Showing papers on "Cardiac cycle published in 2007"

Arrhythmogenic Ion-Channel Remodeling in the Heart: Heart Failure, Myocardial Infarction, and Atrial Fibrillation

Abstract: Rhythmic and effective cardiac contraction depends on appropriately timed generation and spread of cardiac electrical activity. The basic cellular unit of such activity is the action potential, whi...

Heart valve macro- and microstructure

Abstract: Each heart valve is composed of different structures of which each one has its own histological profile. Although the aortic and the pulmonary valves as well as the mitral and the tricuspid valves show similarities in their architecture, they are individually designed to ensure optimal function with regard to their role in the cardiac cycle. In this article, we systematically describe the structural elements of the four heart valves by different anatomical, light- and electron-microscopic techniques that have been presented. Without the demand of completeness, we describe main structural features that are in our opinion of importance in understanding heart valve performance. These features will also have important implications in the treatment of heart valve disease. They will increase the knowledge in the design of valve substitutes or partial substitutes and may participate to improve reconstructive techniques. In addition, understanding heart valve macro- and microstructure may also be of benefit in heart valve engineering techniques.

ECG-gated, mechanical and electromechanical wave imaging of cardiovascular tissues in vivo.

Abstract: In simplistic terms, the motion of the heart can be summarized as an active contraction and passive relaxation of the myocardium However, the local motion of cardiovascular tissues over the course of an entire cardiac cycle results from various transient events such as the valves closing/opening, sudden changes in blood pressure and electrical conduction of the myocardium The transient motion generated by most of these events occurs within a very short time (on the order of 1 ms) and cannot be imaged correctly with conventional imaging systems, due to their limited temporal resolution In this paper, we propose a method for imaging this rapid transient motion of tissues in cardiovascular applications Our method is based on imaging tissues with ultrasound at high frame rates (up to 8000 fps) by synchronizing the two-dimensional (2D) image acquisition on the electrocardiogram (ECG) signals In vivo feasibility is demonstrated in anesthetized mice The propagation of several transient mechanical waves was imaged in different regions of the myocardium and the wave phase velocities were found to be between 044 m/s and 5 m/s These waves may be generated by either a purely mechanical effects or through electromechanical coupling in the myocardium depending on the phase of the cardiac cycle, in which they occur The abdominal aorta was also imaged using the same technique and the propagation of a mechanical pulse wave was imaged The pulse wave velocity was measured and the Young's modulus of the vessel wall was derived based on the Moens-Korteweg equation This method could potentially be used for mapping the stiffness of the myocardium and the artery walls and may lead to the early diagnosis of cardiovascular diseases

Wearable Seismocardiography

Abstract: Seismocardiogram (SCG) is the recording of body vibrations induced by the heart beat. SCG contains information on cardiac mechanics, in particular heart sounds and cardiac output. In this paper we present a new wearable device for SCG recordings during long term monitorings, and the results of a validation test in 4 subjects. The system is based on the integration of the MagIC smart shirt (i.e., a textile-based wearable system for the assessment of ECG and respiratory movements), and an external triaxial MEMS accelerometer positioned on the left clavicle. SCG was estimated as the average of accelerations occurred in each heart beat. The SCG components due to the valve closure and to recoil forces following the heart contraction (ballistocardiogram) were extracted by high-pass (>18 Hz) and band-pass (0.6-20 Hz) filters respectively. Then the difference between the I and J waves of the ballistocardiogram ( lI-Jl index, possibly related to the cardiac output) was identified by an ad-hoc procedure and compared with the model flow indirect estimation of cardiac output. Validation on 4 volunteers showed that: 1) our wearable system provides statistically consistent estimates of both heart- sound related vibrations and recoil movements; 2) reliable estimates of the II-Jl index can be obtained by considering about 1 minute of SCG recording in stationary conditions; and 3) changes of the II-Jl index during exercise correlate well with changes of cardiac output estimated by the model flow.

Comparison between prospective and retrospective triggering for mouse cardiac MRI.

