insensitive to loading conditions, heart rate, and cardiac size. Indices of contractility may be derived from various aspects of the phase of contraction including isovolumic contraction, the end-systolic pressure-volume relationship, the phase of ejection, and the stress-strain relationship. The indices of contractility most commonly employed and arguably closest to 'ideal' are preload recruitable stroke work, an ejection phase index; the dP/dt - end-diastolic volume relationship, an isovolumic contraction phase index; and end-systolic elastance, an index derived from the end-systolic pressure-volume relationship. The active phase of relaxation is most commonly assessed by the time constant (tau) of the exponential ventricular pressure decline that occurs during the isovolumic period of relaxation. The value for tau varies inversely with ventricular function and reflects the active, energy consuming process of relaxation. tau is influenced by many of the same factors which influence contractility. The end-diastolic pressure-volume relationship reflects the passive properties of the left ventricle and may be used to obtain a measure of diastolic stiffness. The end-diastolic pressure-volume relationship is curvilinear (exponential) when end-diastolic pressures are varied over a wide range, but may be approximated by a linear relationship during low filling pressures. Diastolic stiffness is influenced by the viscoelastic properties of the heart, pericardial constraint, the atrioventricular pressure gradient, and ventricular interaction. Knowledge of the indices of the three phases of the cardiac cycle and their interactions are important to the understanding and interpretation of ventricular function in health and disease.

Evaluation of left ventricular diastolic function from the pattern of left ventricular filling

Abstract: The pattern of left ventricular (LV) filling can be determined by Doppler echocardiography. Normally most LV filling occurs early in diastole, with some additional filling occurring during atrial systole, late in diastole. In the absence of mitral stenosis, three patterns of LV filling indicate progressively greater diastolic dysfunction: (1) Reduced early diastolic filling with a compensatory increase in importance of atrial filling, termed a pattern of "impaired relaxation;" (2) "pseudo-normalization" with most filling early in diastole but with rapid deceleration of mitral flow; and (3) "restricted filling" with almost all filling of the LV occurring very early in diastole in association with very rapid deceleration of mitral flow. A large, prolonged atrial regurgitant flow in the pulmonary veins also indicates impaired diastolic performance. The time for early filling deceleration is predominantly determined by LV stiffness: the shorter the deceleration time, the stiffer the LV. Patients with short deceleration time have a poor prognosis.

Spiral scanning computed tomography apparatus, and method for operating same, for cardiac imaging

Abstract: In a computed tomography apparatus, and a method for operating same, for obtaining cardiac images, a spiral scan of a measurement volume containing a patient's heart is conducted, the production of the scanning data during the spiral scanning being synchronized with an ECG signal from the patient, in order to produce a graphic representation of the examination volume, and thus an image of the patient's heart. The ECG signal is employed to control the generation of the data during the spiral scanning at phase of the cardiac cycle wherein minimum movement of the heart takes place. The chronological correlation between the recording of the scanning data and the ECG signal is fixed, so that within each number of successive time intervals, a dataset is obtained completely within that time interval. The datasets from the successive time intervals are then combined to produce an image of the heart. Since the component images are all obtained in a low-motion phase of the heart, the resulting overall image is particularly sharp.

Cardiovascular effects of propofol in dogs with dilated cardiomyopathy.

Abstract: Background The authors tested the hypothesis that propofol improves left ventricular diastolic function in dogs with dilated cardiomyopathy by reducing left ventricular preload and afterload. Methods Seven dogs were instrumented for left ventricular and aortic pressures, aortic blood flow, and subendocardial segment length. Left ventricular afterload and contractility were quantified with aortic input impedance and preload recruitable stroke work, respectively. Diastolic function was evaluated with a time constant of left ventricular relaxation (tau); segment-lengthening velocities and time-velocity integrals during early left ventricular filling (dL/dtE and TVI-E, respectively) and atrial systole (dL/dtA and TVI-A, respectively); and a regional chamber stiffness constant (K). Dogs were paced at 240 beats/min for 18 +/- 3 days, and hemodynamics were recorded in sinus rhythm in the conscious state. Anesthesia was induced with propofol (5 mg/kg) and maintained with propofol infusions at 25, 50, and 100 mg [center dot] kg sup -1 [center dot] h sup -1, and hemodynamics were recorded after 15 min of equilibration at each dose. Results Propofol decreased mean arterial pressure, left ventricular end-diastolic pressure, and K but did not change heart rate. Propofol reduced total arterial resistance and increased total arterial compliance derived from aortic input impedance. Propofol also reduced preload recruitable stroke work. The lowest dose of propofol decreased tau. Propofol decreased dL/dtE and TVI-E and reduced the dL/dt-E/A and TVI-E/A ratios. Conclusions Propofol reduces left ventricular preload, afterload, and regional chamber stiffness, causes direct negative inotropic effects, and impairs early-diastolic left ventricular filling in dogs with dilated cardiomyopathy.

