Showing papers on "Cardiac cycle published in 1981"

Abnormal mitral valve coaptation in hypertrophic obstructive cardiomyopathy: Proposed role in systolic anterior motion of mitral valve

Abstract: Two dimensional echocardiographic evaluation utilizing the apical four chamber and apical long axis views was made in 10 normal subjects and 35 patients with hypertrophic cardiomyopathy, including 16 without and 19 with systolic anterior motion of the mitral valve. Mitral valve leaflets were imaged throughout the cardiac cycle. The normal subjects and the patients with hypertrophic cardiomyopathy without systolic anterior motion demonstrated mitral valve coaptation that seemed to involve the distal tip of the anterior leaflet. In contrast, patients with hypertrophic cardiomyopathy with systolic anterior motion demonstrated abnormal coaptation, so that the posterior leaflet coapted with a mid portion of the anterior leaflet, leaving a distal “residual” anterior leaflet in the left ventricle during systole. A sharp angulation of this distal leaflet in mid systole toward the interventricular septum is thought to represent systolic anterior motion. It is speculated that abnormal mitral leaflet coaptation is necessary for development of leaflet systolic anterior motion, which Is correlated with dynamic left ventricular outflow gradients in hypertrophic obstructive cardiomyopathy.

The design of the normal aortic valve

Abstract: The design parameters of the natural aortic valve in vivo were not known, which may explain why various bioprosthetic valves have been designed differently. The design of the aortic valve was studied in vivo by placing radiopaque markers in the valve. The marker movement revealed that, during a cardiac cycle, the design parameters of the valve were changing continuously with changing aortic pressure and ventricular geometry. During diastole decreasing radius of the commissures (Rc) and increasing radius of the bases (Rb) caused the leaflets to tilt toward the ventricle, thereby decreasing the bottom surface angle (alpha) and increasing the free-edge angle (phi) of the leaflet. During systole Rc increased, Rb decreased, and interleaflet distance decreased, causing a change in the geometry of the open valve from conical to cylindrical. In middiastole the design parameters were Rb/Rc = 1.2, H/Rc = 1.4, phi = 34 degrees, and alpha = 20 degrees, where H is sinus height. How a significant deviation from the design could compromise the efficiency and longevity of the valve is discussed.

Two-dimensional echocardiographic features of atrial septal aneurysms.

Abstract: Aneurysms of the interatrial septum are rare. They have been associated with complications such as embolic phenomena and atrioventricular orifice obstruction. We describe two patients, one adult and one child, with atrial septal aneurysms that were diagnosed by real-time, two-dimensional echocardiography. Atrial septal aneurysms appeared as thin, localized outpouchings of the atrial septum that protruded into the right atrium and showed marked variations in their contour and size during the cardiac cycle. They could be differentiated from other intra-atrial structures such as tumor mass, large eustachian valve and intra-atrial baffle by their relatively low reflectance, relationship to the atrial septum, considerable alterations in their outline during the cardiac cycle and characteristic patterns during peripheral venous contrast echocardiography.

Hemodynamic determinants of pulmonary valve motion during systole in experimental pulmonary hypertension.

Abstract: To clarify the determinants of pulmonary valve (PV) motion in pulmonary hypertension, we examined the correlations among PV echo patterns, the pulmonary artery (PA) flow curve just above the PA orifice and the pulmonary artery-right ventricle (PA-RV) pressure gradient. By constricting the PA, we could produce a variety of PV echo patterns, including midsystolic semiclosure in open-chest dogs. Throughout the experiments, the PV echo pattern and PA flow curve were similar in pattern and timing. When the PV echo showed midsystolic semiclosure with reopening. The PA flow curve showed a transient decrease followed by a transient increase during midsystole. The PA-RV pressure gradient became transiently positive (PA pressure greater than RV pressure) and then negative in midsystole only when the PV echo showed midsystolic semiclosure with reopening. In conclusion, PV motion during systole may be instantaneously determined by PA flow change and the PA-RV pressure gradient during the cardiac cycle in experimental pulmonary hypertension.

Dynamic geometry of the intact left ventricle.