Abstract: High-resolution magnetic resonance imaging (MRI) has evolved into one of the major non-invasive tools to study the healthy and diseased mouse heart. This study presents a Cartesian CINE MRI protocol based on a fast low-angle shot sequence with a navigator echo to generate cardiac triggering and respiratory gating signals retrospectively, making the use of ECG leads and respiratory motion sensors obsolete. MRI of the in vivo mouse heart using this sequence resulted in CINE images with no detectable cardiac and respiratory motion artefacts. The retrospective method allows for steady-state imaging of the mouse heart, which is essential for quantitative contrast-enhanced MRI studies. A comparison was made between prospective and retrospective methods in terms of the signal-to-noise ratio and the contrast-to-noise ratio between blood and myocardial wall, as well as global cardiac functional indices: end-diastolic volume, end-systolic volume, stroke volume and ejection fraction. The retrospective method resulted in almost constant left-ventricle wall signal intensity throughout the cardiac cycle, at the expense of a decrease in the signal-to-noise ratio and the contrast-to-noise ratio between blood and myocardial wall as compared with the prospective method. Prospective and retrospective sequences yielded comparable global cardiac functional indices. The largest mean relative difference found was 8% for the end-systolic volume.

Cancellation of Ventricular Activity in the ECG: Evaluation of Novel and Existing Methods

Abstract: Due to the much higher amplitude of the electrical activity of the ventricles in the surface electrocardiogram (ECG), its cancellation is crucial for the analysis and characterization of atrial fibrillation. In this paper, two different methods are proposed for this cancellation. The first one is an average beat subtraction type of method. Two sets of templates are created: one set for the ventricular depolarization waves and one for the ventricular repolarization waves. Next, spatial optimization (rotation and amplitude scaling) is applied to the QRS templates. The second method is a single beat method that cancels the ventricular involvement in each cardiac cycle in an independent manner. The estimation and cancellation of the ventricular repolarization is based on the concept of dominant T and U waves. Subsequently, the atrial activities during the ventricular depolarization intervals are estimated by a weighted sum of sinusoids observed in the cleaned up segments. ECG signals generated by a biophysical model as well as clinical ECG signals are used to evaluate the performance of the proposed methods in comparison to two standard ABS-based methods

Synchronization of vagus nerve stimulation with the cardiac cycle of a patient

Abstract: Disclosed herein are methods, systems, and apparatus for treating a medical condition of a patient, involving detecting a physiological cycle or cycles of the patient and applying an electrical signal to a portion of the patient's vagus nerve through an electrode at a selected point in the physiological cycle(s). The physiological cycle can be the cardiac and/or respiratory cycle. The selected point can be a point in the cardiac cycle correlated with increased afferent conduction on the vagus nerve, such as a point from about 10 msec to about 800 msec after an R-wave of the patient's ECG, optionally during inspiration by the patient. The selected point can be a point in the cardiac cycle when said applying increases heart rate variability, such as a point from about 10 msec to about 800 msec after an R-wave of the patient's ECG, optionally during expiration by the patient.

Gradually synchronized simultaneous atrial and ventricular pacing for cardiac rhythm discrimination

Abstract: A cardiac medical device used for delivering anti-tachycardia pacing in both the atrial and ventricular regions in a simultaneous manner, while preventing potential of inducing atrial arrhythmia. The pacing pulses may be synchronized in a gradual manner so that simultaneous delivery of the pulses is ultimately achieved at reduced risk of inducing atrial arrhythmia. The pacing pulses may also be synchronized immediately after a determination is made whether simultaneous pacing pulses will be delivered in the vulnerable regions of the cardiac cycle.

Quantifying systolic and diastolic cardiac performance from dynamic impedance waveforms

Abstract: The present invention is related to implantable cardiac devices such as pacemakers and defibrillators that deliver cardiac resynchronization therapy (CRT), and to a method of optimizing acquisition of multi-vector impedance signals from electrodes present on implanted lead systems. Acquired impedance signals associated with dynamic intracardiac impedance are related to specific time frames of the cardiac cycle as to derive indices representative of systolic and diastolic cardiac performance. The impedance signals are further adjusted by non-dynamic or static impedance signals associated with pulmonary impedance as to derive composite indices representative of cardiac performance and pulmonary vascular congestion. The pulmonary impedance signals are preferably obtained during relative periods of apnea in a patient.

