Showing papers on "Cardiac cycle published in 1996"

Stretch-induced voltage changes in the isolated beating heart: importance of the timing of stretch and implications for stretch-activated ion channels

Abstract: Objectives: It is now well recognized that myocardial stretch can cause arrhythmias due to stretch-induced depolarizations. The effects of transient stretch applied during the various phases of the cardiac action potential have not been investigated. This study (1) examined the effects of short stretch pulses and sustained stretch on the monophasic action potential (MAP) repolarization time course and diastolic potential, (2) examined the arrhythmic response to differently timed stretch pulses, and (3) tested by comparison with computer simulations whether these effects are compatible with stretch-activated channel characteristics known from patch-clamp studies. Methods: We studied the MAP changes elicited by short transient stretch pulses applied at different times during the cardiac cycle to 8 isolated Langendorff-perfused rabbit hearts. The left ventricle (LV) was instrumented with a fluid-filled balloon, the volume of which was altered rapidly and precisely by means of a computer-controlled linear motor-driven piston. MAPs were recorded simultaneously from one right ventricular (RV) and two LV sites while short volume pulses of increasing amplitude were applied to the LV at variable delays after the last of 8 regular electrical pacing stimuli. The effect of pulsatile volume pulses applied at different phases of electrical systole and diastole was compared to the effect of sustained stretch pulses (60 s duration) of the same amplitude. The experimental results were compared with computer simulations of stretch-induced effects on the action potential to further validate the experimentally measured effects with theoretical predictions based on the Oxford Heart model with added stretch channel terms. Results: Stretch pulses applied during early systole caused a brief transient repolarization during the LV MAP plateau phase, with a maximal amplitude of 24 ± 10% of the total MAP amplitude. Stretch pulses at the end of the MAP caused a transient depolarization, with a maximal amplitude of 13 ± 5%. These oppositely polarized stretch effects crossed over during a transitional range of repolarization (mean 65 ± 9% of repolarization) when stretch produced neither transient repolarizations nor depolarizations. Only stretch pulses applied at a mean repolarization level of 77 ± 5% or later led to arrhythmias, preceded by transient depolarizations. No corresponding de- or re polarizations were seen in MAPs recorded simultaneously from the unstretched RV. The effects of long pulses on the MAP waveform were nearly identical to an overlay plot of the effects of many differently timed short transient pulses. When the stretch-induced voltage changes in the MAP were plotted against the repolarization level at which they were produced, a linear relationship was found (mean correlation coefficient r = 0.97; P < 0.0001) with a reversal at approximately half the total MAP amplitude. The computer simulations of the influence of stretch-activated channels reproduced both the effects of short and sustained stretch seen in the MAP recordings. Conclusions: We demonstrated in the isolated beating heart that the electrophysiologic effects of sudden myocardial stretch depend on the timing of the stretch relative to electrical systole or diastole. These findings are in agreement with patch clamp studies on stretch-activated ion channels which showed a linear current/voltage relation with a reversal potential between −20 and −30 mV. Only stretch pulses applied at the end of the action potential or during diastole elicit ectopic beats as a result of transient depolarizations, while stretch pulses applied during phase 2 and 3 cause transient repolarizations or no effect, respectively.

Three-dimensional echocardiographic evaluation of fetal heart anatomy and function: acquisition, analysis, and display.

Abstract: The purpose of this work was to assess the functional dynamics and anatomy of the cardiac chambers and great vessels in the fetus (18 to 36 weeks) using in utero three-dimensional ultrasonographic imaging. Fifteen patients were studied using conventional two-dimensional sonographic equipment incorporating a position sensor attached to the transducer and a graphics workstation. Sonographic image data were acquired at 30 images per second and required less than 30 seconds per data set. Fetal heart rate and time in the cardiac cycle were determined and used to synchronize image data for reprojection into a volume at the appropriate part of the cardiac cycle. Volume data were analyzed, rendered, and displayed interactively. Three-dimensional sonographic volume data demonstrated fetal cardiac anatomy from multiple orientations and showed the myocardium, valves, ventricles, and atria clearly. The images showed good correlation with currently available embryologic-anatomic-pathologic data. Dynamic and spatial relationships among chambers, valves, and great vessels were readily appreciated. Three-dimensional sonographic imaging of the fetal heart provides both anatomic and functional information regarding the valves, myocardium, great vessels, and chamber dynamics. Interactive three-dimensional cinegraphic display enhances visualization of cardiac anatomy, which can be difficult to appreciate with two-dimensional methods. The methods presented in this work demonstrate the feasibility of three-dimensional fetal echocardiography.