Abstract: Knowledge of left ventricular chamber dynamics is central to our understanding of cardiac physiology. The complicated changes in left ventricular geometry observed in the dog during various phases of the cardiac cycle can be represented as distinct linear relationships between chamber eccentricity and intracavitary volume during diastole and ejection, and probably represent structural properties of the ventricular wall. Chamber geometry of the left ventricle is a major determinant of overall myocardial function. The slope of the radius of curvature (r) to wall thickness (h) relationship is a geometric constant that determines the mural force at any given transmural pressure. Chronic pressure and volume overload produce changes in this geometric relationship as a result of increased mural force resisting ejection. The adaptive mechanism of ventricular hypertrophy in this setting alters the r/h ratio and returns systolic mural force toward normal. Coronary occlusion induces acute changes in regional geometry characterized by holosystolic wall bulging and systolic wall thinning, which shift the r/h relationship upward and to the left. The geometric alteration during ischemia probably increases systolic mural force and could adversely affect myocardial function. Recent studies with patients have shown the r/h ratio to be of value in distinguishing between reversible and irreversible impairment of myocardial performance. Because most myocardial diseases produce major alterations in the structure of the ventricular wall, analysis of dynamic chamber geometry may prove of prognostic value in assessing patients with cardiac disorders.

Of the human heart

Abstract: An investigation was conducted on six healthy subjects and three patients with an aneurysm of the left ventricle after myocardial infarction. The method used was to record the ECG in 80 unipolar leads, the electrodes of which were uniformly distributed over the surface of the patients' chest, and to obtain data on the momentary distribution of the ECG potential every 5 msec in the course of the QRS complex, T wave, and ST segment (for patients in whom this did not fall on the isoelectric line). The human body was regarded as a homogeneous isotropic conductor* with specific electrical conductance of 2o10 -3 ~-1~cm-~, and the cylindrical coordinates of the points of the leads were determined relative to the center of a transverse section through the body at the level of the 5th intercostal space. The aim of subsequent analysis of the data was to determine the following values for each of the 40 moments of the cardiac cycle:

Automatic determination of cardiac output using an impedance plethysmography.

Abstract: A computer-based system which calculates stroke volume, heart rate and cardiac output automatically from the transthoracic impedance variation has been developed. A beat-by-beat determination was performed on several healthy subjects and patients with atrial fibrillation during spontaneous breathings at rest. The respiratory artifact appearing on the impedance cardiogram was canceled by (1) correcting the base line of dZ/dt for each cardiac cycle on the basis of assumption that the dZ/dt values at ECG-R waves would be invariable regardless of the respiratory phase when the respiratory movement ceases, and (2) averaging the signals for a number of cardiac cycles. Comparisons between the computed stroke volumes and those obtained from a manual calculation showed good agreement.

Ventricular size and shape by two-dimensional echocardiography.

Abstract: The evaluation of cardiac size and shape has been aided by the recent development of high resolution real-time two-dimensional echocardiography, which permits dynamic cross-sectional evaluation of all or a large portion of the left ventricle throughout the cardiac cycle. This review addresses itself to the determination of left ventricular size and shape by two-dimensional echocardiography. A method is described for accurate volume determination in the intact, isolated, ejecting canine heart. By combining the two-dimensional echocardiogram with knowledge of transducer position and orientation with respect to the heart, it is possible to reconstruct a three-dimensional representation of a chamber and thereby measure volume without reliance on major geometric assumptions. Because of the unique ability of two-dimensional echocardiography to produce a cross-sectional image of the beating heart in a large number of planes, it is suitable for the determination of cardiac shape and architecture. The recognition of early regional cardiac dilatation in acute myocardial infarction is described. Changes in ventricular shape brought about by the dynamic alterations lend themselves well to two-dimensional echocardiographic study. The pivotal nature of the interventricular septum renders it susceptible to changes in the functional state of both ventricles. That the interventricular septum may mediate ventricular interaction acutely is suggested by the acute effects of right ventricular loading in man using the Mueller maneuver. Leftward septal displacement and flattening of the septum during the early maximal Mueller maneuver is evidenced by a substantial increase in the radius of curvature of the septal segment, without a change in the left ventricular free wall. This septal flattening occurs in diastole and persists during systole. Diastolic events thus appear to influence systolic shape. Changed septal shape may be an important mechanism of, and evidence for, ventricular interdependence in normal man.

Echocardiography of the Aortic Valve

Abstract: Although detection of echoes from the aortic cusps was described in the early days of echocardiography [1], its application in the diagnosis and management of aortic valve disease has remained limited. This partly is due to the difficulty in obtaining clear recordings of the valve cusps throughout the cardiac cycle; even in normal subjects, this is possible in only about 75% of cases. It is also due to limitations of apparatus resolution, since the small size of the valve necessitates more accurate measurements if, for example, valve area is to be correlated with that found at surgery. Nevertheless, echocardiography can provide a good deal of useful information, which we shall attempt to review.

Left atrial function in acute mitral regurgitation. Factors which modify the regurgitant volume.