Coronary MR angiography at 3T during diastole and systole.

Abstract: A major technical challenge for coronary magnetic resonance angiography (MRA) is cardiac motion (1). Adverse effects of this motion on image quality can be minimized by acquiring images during the most quiescent mid-diastolic period of the cardiac cycle (2– 4) which is typically found in middiastole. This relative motion-free period occurs after relaxation of the ventricles at approximately 75% of the cardiac cycle, and depending on the heart rate, lasts for an average of 187 msec (range 66 –330 msec) (1). Both coronary MRA (2– 4) and computed tomography angiography (CTA) dose modulation (5) protocols are usually set to acquire images or reconstruct images during this period of the cardiac cycle. However, at the end of ventricular systole, (approximately 34% of the cardiac cycle) there is another relatively quiescent period that lasts for approximately 118 msec (range 0 –223 msec) (1). Though both of these periods’ lengths have an inverse relationship with the heart rate (1), the duration of systole is less affected by heart rate variability than that of diastole (6). For example, an increase of 10% in heart rate from 70 to 77 beats per minute (BPM) should shorten diastasis, on average, from 458 msec to 395 msec (63 msec or 14%) but only change systole from 399 msec to 384 msec (15 msec or 4%) (7). Hence, for subjects with high beat-to-beat variability in their RR interval lengths, the temporal position of the middiastolic period may be more variable than that of the end-systolic period. For these reasons, end-systolic imaging may be an alternative to more conventional diastolic imaging as a way to minimize the adverse effects of RR variability. However, the abbreviated systolic rest period necessitates image data collection in a very short acquisition window, which typically prolongs scanning time. In the present study, we used parallel imaging (sensitivity encoding [SENSE]) at 3T to abbreviate the systolic image data acquisition window to 35 msec. The purpose of this study was to investigate the impact of end-systolic imaging on the quality of right coronary MRA in comparison to more conventional diastolic imaging. Simultaneously, the effect of RR variability on image quality was studied for both end-systolic and late diastolic data acquisitions.

Accelerometer-Derived Time Intervals during Various Pacing Modes in Patients with Biventricular Pacemakers : Comparison with Normals

Abstract: Introduction: Changes due to biventricular pacing have been documented by shortening of QRS duration and echocardiography. Compared to normal ventricular activation, the presence of left bundle branch block (LBBB) results in a significant change in cardiac cycle time intervals. Some of these have been used to quantify the underlying cardiac dyssynchrony, assess the effects of biventricular pacing, and guide programming of ventricular pacing devices. This study evaluates a simple noninvasive method using accelerometers attached to the skin to measure cardiac time intervals in biventricularly paced patients. Methods: Ten patients with biventricular pacemakers previously implanted for congestive heart failure were paced in the AAI mode, then in atrioventricular (AV) sequential mode from the right and left ventricles followed by biventricular pacing. Simultaneous recordings were obtained by 2D, Doppler echocardiography as well as by accelerometers. Similar recordings were obtained from 10 gender, aged matched, normal controls during sinus rhythm. Results: Compared to normals, heart failure patients paced in AAI mode had prolonged isovolumetric contraction time (IVCT), shorter ventricular ejection time (LVET), and prolonged isovolumetric relaxation (IVRT). With biventricular pacing the IVCT decreased, but the LVET and IVRT did not change significantly. There was excellent correlation between the echo and accelerometer-measured intervals. Conclusions: Shortening of the IVCT measured by an accelerometer is a consistent time interval change due to biventricular pacing that probably reflects more rapid acceleration of left ventricular ejection. The accelerometer may be useful to assess immediate efficacy of biventricular pacing during device implantation and optimize programmable time intervals such as AV and interventricular (VV) delays. (PACE 2007; 30:1476‐1481)

Doppler study of the embryonic heart in normal pregnant women.

