Onset Of Ventricular Systole Research Articles

Right atrial function: still underestimated in clinical cardiology

As already described in several studies, the left and right atrium acts as a reservoir during ventricular systole to transport blood from, respectively, the caval veins and the pulmonary veins to the right and left ventricle, respectively. However, atrial volume and function is also associated with clinical outcome. In a multivariate risk model for the prediction of age-related events an indexed left atrial volume above 32 ml/m2 was an independent risk factor for the prediction of the first age related cardiovascular event [1]. Although clinical outcome was corrected for age we have to realize that left atrial size and volume could be influenced by age with larger volumes found in the elderly population [2]. However, this finding has been debated in recent studies in which normal younger and elderly individuals were compared as left atrial volume is concerned [3]. Increase of left atrial volume if people get older could be related to increase of cardiac pathology at an older age: atrial fibrillation and diastolic and systolic heart failure. In contrast to the left atrium, right atrial volume and function are less well studied. This could be related to the difficulties one encounters with measuring right atrial volumes and function with 2D echocardiography [4]. Freehand 3D echocardiography and cardiac magnetic resonance imaging showed better results as level of agreement and intra-observer and inter-observer variability is concerned [5]. Right atrial volume and function can be described by atrial filling from the point of minimal atrial volume, at the onset of ventricular systole until maximal atrial flow. It is the sum of forward caval flow and reversed flow through the tricuspid annulus. From maximal right atrial volume until atrial volume at the P-wave is described as passive emptying volume. This occurs during ventricular diastole. The active emptying volume occurs during atrial contraction until minimal atrial volume and closure of the tricuspid valve. The different phases are given in Fig. 1. Fig. 1 Right atrial volume change over time The study of Willens et al [6] in the current issue of the International Journal of Cardiac Imaging shows, that in a limited number of healthy subjects right atrial passive emptying volume and passive emptying fraction decreases with age and active emptying volume and active right atrial ejection fraction increase with age. This could indicate that with increasing age right ventricular diastolic function deceases irrespective of the occurrence of cardiac disease. In patients with pulmonary arterial hypertension right atrial function was even more impaired with larger right atrial maximal volume, minimal volume and volumes at the P-wave, lower passive right atrial emptying fraction and higher active right atrial emptying volume and active right atrial emptying fraction pulmonary artery systolic pressure correlated fairly with active emptying volume The study of Willens gives a nice insight in right atrial mechanics and volumes in healthy individuals and patients with pulmonary hypertension. We have to take in account, that this study has several limitations. First, it is a very small study with a very limited number of patients with pulmonary hypertension included. A more serious limitation is due to the sometimes poor acoustic window of ultrasound and therefore poor definition of the right atrial endocardium and the geometric assumptions, which have been made using single plane planimetry method of discs to calculate right atrial volumes and right atrial function. As indicated, measurement of right atrial function with 3D echo or with cardiac magnetic resonance imaging in a larger cohort of normal individuals and patients could make the results more valid. The results are not without any impact. In the next decades we will see a growing number of patients with right ventricular and right atrial dysfunction: Patients with chronic pulmonary diseases, after pulmonary embolism, after right ventricular infarction, chronic heart failure, valvular heart disease and atrial fibrillation. Especially in a population with a growing number of elderly people and diseases related to higher age as atrial fibrillation and pulmonary hypertension and right ventricular dysfunction right ventricular and right atrial function has to be determined more frequently. Thus proper treatment can be initiated more accurately and the effects of treatment on the right atrium and right ventricle can be evaluated. For this, 3D echocardiography and magnetic resonance imaging are the preferred imaging tools. If these techniques are not available reasonable evaluation of right atrial function can be done with 2D echocardiography.

Mechanisms of venous return and ventricular filling in elasmobranch fish.

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.

