Showing papers on "Cardiac cycle published in 1977"
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TL;DR: Global ventricular function was evaluated by both multiple gated cardiac blood pool scans (MUGA) and contrast ventriculograms in a group of 17 patients with suspected coronary artery disease and revealed the semi-automatic method superior to the standard approach.
Abstract: Global ventricular function was evaluated by both multiple gated cardiac blood pool scans (MUGA) and contrast ventriculograms in a group of 17 patients with suspected coronary artery disease. The contrast ventriculograms were analyzed frame by frame to generate a volume versus time curve for each patient, while the tracer data were analyzed by two methods: 1) the standard method, in which the left ventricle is identified on the end-diastolic frame and the background corrected activity under the region of interest obtained from the entire cardiac cycle, and displayed as a time versus activity curve; and 2) by a semi-automatic method in which the computer applies a threshold detection program to define the ventricular borders, and activity in the chamber at each point in the cardiac cycle is defined after background correction. The tracer data in each patient were analyzed independently by four observers. The tracer data correlated with the contrast data on a point by point basis r = 0.87 for the standard method, and 0.93 for the semi-automatic technique. An F test of variance revealed the semi-automatic method superior to the standard approach (P less than 0.05).
297 citations
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TL;DR: Activity from left ventricular receptors with nonmedullated afferents was recorded in the right cervical vagus in anesthetized, thoracotomized cats and measurement of total conduction times indicated that during the increase in LVEDP the receptors were activated principally in the systolic portion of the cardiac cycle.
Abstract: Activity from left ventricular receptors with non-medullated afferents was recorded in the right cervical vagus in anesthetized, thoracotomized cats. Probing of the open heart demonstrated that the receptors were distributed throughout the free wall and the interventricular septum. Fibers from posterior receptors pass along the posterior descending coronary artery and the lateral surface of the right atrium to join the right main cardiac nerve; those from the anteriolateral region pass behind the aorta and the pulmonary trunk. The control receptor discharge was 1.4 (range, 0-6) impulses/sec at a mean left ventricular end-diastolic pressure (LVEDP) of 4.5 (range, 2-10) mm Hg. It was observed that receptor discharge increased with progressive increase in LVEDP produced either by transfusion or by aortic occlusion. At a mean LVEDP of 8 mm Hg, the mean discharge rate was 3.2 impulses/sec, and at 16 mm Hg it was 7.0 impulses/sec. It was also found that propranolol reduced and isoproterenol increased the discharge frequency at any given LVEDP. Measurement of total conduction times indicated that during the increase in LVEDP the receptors were activated principally in the systolic portion of the cardiac cycle. Despite this there was no obvious relationship between the discharge frequency and left ventricular systolic pressure.
157 citations
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TL;DR: To resolve apparent incongruities between the echocardiographic and necropsy measurements of wall thicknesses that led to uncertainty regarding the actual cardiac diagnosis, the hearts of patients with cardiac disease were studied and septal-free wall ratios obtained at necropsies corresponded most closely to those obtained by eChocardiography in systole.
Abstract: In several patients with asymmetric septal hypertrophy (ASH) diagnosed by echocardiography (septal-free wall thickness ratios greater than or equal to 1.3), we have discovered marked discrepancies between the echocardiographic and necropsy measurements of wall thicknesses that led to uncertainty regarding the actual cardiac diagnosis. To resolve these apparent incongruities, the echocardiograms and hearts of 17 patients with cardiac disease were studied. Six of nine patients with abnormal septal-free wall ratios greater than or equal to 1.3 during life had septal-free wall ratios that were not diagnostic of disproportionate septal thickening at necropsy. Such discrepancies may be explained as follows: 1) echocardiographic measurements during life were made in diastole (as per convention), but measurements at necropsy were made in hearts that appeared to have been in the systolic phase of the cardiac cycle; 2) the left ventricular free wall thickens considerably more than the ventricular septum in systole, as determined by echocardiography. This latter phenomenon resulted in septal-free wall ratios in systole that were consistently smaller than those in diastole. Furthermore, septal-free wall ratios obtained at necropsy corresponded most closely to those obtained by echocardiography in systole.
78 citations
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TL;DR: A technique of post data-acquisition correlation of the angular projection data using the electrocardiogram as a reference signal produced seven "stop action" images of the heart and resulted in delineating morphological detail not recognizable on the conventional CT scan.