Magnetic resonance imaging analysis of left ventricular function in normal and spontaneously hypertensive rats

Abstract: * 1 We have used magnetic resonance imaging (MRI) to examine acute morphological changes in the left ventricle throughout the cardiac cycle in normal Wistar Kyoto rats (WKY) and also to follow the development of chronic changes in spontaneously hypertensive rats (SHR). This involved the development of MRI and quantitative analysis techniques for characterizing contractile changes during the cardiac cycle. * 2 Images of the cardiac anatomy in two age groups (8 and 12 weeks old) of young anaesthetized adult normal WKY and SHR were acquired in planes both parallel and perpendicular to the principal cardiac axis. * 3 Complete coverage of the heart by imaging planes was achieved with high time resolution (13 ms), with typically 12 time frames in the cardiac cycle, using a short echo time (5 ms) multislice gradient-echo imaging sequence. Imaging was synchronized to the R wave of the electrocardiogram. * 4 The image slices could be reconstructed into complete geometrically and temporally coherent three-dimensional data sets. Left ventricular (LV) volumes were thus reconstructed throughout the cardiac cycle by combining transverse cardiac image sections. This volume analysis revealed structural and functional differences between the normal WKY and SHR in both age groups of 8 and 12 weeks. Measurements from the cardiac images were additionally validated against histological measurements. * 5 The SHR showed a raised LV end-systolic volume and a correspondingly poorer ejection fraction as well as LV hypertrophy when compared with the controls. Left ventricular function in the SHR appeared stable between the two age groups. * 6 We developed a simple geometrical model of the left ventricle based on a single longitudinal image section and successfully used this to describe some functional parameters of the left ventricle in the WKY and SHR. This geometrical model has the potential to greatly reduce the imaging time needed to study the beating heart in future serial investigations of cardiac physiology in rats. * 7 Our experimental and analytical methods together form a powerful set of quantitative techniques which combine both imaging and functional analysis and will be applicable for future studies of chronic physiological changes in animal disease models.

Echocardiographic and Hemodynamic Determinations of the Ventricular Filling Pattern in Some Teleost Fishes

Abstract: The current concept of ventricular filling in elasmobranch and teleost fishes is that atrial contraction is the primary, if not the exclusive, determinant of ventricular filling. Recent echocardiographic and on-line hemodynamic data for elasmobranchs, however, have demonstrated a biphasic ventricular filling pattern, characterized by an early phase that occurs during ventricular relaxation and a late phase that follows atrial systole. This study reports echocardiographic and hemodynamic analyses of ventricular filling in three teleost genera (Paralabrax, Channa, Monopterus) having markedly different heart morphologies. Both the profiles of the atrioventricular pressure gradient in Paralabrax and the ventricular inflow velocity in all three genera indicate a biphasic ventricular filling pattern. Although the relative contribution of the early and late filling phases differed among the species studied, interspecific differences in heart structure did not obscure the biphasic pattern. Also, pericardiectomy did not affect the biphasic ventricular filling pattern in Paralabrax. The presence of biphasic filling in teleosts establishes a functional similarity with the elasmobranchs and, because the biphasic ventricular filling pattern predominates in higher vertebrates, suggests that this ventricular filling mechanism may be present in the entire subphylum Vertebrata.

Induction of ventricular collapse by an axial flow blood pump.