Manipulation of external pressure as a method to assist the failing heart

The development and state of the art in circulatory assistance using external pressure variations is reviewed. All of these techniques use the principle that by cyclic external pressure waves properly timed to the cardiac cycle, hemodynamic energy can be noninvasively transmitted to assist the circulation. Cyclic pressure waves to the lower body require that the high pressure phase occurs in diastole in order to augment cardiac output or coronary flow. In contrast, pressure waves to the chest would optimally augment cardiac output if they begin at the onset of ventricular systole. Manipulation of lung pressure by synchronized ventilation may be also utilized to augment cardiac output. The above methods are discussed in detail in the manuscript with special emphasis on the pathophysiology and mechanisms of cardiac assistance.

Real-time measurement of tricuspid valve annular area for annuloplasty: Experimental study

We used real-time measurement of the tricuspid valve annular area in anesthetized dogs to study the optimal size of the annular area for annuloplasty. During control conditions, the maximum tricuspid annular area appeared at the onset of ventricular systole. The minimum tricuspid annular area appeared between the ventricular isovolumic relaxation phase and the early ventricular filling phase. The maximum annular area varied in seven dogs between 2.18 and 3.10 cm2, and the minimum annular area ranged between 1.68 and 2.45 cm2. In regular sinus rhythm (heart rates 97 to 120 beats/min), the maximal decreases in tricuspid annular area during one cardiac cycle ranged from 14.3% to 23.6% of the maximum size. When the tricuspid annular area after the annuloplasty was kept larger than the minimum area that was observed during the cardiac cycle in the control study, cardiac output and right atrial pressure remained unchanged, as a result of unobstructed ventricular filling. On the other hand, when the annular area was reduced to smaller than the minimum area seen in the control study, a decrease in cardiac output and an elevation of right atrial pressure ensued. These findings suggest that the tricuspid annular area can be safely decreased by annuloplasty to the minimum area seen in the control study without causing a reduction of cardiac output or an elevation of right atrial pressure.

Effects of timing of atrial systole on LV filling and mitral valve closure: computer and dog studies

Atrioventricular (AV) delay that results in maximum ventricular filling and physiological mechanisms that govern dependence of filling on timing of atrial systole were studied by combining computer experiments with experiments in the anesthetized dog instrumented to measure phasic mitral flow. Ventricular filling volume is maximized at AV delay of 100 ms in the computer study and 80 ms in the dog study. At any time in diastole atrial contraction accelerates mitral flow, opening the mitral valve widely; atrial relaxation then decelerates mitral flow, moving the valve leaflets toward closure. The time the valve remains closed following atrial systole varies inversely with AV delay. When AV delay is optimal, the mitral valve is moving rapidly toward closure but is not yet closed at onset of ventricular systole. The decline in filling volume as AV delay decreases below its optimum value is primarily the result of premature termination of atrial ejection by ventricular systole. As AV delay increases above its optimal value, filling volume progressively decreases because of premature mitral valve closure that limits effective diastolic filling period. There is no significant retrograde mitral flow at any point in diastole for any AV delay.

Tricuspid stenosis. Atrial systolic murmur, tricuspid opening snap, and right atrial pressure pulse

Observations on the atrial systolic murmur, the tricuspid opening snap, and the right atrial pressure pulse of tricuspid stenosis are presented, based on catheter manometer intracardiac sound and pressure recordings in five patients with hemodynamically significant tricuspid stenosis. The manometer-recorded right atrial pressure pulse of tricuspid stenosis differed from the normal, with (1) elevation of right atrial pressure, (2) different morphologic features (tall, spiky A wave complete before C; small V wave with an interruption, the tricuspid opening snap notch at termination of the gradual Y descent; a diastolic plateau, the relatively flat diastolic segment of the right atrial pressure pulse following the tricuspid opening snap notch prior to the next A wave), and (3) the relative lack of right atrial pressure and right atrial pressure pulse response with normal respiration. The atrial systolic murmur, recorded in the right ventricular inflow tract, was complete by S 1; the crescendo-decrescendo atrial systolic murmur configuration paralleled the right ventricular-right atrial diastolic pressure gradient at the time of the atrial A wave. The right atrial contraction-relaxation process, as reflected by the right atrial A wave ascent and descent, was complete at the onset of ventricular systole with P-R intervals of 170 to 200 msec. Thus, the timing and configuration of the atrial systolic murmur reflected the timing and completion of the right atrial contraction-relaxation process prior to the onset of right ventricular systole and the configuration of the tricuspid diastolic pressure gradient. The tricuspid opening snap was recorded in the right ventricular inflow tract and occurred at the time of a notch at the termination of the Y descent of the right atrial pressure pulse V wave, while right atrial pressure exceeded right ventricular pressure. The sound-pressure events were consistent with angiographic and echocardiographic studies, which showed doming or ballooning of the mobile, fused, stenotic tricuspid valve into the right ventricle during the Y descent of the right atrial pressure pulse. The tricuspid opening snap occurred at the time of the termination of the diastolic movement of the fused tricuspid unit into the right ventricle. These observations are presented within the framework of previous studies in order to trace the development of medical ideas about the pathophysiologic basis for the sound and pressure events of tricuspid stenosis.

