Cardiac cycle

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

A mathematical model of motion of the heart for use in generating source and attenuation maps for simulating emission imaging

Abstract: This manuscript documents the alteration of the heart model of the three-dimensional (3D) mathematical cardiac torso (MCAT) phantom to represent cardiac motion. The objective of the inclusion of motion was to develop a digital simulation of the heart such that the impact of cardiac motion on single-photon emission computed tomography(SPECT)imaging could be assessed and methods of quantitating cardiac function could be investigated. The motion of the gated 3D MCAT's (gMCAT) heart is modeled using 128 separate and evenly spaced time samples from a blood volume curve approximating an average heart cycle. Sets of adjacent time samples can be grouped together to represent a single time interval within the heart cycle. Maximum and minimum chamber volumes were selected to be similar to those of a normal healthy person while the total heart volume stayed constant during the cardiac cycle. Myocardial mass was conserved during the cardiac cycle and the bases of the ventricles were modeled as moving towards the static apex. The orientation of the 3D MCAT heart was changed during contraction to rotate back and forth around the long axis through the center of the left ventricle (LV) using the end systolic time interval as the time point at which to reverse direction. Simple respiratory motion was also introduced by changing the orientation of the long axis of the heart to represent its variation with respiration.Heart models for 24 such orientations spanning the range of motion during the respiratory cycle were averaged together for each time sample to represent the blurring of the heart during the acquisition of multiple cardiac cycles. Finally, an option to model apical thinning of the myocardium was included. As an illustration of the application of the gMCAT phantom, the gated heart model was evaluated by measuring myocardial wall thickening. A linear relationship was obtained between maximum myocardial counts and myocardial thickness, similar to published results. Similar results were obtained for full width at half maximum (FWHM) measurements. With the presence of apical thinning, an apparent increase in counts in the apical region compared to the other heart walls in the absence of attenuation compensation turns into an apparent decrease in counts with attenuation compensation. The apical decrease was more prominent in end systole (ES) than end diastole (ED) due to the change in the partial volume effect. These observations agree with clinical trends. It is concluded that the gMCAT phantom can be used to study the influence of various physical parameters on radionuclide perfusion imaging.

Measurement of intraventricular pressure and cardiac performance in the intact closed-chest anesthetized mouse

Abstract: To fully utilize the potential of newly developed mouse models with specific genetic mutations, it is necessary to study the functional consequences of genetic manipulation in the fully intact animal. To this end, the purpose of the present study was to develop and validate a methodology for the study of myocardial performance in the fully intact, closed-chest mouse. Left ventricular function was evaluated in euthyroid, hypothyroid, and hyperthyroid mice, animals with well-documented alterations in myocardial function. The mice were anesthetized and instrumented with polyethylene catheters in the right femoral artery and vein and with a Millar MIKRO-TIP transducer in the left ventricle via the right carotid artery. Structural and functional evidence suggested that the instrumentation procedure did not cause myocardial damage, valvular insufficiency, or aortic obstruction. Isovolumic indexes of myocardial contractility derived from the left ventricular pressure pulse and its first derivative demonstrated a 40% increase in contractility in the hyperthyroid animals and a 40% decrease in contractility in the hypothyroid animals. Similar differences in the indexes of relaxation were observed. Furthermore, isoproterenol dose-response relationships of these contractile parameters were blunted in the hypothyroid animals and augmented in the hyperthyroid animals compared with euthyroid control animals. Given the small size of the mouse and the high frequency of the cardiac cycle, these data demonstrate the feasibilty of combining a high-fidelity, microtip manometer with a high-speed data-acquisition system to obtain faithful recordings of cardiac performance in the fully intact mouse.

Non-invasive assessment of cardiac physiology by tissue Doppler echocardiography. A comparison with invasive haemodynamics.

Abstract: Background Tissue Doppler echocardiography reveals characteristic patterns of myocardial velocities within systole and diastole which are not well understood. Aim The purpose of this study was to determine the relationship of myocardial velocity patterns, as assessed by tissue Doppler echocardiography, to the contraction and relaxation phases of the cardiac cycle, as determined during cardiac catheterization. Methods Recordings of left ventricular/aortic and left ventricular/pulmonary wedge pressures were obtained simultaneously with apical tissue Doppler echocardiographic images of the left ventricle. A total of 210 cardiac cycles from 22 patients (mean age 58 years, 18 male) undergoing cardiac catheterization were analysed. The time intervals of the different phases of the cardiac cycle were measured from the pressure tracings. These time intervals were correlated to the interfaces of colour myocardial velocity patterns obtained by M-mode tissue Doppler echocardiography. Results There was a good correlation between the time intervals assessed haemodynamically and those based on the different velocity interfaces obtained with M-mode tissue Doppler echocardiography. Comparable time intervals (from the R wave) obtained by pressure recordings and tissue Doppler echocardiography were, respectively: isovolumic contraction (70±14 vs 67±9 ms, r=0·79); rapid ejection (206±54 vs 202±49 ms; r=0·95); late ejection (357±36 vs 346±42 ms, r=0·93); isovolumic relaxation (405±43 vs 409±56 ms; r=0·95); rapid filling (514±67 vs 523±64 ms, r=0·91); diastasis (697±153 vs 709±146 ms, r=0·98); atrial contraction (890±128 vs 899±132 ms, r=0·96). Conclusion Tissue Doppler echocardiography has the potential to accurately measure the different phases of the cardiac cycle which until now could only be determined invasively. It may provide a sensitive method for the assessment of changes in both cardiac contraction and relaxation in different clinical settings.

MRI of the normal pericardium

Abstract: The visibility and thickness of the pericardium, as depicted by MRI, and the changes of these parameters over the cardiac cycle were determined in 18 normal subjects. Gated, cycled, multisection images were obtained in the transaxial orientation. Using a score-point system for quantification, there was better visualization of the low-intensity pericardial line during systole as compared with diastole (p less than 0.005). Pericardial thickness was 1.2 +/- 0.5 mm in diastole and 1.7 +/- 0.5 mm in systole (p less than 0.001) as measured in a midventricular section in front of the right ventricle; both values exceeded the thickness of 0.4 to 1.0 mm reported for anatomic measurements of pericardial thickness. The layer of normal pericardial fluid present in the pericardial space should also have low intensity, and it likely contributes to the overall pericardial thickness as visualized by MRI. Since MRI is sensitive to the small amount of normal pericardial fluid and depicts its anatomic distribution, it should be valuable in detection and quantification of even small pericardial effusions.