Showing papers on "Cardiac cycle published in 1979"

Instantaneous pressure-volume relationship of the canine right ventricle.

Abstract: SUMMARY The instantaneous isovolumic and ejecting pressure-volume relationship of the right ventricle was studied in 11 cross-circulated, isolated canine hearts to characterize the right ventricular contractile state. Accurate measurement of volume was achieved by the use of a water-filled, thin latex balloon in the right ventricle connected to a special volume loading and transducing chamber. Pressure was measured with a miniature pressure transducer mounted within the balloon. Wide variations in loading conditions were achieved by changing the volume of air above the volumetric chamber. The pressure and volume data were collected from multiple beats under a constant contractile state in the same mode of contraction while the left ventricle was vented to air. Linear regression analysis applied to each of the isochronal pressure-volume data sets at 20-msec intervals from the onset of contraction showed a highly linear correlation between the pressure and the volume. Both the slope and the volume intercept of the regression lines changed with time throughout the cardiac cycle. The maximal slope of the regression line (E,,,,) averaged 2.50 ± 0.49 mm Hg/ml (mean ± SD) for ejecting beats and 2.68 ± 0.55 mm Hg/ml for isovolumic beats. Epinephrine infusions of 12.5 fig/min and 25.0 /ig/min increased E^u by 31% and 82%, respectively (P < 0.005). We conclude that: (1) The instantaneous pressure-volume relationships of the right ventricle in the isovolumic and ejecting modes can be regarded as linear, at least within the physiological range; however, these two modes of contraction did not yield an identical relationship. (2) The slope of these pressure-volume relationship curves changes with a change in the contractile state. Ore Res 44: 309-315, 1979 IT IS WELL KNOWN that there are major anatomical and physiological differences between the right and left ventricles. Compared with the left ventricle, the right ventricle has a greater regional variation in wall thickness and a more complex geometric shape. The developed pressure in systole is much smaller, and intraventricular pressure falls considerably while ejection proceeds. Much recent research has been focussed on left ventricular function, yet there is little quantitative information concerning the right ventricle, particularly with respect to the question of how to characterize contractile state and pumping ability. Those indices of contractile state used in characterizing left ventricular function have not been quantified in and shown to be valid for the right ventricle. Since there are major differences between left and right ventricles, we investigated whether right ventricular contractile state could be described in a similar fashion as left ventricular contractile state. In this study we determined the time-varying ratio of instantaneous pressure to volume, which has been shown to be sensitive to changes in left ventricular contractile state and nearly independent of

Equilibrium (Gated) Radionuclide Ventriculography

Abstract: Equilibrium (gated) radionuclide ventriculography is based on the fact that the heart is a periodically contracting organ. The amount of radioactivity in the heart is proportional to the amount of blood in its cavities, provided there is homogeneous distribution in the blood pool. Thus, the precordial count rate changes reflect the cyclic volume changes of the heart. Because the precordial count rate is too low for a reliable determination of a beat-by-beat time-volume curve, Hoffmann and Kleine applied a gating procedure, using the R-wave of the electrocardiograph (ECG) and a multichannel analyzer [24] to synchronize and sum hundreds of heart cycles. This resulted in a representative cardiac cycle and a well-delineated time activity curve, which is analogous to a time-volume curve. Since the left and right ventricles could not be differentiated by this technique, and an additional x-ray investigation was required for their delineation, Adam et al. [1, 4] and Bitter et al. [9] applied the gating procedure to a camera computer system. Representative time-activity (time-volume) curves of the left and right ventricle were obtained using an electronic cursor to isolate the ventricles.

Morphology and classification of atrioventricular defects.

