Cardiac cycle

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

Phasic three-dimensional impedance imaging of cardiac activity.

Abstract: Electrical impedance images were made using the ACT 3 instrument, which applies currents simultaneously to 32 electrodes and measures the resulting voltages on those same electrodes. A reconstruction algorithm was written for a three-dimensional cylinder having electrodes in two or four layers, using current patterns that pass current among different planes of electrodes, as well as within each plane. We have previously reported useful vertical resolution by the use of added layers of electrodes. The aim of the present study was to demonstrate that physiologically useful information can be obtained by examining cephalo-caudal differences in three-dimensional images. Phasic changes throughout the cardiac cycle are seen to be markedly different at the heart compared to lung region, both above and beside it. We formed hydrogel electrodes each 3 cm tall and 7 cm wide and applied them to the thorax of an upright human subject in four horizontal rows; each row contained eight electrodes. During breath-holding, cardiac activity was seen in all layers. With systole, conductivity in the anterior of the lowest layers decreased, but not in the upper layer. In the upper layers, conductivity increased with systole in many regions. These observations are consistent with the opposite changes in blood volume of the heart and lungs and the locations of these organs. This paper demonstrates the feasibility of producing and displaying physiologically interpretable three-dimensional images of the chest in real time.

Effects of noradrenaline on coronary flow and heart contraction, as recorded concurrently in the isolated rabbit heart.

Abstract: In connexion with earlier studies concerning the effects of adrenaline and other agents on coronary flow and heart contractions (Melville & Lu, 1950), the effects of noradrenaline were also similarly investigated. The object of this paper is to present the findings. While the actions of noradrenaline on coronary flow have been tested by a number of different workers, in most of these studies the concomitant effects on the heart contractions were not recorded. Crismon & Tainter (1938) have reported that racemic arterenol is twice as effective as a cardiac stimulant as laevo-adrenaline in cat heart-lung preparations-both agents increasing heart rate, decreasing systolic, diastolic and stroke volumes, and increasing the cardiac output. Using perfused frogs' hearts, West (1947) observed that racemic adrenaline was 8 to 33 times as active (dose for dose) as racemic noradrenaline in inducing cardiac stimulation. Ahlquist (1948) has observed that in the isolated perfused rabbit heart both noradrenaline and adrenaline increase the rate and amplitude of contraction, but concomitantly decrease about equally (18 and 20 %) coronary flow. Some slight increases (3 and 4 %) were also recorded in these experiments. On the other hand, Marsh, Pelletier & Ross (1948), using isolated hearts of cats and rabbits perfused by a modified Langendorf procedure (details not given), concluded that both agentsproduce cardioacceleration, increased cardiac output and increased coronary outflow. Burn & Hutcheon (1949) observed that in the perfused cat heart both adrenaline and noradrenaline produced identical effects (initial brief decrease followed by increase) on coronary flow. The amplitude and rate of contractions were also increased by both agents, though racemic noradrenaline (0-26 ,tg.) had less effect on rate than laevo-adrenaline (0.1 p,g.). With half of these doses the effect on rate was the same for both agents, but the initial

Prediction and assessment of the time-varying effective pulmonary vein area via cardiac MRI and Doppler echocardiography.

Abstract: Accurately estimating left atrial (LA) volume with Doppler echocardiography remains challenging. Using angiography for validation, Marino et al. (Marino P, Prioli AM, Destro G, LoSchiavo I, Golia G, and Zardini P. Am Heart J 127: 886-898, 1994) determined LA volume throughout the cardiac cycle by integrating the velocity-time integrals of Doppler transmitral and pulmonary venous flow, assuming constant mitral valve and pulmonary vein areas. However, this LA volume determination method has never been compared with three-dimensional LA volume data from cardiac MRI, the gold standard for cardiac chamber volume measurement. Previously, we determined that the effective mitral valve area is not constant but varies as a function of time. Therefore, we sought to determine whether the effective pulmonary vein area (EPVA) might be time varying as well and also assessed Marino's method for estimating LA volume. We imaged 10 normal subjects using cardiac MRI and concomitant transthoracic Doppler echocardiography. LA and left ventricular (LV) volumes were measured by MRI, transmitral and pulmonary vein flows were measured by Doppler echocardiography, and time dependence was synchronized via the electrocardiogram. LA volume, estimated using Marino's method, was compared with the MRI measurements. Differences were observed, and the discrepancy between the echocardiographic and MRI methods was used to predict EPVA as a function of time. EPVA was also directly measured from short-axis MRI images and was found to be time varying in concordance with predicted values. We conclude that because EPVA and LA volume time dependence are in phase, LA filling in systole and LV filling in diastole are both facilitated. Application to subjects in select pathophysiological states is in progress.

Ventricular ectopic beats with fixed and variable coupling. incidence, clinical significance and factors influencing the coupling interval.

Abstract: An analysis of possible factors which determine the coupling intervals of ventricular ectopic beats was made in the electrocardiograms of 88 persons who had at least 10 unifocal ventricular ectopic beats. The material was selected at random and included life insurance applicants, outpatients and patients from a psychiatric state hospital and a general hospital. The coupling interval which varied by less than 0.12 sec. was considered as fixed. Forty persons had fixed coupling and 48 variable coupling. Persons with no heart disease and three groups of patients with heart disease of varying severity had a similar incidence of fixed and variable coupling. Measurements of the relation between the duration of the coupling interval and the preceding R-R interval and of the duration of the interectopic intervals allowed us to separate the ventricular ectopic beat with variable coupling interval into several categories. However, we found no feature of ventricular ectopic beats which differentiated persons without heart disease from those with heart disease. Similarly we found no features of ventricular ectopic beats which differentiated persons receiving digitalis from those not receiving the drug. A significant positive or negative correlation between the duration of the preceding R-R interval and coupling interval was rarely found. In the great majority of the persons there was no significant correlation between the two parameters. Possible reasons for such distribution of correlations are discussed. An analysis of the timing of the ventricular ectopic beat during the cardiac cycle frequently revealed a “clear zone” free of ventricular ectopic beats between the end of the U wave and the onset of the P wave. This period of an apparent relative refractoriness of the ventricular myocardium was observed in persons with and without heart disease. Our results suggest that the factors which determine the time of appearance of ventricular ectopic beats with relation to the preceding R-R interval operate in the same manner regardless of the presence or absence of heart disease and treatment with digitalis.