Relation of mitral valve opening and closure to left atrial and ventricular pressures in the intact dog.

The exact times of mitral valve opening and closure were determined in dogs under varying hemodynamic conditions in 143 cardiac cycles (five experiments). Radiopaque markers had been sutured to the cusps and the valve annulus 7-124 wk before the studies. Valve opening and closure times were correlated with simultaneously obtained high-fidelity intracardiac pressures. Closure of the mitral valve was completed 5-105 ms after the atrial-ventricular pressure crossover; the time interval between the onset of ventricular systole and the instance of complete valve closure varied less (10-40 ms). These observations suggest that in the intact heart alpha, rapid mitral cusp closure at the end of diastole is initiated and completed by ventricular systole alone, and beta, the ventricular isovolumic contraction period might be shorter than assumed. Opening of the valve during ventricular relaxation was characterized by 1) initial separation of the markers placed on the free edges of the cusps, of variable duration, apparently due to alterations in ventricular geometry, and 2) a rapid opening motion which clearly preceded the diastolic pressure crossover by 5-60 ms. This finding would suggest that ventricular isovolumic relaxation might be shorter than generally accepted, although the mechanism of early opening is not adequately explained by the data.

Cardiovascular Assist Devices in Cardiogenic Shock

AT PRESENT, mechanical circulatory assistance is practical and advantageous for treatment of patients with cardiogenic shock. This technique utilizes a nonocclusive, intraaortic balloon timed to the electrocardiogram (ECG) and monitored by the arterial pulse wave. The balloon inflates just after the aortic valve closes and deflates with the onset of ventricular systole. The inflation forces blood out of the central aorta during cardiac diastole, thereby decreasing central aortic blood volume and increasing pressure. At the onset of systole, balloon deflation decreases aortic pressure so that the left ventricle has less impedance to ejection. The increase in diastolic aortic pressure increases coronary blood flow, while the decreased aortic volume at the onset of systole decreases the work of the left ventricle. The balloon is inserted through the femoral artery and threaded to the descending thoracic aorta just below the origin of the left subclavian artery. Many balloons are designed so that

Pulmonary vein flow pattern in mitral stenosis before and after commissurotomy.

Pulmonary vein flow (PVF) pattern was studied with an electromagnetic flowmeter in 15 patients with mitral stenosis. ECG, left atrial and left ventricular pressure were recorded simultaneously. Commissurotomy was performed in 8 patients and prosthetic valve replacement in the others. Measurements were performed before and after the intracardiac procedure. The predominating forward flow occurred in ventricular diastole, in contrast to ventricular systole in normal hearts. A small retrograde PVF was observed in 11/15 patients in early ventricular systole, coinciding with the c-wave in left atrial pressure (LAP). The reversed flow did not exceed 13% and showed no correlation to a slight regurgitation demonstrated at left ventricular angiography. The maximum delay in forward systolic PVF after onset of ventricular systole was 0.10 sec. The PVF pattern remained unchanged after commissurotomy in the majority of patients, even after reduction of the mitral valve gradient to less than 5 mmHg. However, holosystolic reversed PVF occurred in one patient, indicating a severe mitral regurgitation. The method of PVF recording is simple and proved useful for haemodynamic analysis and as a control after mitral valve surgery for evaluating the degree of mitral regurgitation.