Abstract: Anatomical studies were made on 114 necropsy specimens of atrioventricular defects with atrioventricular concordance. The malformation is characterised by disproportion between the ventricular inlet and outlet dimensions and a malorientation of the aortic valve relative to the atrioventricular valve or valves. Associated with this there is a characteristic 'scopped-out' appearance of the muscular ventricular septum, gross abnormalities of the membranous components of the septum as compared with the normal heart, and narrowing of the aortic outflow tract. Hearts with these anatomical features can be divided into partial and complete forms depending on the morphology of the atrioventricular annuli. In the partial form the septal leaflets are conjoined to give separate mitral and tricuspid orifices, the conjoined leaflets being displaced into the ventricles and usually attached to the crest of the septum. In the complete form, anterior and posterior components of the 'septal' leaflets are separate, so that a single valve orifice connects the atrial to the ventricular chambers. Further subdivision of the complete form, apart from the morphology of the anterior leaflet, is dependent upon the presence or absence of an ostium primum atrial septal defect.

Dynamic geometry of the left atrium and left ventricle in acute mitral regurgitation.

Abstract: The instantaneous transverse diameter of the left atrium, left ventricular free wall segment length (SEG), and the long axis of the anterior papillary muscle (APM) length were measured throughout the cardiac cycle, using ultrasonic dimension gauges together with left atrial and left ventricular pressures in 12 open-chest dogs. During atrial contraction, left atrial diameter decreased from 19.7 to 18.7 mm, while left ventricular dimensions increased simultaneously. During ventricular ejection, percent shortening was 26% in SEG and 10% in APM, while atrial diameter increased continuously to 20.5 mm, with a concomitant rise in the v wave of left atrial pressure. After normal mitral valve opening, left atrial diameter decreased rapidly simultaneously with the y descent of atrial pressure. Graded mitral regurgitation was then produced by sectioning the chordae tendineae. With moderate mitral regurgitation, end-diastolic length of the SEG increased by 27%, while extent of shortening (delta L) was augmented by 9...

Blood flow in pulmonary veins: II. The influence of events transmitted from the right and left sides of the heart.

Abstract: The wave form of blood flow in the large extra parenchymal pulmonary veins has an inverse relationship to the pressure wave form in the left atrium during each cardiac cycle. However, when vein flow from the lungs is separated from the left atrium by diverting it into a constant pressure reservoir, its wave form then resembles a lung capillary flow pulse, though delayed from it in time and reduced in amplitude. The pulsatility of flow in pulmonary veins separated from the left atrium is further reduced when transcapillary pressure is elevated by lung inflation. However, in the intact state, the relation between the pattern of pulmonary vein flow and left atrial pressure remains unaffected by lung inflation. It is postulated that the thin walled extraparenchymal pulmonary veins together behave as a collapsible reservoir which enables outflow from them to be determined by changes in left atrial pressure, in spite of variations of pulsatile flow into them from the lungs.

Influence of aging on left ventricular hemodynamics and stiffness in beagles.

Abstract: We studied the influence of aging on the contractile performance, stiffness, and contraction time of the canine left ventricle. Eight young (27 +/- 2.5 months, mean +/- SE) and seven old (128 +/- 20.5 months) beagles were placed on complete cardiopulmonary bypass, the arterial pressure was adjusted to 80 mm Hg, and the heart contracted isovolumically at a paced rate of 120 beats/min. Diastolic pressure-volume curves were established for each unpaced left ventricle at the beginning of each experiment, and the volume at the knee of the curve was used during the subsequent data collection when the heart was paced. Stiffness was measured with a sinusoidal forcing function, which imposed a sinusoidal displacement of 1 ml at 20 Hz into a balloon placed in the left ventricle. In each ventricle, stiffness was related linearly to pressure during the cardiac cycle, and was greater for any given pressure in the older beagles. Contraction duration was prolonged in the older dogs. In an additional seven old beagles during right heart bypass time, and duration of contraction were longer than in seven young beagles. Aging of the beagle heart is associated with an increase in left ventricular systolic and diastolic stiffness and prolonged duration of contraction.