Age-related transmural peak mean velocities and peak velocity gradients by Doppler myocardial imaging in normal subjects

Abstract: Doppler myocardial imaging is a new cardiac ultrasound technique based on the principles of colour Doppler imaging which can determine myocardial velocities by detecting the changes of phase-shift of the ultrasound signal returning directly from the myocardium. To determine the normal range of transmural velocities in healthy hearts a prospective study was carried out involving 42 normal subjects (age from 21 to 78, mean 47 +/- 16 years). Using M-mode Doppler myocardial imaging the peak values of the mean velocity and velocity gradient across the left ventricular posterior wall were measured during standardized phases of the cardiac cycle. Peak mean velocities had the following values during the cardiac cycle: isovolumic contraction - 1.3 +/- 1.2 cm. s-1, early ventricular ejection 4.2 +/- 1.2 cm. s-1, late ventricular ejection 1.8 +/- 1.1 cm. s-1, isovolumic relaxation -2.0 +/- 0.8 cm. s-1, rapid ventricular filling -6.6 +/- 2.2 cm. s-1, atrial contraction -2.8 +/- 1.8 cm. s-1, atrial relaxation 1.2 +/- 1.1 cm. s-1. Peak velocity gradients were: isovolumic contraction 1.3 +/- 1.9 s-1, early ventricular contraction 4.7 +/- 1.9 s-1, late ventricular contraction 1.1 +/- 1.0 s-1, isovolumic relaxation -0.6 +/- 0.5 s-1, rapid ventricular filling 6.1 +/- 3.4 s-1, atrial contraction 2.6 +/- 1.7 s-1, atrial relaxation 0.0 +/- 0.3 s-1. Linear regression analysis showed that with the increase of age, peak velocity gradient decreases during rapid ventricular filling (r = 0.83; P < 0.0001) and increases during atrial contraction (r = 0.86; P < 0.0001) while peak mean velocity increases only during atrial contraction (r = 0.80, P < 0.0001). Thus, there was no correlation between increasing age and systolic peak mean velocity and peak velocity gradient but both diastolic filling phases rapid ventricular filling and atrial contraction demonstrated age-related changes. In summary, this study has determined the age-related range of normal transmural myocardial velocities within the left ventricular posterior wall in healthy hearts during the cardiac cycle. We conclude that these measurements of peak mean velocities and peak velocity gradients, should form the baseline for subsequent Doppler myocardial imaging clinical studies on myocardial diseases processes.

Assessment of flow in the right human coronary artery by magnetic resonance phase contrast velocity measurement: Effects of cardiac and respiratory motion

Abstract: Flow in the human right coronary artery was determined using magnetic resonance phase contrast velocity quantification. Two methods were applied to reduce respiratory motion: Imaging during breath holding, which is fast, and retrospective respiratory gating, which has a high temporal resolution (32 ms) in the cardiac cycle. Vessel cross-sectional area, through-plane velocity, and volume flow were determined in six healthy subjects. In-plane vessel displacement during the cardiac cycle, caused by cardiac contraction, was about 2-4 mm within a time frame of 32 ms in systole and early diastole. The motion resulted in blurring of images obtained during breath holding caused by the large acquisition time window (126 ms) within the cardiac cycle. Therefore, only with a high temporal resolution correct velocity images over the entire cardiac cycle could be obtained. The time- and cross-sectionally averaged velocity was 7 +/- 2 cm/s, and the volume flow was 30 +/- 10 ml/min.

Cardiac magnetic resonance fluoroscopy.

Abstract: A technique is described for high speed interactive imaging of the heart with either white or black blood contrast. Thirty-two views of a segmented, magnetization-prepared gradient echo sequence are acquired during diastole. Using three-quarter partial Fourier sampling, data for a complete 128 x 128 image are acquired in three cardiac cycles. High speed reconstruction provides an image update of each cardiac cycle 159 ms after measurement. An independent graphical user interface facilitates interactive control of section localization and contrast by permitting pulse sequence parameter modification during scanning. The efficiency and image quality of the cardiac MR fluoroscopy technique were evaluated in 11 subjects. Compared with the conventional graphic prescription method, the cardiac fluoroscopy technique provides an approximate eightfold reduction in the time required to obtain subject-specific double oblique sections. Image quality for these scout acquisitions performed during free breathing was sufficient to identify small cardiac structures.

Influence of aging on left atrial appendage flow velocity patterns in normal subjects.