Abstract: An important consideration for clinical application of rotary blood pump based ventricular assist is the avoidance of ventricular collapse due to excessive operating speed. Because healthy animals do not typically demonstrate this phenomenon, it is difficult to evaluate control algorithms for avoiding suction in vivo. An acute hemodynamic study was thus conducted to determine the conditions under which suction could be induced. A 70 kg calf was implanted with an axial flow assist device (Nimbus/UoP IVAS; Nimbus Inc., Rancho Cordova, CA) cannulated from the left ventricular apex to ascending aorta. On initiation of pump operation, several vasoactive interventions were performed to alter preload, afterload, and contractility of the left ventricle. Initially, dobutamine increased contractility and heart rate ([HR] = 139; baseline = 70), but ventricular collapse was not achievable, even at the maximal pump speed of 15,000 rpm. Norepinephrine decreased HR (HR = 60), increased contractility, and increased systemic vascular resistance ([SVR] = 24; baseline = 15), resulting in ventricular collapse at a pump speed of 14,000 rpm. Isoproterenol (beta agonist) increased HR (HR = 103) and decreased SVR (SVR = 12), but ventricular collapse was not achieved. Inferior vena cava occlusion reduced preload, and ventricular collapse was achieved at speeds as low as 11,000 rpm. Esmolol (beta1 antagonist) decreased HR (HR = 55) and contractility, and ventricular collapse was achieved at 11,500 rpm. Episodes of ventricular collapse were characterized initially by the pump output exceeding the venous return and the aortic valve remaining closed throughout the cardiac cycle. If continued, the mitral valve would remain open throughout the cardiac cycle. Using these unique states of the mitral and aortic valves, the onset of ventricular collapse could reliably be identified. It is hoped that the ability to detect the onset of ventricular collapse, rather than the event itself, will assist in the development and the evaluation of control algorithms for rotary ventricular assist devices.

Normal Three-Dimensional Pulmonary Artery Flow Determined by Phase Contrast Magnetic Resonance Imaging

Abstract: In this study, an application was developed to measure three-dimensional blood flow in the main, right, and left pulmonary arteries of seven healthy volunteers using phase contrast magnetic resonance imaging (MRI). Presently, no other noninvasive technique is capable of providing this information. Flow, mean velocity, kinetic energy, and cross-sectional area were measured at multiple phases of the cardiac cycle and were consistent with previously reported values measured with one-dimensional velocity encoded MRI and Doppler echocardiography. Additionally, axial, circumferential, and radial shear stresses near the wall of the vessel at multiple phases of the cardiac cycle were estimated using the in-plane velocities. All three shear stresses were relatively constant along the vessel wall and throughout the cardiac cycle (approximately 7 dyn/cm2). This three-dimensional characterization of normal pulmonary blood flow provides a base line to which effects of altered pulmonary artery flow patterns in disease can be compared. [Morgan, V. L., T. P. Graham, Jr., and C. H. Lorenz. Circulation Suppl. 94:I-417 (abstract), 1996].

Tissue motion in blood velocity estimation and its simulation

Abstract: Determination of blood velocities for color flow mapping systems involves both stationary echo cancelling and velocity estimation. Often the stationary echo cancelling filter is the limiting factor in color flow mapping and the optimization and further development of this filter is crucial to the improvement of color flow imaging. Optimization based on in-vivo data is difficult since the blood and tissue signals cannot be accurately distinguished and the correct extend of the vessel under investigation is often unknown. This study introduces a model for the simulation of blood velocity data in which tissue motion is included. Tissue motion from breathing, heart beat, and vessel pulsation were determined based on in-vivo RF-data obtained from 10 healthy volunteers. The measurements were taken at the carotid artery at one condition and in the liver at three conditions. Each measurement was repeated 10 times to cover the whole cardiac cycle and a total of 400 independent RF measurements of 950 pulse echo lines were recorded. The motion of the tissue surrounding the hepatic vein from superficial breathing had a peak velocity of 6.2/spl plusmn/3.4 mm/s over the cardiac cycle, when averaged over the 10 volunteers. The motion due to the heart, when the volunteer was asked to hold his breath, gave a peak velocity of 4.2/spl plusmn/1.7 mm/s. The movement of the carotid artery wall due to changing blood pressure had a peak velocity of 8.9/spl plusmn/3.7 mm/s over the cardiac cycle. The variations are due to differences in heart rhythm, breathing, and anatomy. All three of these motions are handled independently by the simulation program, which also includes a parametric model for the pulsatile velocity in the elastic vessel. The model can be used for optimizing both color flow mapping and spectral display systems.