Cardiac imaging with CT scanner

Abstract: The patient's ECG signal is employed in a traverse-and-rotate type CT scanner as a time base for triggering the beginning of a traverse such that the traveling beam reaches the heart at a desired phase of the cardiac cycle. For a purely-rotational-type CT scanner, continuously generated scan data is only stored for corresponding phases of successive cardiac cycles. Alternatively, gating of the beams themselves can be controlled by the ECG signal. The use of a pacemaker to stabilize the cardiac period is described along with a system for recognizing unacceptable variations in the cardiac period. In a traverse-and-rotate-type fan-beam CT scanner, the effective beam width is narrowed to hasten the traverse of the heart.

Characterization of the extravascular component of coronary resistance by instantaneous pressure-flow relationships in the dog.

Abstract: SUMMARY To investigate the mechanical effects of the myocardium on the blood perfusion of the canine left ventricle, phasic total left ventricular (LV) coronary blood flow, perfusion pressure, LV pressure, aortic flow rate, and LV segment length were recorded continuously in an open-chested dog heart preparation. These variables were analyzed on a digital computer and time synchronized so that coronary pressure-flow curves could be drawn for various instants in the cardiac cycle. During diastole, the pressure-flow relationship is linear, changing to a nonlinear curve with the onset of systole. To estimate phasic patterns of coronary resistance and intramyocardial pressure (IMP), a model based on the vascular waterfall mechanism was developed and fitted to the experimental data. The results of this operation show inferred coronary resistance patterns that increase during ejection and remain constant during diastole and isovolumic contraction. Assuming LV pressure to represent endocardial IMP, the estimated epicardial IMP signal averages 42.1 ± 13.3% of peak LV pressure at this instant of peak pressure. Furthermore, increases in end-diastolic volume reduced the changes in inferred coronary resistance taking place during ejection, but the epicardial IMP signal remained practically unchanged. Circ Res 45: 378-390, 1979

Echocardiographic analysis of interatrial septal motion.

Abstract: Interatrial septal motion was analyzed in 12 normal subjects and 19 patients with right or left atrial overloading using a new method for recording echograms of the mid portion of the interatrial septum through each cardiac cycle. In normal subjects, septal motion was characterized by eight distinct points that were identified and designated on the septal echogram. The septum showed gradual anterior motion (toward the right atrium) in mid and end systole and in early diastole. After reaching the most anterior point, it moved posteriorly (toward the left atrium). During mid diastole it showed very little motion. After the P wave of electrocardiogram it showed slight posterior and then anterior motion. In all eight patients with mitral stenosis, the motion of the interatrial septum was diminished. In all seven patients with mitral regurgitation due to chordal rupture, the septal motion was increased. Systolic fluttering of the septum was observed in four of seven patients. In two patients with Ebstein's anomaly, paradoxical motion of the interatrial septum (posterior motion in systole) was observed. In two patients with primary pulmonary hypertension, septal motion was very much decreased. Interatrial septal motion was thought to result from the interatrial pressure gradient through each cardiac cycle. This method of recording the motion of the interatrial septum seems to be useful for diagnosing right or left atrial overloading and for studying hemodynamic events in both atria.

Persistence and effects of sinus rhythm after Fontan procedure for tricuspid atresia.

Abstract: Four patients who had had a Fontan type of procedure for tricuspid atresia 23, 6, 6, and 11 months previously were investigated by ambulatory electrocardiographic recording and simultaneous recording of the jugular venous pressure and echocardiogram of the conduit or pulmonary valve. All had been considerably improved by the operation. In 1 patient episodes of supraventricular tachycardia were recorded but no rhythm disturbance was detected in the other 3. Pulmonary blood flow was shown to be pulsatile and atrial systole is an important factor in this. The conduit valve showed delayed opening and slow closure suggesting that its presence in the pulmonary circuit may be unnecessary.

Changes in the sensitivity of left atrial receptors following reversal of heart failure.