Abstract: Transesophageal pulsed Doppler echocardiography was performed to examine changes with age in the left atrial appendage flow velocity patterns in 50 normal subjects (15 to 80 years) in sinus rhythm. There was a significant negative correlation between the peak early diastolic forward and backward left atrial appendage flow velocities and age, as well as a significant positive correlation between the peak early diastolic forward left atrial appendage flow velocity and the peak early diastolic transmitral and pulmonary venous flow velocities. Although there was a significant positive correlation between the peak atrial systolic transmitral flow velocity and age, there was a negative correlation between the peak atrial systolic forward and backward left atrial appendage flow velocities and age. There was a positive correlation between both the maximum left atrial diameter and the amplitude of the interatrial septal motion during atrial systole and age. There was a significant negative correlation between the left atrial appendage ejection fraction during atrial systole and age. Left atrial appendage thrombi and spontaneous echo contrast were detected in two subjects with low peak early diastolic and atrial systolic left atrial appendage flow velocities. In conclusion, both peak early diastolic and atrial systolic left atrial appendage flow velocities decreased with age. A decrease in the peak atrial systolic flow velocity appeared to be an important sign of left atrial appendage thrombus formation even in normal elderly subjects in sinus rhythm.

Dual-chamber implantable stimulation device having adaptive AV intervall and method for treating cardiomyopathy thereof

Abstract: A dual-chamber implantable pacemaker configured to operate in the DDD or DDDR mode automatically sets its AV (or PV) interval to an amount that is equal to the natural conduction time of a patient plus or minus a small prescribed amount, e.g., 1-100 msec. When set to a value that is less than the natural conduction time, preemptive ventricular pacing thus occurs at a time in the patient's cardiac cycle that is near when a natural ventricular contraction (an R-wave) would occur. Such ventricular pacing causes a mechanical contraction sequence of the patient's heart that differs from the natural contraction sequence following a natural depolarization, resulting in improved cardiac output. The pacemaker includes a pulse generator that generates ventricular stimulation pulses (V-pulses) at the conclusion of a pacemaker-defined AV (or PV) interval if no natural ventricular activity (an R-wave) is sensed during such AV (or PV) interval. The AV (or PV) intervals are automatically adjusted by the pacemaker to be a function of the natural conduction time sensed by the pacemaker, where the natural conduction time is the time between atrial activity (a sensed P-wave or a delivered A-pulse) and the subsequent natural ventricular activity (R-wave).

Dynamic anatomical study of cardiac shunting in crocodiles using high-resolution angioscopy

Abstract: Prolonged submergence imposes special demands on the cardiovascular system. Unlike the situation in diving birds and mammals, crocodilians have the ability to shunt blood away from the lungs, despite having an anatomically divided ventricle. This remarkable cardiovascular flexibility is due in part to three anatomical peculiarities: (1) an 'extra' aorta (the left aorta) that leaves the right ventricle and allows the blood from the right ventricle to take an alternative route into the systemic circulation instead of going to the lungs; (2) the foramen of Panizza, an aperture that connects the right and left aortas at their base immediately outside the ventricle; and (3) a set of connective tissue outpushings in the pulmonary outflow tract in the right ventricle. Using high-resolution angioscopy, we have studied these structures in the beating crocodile heart and correlated their movements with in vivo pressure and flow recordings. The connective tissue outpushings in the pulmonary outflow tract represent an active mechanism used to restrict blood flow into the lungs, thus creating one of the conditions required for a right-to-left shunt. We observed that the foramen of Panizza was obstructed by the medial cusp of the right aortic valve during most of systole, effectively differentiating the left and right aortic blood pressure. During diastole, however, the foramen remained open, allowing pressure equilibration between the two aortas. Contrary to current theories, we found that the left aortic valves were unable to cover the foramen of Panizza during any part of the cardiac cycle, supporting the reversed foramen flow hypothesis. This would ensure a supply of blood to the coronary and cephalic circulation during a complete shut-down of the left side of the heart, such as might occur during prolonged submergence.

Transvalvular Impedance (TVI) Recording Under Electrical and Pharmocological Cardiac Stimulation

Abstract: The cardiac electric impedance was recorded between right atrium and ventricle, throughout the cardiac cycle, by means of a tripolar single pass lead for VDD pacing. The transvalvular impedance signal (TVI) is a sharp periodic wave, with high signal-to-noise ratio, that is detected exclusively in the presence of cardiac mechanical activity. The minimum TVI value is attained during the atrial systole, the maximum at the end of ventricular systole. Different parameters of TVI waveform are affected by changes in the inotropic state, and could therefore be proposed as potential signals for new rate responsive algorithms based on the correlation between inotropic and chronotropic regulation. The signal might be used, moreover, for pacing and sensing validation in autoregulating pacemakers and for fibrillation recognition in ICDs.

Variation of heart rate and electrocardiograph trigger interval during ultrafast computed tomography.

