Cardiac cycle

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

Four-dimensional superquadric-based cardiac phantom for Monte Carlo simulation of radiological imaging systems

Abstract: A four-dimensional (x,y,z,t) composite superquadric-based object model of the human heart for Monte Carlo simulation of radiological imaging systems has been developed. The phantom models the real temporal geometric conditions of a beating heart for frame rates up to 32 per cardiac cycle. Phantom objects are described by boolean combinations of superquadric ellipsoid sections. Moving spherical coordinate systems are chosen to model wall movement whereby points of the ventricle and atria walls are assumed to move towards a moving center-of-gravity point. Due to the non-static coordinate systems, the atrial/ventricular valve plane of the mathematical heart phantom moves up and down along the left ventricular long axis resulting in reciprocal emptying and filling of atria and ventricles. Compared to the base movement, the epicardial apex as well as the superior atria area are almost fixed in space. Since geometric parameters of the objects are directly applied on intersection calculations of the photon ray with object boundaries during Monte Carlo simulation, no phantom discretization artifacts are involved.

The Measurement of Left Ventricular Function and the Detection of Wall Motion Abnormalities with High Temporal Resolution Ecg-Gated Scintigraphic Angiocardiography

Abstract: An ECG-gated, scintigraphic imaging procedure is described in which a complete, average cardiac cycle is visualized with high temporal resolution. The ability of this method to detect wall motion abnormalities and quantitate left ventricular function is illustrated in a patient with severe coronary artery disease. These results are compared to (contrast) angiographic findings in the same patient.

Maximum atrial tracking rate for cardiac rhythm management system

Abstract: A cardiac rhythm management system includes an operational mode in which ventricular pacing pulses are delivered at a rate that tracks a sinoatrial rate up to an appropriate maximum atrial tracking rate (MATR) value determined by the system. In one example, the MATR value is based on a patient activity level and a hemodynamic maximum rate (HMR) determined from a QRS-to-S2 interval, where S2 is an accelerometer-generated fiducial correlative to aortic valve closure (AVC). In a further example, a correlation between the QRS-to-S2 interval and heart rate is established, and the MATR is based on the patient activity level and heart rate. In a further example, a lower rate threshold for providing antitachyarrhythmia therapy is modified based on the MATR. For example, when the MATR exceeds a default value of the antitachyarrhythmia therapy lower rate threshold, the threshold tracks the MATR. In another example, the MATR is based on an active time between a QRS complex and a heart impedance signal maximum slope during the same cardiac cycle.

Twenty-four Segment Transverse Ventricular Fractional Shortening: A New Technique to Evaluate Fetal Cardiac Function

Abstract: Objectives Because of various fetal and maternal disease states, this study was conducted to evaluate the fractional shortening of 24 transverse segments distributed from the base to the apex of the ventricular chambers. Methods Two hundred control fetuses were examined between 20 and 40 weeks' gestation. The transverse displacement of the ventricular endocardium during the cardiac cycle was computed by using offline software. From the output of the analysis, 24 end-diastolic and end-systolic segments were measured from the base (segment 1) to the apex (segment 24) of the right and left ventricles, and the fractional shortening was computed: [(end-diastolic length – end-systolic length)/end-diastolic length] × 100. Examples of fetal cardiovascular abnormalities were selected to demonstrate the utility of this technique. Results The fractional shortening for each segment was independent of gestational age and fetal biometric measurements. There was no significant difference in fractional shortening for segments 1 to 5 between the right and left ventricles. However, the fractional shortening of the left ventricle was significantly greater (P < .0001) than that of the right ventricle for segments 6 to 24, suggesting that the mid and apical segments of the left ventricle have increased displacement toward the center of the chamber compared to the right ventricle. Fetuses with various cardiac structural abnormalities had abnormal fractional shortening values. Conclusions The fractional shortening of 24 segments of the right and left ventricles provides a comprehensive method to examine the contractility of the ventricular chambers.