Abstract: Recordings were made from left atrial type B receptors in six mongrel dogs after recovery from the cardiac effects of a chronic AV fistula. All animals showed hemodynamic and clinical signs of congestive heart failure after 44.5 +/- 3.6 days with a patent Dacron shunt between the aorta and inferior vena cava below the level of the renal arteries. The stimulus-response curves of the left atrial stretch receptors (change in spikes/cardiac cycle or in spikes/minute vs. change in left atrial pressure) after 45.2 +/- 7.2 days of shunt closure were similar to those seen in sham-operated dogs from a previous study. However, the slope of the stimulus-response curve of the dogs in which the AV fistula was closed was significantly greater than the slope of the curve from the AV fistula dogs with heart failure. Radiographs indicated that after shunt closure, cardiac dilatation had regressed. This study incidates that a decrease in the sensitivity of left atrial receptors in dogs with congestive heart failure is a reversible phenomenon and that the initial depression is most likely related to the concomitant cardiac dilatation that accompanies the failure state.

Instantaneous pressure-volume relationship of right atrium during isovolumic contraction in canine heart.

Abstract: We studied the contraction of the right atrium in an excised cross-circulated heart preparation. Atrial volume and instantaneous atrial pressure were measured in a water-filled balloon fitted in the spontaneously contracting right atrium. The relation of instantaneous pressure to volume was analyzed by collecting pressure data from multiple isovolumic contractions with different volumes but measured at multiple identical time points in the contraction cycle. The relation was found to be quasi-linear during most of atrial systole and diastole. A linear regression formula P(t) = K(t)[V- VD(t)] was therefore fitted to the data. K(t) and VD(t) of the regression formula are the slope and the volume axis intercept in the pressure-volume plane, respectively. When the atrium beat spontaneously at a regular sinus rhythm with no inotropic intervention. K(t) increased during systole and decreased during diastole, whereas VD(t) decreased during systole and increased during diastole. The average value of K was 13 +/- 1.7 (SE) mmHg . kg . ml-1 at the end of diastole and 33 +/- 0.02 (SE) mmHg . kg . ml-1 at the end of systole. The average value of VD was 0.303 +/- 0.017 (SE) ml . kg-1 at the end of diastole and 0.212 +/- .025 (SE) ml . kg-1 at the end of systole. Enhancement of contractility with epinephrine or Ca2+ significantly increased the value of K at the end of systole, but it did not significantly affect either K at the end of diastole or VD at the end of systole and diastole.

Effects of repetitive bursts of vagal activity on atrioventricular junctional rate in dogs.

Abstract: A stable atrioventricular (AV) junctional rhythm was produced in open-chest dogs by injecting pentobarbital into the sinus node artery. When the cervical vagus nerves were stimulated repetitively, the junctional pacemaker cells tended to become synchronized with the vagal activity. During such synchronization, the junctional rate varied directly rather than inversely with the frequency of vagal stimulation. The magnitude of the chronotropic response depended on the timing of the vagal stimuli within the cardiac cycle. In 9 dogs, when the mean heart periods were plotted as a function of the R-st intervals (i.e., the time from the beginning of ventricular depolarization to the beginning of the stimulus burst), the mean heart periods varied from a maximum of 1,815 ms to a minimum of 1,160 ms, depending on the R-st interval. A small change in the R-st interval was capable of evoking a relatively large change in cycle length. Therefore, the impulses from various efferent vagal fibers to the AV junction must arrive almost synchronously, the released acetylcholine must be removed rapidly, and the sensitivity of the pacemaker cells to acetylcholine must change rapidly at some critical time during the cardiac cycle.

Model analysis of the contribution of atrial contraction to ventricular filling.

Abstract: We studied the contribution of atrial contraction to ventricular filling by modelling the right heart and the associated vasculature. Right atrial and ventricular contractions were represented by periodically varying volume elastances which are independent of loading conditions. The values of these elastances were experimentally determined. The systemic veins, the tricuspid valve and the pulmonary arteries were all represented by impedance networks. For these impedances we used as much experimentally obtained information as possible. The dynamic pressure and flow waveforms observed in the model under control conditions generally agreed with those reported in the literature. We therefore proceeded to analyze the effects of changing the time interval between atrial systole and ventricular systole, atrial contractility, heart rate, and blood inertance. There was an optimal atrial systole-ventricular systole interval of about 0.1 sec for ventricular filling. Stroke volume of the ventricle was enhanced by an increase in atrial contractility, a decrease in heart rate, and an increase in blood inertance. The effect of changing atrial compliance was found to be dependent on heart rate. Contribution of atrial contraction to ventricular filling was also found to be more significant during exercise than at rest.