Abstract: OBJECTIVES Electrocardiographic (ECG) trigger records obtained during cardiac ultrafast computed tomography (UFCT) scanning were analyzed to estimate the variability in heart rate and ECG trigger interval to develop a protocol that would allow the development of better ECG triggering software. METHODS One-hundred-eighteen patients underwent cardiac UFCT imaging for diagnostic purposes. All subjects were divided into three groups according to the heart rate and ECG trigger condition. Thirty slices were obtained in the high-resolution volume mode for each patient. RESULTS A decrease in heart rate and ECG trigger interval was found during image acquisition of the first four slices in all three groups. The nadir of the heart rate occurred during acquisition of the 4th slice, 5.3, 3.5, and 5.6 beats per minute less than the initial heart rate in groups 1, 2, and 3 respectively, with a 6.9%, 2.8%, and 5.0% shorter ECG trigger interval (p < .001, p = .08, p < .05, respectively). From the 4th to the 30th slices, heart rate and ECG trigger interval progressively increased, but less variability was found in the last 20 slices in all three groups. CONCLUSIONS Significant variation in heart rate and ECG trigger interval was seen during 30-level cardiac UFCT imaging, especially during image acquisition of the first four slices (approximately 1-6 seconds after breatholding). This can result in scanning during the suboptimal phase of the cardiac cycle by the current UFCT triggering software. A delay in the initiation of scanning to approximately 6 to 10 seconds after breatholding would result in imaging during a time when the heart rate is relatively stable, and a smaller variability in ECG trigger interval occurs. Recalculation of the required delay before each heart beat may improve the precision of ECG triggering.

Cardiac functional changes in the human fetus in the late first and early second trimesters.

Abstract: Fetal cardiac function was studied in 52 women at 10–20 weeks of normal gestation using Doppler ultrasonography. According to a cross-sectional study design, transmitral and ascending aortic flow velocity waveforms were obtained simultaneously, in order to calculate filling and ejection time as well as isovolumic contraction and relaxation time. A statistically significant gestational age-dependent increase was established for both transmitral and ascending aortic flow velocities. Cardiac cycle length and filling time displayed a statistically significant increase with advancing gestational age, whereas ejection time and isovolumic relaxation time showed a gestational age-related decrease. No relationship existed between isovolumic contraction time and gestational age. A statistically significant decrease was demonstrated for atria1 contribution to ventricular filling at 10–l4 weeks of gestation, with a constant pattern during the remainder of the study period. No relationship existed between the different components of the cardiac cycle and mitral and aortic flow velocity parameters. This study shows that the late first and early second trimesters of pre,gnancy are characterized by gestational age-related changes in fetal cardiac function. Copyright © 1996 International Society of Ultrasound in Obstetrics and Gynecology

Evaluation of K-space Segmented Cine Sequences for Fast Functional Cardiac Imaging

Abstract: RATIONALE AND OBJECTIVES In functional cardiac magnetic resonance imaging, reduction of measuring time is very important for many patients who are not able to rest motionless for long-lasting examinations. In this study, the image quality of sequences with k-space segmented data recording was compared with conventional gradient-echo sequences for cine imaging with flow compensation in applications on patients with normal and reduced ejection fractions. METHODS Thirty-one subjects (4 volunteers and 27 patients with cardiac diseases) were examined using different techniques for cine imaging of the left and right ventricles. The ejection fraction in the patients was calculated based on images of a conventional two-dimensional gradient-echo technique using a biplane ellipsoid model. The results from k-space segmented methods (3 to 9 Fourier lines per cardiac cycle for each phase image) were compared with the conventional images of the same short-axis view separately for groups of subjects with normal and reduced ejection fraction. The contrast between blood and myocardium at several sites of the heart and the homogeneity of the blood signal in the ventricle were evaluated for several phases of the heart cycle. RESULTS The segmentation in the acquisition of raw data allows reduction of measuring time to approximately 20% to 40% of the time required for conventional sequences in cine imaging of the heart. In patients with normal or only slightly reduced heart function (ejection fraction > or = 60%) the image quality of k-space segmented sequences was not significantly different from the conventionally recorded images. In contrast, patients with markedly lowered ejection fraction (< 60%) showed degraded results of the k-space segmented sequences compared with the conventional sequence (P < 0.001). The anterolateral border and the right ventricle especially were not sufficiently delineated by the k-space segmented sequences in these patients. CONCLUSION The k-space segmentation for the reduction of examination time is suitable for measuring heart volumes and functional parameters of patients expected to have a nearly normal ejection fraction, whereas for patients with markedly reduced cardiac function further technical improvements of segmented techniques are necessary.

Cardiac, Respiratory, and Locomotor Coordination during Walking in Humans

Abstract: Interactions between locomotor, respiratory, and cardiac rhythms were investigated in human subjects (n = 11) walking on a treadmill. Investigation of the phase relationship between heart rate and gait signals revealed that cardiac rhythms were entrained to locomotor rhythms when both frequencies were close to an integer ratio. Coherence spectra were estimated between heartbeat fluctuation, respiratory, and gait signals, and their magnitudes were evaluated. The results suggest that the respiratory-induced fluctuation in heartbeat would vary depending on the strength of the cardiolocomotor coupling. The synchronization tends to occur for one or two specific phases in an individual subject, but there was some variation among subjects. When the subjects voluntarily synchronized their cadence with the cardiac rhythm, the heart rate and blood pressure varied depending on the phase lag within a cardiac cycle. The coordination of locomotor and cardiac rhythms is discussed.