Abstract: Objective To describe normal fetal cardiac and hemodynamic development in normal early first trimester pregnanciesMaterials and methods Eighty-eight women with singleton, uncomplicated pregnancies were prospectively studied with transvaginal ultrasound, pulsed and color Doppler Heart diameter, heart rate, and inflow and outflow waveforms with valve signals were documented The proportion of the cardiac cycle of isovolumetric relaxation time (IRT%) and isovolumetric contraction time (ICT%) as well as Tei index were calculatedResults Ninety-one percent of studies were successful Heart diameter and the fetal heart rate showed a positive correlation with increasing gestational age: R = 080 (p < 0000001), R = 076 (p < 0000001), respectively Mean heart diameter at 6 weeks was 128 ± 026 mm and mean fetal heart rate was 117 ± 6 bpm compared to 388 ± 054 mm and 171 ± 6 bpm at 10 weeks The inflow waveform was monophasic (atrial contraction) in all cases from 6 to 9 weeks Eight pregnancies (9%) mis

A model of blood flow in the mesenteric arterial system.

Abstract: There are some early clinical indicators of cardiac ischemia, most notably a change in a person's electrocardiogram. Less well understood, but potentially just as dangerous, is ischemia that develops in the gastrointestinal system. Such ischemia is difficult to diagnose without angiography (an invasive and time-consuming procedure) mainly due to the highly unspecific nature of the disease. Understanding how perfusion is affected during ischemic conditions can be a useful clinical tool which can help clinicians during the diagnosis process. As a first step towards this final goal, a computational model of the gastrointestinal system has been developed and used to simulate realistic blood flow during normal conditions. An anatomically and biophysically based model of the major mesenteric arteries has been developed to be used to simulate normal blood flows. The computational mesh used for the simulations has been generated using data from the Visible Human project. The 3D Navier-Stokes equations that govern flow within this mesh have been simplified to an efficient 1D scheme. This scheme, together with a constitutive pressure-radius relationship, has been solved numerically for pressure, vessel radius and velocity for the entire mesenteric arterial network. The computational model developed shows close agreement with physiologically realistic geometries other researchers have recorded in vivo. Using this model as a framework, results were analyzed for the four distinct phases of the cardiac cycle – diastole, isovolumic contraction, ejection and isovolumic relaxation. Profiles showing the temporally varying pressure and velocity for a periodic input varying between 10.2 kPa (77 mmHg) and 14.6 kPa (110 mmHg) at the abdominal aorta are presented. An analytical solution has been developed to model blood flow in tapering vessels and when compared with the numerical solution, showed excellent agreement. An anatomically and physiologically realistic computational model of the major mesenteric arteries has been developed for the gastrointestinal system. Using this model, blood flow has been simulated which show physiologically realistic flow profiles.

Cardiac micro-computed tomography for morphological and functional phenotyping of muscle LIM protein null mice.

Abstract: The purpose of this study was to investigate the use of micro-computed tomography (micro-CT) for morphological and functional phenotyping of muscle LIM protein (MLP) null mice and to compare micro-CT with M-mode echocardiography. MLP null mice and controls were imaged using both micro-CT and M-mode echocardiography. For micro-CT, we used a custom-built scanner. Following a single intravenous injection of a blood pool contrast agent (Fenestra VC, ART Advanced Research Technologies, Saint-Laurent, QC) and using a cardiorespiratory gating, we acquired eight phases of the cardiac cycle (every 15 ms) and reconstructed three-dimensional data sets with 94-micron isotropic resolution. Wall thickness and volumetric measurements of the left ventricle were performed, and cardiac function was estimated. Micro-CT and M-mode echocardiography showed both morphological and functional aspects that separate MLP null mice from controls. End-diastolic and -systolic volumes were increased significantly three- and fivefold, respectively, in the MLP null mice versus controls. Ejection fraction was reduced by an average of 32% in MLP null mice. The data analysis shows that two imaging modalities provided different results partly owing to the difference in anesthesia regimens. Other sources of errors for micro-CT are also analyzed. Micro-CT can provide the four-dimensional data (three-dimensional isotropic volumes over time) required for morphological and functional phenotyping in mice.