Abstract: Computed tomographic (CT) cardiac imaging in vivo has been hampered by motion of the heart during its cardiac cycle A technique of post data-acquisition correlation of the angular projection data using the electrocardiogram as a reference signal is described This method produced seven "stop action" images of the heart and resulted in delineating morphological detail not recognizable on the conventional CT scan
71 citations
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TL;DR: Premature pulmonary valve opening does not appear specific for any particular clinical entity but reflects the relative pressures in the right ventricle and pulmonary artery during diastole.
Abstract: Premature opening of the pulmonary valve (opening independent of atrial or ventricular systole) was originally described in a case of sinus of Valsalva rupture into the right atrium. Since that time we have observed five additional cases in which the pulmonary valve opened prematurely. Entities encountered included: 1) constrictive pericarditis; 2) Loeffler's endocarditis; 3) Ebstein's anomaly with tricuspid regurgitation; 4) tricuspid regurgitation following tricuspid valvulectomy, and 5) pulmonary regurgitation accompanied by atrial septal defect. In the first two cases, premature pulmonary valve opening is felt to be due to restriction of diastolic filling of the right ventricle with subsequent early diastolic rise in pressure equalling or exceeding pulmonary artery diastolic pressure. In the latter three cases, the increased volume of blood entering the right ventricle again appeared to result in a rapid rise in initial right ventricular diastolic pressure and to produce premature opening of the pulmonary valve. Premature pulmonary valve opening, therefore, does not appear specific for any particular clinical entity but reflects the relative pressures in the right ventricle and pulmonary artery during diastole.
60 citations
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TL;DR: The results constitute the first demonstration in intact man of differential modification of heart period with temporal variations of the placement of “significant” sensorimotor events within the cardiac cycle.
Abstract: In a fixed-foreperiod reaction time experiment with 66 male college students, the heart rate for the same cardiac cycle within which the imperative stimulus occurred was slowed. The slowing was greater for imperative stimuli presented early in the cardiac cycle than late. The “monotonic” (linear) trend was highly significant, p< 10-8. There was also a significant “bitonic” (quadratic) trend, p <.01. Three subgroups of subjects, split on the basis of heart rate level, each showed significant trends with significant differences in the trend-components among groups. Analyses of ready signal presentations and of a control point in the intertrial interval revealed no comparable effects. The results were replicated in a second experiment in which 20 male college students self-initiated tachistoscopic exposures. In this experiment, the next cardiac cycle, subsequent to the cardiac cycle in which the self-initiated response occurred, was also shown to exhibit systematic modification with changes in the temporal placement of the response within the preceding cycle. The phenomena described are strikingly parallel with results obtained in animals upon direct stimulation of the vagus and carotid sinus nerves, and in man upon stimulation of the carotid sinus with neck suction. The results constitute the first demonstration in intact man of differential modification of heart period with temporal variations of the placement of “significant” sensorimotor events within the cardiac cycle.
55 citations
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TL;DR: The regional contraction patterns of the left ventricle, shortly after myocardial infarction, were assessed from computer-processed scintigraphic images and histograms of the first transit of an intravenously injected radionuclide bolus, and indicated wall-motion and stroke-volume anomalies corresponding with the electrocardiographic location of the infarct.
Abstract: The regional contraction patterns of the left ventricle, shortly after myocardial infarction, were assessed from computer-processed scintigraphic images and histograms of the first transit of an intravenously injected radionuclide bolus. Seventy-seven patients with documented myocardial infarction were injected with a compact bolus of /sup 99m/Tc-pertechnetate which was coordinated with the ECG so that it arrived in the superior vena cava during diastole. Precordial activity during the initial passage was recorded in 50-msec intervals with a multicrystal scintillation camera interfaced to a dedicated minicomputer. Data frames of 4 to 7 cardiac cycles were summed into one representative cardiac cycle. In 73 of the 77 patients the images of the representative cycle, along with the corresponding time-activity curves, indicated wall-motion and stroke-volume anomalies corresponding with the electrocardiographic location of the infarct. This nontraumatic, essentially noninvasive technique permits serial examinations of the acutely ill patient for the spatial identification and estimation of suspected myocardial infarcts.
49 citations
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TL;DR: Gated radionuclide cardiac blood pool scans of end-systole and end-diastole or eight images subtending the entire cardiac cycle were performed on patients with left atrial myxomas, finding three patterns of tumor motion.