Isoflurane, but Not Halothane, Improves Indices of Diastolic Performance in Dogs with Rapid Ventricular, Pacing-induced Cardiomyopathy

Abstract: Background The left ventricular (LV) mechanical effects of isoflurane and halothane were examined in dogs with rapid LV pacing-induced cardiomyopathy. These experiments tested the hypothesis that isoflurane and halothane differentially enhance indices of diastolic performance in dogs with moderate LV dysfunction. Methods Eight dogs were chronically instrumented for measurement of LV and aortic pressures, subendocardial segment length, and cardiac output. Contractility was quantified by preload recruitable stroke work (Mw). Diastolic function was evaluated with a time constant of isovolumic relaxation (tau), segment lengthening velocities and time-velocity integrals during early filling (dL/dtE and TVI-E) and atrial systole (dL/dtA and TVI-A), and a regional chamber stiffness constant (Kp). Hemodynamics and LV function were recorded in the conscious state before pacing. The left ventricles of the dogs were then continuously paced at ventricular rates between 220 and 240 beats *symbol* min sup -1 for 10 plus/minus 1 days and monitored on a daily basis. After the development of moderate LV dysfunction, pacing was temporarily discontinued, and dogs were studied in sinus rhythm in the conscious state and after 20 min equilibration at 1.1, 1.4, and 1.7 minimum alveolar concentration isoflurane and halothane on separate days. Results Chronic rapid pacing increased baseline (sinus rhythm) heart rate, LV end-diastolic pressure, and end-diastolic segment length and decreased mean arterial pressure, LV systolic pressure, and cardiac output. Mw decreased and tau and Kp increased, consistent with LV systolic and diastolic dysfunction. Reductions in dL/dtE /dL/dt sub A and TVI-E/A occurred, which indicated that LV filling was more dependent on atrial systole. In dogs with cardiomyopathy, isoflurane and halothane increased heart rate and decreased mean arterial pressure, LV systolic pressure, LV end-diastolic pressure, cardiac output, Mw, and Kp. Decreases in LV end-diastolic pressure were more pronounced in dogs anesthetized with 1.1 minimum alveolar concentration isoflurane compared with halothane. Halothane-induced decreases Mw were greater than those observed with equi-minimum alveolar concentration isoflurane. A reduction in tau and increases in TVI-E/TVI-A and the ratio of early to total LV filling were observed with isoflurane. In contrast, halothane caused dose-related reductions in dL/dtE, dL/dt sub A, TVI-E, and TVI-A, and did not improve the ratios of these variables. Conclusions Isoflurane, but not halothane, improved several indices of diastolic performance in dogs with pacing-induced LV dysfunction, despite producing simultaneous negative inotropic effects. These findings can probably be attributed to favorable reductions in LV preload and not to direct lusitropic effects. Improvement of filling dynamics may partially offset the decrement in LV systolic function by isoflurane in the setting of LV dysfunction.

Ultrasonography characterization of heart morphology and blood flow of lower vertebrates.

Abstract: Echocardiography is an noninvasive technique that utilizes high frequency ultrasound to evaluate structural, functional, and hemodynamic status of the cardiovascular system. With all the inherent potentials of this technique, its application has not been explored on lower vertebrates. The objective of our work was to apply ultrasonography technique, with an available commercial equipment (Echo camera--Aloka SSD 830 and Toshiba using probes of 5 and 7.5 MHz frequency emission) and to identify and characterize cardiac structures and blood flow in lower vertebrates. Specimens studied were Lophius piscatorius, Halobatrachus didactylus, and Bufo bufo. The probe was applied on the ventral middle line over heart chambers. Two-dimensional images were obtained from long and short axis incidences at various levels of cardiac chambers. During each cardiac cycle and for every specimen it was possible to identify the relation between each structure, to measure longitudinal and transversal diameters, to identify blood fluxes, and measure their velocities. The work we describe and discuss in our preliminary experience and data concerning the ultrasound study of some lower vertebrates. The cardiovascular apparatus of the different species we studied was a dynamic, phasic, and efficient contraction and relaxation mechanism. The phenomena could be well documented with two-dimensional echocardiography. The effect of the coupling phenomena of contraction and relaxation was also studied through the application of pulsed and color Doppler ultrasound. Two-dimensional and Doppler echocardiography can be easily applied to the study of the anatomy, morphology, and physiology of lower vertebrates. Well defined structures and cardiac chambers were displayed with this noninvasive imaging technique. Echo-Doppler ultrasonography is a reliable technique in these lower vertebrate specimens, to study cardiac structure and kinetics, and to identify and measure blood flow velocity. It can be used as an experimental model for cardiac function.