Automatic Detection of End Systole within a Sequence of Left Ventricular Echocardiographic Images using Autocorrelation and Mitral Valve Motion Detection

Abstract: The automatic detection of end diastole and end systole is the first step of any software developed for a fully automatic calculation of the ejection fraction. In this study, methods of image processing were applied to black and white echocardiographic image sequences corresponding to a cardiac cycle and the end systolic image number was automatically estimated. The first method took the advantage of the rapid mitral valve motion to estimate the end systole from the time signal intensity variation in a cavity region defined thanks to three landmarks usually used for the standard left ventricular segmentation. The second method was fully automatic; it was based on the left ventricular deformation during the cardiac cycle. The deformation curve was estimated using correlation and its minimal value was used to detect end systole. Method 3 was a combination of the two previous methods to overcome their limitations. The three methods were tested on a group of 37 patients (four chambers and two chambers apical views). The first image exhibiting the beginning of the mitral opening was considered as the end systolic on the visual readings. Compared with this visual reference reading, a linear regression led to a correlation coefficient r of 0.84 for the first method. This coefficient was improved to 0.87 for the second method and increased significantly to r= 0.93 for the third method.

Non-invasive visualization of coronary atherosclerosis: state-of-art.

Abstract: Coronary artery disease remains the leading cause of death in the Western world. Non-invasive coronary artery imaging challenges any diagnostic modality because the coronary arteries are small and tortuous, whereas cardiac contraction and respiration cause motion artifacts. Therefore, non-invasive coronary imaging requires high spatial and temporal resolution. This review discusses the feasible applications in coronary imaging of magnetic resonance imaging and multi-slice computed tomography (MSCT), which are currently the only non-invasive diagnostic modalities for direct coronary atherosclerosis imaging. Particular attention and focus is devoted to the potential indications and clinical impact of MSCT due to its fast development and the robust results recently reported. MSCT of the coronary arteries is a promising imaging modality for the assessment of the coronary lumen and wall.

Systems and methods for cardiac contractility analysis

Abstract: A method and system of cardiac contractility analysis is provided. Cardiac contractility may include indices such as ejection fraction (EF) and rate of change in pressure (dP/dt) in a heart. Heart sounds may be measured and calibrated by attenuation. Likewise, a first acoustic peak in the first heart sound (S1), and a second acoustic peak of the second heart sound (S2) may be identified. The first heart sound (S1) may be calibrated by the second heart sound (S2). Amplitudes of calibrated heart sounds may be correlated to cardiac contractility. Electrical activity and acoustics of the heart are measured. The pre-ejection period of the cardiac cycle may be calculated. The left ventricular ejection time of the cardiac cycle may likewise be calculated. Then a ratio of pre-ejection period over left ventricular ejection time may be calculated and correlated to cardiac contractility. Pressure on the acoustic sensor may be used to calibrate acoustic data.

Further information from a sonometric study of the normal tricuspid valve annulus in sheep: geometric changes during the cardiac cycle.

Abstract: BACKGROUND AND AIM OF THE STUDY: In a previous sono-metric study, changes were described that occurred in the normal tricuspid valve during the cardiac cycle. However, the wealth of data available suggested the need for reporting further findings that should contribute to a better understanding of the dynamics of the tricuspid valve. METHODS: Thirteen sonomicrometry transducers were placed in the hearts of each of seven sheep. Six transducers were placed in the tricuspid annulus (TA), at the base of each leaflet, and at each commissure; three at the tips of the papillary muscles (PMs); three in the free edges of the leaflets; and one transducer was placed at the apex. Distances between transducers, pulmonary and right ventricular pressures, and pulmonary flow were recorded simultaneously. RESULTS: The TA area underwent two major contractions and expansions during the cardiac cycle, reaching its maximum during isovolumic relaxation and its minimum in diastole. The TA height-to-width ratio changed from 8.4 +/- 1.9% to 15.3 +/- 4.2%. The leaflets began to open before end-systole. By the end of isovolumic relaxation, the leaflets had completed 54.1 +/- 13.4% of their opening. The PM and TA planes were not parallel, but were offset by 11.5 +/- 1.9 degrees to 17.8 +/- 2.1 degrees. The PM rotated 6.9 +/- 0.9 degrees with respect to the TA, with 3.1 +/- 1.1 degrees of the rotation occurring during ejection. CONCLUSION: The tricuspid valve is not a passive structure but rather forms a dynamic part of the right ventricle. Its orifice area changes not only due to the contraction and expansion of its perimeter but also to changes in its saddle shape. Leaflet opening and closure is not simply a response to pressure. The PMs rotate in relation to the TA. These data should impact upon the diagnosis and surgery of functional tricuspid regurgitation.