Abstract: Gated radionuclide cardiac blood pool scans (GCS) of end-systole and end-diastole or eight images subtending the entire cardiac cycle were performed on seven patients with left atrial myxomas documented by pulmonary cineangiography with left atrial follow-through. The ethocardiogram was either suggestive or diagnostic in all patients. In addition to demonstration of the tumor (6 patients), the GCS detected three patterns of tumor motion: 1) a defect which moved from the left atrium in end systole to the left ventricle in end diastole (2 patients); 2) a defect which remained within the region of the left atrium but decreased in size between end diastole and end systole (3); and 3) a defect which was observed within the region of the left ventricle in end diastole but disappeared in end systole (1). Thus, the GCS is a noninvasive method for detection and evaluation of motion of left atrial myxomas.
46 citations
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TL;DR: The equatorial X‐ray diffraction pattern was recorded from a papillary muscle of a cross‐circulated canine heart at different phases of the cardiac cycle and the peak systolic tension was roughly proportional to the proportion of the projections present in the vicinity of the thin filaments during systole.
Abstract: 1. The equatorial X-ray diffraction pattern was recorded from a papillary muscle of a cross-circulated canine heart at different phases of the cardiac cycle. The intensity ratio of the 1, 0 and the 1, 1 reflexions (I1, o/I1,1) was 0-79 in the systolic phase and 1-19 in the diastolic phase. 2. Using the intensity ratio obtained, the approximate proportion of the myosin projections present in the vicinity of the thin filaments was calculated. This was 70-71% in the systolic phase and 51-52% in the diastolic phase of the total myosin projections. 3. The peak systolic tension was roughly proportional to the proportion of the projections present in the vicinity of the thin filaments during systole. 4. The projections which stayed in the vicinity of the thin filaments during diastole did not produce significant contractile force.
30 citations
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TL;DR: The patient was a 19 year old woman who presented clinically with bacterial endocarditis involving a mildly stenotic pulmonary valve and a large myxoma was found in the right ventricular outflow tract with a polypoid extension that projected into the pulmonary artery in systole and contained a fibrinous vegetation at its tip.
Abstract: The echocardiographic features of a tumor in the right ventricular outflow tract that prolapsed into the pulmonary artery during systole are described. The patient was a 19 year old woman who presented clinically with bacterial endocarditis involving a mildly stenotic pulmonary valve. An echocardiogram, obtained to evaluate the pulmonary valve for bacterial vegetations, showed abnormal echoes throughout the cardiac cycle; they suggested a tumor mass in the right ventricular outflow tract in front of the pulmonary valve with possible extension into the pulmonary artery during systole. Additional tumor echoes confined to diastole were recorded in front of the aortic root and the tricuspid valve. These features were further elucidated with a computer-generated two dimensional cineechocardiogram that clearly showed a portion of the tumor mass passing beyond the position of the pulmonary valve into the main pulmonary artery in systole and returning into the right ventricular outflow in diastole. At surgery, a large myxoma was found in the right ventricular outflow tract with a polypoid extension that projected into the pulmonary artery in systole and contained a fibrinous vegetation at its tip. The left cusp of the pulmonary valve was normal, but the other two leaflets showed evidence of endocarditis.
29 citations
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TL;DR: This technique can safely and reliably induce post-extrasystolic potentiation during echocardiography and is a potentially important adjunct to the noninvasive evaluation of left ventricular function.
Abstract: Left ventricular function was evaluated in 34 patients with the echocardiogram, and an external mechanical cardiac stimulator was used to induce a ventricular premature contraction (VPC) noninvasively. Extent of post-extrasystolic potentiation (PESP) was determined by comparing systolic dimensional shortening and ejection fraction of the sinus beat preceding the VPC to that of the potentiated beat which followed it. Using this technique, a VPC could be introduced into the cardiac cycle of 30 of the 34 patients, six of whom were free of obvious cardiac disease and 24 of whom had valvular, coronary or myopathic heart disease. The only complication observed was mild breast ecchymosis in a female patient. Systolic dimensional shortening and ejection fraction increased from control values by an average of 21% and 17% respectively, with a range of 0-100%. The degree of PESP was very reproducible in repeat studies and when the same patients were subsequently evaluated during a spontaneously occurring or catheter-induced VPC. The technique can safely and reliably induce post-extrasystolic potentiation during echocardiography and is a potentially important adjunct to the noninvasive evaluation of left ventricular function.