Coronary artery counterpulsation device and method

Abstract: A device and method are shown for improving coronary blood circulation and cardiac contractile function, synchronizing coronary perfusion pressure with the patient's cardiac cycle, by alternately pressurizing and depressurizing an inflatable balloon located within the interior of the device. The device comprises a catheter having a distal end which is installed at the ostium of the coronary artery of a patient. The device is alternately pressurized during the relaxation phase of a patient's cardiac cycle and then depressurized during the contraction phase of the cardiac cycle to thereby modulate the coronary perfusion pressure and blood flow.

Biventricular Long Axis Function After Repair of Tetralogy of Fallot

Abstract: Right ventricular restrictive physiology is common after repair of tetralogy of Fallot and relates to exercise performance and symptomatic arrhythmias. In this study, we examined biventricular long axis function in an attempt to clarify further the mechanical substrate of this phenomenon. We studied prospectively 95 patients with tetralogy of Fallot (age range 1–44.3 years) at a median of 4.3 years after repair with Doppler and M-mode echocardiography. Pulmonary arterial, tricuspid, and mitral Doppler spectrals and 2-D guided M-mode recordings of ventricular minor and long axes were obtained with simultaneous phonocardiogram and respirometer recordings. Right ventricular restriction was defined by the presence of antegrade pulmonary arterial flow during atrial systole throughout the respiratory cycle. Restrictive right ventricular physiology was demonstrated in 36 (39%) [group 1] of the 92 patients in whom the data were analyzed. Left ventricular function (FS, isovolumic relaxation time and transmitral E wave deceleration time) was not different in the two groups (p < 0.1, p < 0.6, and p < 0.8, respectively). The presence of antegrade diastolic flow shortened the pulmonary regurgitation in the restrictive group (PR duration/√RR 10.7 ± 2.1 vs 12.1 ± 2.1, p < 0.01). There was delayed onset of shortening (97.4 ± 24 vs 88.8 ± 24 ms, p= 0.01), and the amplitude of right atrioventricular ring excursion, corrected for body surface area, was significantly lower during atrial systole in the restrictive group (0.43 ± 0.15 vs 0.54 ± 0.2 cm/m2, p < 0.01). There was also a tendency toward a smaller ratio of right to left total atrioventricular ring excursion in the same group (1.14 ± 0.19 vs 1.22 ± 0.23, p= 0.1). Impaired long axis function in patients with restrictive right ventricular physiology following repair of tetralogy of Fallot is associated with abnormal diastolic filling and may contribute to the long-term cardioprotective effect of restrictive physiology by limiting the degree of right ventricular dilatation.

Left ventricular diastolic dysfunction: pathophysiology, diagnosis and treatment

Abstract: The prevalence of left ventricular diastolic dysfunction increased mass) is present or not. This geometrical is increasing, and diagnosis and treatment are not easy. shape is found in cases of pressure overload of the LV, Heart failure with normal systolic function (a wording the latter being secondary to systemic hypertension, preferable to ‘heart failure by diastolic dysfunction’) aortic stenosis or more often only as a consequence of mainly aVects elderly or hypertensive patients. Its the decreased distensibility of the whole arterial tree incidence varies greatly with age. 70% in those aged greater than 80. interdependence, when the LV is compressed by enlarged right cavities or major pericardial eVusion within a poorly distensible pericardium. Finally, the Pathophysiology LV muscle itself can be stiVened by ischaemia, infiltration by amyloid or iron deposits, or oedema (in case Left ventricular filling during diastole is a crucial phase of amyloidosis, haemochromatosis or rejection after of the cardiac cycle, which determines cardiac output cardiac transplantation, respectively). In all these situations, the dual consequence of diastolic and filling pressure. It comprises three steps: (i) rapid

Relationship between left atrial function and plasma level of atrial natriuretic peptide in patients with heart disease.

Abstract: To investigate the relationship between left atrial function and secretion of atrial natriuretic peptide (ANP), we analyzed left ventricular inflow and pulmonary venous flow, left atrial dynamics, intracardiac pressures, and plasma ANP level in 92 patients with various cardiac diseases. From the apical four-chamber view, maximal left atrial volume and percent fractional change of the left atrial area during atrial systole (LA-%AC) were calculated. The ratio of peak early filling velocity to peak atrial systolic velocity (E/A) in the left ventricular inflow and the ratio of peak systolic velocity to peak diastolic velocity (S/D) in the pulmonary venous flow were measured with the pulsed Doppler method. A significant linear correlation was found between plasma ANP levels and pulmonary capillary wedge pressure. Significant linear correlations were also found between left ventricular end-diastolic pressure and both maximal left atrial volume and LA-%AC. Plasma ANP level was significantly correlated with maximal left atrial volume, LA-%AC, E/A, and S/D. A multivariate analysis revealed that only LA-%AC was significantly correlated with the plasma ANP level. These results suggest that left atrial systolic dysfunction associated with a left atrial afterload mismatch is closely related to the ANP secretion.

