Cardiac cycle

About: Cardiac cycle is a research topic. Over the lifetime, 3290 publications have been published within this topic receiving 96159 citations.

Magnetic resonance imaging analysis of left ventricular function in normal and spontaneously hypertensive rats

Abstract: * 1 We have used magnetic resonance imaging (MRI) to examine acute morphological changes in the left ventricle throughout the cardiac cycle in normal Wistar Kyoto rats (WKY) and also to follow the development of chronic changes in spontaneously hypertensive rats (SHR). This involved the development of MRI and quantitative analysis techniques for characterizing contractile changes during the cardiac cycle. * 2 Images of the cardiac anatomy in two age groups (8 and 12 weeks old) of young anaesthetized adult normal WKY and SHR were acquired in planes both parallel and perpendicular to the principal cardiac axis. * 3 Complete coverage of the heart by imaging planes was achieved with high time resolution (13 ms), with typically 12 time frames in the cardiac cycle, using a short echo time (5 ms) multislice gradient-echo imaging sequence. Imaging was synchronized to the R wave of the electrocardiogram. * 4 The image slices could be reconstructed into complete geometrically and temporally coherent three-dimensional data sets. Left ventricular (LV) volumes were thus reconstructed throughout the cardiac cycle by combining transverse cardiac image sections. This volume analysis revealed structural and functional differences between the normal WKY and SHR in both age groups of 8 and 12 weeks. Measurements from the cardiac images were additionally validated against histological measurements. * 5 The SHR showed a raised LV end-systolic volume and a correspondingly poorer ejection fraction as well as LV hypertrophy when compared with the controls. Left ventricular function in the SHR appeared stable between the two age groups. * 6 We developed a simple geometrical model of the left ventricle based on a single longitudinal image section and successfully used this to describe some functional parameters of the left ventricle in the WKY and SHR. This geometrical model has the potential to greatly reduce the imaging time needed to study the beating heart in future serial investigations of cardiac physiology in rats. * 7 Our experimental and analytical methods together form a powerful set of quantitative techniques which combine both imaging and functional analysis and will be applicable for future studies of chronic physiological changes in animal disease models.

Improved method for quantification of regional cardiac function in mice using phase-contrast MRI.

Abstract: Phase-contrast magnetic resonance imaging is a technique that allows for characterization of regional cardiac function and for measuring transmural myocardial velocities in human hearts with high temporal and spatial resolution. The application of this technique (also known as tissue phase mapping) to murine hearts has been very limited so far. The aim of our study was to implement and to optimize tissue phase mapping for a comprehensive assessment of murine transmural wall motion. Baseline values for regional motion patterns in mouse hearts, based on the clinically used American Heart Association's 17-segment model, were established, and a detailed motion analysis of mouse heart for the entire cardiac cycle (including epicardial and endocardial motion patterns) is provided. Black-blood contrast was found to be essential to obtain reproducible velocity encoding. Tissue phase mapping of the mouse heart permits the detailed assessment of regional myocardial velocities. While a proof-of-principle application in a murine ischemia–reperfusion model was performed, future studies are warranted to assess its potential for the investigation of systolic and diastolic functions in genetically and surgically manipulated mouse models of human heart disease. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.

Comparison of Patterns of Pulmonary Venous Blood Flow in the Functional Single Ventricle Heart After Operative Aortopulmonary Shunt Versus Superior Cavopulmonary Shunt

Abstract: In this study we investigated the patterns of pulmonary venous flow in children with functional single ventricles to obtain a better understanding of the determinants of transpulmonary blood flow Sixty-eight patients with functional single ventricles and aortopulmonary shunt (n = 34, group I), or superior cavopulmonary connection (n = 34, group II) underwent transesophageal Doppler echocardiographic assessment of flow in the left upper pulmonary vein before undergoing the next stage of surgery Twelve patients from group II also underwent simultaneous evaluation of superior vena caval flow Biphasic forward pulmonary venous flow was noted in 62 patients in sinus rhythm (S wave in systole, D wave in diastole); in 6 patients with junctional rhythm, significant early systolic reversal of flow was present Both the S- and D-wave velocity-time integrals (VTI) were greater in group I than in group II (S(VTI) 99 +/- 42 vs 80 +/- 26, p = 002; D(VTI) 80 +/- 35 vs 42 +/- 26, p <0001) In both groups, pulmonary venous flow was predominantly systolic; however, the proportion of flow during ventricular systole was significantly greater in group II than in group I (S(VTI)/D(VTI) group II: 24 +/- 15; group I 14 +/- 05, p = 0001; percent systolic fraction of pulmonary venous flow group II = 67%, group I = 56%, p <0001) Analysis of superior vena caval flow in group II revealed a single predominant wave with onset at early systole and peak in late systole at a mean of 150 ms after the pulmonary venous S-wave peak Our data suggest that ventricular systole (ie, atrial relaxation, atrioventricular valve descent) asserts great influence on transpulmonary blood flow in the functional single ventricle

The First Heart Sound in Normal and Ectopic Ventricular Contractions: Mechanism of Closure of the A-V Valves

Abstract: Phasic right atrial and ventricular pressures and heart sounds were simultaneously recorded from dogs with normal and ectopic ventricular contractions. Heart sounds and electrocardiograms were recorded from humans. The first heart sound is significantly delayed in the absence of atrial systole. The time between onset of the ventricular pressure rise due to ventricular contraction and the beginning of the first heart sound is minimal at normal AS-VS intervals. These findings support the view that normally the A-V valves are closed or nearly closed before ventricular systole. In ectopic ventricular beats the A-V valves are closed from an open position by ventricular contraction.

Propagation of depolarization and repolarization processes in the myocardium-an anisotropic model

Abstract: A three-dimensional finite-elements model of the left and right ventricles has been developed to study the process of myocardial electrical activation. The anisotropic properties are demonstrated during simulation of an abnormal cardiac cycle, when propagating is initiated at an ectopic ventricular site. Ischemia is simulated by low conduction velocities in the ischemic zone and wide dispersion of values in nearby locations; automaticity is described by restimulating cells in the injured area; the dangerous effects of a premature beat leading to reentry are simulated by reduction of propagation velocity in cells that are reactivated while they repolarized. The different activation patterns are calculated throughout the myocardium and on its surface. The generated surface activation maps are not sensitive to minute changes in location of the foci of activation within the normal conduction system. The maps show sensitivity to pathological velocities, ischemic areas, and the existence of ectopic foci. Thus, the model, with its distributed properties, may be useful for electrocardiographic studies due to its low sensitivity to normal cell-to-cell variability, but high sensitivity to the existence of abnormally propagating myocardial activity. >