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TL;DR: The cardiac respiratory motion indicates that gating of the respiratory cycle as well as the cardiac cycle is necessary in three-dimensional reconstruction of the heart using a large number of heart beats for recording.
Abstract: Based on 39 cineangiographies in 23 patients performed during respiration with tracing of the cardiac chambers and the diaphragm, it has been found that the heart moves significantly with respiration, approximately half as much as the diaphragm during shallow or normal respiration. The cardiac respiratory motion indicates that gating of the respiratory cycle as well as the cardiac cycle is necessary in three-dimensional reconstruction of the heart using a large number of heart beats for recording.
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TL;DR: The purpose of this study is to quantitate separately the hemody namic significance of active atrial transport compared with passive atrial Transport of the atrium at two different heart rates in patients with mitral stenosis.
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TL;DR: Contrast echocardiography during cardiac catheterization was used to confirm ventricular anatomy and to characterize blood flow dynamics in 35 patients with common ventricle, establishing the presence of a single atrioventricular valve.
Abstract: Common ventricle is a rare congenital anomaly in which the ventricular chamber receives blood from two separate atrioventricular valves or from a common atrioventricular valve. We used contrast echocardiography during cardiac catheterization to confirm ventricular anatomy and to characterize blood flow dynamics in 35 patients with common ventricle. After injections of dye, a cloud of echoes anterior to the mitral valve echo during the rapid inflow phase of ventricular diastole is indirect evidence of common ventricle with two atrioventricular valves. Common ventricle with an outflow chamber is characterized by a smaller ventricular chamber visualized anterior to both atrioventricular valves which opacifies with subsequent ventricular systole. The arrival of all dye posterior to the only recorded atrioventricular valve further established the presence of a single atrioventricular valve. These contrast flow patterns gave greater specificity to the standard M-mode echocardiographic assessment of patients suspected of having common ventricle.
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TL;DR: The results support the hypothesis that phasic changes in left atrial dimension are largely responsible for the echocardiographically observed movement of the aortic root and indicate a potential role for eChocardiography in the analysis ofleft atrial events.
Abstract: The echocardiographically recorded movement of the aortic root was studied by analysing the relation between posterior aortic wall motion and other intracardiac events. The systolic anterior movement of the aortic root continued beyond aortic valve closure and in cases with mitral regurgitation began significantly earlier than in normal subjects. The diastolic rapid posterior movement began after mitral valve opening but did not occur in patients with mitral stenosis. The total amplitude of aortic root motion was increased in patients with mitral regurgitation, diminished in cases of mitral stenosis, and was normal with aortic regurgitation. In patients with atrioventricular block an abrupt posterior movement followed the P wave of the electrocardiogram irrespective of its timing in diastole. These observations correlate with the expected changes in left atrial volume during the cardiac cycle both in the normal subjects and patients with heart disease. The results support the hypothesis that phasic changes in left atrial dimension are largely responsible for the echocardiographically observed movement of the aortic root and indicate a potential role for echocardiography in the analysis of left atrial events.
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TL;DR: In this paper, a basic understanding of the dynamics of cardiac contraction involving the wall and fluid motion was acquired, starting from the equations of motion for the ventricle wall, the stress distributions in the longitudinal and latitudinal directions were obtained by integration of the equations across the wall for various arbitrarily shaped left ventricles.
Abstract: An investigation was carried out to acquire a basic understanding of the dynamics of cardiac contraction involving the wall and fluid motion. Starting from the equations of motion for the ventricle wall, the stress distributions in the longitudinal and latitudinal directions were obtained by integration of the equations across the wall for various arbitrarily shaped left ventricles. Specific discussion is included of ventricular acceleration, nonlinear effects, simplified models, the significance of bending moments, ventricular work and volume change, wall thickness effects, ventricular dysfunction, and the coupled fluid dynamics. The results were appraised by application to patient and animal data, which indicated that the first order theory presented is a reasonable approximation for the coupled ventricular wall and fluid dynamic interaction, and has application to clinical studies.
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TL;DR: It is concluded that diminished obstruction resulted from augmented ventricular end-diastolic volume produced by atrial contraction.