Experimental studies on the mechanisms of closure of cardiac valves with use of roentgen videodensitometry

Dilution curves of roentgen contrast medium sampled just upstream to the mitral or aortic valves at a rate of 60/sec by means of a roentgen videodensitometer have been used to detect and study the phasic relations of retrograde flow across the valve orifice. Normally, vigorous ventricular systoles produce competent closure of the anatomically normal mitral valve irrespective of the presence or absence of atrial contractions. The rapid increase in ventricular pressure and the decrease in size of the annulus of the valve at the onset of ventricular systole are the major factors producing efficient closure of the atrioventricular valves. Vigorous ejection of blood by way of the aortic valve also aids in the closure of the aortic valve.

Studies on the coronary microcirculation by direct visualization

With use of high speed cinematography of the coronary microcirculation, countercurrents and asymmetric capillary arrangement were found. This has far-reaching importance for the oxygenation of the heart muscle and makes doubtful previous calculations for the oxygen transport from the capillary to the surrounding tissue. Recruitment, denoting an increase in the number of capillaries, was observed with a rise in perfusion pressure in the arrested heart and after the administration of nitroglycerin in the beating heart. It can occur in the presence of autoregulation. Definite patterns of red cell velocity in the capillaries of the left atrium emerged. Nicotine and nitroglycerin had little effect on red cell velocity. However, after hemorrhage alone, and following the administration of nitroglycerin after hemorrhage, marked changes in red cell velocity were seen. Hemorrhage alone caused a marked diminution in red cell velocity; hemorrhage followed by nitroglycerin reversed red cell velocity to normal values despite a persistent diminution in blood pressure. Two major peaks in red cell velocity were observed, the first, large peak immediately preceding or at the onset of ventricular systole, the second small peak immediately after ventricular systole. Some alterations in this pattern were seen after hemorrhage and after the administration of nitroglycerin.

Heart sounds in patients with homograft replacement of the mitral valve.

Phonocardiographic, hemodynamic, angiographic, and cardiac echographic studies have been performed on 11 patients whose diseased mitral valves have been replaced by a supported aortic valve homograft. The chordae tendineae and papillary muscles were removed in all patients during the operation. Apical first heart sounds of normal intensity were present in all patients after surgery. Nine patients exhibited splitting of the first sound. The initial component occurred when bulging of the homograft leaflets into the atrium was suddenly checked after the onset of ventricular systole. The second component occurred at the onset of rapid annular motion toward the base. Both sounds thus appear to originate in the homograft valve. Four patients had third heart sounds of left ventricular origin. The homograft leaflets were open and demonstrated no abrupt motion at the time of the third sound. It is evident that the third heart sound may occur in the absence of chordae tendineae and papillary muscles.

Mitral valve movement: a study using an ultrasound technique.

The movement of the anterior leaflet of the mitral valve has been recorded with an ultrasound echo technique. The intrinsic mobility of the valve cusps and the rate of ventricular filling are thought to influence the closure of the valve during diastole. Atrial contraction occurs at the end of ventricular diastole and reopens the valve before the mitral valve returns to the closed position before the onset of ventricular systole. The relation of the opening snap and third heart sound to the movement of the cusp is shown. In mitral stenosis ventricular systole occurs when the mitral valve is still far away from the closed position and the rapid movement of the cusp to the closed position may be the cause of the high intensity vibrations of the first heart sound. The EF slope (representing the rate of the closing movement of the cusp in end diastole) is decreased and a good correlation has been found with the degree of stenosis. After mitral valvotomy the EF slope increases significantly. The validity of these methods in assessing mitral incompetence or relative predominance of stenosis or incompetence in mixed mitral lesions is discussed. The ultrasound cardiograph is a fairly simple and completely atraumatic technique with proven diagnostic value in mitral valve disease. In addition, because of the new type of information that is given, it has potential as a research tool which is, as yet, largely unexplored.