Mitral stenosis with high left ventricular diastolic pressure.

Abstract: Three patients with mitral stenosis are described, in whom the haemodynamic findings at cardiac catheterisation were more suggestive of left ventricular myocardial disease, in that the left ventricular diastolic pressure was high and the mitral valve gradient small. However, their echocardiograms showed abnormal wall movement during diastole characteristic of severe inflow obstruction, with slow and protracted filling, and at operation mitral stenosis was confirmed. Left ventricular wall stress was estimated throughout the cardiac cycle in one patient, and the diastolic stress-strain relation shown to be abnormal. The effects of mitral stenosis on left ventricular function are complex, and are not explicable simply by reduction in size of the mitral orifice.

Presystolic Pulmonary Valve Opening in Constrictive Pericarditis

Abstract: Right heart pressure tracings were studied in 5 cases with constrictive pericarditis. The pressure of the A-wave in the right atrium of these cases was higher than the pulmonary arterial diastolic pressure. In addition, a presystolic wave appeared in the pulmonary arterial and the right ventricular pressure tracings, in coincidence with atrial systole. The pressure of this presystolic wave was similar to that of the right atrial A-wave. This suggests that the pulmonary valve opens following atrial systole, and then the blood flows into the pulmonary artery in the presystolic phase in patients with constrictive pericarditis. In 2 cases, pulmonary valve echograms were recorded. The a-dip in these 2 cases was as deep as 8.4 mm and 9.6 mm (1.8-4.1 mm with a mean of 2.80 mm for normal men), and its duration was prolonged to 0.17 sec and 0.18 sec (0.10-0.13 sec with a mean of 0.115 sec for normal men). In conclusion, such a deep and prolonged a-dip on pulmonary valve echogram is presumably a sign of presystolic pulmonary valve opening.

Use of M-Mode Echocardiography in Clinical Pharmacology

Abstract: M-mode echocardiography is a method of using pulsed ultrasound to detect the position and movement of intracardiac structures. The technique itself, and its use in the study of left ventricular disease has been described in a number of recent monographs and reviews (Feigenbaum, 1976; Roelandt, 1977; Mason and Fortuin, 1978). It allows a number of aspects of left ventricular function to be studied. Of these, the simplest is the measurement of the transverse dimension of the left ventricular cavity at the level of the mitral valve apparatus. The technique has considerable potential advantages for clinical pharmacological studies in that it is non-invasive, has a repetition rate of 1000/s, compared with 50/s for angiography, or even less for nuclear methods. It shows endo- and epicardial surfaces of the posterior left ventricular wall unequivocally throughout the cardiac cycle, and allows septal movement to be studied. In addition, it is totally safe, so that it can be used on normal volunteers. Performing echocardiography, however, is difficult, and at least 6 months’ practice is likely to be required before records of adequate technical quality are obtained.

Patterns of atrial activation during right ventricular pacing in patients with concealed left-sided Kent pathways.

Abstract: A 'concealed' accessory pathway was suspected in 12 patients because of eccentric left atrial activation during tachycardia. Retrograde conduction during ventricular pacing may occur over the atrioventricular node, the accessory pathway, or both. There were 4 patterns of ventriculoatrial conduction in response to ventricular extrastimuli (V2) at various coupling intervals: (1) exclusive accessory pathway conduction throughout the cardiac cycle in 2 patients; (2) exclusive accessory pathway conduction at long coupling intervals and exclusive atrioventricular node conduction at short coupling intervals in 2 patients; (3) variably fused accessory pathway/atrioventricular node conduction at long coupling intervals but exclusive accessory pathway conduction at short coupling intervals in 4 patients; (4) fused accessory pathway/atrioventricular node conduction at long coupling intervals but exclusive atrioventricular node conduction at short coupling intervals in 4 patients. With increased prematurity of V2 the ventricle to right atrial interval prolonged conspicuously in 11 of 12 patients whereas the ventricle to left atrial interval remained constant until the refractory period of the accessory pathway in all but 2 instances where intraventricular delay occurred. This study emphasises the importance of left atrial recordings in these patients.