Abstract: Dynamic geometry of the left atrium was studied in open-chest dogs instrumented with ultrasonic dimension gauges for the measurement of the transverse diameter together with left ventricular dimensions and left atrial and ventricular pressures. Three definite phasic changes of the left atrial diameter were observed during the cardiac cycle at the control state; shortening of left atrial diameter with atrial contraction, continuous chamber expansion during ventricular ejection, and either a reduction in the diameter or a plateau during mitral valve opening to onset of the next atrial contraction. Acute onset of mitral regurgitation initially induces a remarkable augmentation of atrial shortening with chamber dilation as a result of an optimal use of the Frank-Starling mechanism of the atrial muscle. When mitral regurgitation is progressively increased, the extent of the atrial shortening and expansion is diminished despite the geometrical advantage of a further increase in atrial diameter, indicating that this extreme dilation no longer provokes the Frank-Starling response and the atrial myocardium is made to operate on a descending limb of function. The amount of regurgitation is highly dependent on the geometry of the mitral orifice and a decrease in regurgitation with vasodilator therapy or with positive inotropic agents may be largely related to a decrease in the size of the left heart cavity, which brings closer together components of the mitral apparatus and increases its competence.

Effect of atrial systole on canine and porcine coronary blood flow.

Abstract: A feature of phasic coronary flow patterns recorded in conscious chronically instrumented dogs is the atrial cove--a transient depression of arterial flow that occurs during atrial systole. The association between the hemodynamic effects of atrial systole and the atrial cove was studied in anesthetized dogs and pigs with complete heart block. Many atrial coves are available for study in these preparations because atrial activity continues unabated during the diastolic ventricular arrest that follows cessation of electrical pacing. The effect of atrial systole is to translate the pressure-flow relation found during diastole to a higher intercept pressure without change in slope. The increase in the intercept pressure equals the increase in intramyocardial pressure measured with microtransducers embedded in the left ventricular wall. The decrement in flow during the atrial cove is a direct function of the change in intramyocardial pressure and an inverse function of coronary vascular resistance. Each atrial systole is associated with a forward flow transient in the coronary veins, the peak of which occurs at the same instant as does the nadir of atrial flow. These data suggest that the coronary vessels are acting as collapsible tubes and that the waterfall model of the coronary circulation is applicable. The following sequence is proposed to account for the atrial cove. Atrial systole ejects a bolus of blood into the left ventricle increasing both ventricular cavity and intramyocardial pressures. The increase in intramyocardial pressure raises the back pressure opposing coronary flow, reducing the arterial perfusion pressure gradient and causing flow to fall.

Surface topography of endocardial endothelium

Abstract: Publisher Summary The walls of the heart are composed of bundles and sheets of muscle fibers intertwined in a complex fashion. This mass of tissue, referred to as the “myocardium,” lies adjacent to the endocardium, which forms the luminal boundaries of the atria and ventricles and is consistent with the tunica intima of the peripheral vasculature. As its counterpart throughout the vascular tree, the innermost layer of endocardium is composed of a continuous sheet of simple squamous epithelial-like cells, referred to as “endothelium.” Lining the atria and ventricles of the heart, endocardial or cardiac endothelium covers all structures projecting into these chambers. Vascular endothelial cells align themselves along or parallel to the longitudinal axis of blood flow; in the heart, such cellular arrangements or orientations are not necessarily the same especially with regard to those populations over the valves. As a component of the endocardium, cardiac endothelium is supported by two layers of connective tissue composed of collagen intermixed with elastic fibers. The outermost layer of the endocardium consists of an irregular arrangement of connective tissue that is continuous with the endomysium of the adjacent myocardium. The contractile activity of the latter during the cardiac cycle should physically affect a response from the endocardium manifested by an alteration in the surface morphology of its endothelium.

Redistribution of canine left ventricular myocardial blood flow in unloaded systole.

Abstract: The left coronary arteries of dogs were cannulated and perfused with blood from support dogs. The experimental hearts were unloaded by severing the aortas to maximize strains and minimize fiber stress. In each heart we compared the transmural distribution of blood flow in two states: (1) provision of perfusion pressure (40 mm Hg) only during systole and then (2) provision of perfusion pressure throughout the cardiac cycle. The distribution of flow in each of these perfusion states was labeled with a diffusible radioisotope (42K or 86Rb, one labeling the first state; the other labeling the second). Quantitative, paired autoradiography was used to visualize the two flow distributions. The differences between the two distributions after standardization was plotted as differences between activity vs. depth in the myocardium (r = 0.91). This was fitted with a line by least squares, the slope of which was significantly different from zero at the 0.005 level. The magnitude of the gradient of the systolic flow was represented by the ratio of deep to shallow flow. The mean of these ratios was 0.54 +/- 0.12 (95% confidence interval). A graphical analysis shows that the data are consistent with a gradient of extravascular compression across the left ventricular wall.