The influence of cardiac phase on reaction time depending on heart period length and on stimulus and response laterality

Abstract: The aim of this study was twofold: (1) to reinvestigate the question of cardiac cycle time effect on sensorimotor performance, and (2) to examine the dependence of this effect on stimulus and response laterality Thirty-eight right-handed subjects performed a simple visual reaction time task, where stimuli were presented randomly to the right or to the left of the fixation point, or centrally Half of the responses were given by the right hand, and the other half by the left hand The stimuli occurred at either 150- or 600-msec delays from the R wave of the electrocardiogram, that is, during the systolic or diastolic part of the cardiac cycle, respectively For right stimuli and right-hand responses, the reaction time was marginally longer for systolic than for diastolic stimuli No such effect emerged for central and left stimuli and for left-hand responding This result suggested—albeit weakly—that the sensorimotor functions of the left cerebral hemisphere might be influenced to a greater extent by the physiological changes accompanying cardiac activity than those of the right hemisphere Additionally, it was shown that in females characterized by long heart periods, the reaction time was longer for stimuli presented during systole than for stimuli presented during diastole, but the opposite was true in females with short heart periods In males, a similar but nonsignificant tendency was found This result does not contradict the Laceys’ (1970) baroreceptor hypothesis The limitations of this and similar approaches are discussed

Comparison of two techniques for measuring two-dimensional strain in rat left ventricles

Abstract: Measurements of regional deformation in the left ventricle are needed to understand the structural basis of ventricular function. Two techniques were employed to measure two-dimensional strain in the intact, beating rat heart. Rats were anesthetized and ventilated, and the chest of each rat was opened. Homogeneous two-dimensional strains were measured during the cardiac cycle relative to end diastole with either a triangle of miniature (0.3-0.5 mm) piezoelectric crystals implanted at midwall or with three epicardial surface markers imaged with a 60-Hz video system. Average heart rate was 303 +/- 37 beats/min, end-diastolic pressure was 2 +/- 2 mmHg, and peak-systolic pressure was 106 +/- 31 mmHg in all of the hearts. In general, strains during the cardiac cycle showed similar trends to those previously reported in the dog. The magnitudes of peak systolic cardiac strains on the epicardium and at midwall were -0.076 +/- 0.055, -0.068 +/- 0.014 (circumferential), -0.102 +/- 0.040, -0.082 +/- 0.039 (longitudinal), and 0.065 +/- 0.016, 0.064 +/- 0.043 (in-plane shear). There were mechanical side effects due to the crystal implantation that may limit the usefulness of this technique in its present form in the contracting rat heart. The epicardial surface technique does not have these side effects and will allow measurements of regional systolic cardiac function in rats with pathological interventions or genetic modifications that may alter regional ventricular function.

Assessment of right and left atrial function in patients with transplanted hearts with the use of magnetic resonance imaging

Abstract: Background : The purpose of this study was to determine the volumes and cyclic volume changes of the cardiac atria after heart transplantation in physically healthy recipients. Methods : Ten heart transplant recipients (New York Heart Association grade I) entered the protocol. All operations had been made with classic biatrial anastomoses. Eight healthy volunteers were studied as controls. To measure the volumes of both atria and left ventricular cavity, we used a gradient-echo cine sequence. The 10 mm slices covered both atria over the total cardiac cycle. Images were planimetered, and simultaneous volumes were totalled to give the cavity volume at each time phase. Results : The heart rate of the heart transplant recipients was faster than in controls, which resulted in higher cardiac output. The atrial minimum volumes were significantly larger, and fractional emptying was smaller in transplanted hearts when compared with controls. Reservoir and stroke volumes were smaller and conduit volumes were larger in transplanted hearts than in controls. The atrial filling and emptying rates were lower in heart transplant recipients than in controls. Conclusions : The classic surgical technique used in heart transplantation results in large atria with decreased volume changes and filling rates even in physically healthy transplant recipients. Magnetic resonance imaging is a reliable tool in assessment of atrial volumes and cyclic function after heart transplantation.

Mechanisms of venous return and ventricular filling in elasmobranch fish.