Pattern of blood flow in the pulmonary veins of the dog

The pattern of blood flow in the large pulmonary veins was studied in dogs by chronic implantation of sine-wave electromagnetic flowmeters and cineangiographic observations. These revealed that: 1) pulmonary venous flow is continuous and pulsatile with peak rate of flow of approximately twice the mean flow; 2) the initial rapid increase in venous flow occurs 0.10 sec after the onset of ventricular systole, reaching a peak at the time of closure of the A-V valves; 3) left atrial contraction produces a fleeting slowing or reversal of flow; and 4) respiratory variations in pulmonary venous flow follow those in pulmonary arterial flow, beat by beat. The genesis of phasic pulmonary venous flow was investigated by analysis of pressure and flow curves from the two sides of the heart, by consideration of the energy required for left ventricular filling, and by reconstruction of the pulmonary venous flow pulse using a mathematical model of the pulmonary circulation. These three lines of evidence are consistent in indicating that the transmitted right ventricular pressure is the major determinant of the pulmonary venous flow pattern in the dog. pulsatile pulmonary venous flow; pulmonary venous flow; pulmonary circulation; ventricular suction; respiration on pulmonary circulation; pulmonary venous angiography; pulmonary veno-atrial junctions; electromagnetic flowmeter; cineangiography Submitted on November 16, 1964

Movements of the mitral valve.

Cinefluorographic analysis of mitral valve motion in intact dogs provided evidence that the motility of the valve cusps is restrained by tension exerted through the chordae tendineae throughout the cardiac cycle, except for the rapid filling phase. At the onset of ventricular systole, early contraction of the papillary muscles may play an important role in approximating the mitral valve cusps. During ventricular ejection, the mitral cusps and valve ring move toward the apex of the heart. During diastole, separation of the valve cusps is remarkably slight. The valves were observed to fling wide during rapid ventricular filling when the heart was much smaller than normal, immediately after surgery.

Right Ventricular Contraction

Cyclic changes in the dimensions of the right ventricular wall were recorded continuously in 17 intact, unanesthetized dogs. The free wall of the right ventricle contracts synchronously. At six different locations on its surface, the average relative shortening was about 15%. At the onset of ventricular systole, the right ventricular wall expands while the intraventricular pressure abruptly rises. This initial systolic expansion of the wall represents a change in shape of the chamber without a change in volume since the valves are all closed at this instant. It may result from early contraction of papillary muscles, drawing the tricuspid valves down into the ventricular chamber, supplemented by the bulging of the interventricular septum which accompanies sphericalization of the left ventricle at the onset of systole. During feeding, the heart rate accelerates, and the systolic and diastolic dimensions are promptly reduced. During exertion, the heart rate increased, systolic ejection was much more complete and diastolic filling was somewhat reduced.

The Flow of Blood Supplying the Cardiac Atria

The flow of blood into the left anterior auricular artery was measured phasically and quantitatively in the heart-lung preparation. The curves indicate that forward flow into the auricular artery occurs during ventricular systole and diastole, with abrupt, momentary interruptions of inflow at the onset of ventricular systole and diastole. Elevation of tension within the left auricle diminishes auricular arterial inflow; inflow again increases as pressure within the auricle is restored to normal levels. It is suggested that the interference with auricular blood supply, due to increased intra-auricular tension (as in heart failure) may enhance the establishment of aberrant auricular mechanisms.

The Form of the Electrocardiogram. III. Opposed Potential Differences

At the onset of ventricular systole the excitation process is spreading within the ventricular muscle in many different directions simultaneously. Many of the electrical forces, or potential differences, produced are opposed by forces opposite in direction, and their effects are consequently neutralized. Other potential differences are not opposed; it is these potential differences and these alone which have an effect upon the electrocardiogram.Consider the simple strip of muscle AB (Fig. 1) immersed in a large body of physiological saline solution or other similar conducting material. Place one electrode at R, and a second electrode at S and connect these electrodes to a string galvanometer in such a way that relative negativity at R will cause an upward deflection when the electro gram of the muscle is recorded. Given that RX equals SX (Fig. 1). Stimulate this muscle at X; given that XA equals XY. It is obvious that the excitation process will spread toward A and toward Y simultaneously; that the potent...