Beat-by-beat changes in pre-ejection period during functional tests evaluated by impedance aortography: a step to a left ventricular contractility monitoring

Abstract: Pre-ejection period (PEP) is used as a noninvasive index of left ventricular (LV) inotropy. PEP is conventionally defined as the interval between the onset of ECG Qwave and the impedance dZ/dt B-point, indicating the aortic valve opening. However, the problem of reliable and accurate detection of point B in every cardiac cycle, especially during a physiological test, is not solved yet. We proposed a new algorithm of PEP evaluation (PEPM): from the steepest slope point in ECG R-wave to the moment when the second derivative of the impedance aortogram attains the maximum (d2Z/dt2 max). Testing this method during head-up tilt, Valsalva manoeuvre and isometric handgrip revealed the specific beat-by-beat patterns of PEPM responses. During tilt and the early phase of Valsalva straining, PEP became longer, while near the end and briefly after that of handgrip and Valsalva manoeuvre PEP drastically decreased. In preliminary experiments with simultaneous application of impedance and ultrasound techniques, it was revealed that visually determined B-point could be slightly delayed after the onset of LV output tract flow. The d2Z/dt2 max point appeared about 20 ms later than B-point. The proposed method allows a stable tracking of PEP changes including transients induced by the functional tests.

A model for temporal resolution of multidetector computed tomography of coronary arteries in relation to rotation time, heart rate and reconstruction algorithm

Abstract: A model is presented that describes the image quality of coronary arteries with multidetector computer tomography. The results are discussed in the context of rotation time of the scanner, heart rate, and number of sectors used in the acquisition process. The blurring of the coronary arteries was calculated for heart rates between 50 and 100 bpm for rotation times of 420, 370, and 330 ms, and one-, two-, three-, and four-sector acquisition modes and irregular coronary artery movement is included. The model predicts optimal timing within the RR cycle of 45±3% (RCA), 44±4% and 74±6% (LCX), and 35±4% and 76±5% (LAD). The optimal timing shows a negative linear dependency on heart rate and increases with the number of sectors used. The RCA blurring decreases from 0.98 cm for 420 ms, one-sector mode to 0.27 cm for 330 ms, four-sector mode. The corresponding values are 0.81 cm and 0.29 cm for LCX and 0.42 cm and 0.17 cm for LAD. The number of sectors used in a multisector reconstruction and the timing within the cardiac cycle should be adjusted to the specific coronary artery that has to be imaged. Irregular coronary artery movement of 1.5 mm justifies the statement that no more than two sectors should be used in multisector acquisition processes in order to improve temporal resolution in cardiac MDCT.

Method and system for external counterpulsation therapy

Abstract: An improved system for delivering external counterpulsation therapy is described. The system employs muscle stimulation transducers such as cutaneous electrodes in order to stimulate skeletal muscle and/or vascular smooth muscle in synchronization with the cardiac cycle in a manner that increases the fluid pressure within veins and/or arteries during cardiac diastole.

Monitoring ventricular synchrony

Abstract: An exemplary method includes providing a maximum right ventricular systolic pressure value and corresponding time during a cardiac cycle, providing a left ventricular displacement value for the corresponding time, determining a product of the maximum right ventricular systolic pressure value and the magnitude of the left ventricular displacement value and assessing ventricular synchrony for the cardiac cycle based at least in part on the product. Such a method may include adjusting one or more cardiac pacing parameters based at least in part on the product. Other exemplary methods, devices, systems, etc., are also disclosed.

Atrial pacing therapy for treating mitral regurgitation

Abstract: A method and apparatus are disclosed for treating mitral regurgitation with electrical stimulation. By providing pacing stimulation to the left atrium during ventricular systole, a beneficial effect is obtained which can prevent or reduce the extent of mitral regurgitation.