Importance of sequential atrioventricular pacing in obstructive myocardiopathy with atrioventricular block

Abstract: A case of atrioventricular block (AVB) complicating hypertrophic obstructive cardiomyopathy is reported and analysed with respect to the results of cardiac catheterisation. The installation of 2nd degree AVB was associated with an increase of the intraventricular pressure gradient from 36 to 128 mmHg. This aggravation was related to the lenghtening of diastole which lowered the aortic diastolic pressure and allowed a more forceful ventricular contraction with a reduction in the calibre of the intraventricular stenosis. The sudden lenghtening of diastole also led to an increased contractility of the following systole. In complete AVB the increased gradient was related to a reduction in ventricular volume secondary to the loss of atrial systole. The 33 mmHg pressure gradient disappeared when spontaneous atrial systole or an atrial systole provoked by sequential atrioventricular pacing preceded ventricular contraction. Sequential atrioventricular pacing would seem to be the most appropriate pacing technique in hypertrophic obstructive cardiomyopathy complicated by complete AVB.

Cardiac responses of dogs to nonsynchronous and heart synchronous whole-body vibration

Abstract: Changes in cardiac function produced by synchronizing vibration-induced forces with events in the cardiac cycle were compared to those for the nonsynchronous case in eight chronically instrumented,...

Aortic nerve activation: effect of stimulus train composition on heart rate.

Abstract: The central end of the sectioned left aortic nerve was stimulated within one heart cycle by a train of electrical pulses, producing a reflex reduction in heart rate in the anesthetized rabbit. Relative importance of the stimulation variables (train duration, pulse frequency, and pulse number) in producing bradycardia was investigated by maintaining one variable constant, while altering the other two over a wide range. At each fixed pulse frequency, maximal bradycardia was obtained by the longest train duration that corresponded with the greatest pulse number. At each fixed train duration, maximal bradycardia was achieved with pulse frequencies between 80--120 Hz and remained maximal up to 160 Hz. Stimulating over wide variations in train duration and pulse frequency at any fixed pulse number produced no significant differences in heart rate reduction at that pulse number. These results indicate the dominant importance of total pulse number per cardiac cycle in determining the magnitude of the heart rate response and reveal an apparent frequency limitation within the reflex.

Quantitation of Aortic Regurgitation by a Percutaneous 128-Channel Digital Ultrasound Doppler Instrument

Abstract: A newly developed 128-channel pulsed ultrasound Doppler instrument with digital signal processing permits a non-invasive analysis of the blood stream in larger vessels within a range of about 10 cm (1). It utilizes a microcomputer and provides quasi-instantaneous velocity profiles at 0.016 sec intervals which may be averaged over 8–16 heart cycles. To compute the volume flow rate pattern the vessel cross-section is assumed to be circular and the velocities in each of the channels are considered as constant within the corresponding half-annulus of the lumen. One of the potential applications of this instrument in cardiology appears to be the non-invasive determination of the regurgitation fraction fao in patients with aortic insufficiency (A.I.). Theoretically fao is defined as (2): $${\rm f}_{\rm ao}(\%)={\rm TSV-SV\over TSV}\cdot 100,$$ where TSV is the total stroke volume and SV the net forward stroke volume. If the coronary blood flow can be disregarded, one may approximate fao as the ratio of back flow to total forward flow in the ascending aorta during a cardiac cycle. Such volume flow quantifications require on one hand a continuous recording of the velocity profiles in the ascending aorta during several heart beats, and on the other, a sufficiently accurate evaluation of the flow on the basis of the recorded profiles (Fig. 1). The first of these two requirements implies that the transducer can be positioned and oriented such that the ultrasound beam intersects the axis of the ascending aorta at all times and that the angle between the beam and this axis remains essentially constant, even though the aorta exhibits rhythmic displacements during the heart cycle.

