Cardiac cycle

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

The mechanism of the generation of the third and fourth heart sounds.

Abstract: A simple unitarian concept of the mechanism of third and fourth sounds is presented. This study demonstrates that the third sound occurs during early rapid diastolic ventricular filling at a time when atrial pressure exceeds ventricular pressure. It is recorded within the ventricle and on the ventricular wall. It coincides with ventricular muscle vibrations. The fourth sound is demonstrated to consist of two components, both occurring when atrial pressure exceeds ventricular. The first component coincides with the peak of atrial contraction, is recorded within the atria, and is inaudible. The second component, which is audible (25 to 70 cycles per second) and follows the first by 0.01 to 0.02 second, is recordable within the ventricle coinciding with the impact of blood from atrial systole against the ventricular wall. These observations demonstrate that the audible third and fourth heart sounds have a common origin in the ventricles and have the same temporal and hemodynamic relationships regardless of e...

Aortic annulus dimension assessment by computed tomography for transcatheter aortic valve implantation: differences between systole and diastole

Abstract: Accurate assessment of aortic annular dimensions is essential for successful transcatheter aortic valve implantation (TAVI). Annular dimensions are conventionally measured in mid-systole by multidetector computed tomography (MDCT), echocardiography and angiography. Significant differences in systolic and diastolic aortic annular dimensions have been demonstrated in cohorts without aortic stenosis (AS), but it is unknown whether similar dynamic variation in annular dimensions exists in patients with severe calcific AS in whom aortic compliance is likely to be substantially reduced. We investigated the variation in aortic annular dimensions between systole and diastole in patients with severe calcific AS. Patients with severe calcific AS referred for TAVI were evaluated by 128-slice MDCT. Aortic annular diameter was measured during diastole and systole in the modified coronal, modified sagittal, and basal ring planes (maximal, minimal and mean diameters). Differences between systole and diastole were analysed by paired t test. Fifty-nine patients were included in the analysis. Three of the five aortic dimensions measured increased significantly during systole. The largest change was a 0.75 mm (3.4%) mean increase in the minimal diameter of the basal ring during systole (p = 0.004). This corresponds closely to the modified sagittal view, which also increased by mean 0.42 mm (1.9%) during systole (p = 0.008). There was no significant change in the maximal diameter of the basal ring or the modified coronal view during systole (p > 0.05). There is a small magnitude but statistically significant difference in aortic annulus dimensions of patients with severe AS referred for TAVI when measured in diastole and systole. This small difference is unlikely to alter clinical decisions regarding prosthesis size or suitability for TAVI.

Human fetal pulmonary artery velocimetry: repeatability and normal values with emphasis on middle and distal pulmonary vessels.

Abstract: Objectives To establish the nature and gestational age dependency of flow velocity waveforms from fetal middle and distal arterial pulmonary branches in the second half of normal pregnancy and to determine repeatability and inter–relationship of flow velocity waveform recordings from proximal, middle and distal arterial pulmonary branches. Design Cross-sectional study. Subjects/methods A total of 111 singleton normal pregnancies between 20 and 40 weeks of gestation were studied using a color-coded Doppler ultrasound system. Pulmonary waveforms were obtained at the level of the fetal cardiac four-chamber view. Repeatability was tested from two recordings at 15 min time-intervals in 25 separate normal pregnancies. Results Acceptable repeatability of flow velocity waveforms from fetal arterial pulmonary branches was established with coefficients of variation below 15%. The nature of middle arterial pulmonary flow velocity waveforms was similar to that of proximal waveforms and showed a gestational age-related change for diastolic velocity parameters, peak systolic/peak diastolic ratio and pulsatility index. The distal arterial pulmonary branch displayed a monophasic forward flow velocity profile throughout the cardiac cycle. All velocity parameters of the distal branch remained unchanged with advancing gestation, with the exception of the pulsatility index. Significant inter–pulmonary changes were found for all pulmonary arterial waveform parameters. Conclusions Alteration in pulmonary vascular resistance may play a role in gestational age-related changes, whereas changes in vessel branching/diameter and in the distance between the heart and more distal arterial pulmonary vessels may cause inter–pulmonary differences. Copyright © 2000 International Society of Ultrasound in Obstetrics and Gynecology

Superior vena caval blood flow velocities in adults: a Doppler echocardiographic study.

Abstract: Superior vena caval blood flow velocity was measured in 30 normal adults (age 20–65, mean 36 yr). The flow velocities were measured by pulsed Doppler echocardiography, using a Duplex system with the transducer at the right supraclavicular fossa, approximating a 0 degrees Doppler angle. Four distinct flow waveforms were found during each cardiac cycle: A, a small retrograde flow during right atrial contraction (peak flow velocity 12.4 +/- 2.2 cm/s); B, a small antegrade flow during right atrial relaxation (15.7 +/- 5.0 cm/s); S, a large antegrade flow during ventricular systole (35.2 +/- 7.3 cm/s); and D, a large antegrade flow during ventricular diastole (23.2 +/- 3.1 cm/s). The wave duration was inversely related to heart rate. The peak flow velocities of the S and D waves were inversely related to the patients' ages. This study provides recognition of the pattern and range of normality essential to extension of this noninvasive technique to the diagnosis of pathological conditions.