Abstract: The current concept of ventricular filling in the elasmobranch fish (sharks and rays) is that a subambient pericardial pressure establishes a negative diastolic pressure gradient for the atrium and that ventricular end-diastolic volume is exclusively determined by atrial systole. In contrast, recent findings using echo-Doppler and digital imaging techniques have demonstrated two filling phases in the elasmobranch ventricle. In this study, simultaneous atrial and ventricular pressure measurements made on sharks with an open or intact pericardium establish that atrial pressure is above ventricular diastolic pressure until the onset of ventricular systole. A positive biphasic atrioventricular pressure gradient thus ensures ventricular filling during early diastole, as a result of ventricular relaxation, as well as during atrial systole. Although a reduction in pericardial pressure resulted in a decline in the atrial and ventricular pressure, a positive atrioventricular pressure gradient is conserved. The finding that atrial diastolic pressure is not lower than ventricular diastolic pressure, when combined with previous results showing that pericardial pressure is generally at or above ambient and that ventricular filling is biphasic, constitutes a strong body of evidence favoring the operation of a direct venous inflow as the mechanism by which the elasmobranch heart fills.

Cardiac-gated 3-dimensional MR angiography

Abstract: A three-dimensional gadolinium-enhanced MR study of eg the patient's thoracic vasculature is carried out while the patient holds his or her breath Acquisition of all data in each three-dimensional partition takes place during one and only one heartbeat By synchronizing the MR pulse sequence to the patient's cardiac cycle, and advantageously by acquiring the MR data during the diastolic phase of the cardiac cycle, image artifacts caused by cardiac motion and pulsatile flow are eliminated or minimized

Phase-sensitive interaction of cardiac and respiratory timing in humans

Abstract: We asked whether the heart rate response to respiratory change varied as a function of timing within the cardiac cycle. Respiratory and electrocardiographic data were collected from seven men and seven women during three weekly sessions under conditions of normal and visually paced breathing. Results revealed that, when inspiration began sooner than 500 ms before the subsequent heart beat, inspiration had little effect on the subsequent interbeat interval. However, the timing of the subsequent beat was accelerated when inspiration began later than 450 ms before this heart beat. Similar relationships were observed for expiratory onset. Results were not attributable to volitional control or rate of breathing. The modulation of respiratory sinus arrhythmia by the timing of respiratory events in the cardiac cycle has implications for the role of vagal control in the synchronization of heart rate with respiratory and behavioral actions.

Anatomical structures determining blood flow in the heart left ventricle

Abstract: The presence of twisted helical flow patterns in the cardiac cavities during ventricular filling and ejection was supposed. This work was intended in order to show that the intra-ventricular trabeculation plays the determining role in such a flow formation and to find some analytical approaches for its analysis. The morphometric study of human left-ventricular and aortic corrosion casts and dynamic measurement of the aorta by MRI-technique were performed. The data were analysed by means of the “Mathematica” program. Two groups of trabecules were identified that refer to the inlet and outlet of the ventricular blood flow. The first group consists of trabecules of the free left-ventricular wall. The second group consists of long trabecules going along the anterior left-ventricular wall and intracavital lines of the papillary muscles. Both are twisted clockwise and converge in the flow direction. Each group of trabecules is oriented towards the mitral or aortic valve orifices, correspondingly. It was concluded that the helical trabecular organization acts as flow directing paddles that change their mutual orientation during the cardiac cycle evolution. The reorientation of the flow takes place due to sequential contraction of the ventricular structures. The formalization of trabecular orientation will allow one to calculate improved models of implantable substitutes and auxiliary devices for cardio-vascular surgery.

Importance of Atrial Contraction in Hypertrophic Obstructive Cardiomyopathy: Implications for Pacing Therapy

Abstract: Hypertrophic cardiomyopathy is a primary myocardial disease characterized anatomically by left ventricular (LV) asymmetric hypertrophy and pathophysiologically by normal or even supernormal systolic ejection performance contrasting with impaired diastolic function. Altered ventricular relaxation tends to reduce the contribution of rapid ventricular filling to total LV filling volumes. Consequently, the contribution of left atrial (LA) contraction can be significantly increased. In some patients LV filling, and thus stroke volume, critically depend upon atrial systole. These data may have important clinical implications especially in patients treated with permanent cardiac pacing. Preserving a fully efficient LA contribution to LV filling is probably a key point in those patients.

Fourier phase mapping of the human heart. The use of spatial modulation of magnetization cine magnetic resonance imaging.

