Cardiac cycle

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

Rest period duration of the coronary arteries: implications for magnetic resonance coronary angiography.

Abstract: Magnetic resonance (MR) and computed tomography coronary imaging is susceptible to artifacts caused by motion of the heart. The presence of rest periods during the cardiac and respiratory cycles suggests that images free of motion artifacts could be acquired. In this paper, we studied the rest period (RP) duration of the coronary arteries during a cardiac contraction and a tidal respiratory cycle. We also studied whether three MR motion correction methods could be used to increase the respiratory RP duration. Free breathing x-ray coronary angiograms were acquired in ten patients. The three-dimensional (3D) structure of the coronary arteries was reconstructed from a biplane acquisition using stereo reconstruction methods. The 3D motion of the arterial model was then recovered using an automatic motion tracking algorithm. The motion field was then decomposed into separate cardiac and respiratory components using a cardiac respiratory parametric model. For the proximal-to-middle segments of the right coronary artery (RCA), a cardiac RP (<1 mm 3D displacement) of 76+/-34 ms was measured at end systole (ES), and 65+/-42 ms in mid-diastole (MD). The cardiac RP was 80+/-25 ms at ES and 112+/-42 ms at MD for the proximal 5 cm of the left coronary tree. At end expiration, the respiratory RP (in percent of the respiratory period) was 26+/-8% for the RCA and 27+/-17% for the left coronary tree. Left coronary respiratory RP (<0.5 mm 3D displacement) increased with translation (32% of the respiratory period), rigid body (51%), and affine (79%) motion correction. The RCA respiratory RP using translational (27%) and rigid body (33%) motion correction were not statistically different from each other. Measurements of the cardiac and respiratory rest periods will improve our understanding of the temporal and spatial resolution constraints for coronary imaging.

Echocardiographic features of right ventricular outflow tumor prolapsing into the pulmonary artery

Abstract: The echocardiographic features of a tumor in the right ventricular outflow tract that prolapsed into the pulmonary artery during systole are described. The patient was a 19 year old woman who presented clinically with bacterial endocarditis involving a mildly stenotic pulmonary valve. An echocardiogram, obtained to evaluate the pulmonary valve for bacterial vegetations, showed abnormal echoes throughout the cardiac cycle; they suggested a tumor mass in the right ventricular outflow tract in front of the pulmonary valve with possible extension into the pulmonary artery during systole. Additional tumor echoes confined to diastole were recorded in front of the aortic root and the tricuspid valve. These features were further elucidated with a computer-generated two dimensional cineechocardiogram that clearly showed a portion of the tumor mass passing beyond the position of the pulmonary valve into the main pulmonary artery in systole and returning into the right ventricular outflow in diastole. At surgery, a large myxoma was found in the right ventricular outflow tract with a polypoid extension that projected into the pulmonary artery in systole and contained a fibrinous vegetation at its tip. The left cusp of the pulmonary valve was normal, but the other two leaflets showed evidence of endocarditis.

Electromechanical coupling in the cardiac myocyte; stretch-arrhythmia feedback

Abstract: The macroscopic hallmarks of the normal heartbeat are rapid onset of contraction and rapid relaxation and an inotropic response to both increased end diastolic volume and increased heart rate. At the microscopic level, the calcium ion (Ca2+) plays a crucial role in normal cardiac contraction. This paper reviews the cycle of Ca2+ fluxes during the normal heartbeat, which underlie the coupling between excitation and contraction (ECC) and permit a highly synchronized action of cardiac sarcomeres. Length dependence of the response of the regulatory sarcomeric proteins mediates the Frank–Starling Law of the heart. However, Ca2+ transport may go astray in heart disease and both jeopardize the exquisite mechanism of systole and diastole and triggering arrhythmias. The interplay between weakened and strong segments in nonuniform cardiac muscle may further lead to mechanoelectric feedback—or reverse excitation contraction coupling (RECC) mediating an early diastolic Ca2+ transient caused by the rapid force decrease during the relaxation phase. These rapid force changes in nonuniform muscle may cause arrhythmogenic Ca2+ waves to propagate by activation of neighbouring SR by diffusing Ca2+ ions.

Selective cardiac activity analysis atrial fibrillation detection system and method and atrial defibrillator utilizing same

Abstract: An atrial defibrillator applies cardioverting electrical energy to the atria of a human heart in need of cardioversion. The defibrillator includes an electrode pair and a sense amplifier associated with the atria of the heart for sensing electrical activity of the heart during a plurality of cardiac cycles to provide a cardiac signal. A detector is responsive to the cardiac signal for detecting cardiac events. During each cardiac cycle of the plurality of cardiac cycles, a time for counting is established wherein each time for counting has a total duration less than the duration of its corresponding cardiac cycle. A counter counts the cardiac events detected by the detector during the time for counting of the plurality of cardiac cycles to provide a cardiac event count. A comparator compares the cardiac event count to a predetermined cardiac event count. If the cardiac event count is greater than the predetermined cardiac event count, the atria are deemed to be in fibrillation and a cardiovertor applies cardioverting electrical energy to the atria to cardiovert the detected atrial fibrillation.

Magnetic resonance evaluation of regional left ventricular function. Effect of through-plane motion.

Abstract: Rationale and objectives Measurements of segmental contraction of the left ventricle by standard magnetic resonance imaging (MRI) and two-dimensional echocardiography involve the comparison of diastolic and systolic time frames acquired from the same imaging plane in space. As the cone-shaped left ventricle shortens along its long axis during systole, the observed contraction may differ from the true myocardial contraction. Methods Spin-echo MRI examinations in 21 healthy subjects were performed to evaluate the error caused by failing to compensate for through-plane motion. Results The authors found that at the base and the mid-ventricle the observed contraction systematically underestimates true contraction by an average of 16% and 21%, respectively (P less than .001). At the apex, the segmental contraction may be overestimated or underestimated. Conclusions Because of this error, standard MRI and echocardiography are less suited for basic research on cardiac contraction patterns. However, standard imaging techniques are valuable in clinical studies comparing groups of patients, because all measurements will suffer from the same systematic error.