A model for the cardiac-associated changes of the thoracic electrical impedance in man.

Abstract: A simple mathematical model has been developed which is able to fit the impedance waveform produced by normal and abnormal subjects throughout the cardiac cycle with reasonable precision. Contributions from both the aorta and vena cava are significant. Fitted values of model parameters offer potentially useful clinical information. Estimates of the stroke volume obtained from the model correlate well with values derived from the maximum rate of change of the thoracic impedance during systole but are in poorer agreement with values obtained using tracer dilution techniques.

Cardiac conducting system of Gallus domesticus with special reference to the atrial bundles.

Abstract: Gross anatomy and histology of the cardiac conducting system of Gallus domesticus has been studied. Detailed histology of the atrium revealed for the first time, in the avian heart, the presence of three atrial bundles which communicate between the sinuatrial node and the atrioventricular node. Purkinje fibres in the subendocardium of the right atrium are observed. An atrioventricular segment comprising of the posterior end of the interatrial septum and the atrioventricular nodal region has been reported in which the three atrial bundles converge. The role of the atrial bundles in the cardiac contraction has been discussed.

Observations on the mechanism of human ventricular vulnerability during premature stimulation

Abstract: Spontaneous ventricular extrasystoles (V3-beats) occur frequently after premature ventricular stimuli induced during a paced ventricular rhythm. The V3 phenomenon was observed in 100 of 158 patients (63.3%) with and without heart disease being studied for the evaluation of various rhythm disorders. In patients with an old myocardial infarction there was an increased tendency to exhibit short ventricular salvos (V3–V5 beats) after prematurely elicited test pulses. V3-beats occurred less frequently in patients with a bundle branch block than in patients with normal intraventricular conduction. The statistical analysis of several variables obtained during the investigation revealed that the frequency and the appearance time of the V3 beats and the vulnerable period of the cardiac cycle are related to a critical delay of the retrogradePurkinje-His conduction time of the premature test pulse, the basic rate of the drive rhythm and the state of excitability of the ventricular myocardium. The results strongly suggest a re-entry mechanism generating the spontaneous ventricular extrasystoles. The main delay of conduction of the permature test pulse seems to be localized not within the working myocardial fibers or the proximalHis-Purkinje system but rather within the distalPurkinje fiber system. Therefore, the re-entry pathway of the V3 beats is thought to be confined to the right ventricularPurkinje fiber network near the site of stimulation. Clinically, it can be deduced that an artificially induced ventricular re-entry beat is tolerated and extinguished in the stable heart by physiological protective mechanisms. In the diseased heart, however, an increased state of fiber inhomogenity may be generated by the V3 beat leading to recurrent re-entry impulses.

Correlation between atrial and ventricular contractility a possible use of the atria to control the artificial heart

Abstract: The possibility of using the atrial myocardium to control artificial ventricles is examined. Correlation was studied between the tension of the atrial wall and the tension and pressure in the ventricles during random variation of the cardiac rhythm was studied. Tension in the wall of the corresponding part of the heart was recorded by means of arch strain gauges and the intraventricular pressure by means of an electromanometer during catheterization of the chambers of the ventricles. The cardiac rhythm varied from 2.0 to 4.0 sec−1. Correlation was demonstrated in the atria between the tension and interspike interval (coefficient of correlation 0.62±0.05). Close correlation was detected between tension in the atrial wall and the intraventricular pressure. The coefficient of correlation in this case varied from 0.713±0.09 to 0.874±0.02 depending on the mean duration of the interspike interval. Information on atrial contractions can be used to control an artificial heart.