Noninvasive detection of coronary artery disease based on heart sounds

Abstract: In this study, four channel heart sounds of normal persons and patients with coronary artery disease (CAD) were detected by a highly sensitive sound sensor array placed in special positions on the thorax. The acquired signals were analyzed using wavelet transform and neural networks. The wavelet transform is a highly applicable method to separate complicated heart sounds into various frequency segments and can also give time localization of the event in the cardiac cycle. Each and every channel's four average power ratios of whole cycle heart sound to diastolic period heart sound at four frequency segments based on WT coefficients were calculated. The sixteen power ratios of four channels decomposed into sixteen parameters input pattern of radial basis function (RBF) neural networks. After training, the neural networks can diagnose the CAD automatically.

Cross-Sectional Deformation of the Aorta as Measured With Magnetic Resonance Imaging

Abstract: Vessel geometry is commonly accepted as one of the primary factors influencing blood flow patterns. The vessels near the heart present a particular challenge because myocardial contraction creates dynamic changes in vessel geometry due to the movement created by the contraction of the myocardial muscle. The importance of vessel movement and deformation on blood flow patterns in the coronary arteries has been previously demonstrated. For larger vessels such as the aorta, the effects are less well understood, partially because no estimates of the dynamic variations in vessel cross section shape geometry have been reported. This study was undertaken to provide an estimate of the amount of dynamic variation in cross-sectional shape present in the aorta. Two young healthy male subjects were used, with measurements taken in the ascending aorta, aortic arch, and descending thoracic aorta using Magnetic Resonance Imaging (MRI). The magnitude of elliptical deformation was measured throughout the cardiac cycle by taking a discrete Fourier transform of the radius versus angle plot. Deformations of more than 7 percent of the mean vessel radius were noted. This level of deformation may be enough to influence flow patterns in the aorta significantly, and thus should be included in future flow studies.

Application of Pulsed‐Doppler Tissue Imaging in Patients with Dual Chamber Pacing: The Importance of Conduction Time and AV Delay on Regional Left Ventricular Wall Dynamics

Abstract: UNLABELLED Pulsed-Doppler tissue imaging (pDTI) is able to measure myocardial wall velocities (systolic: S; early diastolic: E; late diastolic: A) and their timings. Relationships have been demonstrated between the pre-ejection period and indexes of left ventricular systolic function. This study was designed to examine with pDTI the effects of variations in atrioventricular delay (AVD) (100 ms, 150 ms, 200 ms) on myocardial dynamics and on their timings at the basal interventricular septum (IVS) from an apical approach and at the posterior wall (PW) from the parasternal view. These data were compared with stroke volume measurements recorded from the left ventricular outflow tract. Seventeen patients with dual chamber pacemakers (7 because of complete heart block, 10 with sick sinus syndrome and first-degree AV block) were studied; full atrial and ventricular capture was present at any AVD. These data were also compared with those obtained in 10 age-matched healthy volunteers with comparable heart rates. RESULTS Optimal atrial contribution to left ventricular filling and, consequently, best systolic performance were achieved when AVD was programmed such that a mean interval of 77 ms was allowed between the end of the A wave and the beginning of the S wave, similar to what was measured in the healthy control group by pDTI. CONCLUSION The noninvasive measurement of timings of the cardiac cycle by pDTI is helpful to determine the optimal AVD in individual patients.

Heart rate control of blood pressure variability in children: a study in subjects with fixed ventricular pacemaker rhythm.