Abstract: RATIONALE AND OBJECTIVES Fourier phase mapping of cine cardiac magnetic resonance (MR) imaging offers noninvasive analysis of temporal cardiac activation patterns. The aim of our investigation was to extend this analysis to intramyocardial dynamics. METHODS A fast-imaging with steady-state precision (FISP) two-dimensional gradient echo spatial modulation of magnetization (SPAMM) sequence and a segmented two-dimensional FISP-SPAMM sequence were applied to acquire cine MR images of the complete cardiac cycle on a 1.5-tesla imager. Signal intensity data were submitted to pixel-wise Fourier phase analysis. Color-encoded amplitude and phase maps were displayed for visual analysis. RESULTS Using the unsegmented SPAMM two-dimensional FISP sequence, a more consistent tag-to-myocardium contrast and a higher number of cardiac phases was achieved than by using the segmented version of this sequence. The typical tag displacement reflected complex intramyocardial dynamics, including rotation. Phase mapping displayed a pattern of contraction consistent with electrophysiologic concepts of cardiac activation. In contrast, the segmented sequence did not reflect any differences in the onset of cardiac contraction, although tag displacement was apparent with this sequence as well. CONCLUSIONS. Fourier phase mapping of cardiac MR imaging tagging studies allows for noninvasive analysis of intramyocardial activation patterns. A temporal resolution of 50 mseconds per image at a heart rate of 75 beats per minute allows for an assessment of spatial differences in the onset of myocardial activation.

Cardiac-related changes in lung resistivity as a function of frequency and location obtained from EITS images

Abstract: ECG-gated electrical impedance tomographic spectroscopy (EITS) measurements of the lungs were taken on seven normal subjects in the frequency range 9.6 kHz to 614.4 kHz. The results show that in late systole the resistivity relative to the R-wave (i.e. at the R-wave) decreases consistently within the lung. In addition there arises an increase in in early systole towards the periphery of the lung. Frequency behaviour of changes with location. At all times after the R-wave, in the centre of the lung is higher at higher frequency f whereas in the periphery it is lower at higher f. The principal decrease in can be explained by increasing pulmonary blood volume due to cardiac contraction. The early systolic increase is presumably due to venous return to the left atrium locally leading blood output from the right ventricle which is delayed by the windkessel effect. Based on a model taking extracapillary and capillary blood volume increase into account, the change in frequency behaviour of is explained by regional variations in extracapillary blood vessel size determining the relative contributions of extracapillary blood volume change and capillary blood volume change to at a certain frequency.

Functional Properties of the Heart

Abstract: In the preceding chapter the overall behavior of the heart has been considered as it is reflected in the periodical alternation of diastole and systole and of filling and ejection of the atria and ventricles. This description of the cardiac cycle included the accompanying changes in pressure and volume of the cardiac chambers. However, a deeper comprehension of cardiac function has to take into account some specific properties of the myocardial tissue as opposed to other types of muscle, mainly skeletal muscle, and the transformation of wall tension into pressure by the hollow muscular organ. Moreover, the compensatory changes in the heart in response to different degrees of filling (preload) or of resistance against ejection (afterload) are also discussed in this chapter, as are regulatory influences on myocardial contractility.

Atrial natriuretic factor secretion: a role for atrial systolic ejection force?

Abstract: The increase in plasma concentration of atrial natriuretic factor in heart transplant patients has not been fully elucidated. Besides an eventual pressure or volume overload leading to passive atrial distension, the atrial tension developed during atrial systole, or atrial ejection force, which may be increased by the transplantation procedure, is an important determinant of atrial natriuretic factor release. We therefore determined the plasma concentration of atrial natriuretic factor and the maximal atrial ejection force in 15 heart transplant patients and 8 controls, matched for age and body mass. Atrial ejection force, as defined as the force exerted by the left atrium to accelerate blood into the left ventricle during atrial systole, was obtained using combined two-dimensional imaging and doppler echocardiography. Serum creatinin concentrations, heart rate [91.9 (SD 13.2) vs 71.8 (SD 10.9) beats · min−1], mean arterial blood pressure [103.9 (SD 9.8) vs 87.4 (SD 5.8) mmHg, 13.85 (SD 1.31) vs 11.65 (SD 0.77) kPa], left ventricular posterior wall thickness and interventricular septum thickness were higher in heart transplant patients compared to controls. Plasma concentration of atrial natriuretic factor was also elevated in heart transplant patients [63.9 (SD 18.1) vs 34.0 (SD 3.2) pg · ml−1; P<0.001]. In contrast, although the left atrial area was greater in heart transplant patients [28.2 (SD 4.8) vs 15.8 (SD 2.5) cm2; P<0.001], mitral area, transmitral Doppler A-wave maximal velocity and atrial ejection force were similar in transplant and in control patients [7.7 (SD 3.5) vs 8.9 (SD 2.8) kdyn, 77 (SD 35) vs 89 (SD 28) mN]. No significant correlation was observed between concentration of atrial natriuretic factor and atrial ejection force, either in heart transplant patients or in controls. Thus, the elevated plasma concentration of atrial natriuretic factor observed in these heart transplant patients was multifactorial in origin, and was considered to depend upon an hypersecretion rather than upon a decreased clearance rate. Moreover, it is suggested that the atrial ejection force was unlikely to have participated in this enhanced release of atrial natriuretic factor.