Abstract: A young man with IHSS who developed complete heart block was successfully treated with a permanent pacemaker. Echocardiography and other noninvasive techniques showed marked cycle-to-cycle variation in the evidence of subvalvular obstruction which decreased markedly when atrial systole preceded the ensuing paced complex by an appropriate interval. Because cycle length and therefore afterload were constant, it is concluded that diminished obstruction resulted from augmented ventricular end-diastolic volume produced by atrial contraction. The mitral valve echocardiogram showed unusual movements in diastole dependent upon the timing of atrial systole. Early reopening of the leaflets was a direct result of atrial contraction when the P waves were appropriately timed in presystole, whereas late reopening was passive and a result of ventricular filling in mid-diastole. Variations in intensity of the first heart sound correlated with the position of the mitral valve leaflets at the onset of ventricular systole.
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TL;DR: The ventromedial cardiac nerve is implicates in the genesis of cardiac arrhythmias, probably the result of enhanced automaticity in the atrioventricular junction area and in the ventricles produced by stimulating the sympathetic nerve fibers.
Abstract: The effects of ventrolateral and ventromedial cardiac nerve (left sympathetics) stimulation on cardiac force, on rate, and on arrhythmogenic responses were characterized and quantitated. The stimulation of left sympathetic nerves produced augmentation in cardiac contraction in 45% of the experiments, an augmentation of both a cardiac rate and force in 47%, and in cardioacceleration alone in 8%. Two characteristic patterns of arrhythmogenic responses were elicited from stimulations of 100 sympathetic nerves. The two types of neurally induced arrhythmias were atrioventricular junctional or ventricular in origin. The onset and duration of the arrhythmias were quantitated. Both types of neurally induced arrhythmias were prevented either by blocking the beta receptors with propranolol or by preventing the neural release of norepinephrine with bretylium tosylate. The neurally induced arrhythmias were probably the result of enhanced automaticity in the atrioventricular junction area and in the ventricles produced by stimulating the sympathetic nerve fibers. This report thus implicates the ventromedial cardiac nerve in the genesis of cardiac arrhythmias.
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TL;DR: The pulmonary valve echogram had the remarkable variation from presystolic opening to shallow 'a' wave with respiration, and pulmonary ' a' wave seemed to be produced mainly by the motion due to the ventricular filling or pressure change during atrial systole superimposed on the entire cardiac motion, especially during inspiration.
Abstract: Echocardiogram of the pulmonary valve was obtained in 31 normal subjects to examine the effects of atrial contraction on the valve motion.In normal echograms, the mid to late diastolic slope was 5.7 mm/sec (range: 0-18), the depth of 'a' wave 3.5 mm (2-6), opening slope 297 mm/sec (190-460), and right-sided pre-ejection period (RPEP) 92 msec (70-120). The RPEP was not influenced by the heart rate. The 'a' wave width showed good correlation (r=0.81) with the PQ interval, though the latter was longer than the former. There was no statistically significant difference in the width and amplitude of the 'a' wave between aortic and pulmonary valve echoes during expiratory apnea. Typical respiratory change of the normal pulmonary valve echo was such that, during inspiration, the 'a' wave became exaggerated and caused a presystolic opening, although the degree of the change in individual cases was variable. It was concluded: 1) the pulmonary valve echogram had the remarkable variation from presystolic opening to shallow 'a' wave with respiration, 2) pulmonary 'a' wave seemed to be produced mainly by the motion due to the ventricular filling or pressure change during atrial systole superimposed on the entire cardiac motion, especially during inspiration. The 'a' wave appeared to reflect the diastolic hemodynamics of right heart, 3) the pulmonary valve echogram recorded during expiratory phase should be adopted for the assessment of right cardiac dynamics.It was preliminarily reported that presystolic opening of the pulmonary valve was observed also in constrictive pericarditis.
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TL;DR: In the canine model there exist major differences in the velocity-displacement relationships of systolic contraction between normal and ischemic myocardium, which can be detected within the time period of one cardiac cycle.
Abstract: In the canine model there exist major differences in the velocity-displacement relationships of systolic contraction between normal and ischemic myocardium. These differences are noninvasively measurable in vivo from video recordings of the fluoroscopic image of the heart, and can be detected within the time period of one cardiac cycle. Velocity data is plotted against the corresponding wall displacement on orthogonal axes (phase-space), producing characteristic loops which give an immediate visual indication of myocardial dysfunction.
