Cardiac cycle

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

Radionuclide angiographic evaluation of left ventricular diastolic function.

Abstract: Left ventricular diastolic function is altered in the majority of patients with cardiac diseases, especially those characterized by myocardial ischemia or hypertrophy. In many circumstances, such abnormalities related to impaired relaxation or reduced distensibility may precede evidence of left ventricular systolic dysfunction. Radionuclide angiography may be adapted to study the rapid filling phase of diastole, the duration of the isovolumic relaxation phase, the relative contributions of rapid filling and atrial systole to left ventricular stroke volume, and the relation between regional nonuniformity of left ventricular function and global filling properties. Technical aspects of data acquisition that must be considered for such studies include the effects of cardiac cycle length fluctuations, temporal resolution, temporal smoothing, and normalization parameters. As noninvasive radionuclide methods (and any other analyses using purely noninvasive techniques) do not permit assessment of the left atrial-left ventricular pressure gradient or the simultaneous evaluation of changes in left ventricular pressure and volume during relaxation and filling, complete clinical interpretation of "abnormal" left ventricular filling indexes, or changes in these indexes after interventions, is not possible. Despite the inherent limitations of noninvasive assessment of left ventricular diastolic function, radionuclide evaluation of left ventricular filling may provide clinically useful insights, especially in patients with congestive heart failure symptoms and normal left ventricular systolic function.

Impact of Chronic Left Ventricular Preload and Afterload on Doppler Tissue Imaging Velocities: A Study in Congenital Heart Disease

Abstract: Background Doppler tissue imaging (DTI) velocities have been reported to be relatively independent of changes in ventricular loading conditions in adult studies. The clinical impact of altered left ventricular (LV) preload and afterload on DTI velocities in children with congenital heart disease has not been adequately evaluated. The purpose of this study was to evaluate the impact of chronic LV preload and afterload on DTI velocities in children with isolated ventricular septal defect and aortic valve stenosis compared with age-matched normal and abnormal (dilated cardiomyopathy) control groups. Methods From an apical 4-chamber view, DTI velocities were obtained at the cardiac base at the lateral mitral annulus, lateral tricuspid annulus, and interventricular septum in early diastole, late diastole, and ventricular systole. Results The majority of DTI velocities did not change significantly in patients with increased LV preload. Patients with increased LV afterload had significantly decreased systolic and early diastolic DTI velocities at both the lateral mitral annulus and ventricular septum compared with control subjects. Children with dilated cardiomyopathy had significantly decreased DTI velocities at all myocardial annular locations. Conclusions We conclude that increases in chronic LV preload do not significantly affect the majority of DTI velocities in children with ventricular septal defects. In addition, significantly increased chronic LV afterload in children with aortic valve stenosis is associated with decreased DTI velocities in the absence of other identifiable abnormalities of LV function. Decreased DTI velocity may be secondary to increased afterload or may alternatively be an early marker of subclinical LV longitudinal dysfunction.

Cardiac imaging with CT scanner

Abstract: The patient's ECG signal is employed in a traverse-and-rotate type CT scanner as a time base for triggering the beginning of a traverse such that the traveling beam reaches the heart at a desired phase of the cardiac cycle. For a purely-rotational-type CT scanner, continuously generated scan data is only stored for corresponding phases of successive cardiac cycles. Alternatively, gating of the beams themselves can be controlled by the ECG signal. The use of a pacemaker to stabilize the cardiac period is described along with a system for recognizing unacceptable variations in the cardiac period. In a traverse-and-rotate-type fan-beam CT scanner, the effective beam width is narrowed to hasten the traverse of the heart.

Auscultatory and Phonocardiographic Assessment of Pulmonary Stenosis with Intact Ventricular Septum

Abstract: A clinical and phonocardiographic study has been made on pulmonary and infundibular stenosis with intact ventricular septum, in order to determine the value of auscultation and phonocardiography in assessing the severity of the stenosis. There were 43 cases of pulmonary valve stenosis with intact ventricular septum and 8 cases of infundibular stenosis with intact ventricular septum. The severity of the stenosis, as determined by the right ventricular pressure, was correlated with the duration of right ventricular systole, as determined both by the length of the systolic murmur and the width of splitting of the second heart sound. It was shown that increasingly severe stenosis resulted in progressive lengthening of the murmur in relation to the aortic second sound and delay in pulmonary valve closure. Criteria were defined whereby the severity of the stenosis could be predicted; these proved more accurate than other clinical methods. In mild stenosis (RVP under 60 mm. Hg), the murmur was soft to loud in in...

Cardiac mechanics and energetics: chemomechanical transduction in cardiac muscle

Abstract: When a heart is in a stable inotropic state, the end-systolic pressure-volume points of each work cycle fall on a straight line regardless of the magnitude of the afterload or the initial end-diastolic volume: cardiac O2 consumption (MVO2) per beat is linearly correlated with ventricular systolic pressure-volume area (PVA), defined in terms of stroke work and potential energy components. Moreover, if the basal and activation components of the cardiac energy cycle are subtracted, hearts operate at a constant PVA/MVO2 efficiency. The present review examines the energetic implications of these results for current muscle models, discussing the energetic background of earlier skeletal muscle viscoelastic models and examining differences between the vectorial outputs of ion transport ATPases and myofibrillar ATPases. The PVA data point to a unique stoichiometric relationship between myocardial energy flux and vectorial output, and it is shown that most existing myocardial O2 consumption data can be reconciled with the PVA concept. However, most muscle models would not predict a linear stoichiometric relation between energy flux and pressure-volume potential energy. We pose the question as to whether there is an undiscovered autoregulatory process at work in muscle.