Abstract: 1. To investigate the influence of heart rate variability on blood pressure variability, short-term variability in heart rate and blood pressure was studied in 10 children with fixed ventricular pacemaker rhythm (80 beats/min). Ten healthy children, in sinus rhythm, served as a reference population. 2. Arterial blood pressure and heart rate were measured continuously using a finger arterial device and an ECG respectively. Power spectra for heart rate and blood pressure (systolic and diastolic) were calculated in both supine and orthostatic positions. In addition, acute changes in blood pressure and heart rate during active standing were studied. 3. Healthy children exhibited considerable heart rate variability, which was slightly more pronounced in the supine position, while children with a fixed ventricular rate had no heart rate variability in either position. 4. Despite the differences in heart rate variability, mean systolic blood pressure and its variability profiles were poorly affected by the suppression of heart rate variability. The lack of autonomic control on the sinus node was associated with a reduction in magnitude of the changes in systolic blood pressure variability induced by orthostatic posture. 5. The suppression of heart rate fluctuations induced a noticeable decrease in diastolic blood pressure fluctuations, which was most conspicuous in the children with fixed cardiac rhythm when in the supine position. This may be explained by the lack of diastolic blood pressure fluctuations, physiologically due to heart rate fluctuations through the run-off effect: the longer the cardiac cycle, the greater the diastolic pressure decay. These results may challenge the classical theory of baroreflex-mediated diastolic blood pressure control described in adult patients. 6. During active standing, the early drop in systolic blood pressure was greater in subjects with fixed ventricular rhythm. A rise in heart rate of 36 beats/min was observed in the healthy subjects in response to active standing. 7. We conclude that in normal children, heart rate fluctuations increase the blood pressure variability rather than buffering it. However, during acute orthostatic stress, the abrupt baroreflex-mediated heart rate rise may partly compensate for the reduction in blood pressure.

Pulmonary Venous Flow in Normal Dogs Recorded by Transthoracic Echocardiography: Techniques, Anatomic Validations and Flow Characteristics

Abstract: To observe pulmonary venous flow in dogs, the echocardiographic imaging planes and the techniques for examination, and the validations of anatomic location were investigated. Then, the velocity pattern of pulmonary venous flow was recorded in normal conscious dogs. Six imaging planes were available for observing the right or left caudal lobe pulmonary venous flow with two-dimensional or pulsed Doppler echocardiography. Of these, the left lateral apical 4-chamber view can be applied as standard view, because the pulmonary venous flow and transmitral flow could be recorded in this view simultaneously with small sampling angle. The velocity pattern of pulmonary venous flow demonstrated two forward waves in 19 of 20 dogs examined, with one peak occurring during ventricular systole and another during ventricular diastole. A reversed flow during atrial contraction was also seen in 11 dogs. In the two forward waves, the mean peak velocity and velocity-time integral of ventricular diastolic forward flow were significantly higher than those of systolic forward flow (46.49 +/- 6.79 vs. 31.13 +/- 4.92 cm/s, p < 0.0001 and 8.18 +/- 1.84 vs. 5.14 +/- 0.82 cm, p < 0.0001, respectively). The deceleration time of diastolic forward flow shortened with the increase of heart rate (r = -0.87, p < 0.0001). Pulmonary venous flow in dogs can be observed under transthoracic two-dimensional or pulsed Doppler echocardiography.

Impairment of contraction increases sensitivity of epicardial lymph pressure for left ventricular pressure

Abstract: In the present study, cardiac contraction was regionally impaired to investigate the relationship between contractility [maximum first time derivative of left ventricular pressure (dPLV/dt max)] an...

Left coronary pressure–flow relations of the beating and arrested rabbit heart at different ventricular volumes

Abstract: Objective: To study the effect of cardiac contraction on left coronary artery pressure–flow relations at different vascular volumes and to compare these relations in the beating heart with those in the heart arrested in systole and diastole. Methods: Maximally vasodilated, Tyrode perfused, rabbit hearts ( n =6) with an intra-ventricular balloon were used. The left coronary artery was separately perfused via a cannula in the left main coronary artery. The slopes and the intercepts of left coronary pressure-flow relations were determined in the beating and arrested heart at different chamber volumes. A 3-factor design with repeated measures was used to compare the effect of three factors: phase of contraction (systole and diastole), chamber volume ( V and V 1, left ventricular end-diastolic pressure 1.4 and 20 mm Hg, respectively) and the type of contraction (beating and arrested; a measure of capacitive effects). Results: The phase of contraction has a significant effect on the intercepts (>40 mmHg, p =0.00032) but not on the slopes of the pressure–flow relations. Chamber volume had a small effect on the intercepts (<5 mm Hg, p =0.037), but not on the slopes of the pressure–flow relations. The type of contraction has a significant effect on the slopes (∼10%, p =0.00021) but not on the intercepts of the pressure–flow relations. Conclusions: In the isolated Tyrode perfused rabbit heart left coronary pressure–flow relations are mainly determined by contraction, while left ventricular chamber volume and capacitive effects contribute little.