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TL;DR: The potential advantages of myocardial imaging are numerous and include the ability to differentiate the myocardium from the blood pool which would permit volume analysis, determination of ejection fraction, study of akinesis and dyskinesis, evaluation of ischemicMyocardium and, ultimately, the visualization of the lumen of coronary arteries.
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TL;DR: The pressure gradient of the Abrams-Lucas valve was significantly lower than that of the 29 mm Björk-Shiley valve and all other prostheses tested, but its reflux level was higher at 12 ml per stroke.
Abstract: As a result of the durability problems associated with the first Abrams-Lucas mitral valve, a redesigned model has recently been introduced into limited clinical trials. The new valve was subjected to in-vitro pulsatile flow studies, and measurements were made of mean diastolic pressure gradient and volume of reflux on closure. Similar measurements were made on other mitral valve prostheses of comparable size. High-speed cinematography was used to analyse the motion of the occluder during the simulated cardiac cycle, and the flow patterns produced by the valve in the model ventricular cavity were observed and photographed. The pressure gradient of the Abrams-Lucas valve was significantly lower than that of the 29 mm Bjork-Shiley valve and all other prostheses tested, but its reflux level was higher at 12 ml per stroke. The valve opened and closed smoothly and the flow visualisation study revealed that the valve produced a large vortex or swirl in the model ventricular cavity.
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TL;DR: This report demonstrates a spontaneous gap produced by His extrasystoles within the cardiac cycle during which premature impulses are blocked in the conduction system, while impulses of greater or lesser prematurity are conducted.
01 Jan 1977
TL;DR: The clinical characteristics in all the reported cases of left ventricular myxoma prolapsing through the aortic valve during each ventricular systole are reviewed.
Abstract: A 33 year old man with the findings of mild aortic stenosis had an echocardiographic diagnosis of left ventricular myxoma prolapsing through the aortic valve during each ventricular systole. The M-mode echocardiogram, B-scan ultrasonogram and angiograms of this patient are presented. The clinical characteristics in all the reported cases of left ventricular myxomas are reviewed.
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01 Jan 1977•
TL;DR: It was shown that bursting activity of the superior cardiac nerves belongs to mechanoreceptors which are located in the ventricle and the adjacent arterial vessels, and the discharge in these mechano-receptors coincides with ventricular systole.
Abstract: On the basis of changes in afferent impulsation emerging from the heart of the tortoise A. horsfieldi under various conditions of cardiac haemodynamics, it was shown that bursting activity of the superior cardiac nerves belongs to mechanoreceptors which are located in the ventricle and the adjacent arterial vessels. The discharge in these mechano-receptors coincides with ventricular systole. The second, predominant, type of afferentation is presented by irregular continued activity in both the superior and inferior vagal branches. The origin of this activity remains uncertain.
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01 Jan 1977
TL;DR: The timing of contraction and the contraction pattern of both septal and posterior wall in patients with W.P.W. syndrome is studied to gain information about the timing of excitation.
Abstract: By echocardiography it is possible to localize both septal and left ventricular posterior wall motion during the cardiac cycle 1)–3). Timing of contraction of any part of the heart is effected by timing of excitation of that particular area. We studied the timing of contraction and the contraction pattern of both septal and posterior wall in patients with W.P.W. syndrome, to gain information about the timing of excitation.
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TL;DR: The effect of ectopic stimulation of atria (premature ventricular contraction) on the activity of atrial type B receptors has been studied in dogs and the results show clear associations with prolapse in dogs.
Abstract: SUMMARY
1. The effect of ectopic stimulation of atria (premature ventricular contraction) on the activity of atrial type B receptors has been studied in dogs.
2. In sixteen open-chest dogs, discharge from right or left atrial type B receptors (identified by their response to pulmonary artery occlusion) was recorded. Direct stimulation of either atrium produced an increase in the activity of the left atrial but a decrease in the right atrial receptors. The earlier during the ventricular systole that the premature ventricular contraction occurred the more marked was the effect.
3. In a separate series of fourteen closedchest experiments the right atrium was stimulated internally via the external jugular vein. The effects on the activity of the atrial type B receptors were similar to those observed during the open-chest experiments.
4. It is concluded that in the dog the technique of internal stimulation of the right atrium without opening the chest can be used to distinguish between the right and left atrial type B receptors.