Atrial Systole and Ineffective Pacemaker Stimuli

Abstract: An unusual case of pacemaker failure induced by atrial activity is presented. The pacemaker stimulus was ineffective for ventricular capture not only with low energy output (decreased pulse duration) of the generator, but also with pulse width two to three times the stimulation threshold. The two possible mechanisms of this phenomenon, one electrotonic and the other mechanical, are discussed. This report strongly supports the mechanical hypothesis. (PACE, Vol. 4, September-October, 1981)

[Digital image processing of the two-dimensional echocardiogram for the evaluation of regional contractility of the left ventricular wall (author's transl)].

Abstract: Short-axis cross-sectional images of the left ventricle at the levels of the mitral valve, papillary muscles and apex were recorded on video tape by using a phased-array sector scanner. Endocardial and epicardial outlines of the cross-sectional left ventricular wall were determined automatically by a computer tracing process including digital image processing system. Short axis cross-sectional left ventricular walls of upper-, middle- and lower parts of the left ventricle were divided into eight segments, the center of gravity of end-diastolic left ventricular cavity being used as the reference point. Various parameters such as segmental radius, segmental wall thickness, cross-sectional area, left ventricular circumference and those changes during the cardiac cycle were determined in eight segments at three levels of the left ventricle. Regional contractility of the left ventricular wall was evaluated by systolic shortening of segmental radius and systolic thickening of segmental wall thickness. Contractility and pumping function of the overall left ventricle was assessed by shortening velocity of left ventricular circumference and fractional changes of cross-sectional area at three levels of the left ventricle. These were significantly and diffusely reduced in a patient with congestive cardiomyopathy (CCM), contrasting with a normal subject. Systolic changes in segmental radius and segmental wall thickness were significantly reduced in infarcted myocardium. Digital image processing system and segmental analysis of the left ventricular short-axis two-dimensional echocardiogram are very useful to evaluate the regional contractility of the left ventricle, quantitatively and automatically, especially in patients with myocardial disease including CCM and myocardial infarction with left ventricular asynergy.

Stroke volume estimated at aortic root in M-mode echocardiography.

Abstract: A noninvasive method for the determination of stroke volume which can be applicable even to a heart contracting asymmetrically is desired. The momentum of blood ejected from heart will be divided into 2 forms; the one is that of blood running away distally and the other is the momentum of the aortic root. SV is estimated by an equation; SVa0 = kXD2XVao1/2XAOT, where D is the diameter of the aortic root, Vao is the mean velocity of the systolic movement of anterior wall, and AOT is the duration of the valve opening of the aortic leaflets. A good correlation was found between SVao and SV measured by the thermodilution method (r = 0.85, p less than 0.001). Since the parameters used in the present method are not affected directly by the mode of cardiac contraction; symmetrical or asymmetrical, it may be useful to determine SV in man.

Determination of Quantitative Left Ventricular Function by M-mode Echocardiography Together with Other Noninvasive Parameters

Abstract: M-mode echocardiography, which was first introduced in cardiology in order to identify valve disease, has since been shown to be very useful for studying left ventricular (LV) function. The advantage of this method is its noninvasive nature and therefore its suitability for sequential studies in the same patient. Due to its high repetition rate in comparison with angiography and radionuclide techniques, M-mode echocardiography allows a detailed analysis of the dynamic changes in LV dimension and wall thickness within one cardiac cycle. In order to take full advantage of the high repetition rate of this technique for LV dimension analysis, echocardiograms must be digitized. Computer analysis of the M-mode echocardiogram then enables continuous computation of a number of variables throughout one cycle and hence the possibility of following LV cavity dimension, and its rate of change, during systole and diastole. It is also possible to analyse wall thickness changes of the septum and of the left ventricular posterior wall, which is not possible using any other technique.

The carotid and ECG pulses as indices for nuclear cardiography imaging

Abstract: Nuclear cardiography has emerged from nuclear medicine to help the cardiologist in assessing the heart's performance. One of the examinations practiced is imaging of the cardiac muscle at its two extreme phases: End-Systole (ES) and End-Diastole (ED). Images of those two phases of the cardiac cycle may provide information for the calculation of Ejection Fraction (EF) and the asynergy and dysynergy of the heart muscle.