First-pass radionuclide angiographic analysis with two regions of interest to improve left ventricular ejection fraction accuracy.

Abstract: UNLABELLED First-pass radionuclide angiographic (FPRNA) analysis, using the standard, single-fixed region of interest (ROI) drawn at end-diastole, often underestimates the left ventricular ejection fraction (LVEF) as determined by other standard techniques. This study examined the hypothesis that correction for the anatomic motion of the aortic valve plane toward the apex during systole, which results in improper inclusion of aortic counts within the single-fixed ROI, using a two-ROI method to compensate for this motion would eliminate this underestimation. METHODS In 70 patients who underwent FPRNA and planar gated equilibrium radionuclide angiography (GERNA) on the same day, Fourier transform phase and amplitude images were used to generate functional maps of the aorta and the left ventricle on the FPRNA representative cycle. The region of low amplitude between the aorta and left ventricle, which corresponds to the degree of aortic valve plane motion, was used to guide the manual placement of two ROIs. The first was over the left ventricle at the end-diastole including the aortic valve plane area, and the second was a smaller end-systolic ROI drawn over the first ROI, excluding the valve plane area. RESULTS Both the fixed- and dual-ROI FPRNA methods had excellent correlation with GERNA (r = 0.92 and 0.91, respectively). The mean FPRNA LVEF using a fixed ROI (45% +/- 14%) was significantly lower than GERNA (51% +/- 15%, p < 0.001), but the mean LVEF calculated from the dual-ROI (51% +/- 14%) was essentially identical to those obtained with GERNA. The method of manual placement of the two ROIs had extremely high levels of inter- and intraobserver reproducibility (r = 0.98 and 0.99, respectively). CONCLUSION Despite good correlation, the standard, fixed-ROI method of FPRNA analysis systematically underestimates the LVEFs of GERNA. This problem can be eliminated by taking into account valve plane motion during the cardiac cycle by using Fourier-guided, dual-ROI analysis on FPRNA. These differences in methods and results should be considered when substituting or comparing LVEFs derived from these techniques.

Acquisition of segmented MRI cardiac data using an EPI pulse sequence

Abstract: A method is disclosed to reconstruct multiphase MR images that accurately depict the entire cardiac cycle. A segmented, echo-planar imaging (EPI) pulse sequence is used to acquire data continuously during each cardiac cycle. Images are retrospectively reconstructed by selecting views from each heartbeat based on cardiac phase.

Contribution of Synchronized Atrial Systole to Left Ventricular Contraction in the Newborn Pig Heart

Abstract: Synchronized atrial contraction may be much more important in the newborn, who has a faster heart rate and a less compliant ventricle, than in the adult. We therefore investigated the extent by which synchronized atrioventricular contraction contributes to cardiac output and cardiac work in a neonatal circulation, and whether this effect can be fully explained by the Starling mechanism. In neonatal piglets, left ventricular pressure and volume (conductance catheter) were measured during atrial and ventricular pacing. By manipulating preload during atrial pacing, end-systolic pressure and volume, stroke work, and dP/dtmax were compared at the same end-diastolic volume as indices of contractility. Finally, end-diastolic pressure-volume relationships were assessed to investigate the validity of using end-diastolic pressure as an indicator of preload. We found a significant contribution of synchronized atrial contraction; cardiac output increased 27% when pacing mode was switched form ventricular to atrial. The mechanism by which this was achieved is entirely the enhancement of ventricular filling and thus the Starling effect; contractility was unaffected by pacing mode. This large and important effect can be explained by slowed relaxation (compared with the adult ventricle), which impairs passive filling during the ventricular relaxation phase, and makes active filling during atrial contraction more important. In addition, we found that the use of end-diastolic pressure as an indicator of preload, instead of end-diastolic volume, leads to serious misinterpretations, due to not only the nonlinearity of this relationship, but also the possible shifts in this relationship with certain interventions.