The Cross-Bridge Dynamics during Ventricular Contraction Predicted by Coupling the Cardiac Cell Model with a Circulation Model

Abstract: The force-velocity (F-V) relationship of filament sliding is traditionally used to define the inotropic condition of striated muscles. A simple circulation model combined with the Laplace heart was developed to get a deeper insight into the relationship between the F-V characteristics and the cardiac ventricular inotropy. The circulation model consists of a preload and an afterload compartments. The linear F-V relationship for filament sliding in the NL model (Negroni and Lascano 1996) was replaced by the exponential F-V relation observed by Piazzesi et al. (2002). We also modified the NL model to a hybrid model to benefit from the Ca2+ cooperativity described by the Robinson model (Robinson et al. 2002). The model was validated by determining the diastolic ventricular pressure-volume relationship of the Laplace heart and the F-V relation of the new hybrid model. The computed parameters of the cardiac cycle agreed well with the physiological data. Computational results showed that the cross-bridge elongation (h in the NL model) temporally undershot the equilibrium hc during the ejection period and overshot it during the rapid refilling phase. Thereby the time course of ejection and refilling was retarded. In a simulation where the velocity of the mobile myosin head (dX/dt) was varied, the systolic peak pressure of the ventricle varied from a minimum value at dX/dt = 0 to a saturating value obtained with a constant hc, providing in silico evidence for a functional impact of the cross-bridge sliding rate on the ventricular inotropy.

Solid tissue impedance estimating method, cardiac output calculating method, pulmonary artery wedge pressure calculating method, cardiac output monitoring device, cardiac output monitoring system, pulmonary artery wedge pressure monitoring device, and pulmonary artery wedge pressure monitoring system

Abstract: A practical method for estimating cardiac output and pulmonary artery wedge pressure with good accuracy is provided. The present invention provides a method for estimating the impedance arising from solid tissue by determining the impedance at the intersection between the line of identity and the extrapolated regression line, where the regression line is obtained by linearly regressing the maximum value to the minimum value of the impedance signal of each of multiple data sets, where each data set contains the maximum value and the minimum value of the impedance signal during one cardiac cycle, where impedance signal is obtained between a can electrode implanted in the left thoracic wall and an electrode inserted into the coronary vein, over a specific period of time following the infusion of hypertonic saline into the pulmonary circulation.

Effect of Chronotropy and Inotropy on Stitch Tension in the Edge-to-Edge Mitral Repair

Abstract: Background— Our prior studies suggest that mitral annular septal-lateral (SL) diameter is the chief determinant of “Alfieri stitch” tension, but hemodynamic parameters may also play a role. We approximated the central edge of the mitral leaflets with a miniature force transducer to measure tension (T) at the leaflet approximation point during inotropic and chronotropic stimulation. Methods and Results— Eight sheep were studied under open-chest conditions immediately after surgical placement of a miniature force transducer to approximate the leaflets and implantation of radiopaque markers on the LV and mitral annulus (MA). Chronotropic stimulation was induced with atrial pacing at 130 minutes−1 (n=5) whereas inotropic state was increased with IV CaCl2 bolus (n=8). Hemodynamic data, stitch tension, and 3-D marker coordinates were obtained throughout the cardiac cycle before and during each intervention. Peak stitch tension (TMAX) under all conditions was observed in diastole and temporally correlated with peak annular SL (SLMAX) size. Atrial pacing did not change peak transducer tension or annular size. Calcium infusion also did not alter peak transducer tension (0.29±0.11 versus 0.32±0.10 N; P =NS) and only slightly reduced SL dimension (29.9±3.3 versus 29.3±3.5 mm; P <0.05). Conclusion— Isolated increase in heart rate or inotropic state did not alter peak stitch tension whereas enhanced contractile state decreased SL diameter minimally. These data, combined with those from our previous study, suggest that geometric (SL diameter) rather than hemodynamic parameters are the main determinants of “Alfieri stitch” tension. This implies that any interventional or surgical edge-to-edge repair performed without concomitant annular reduction to limit the SL dimension could expose the leaflet junction to forces which could limit repair durability.