Cardiac cycle

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

Cardiac function: evaluation with fast-echo MR imaging.

Abstract: Magnetic resonance (MR) imaging of the heart has, to date, been limited in its ability to evaluate cardiac function. The authors have implemented a technique for functional assessment of the heart using shorter echo times than those generally used for conventional spin-echo imaging. With these short echo times, multiple images can be obtained in a multisection mode approximately within the isovolumetric phases of the cardiac cycle. This permits a pair of image stacks to be obtained, one in end systole and the other in end diastole. With the use of a modified Simpson rule, left ventricular volume and ejection fraction were calculated and compared with results obtained from contrast material-enhanced ventriculography. Preliminary results indicate that this method has promise for the evaluation of a variety of functional parameters in the heart. The short acquisition times for this functional study permit it to be combined with a tissue characterization study within the time constraints of a clinical MR imag...

Reversal of volatile anesthetic-induced depression of myocardial contractility by extracellular calcium also enhances left ventricular diastolic function.

Abstract: BACKGROUND Volatile anesthetics depress global left ventricular function by altering intracellular calcium (Ca2+) homeostasis at several sites within the myocyte. Although extracellular Ca2+ partially reverses the negative inotropic effects of volatile anesthetics, the actions of extracellular Ca2+ on anesthetic-induced diastolic dysfunction are unexplored. This investigation examined and compared the direct effects of extracellular Ca2+ on left ventricular systolic and diastolic function in conscious and anesthetized dogs. METHODS Experiments were conducted in the presence of pharmacologic blockade of the autonomic nervous system because autonomic nervous activity may significantly influence the hemodynamic actions of anesthetics and Ca2+ in vivo. Three groups comprised a total of 27 experiments conducted using nine dogs chronically instrumented for measurement of aortic and left ventricular pressure, left ventricular dP/dt, subendocardial segment length, and cardiac output. Myocardial contractility was evaluated using the preload recruitable stroke work relationship slope (Mw). Diastolic function was assessed using a time constant of isovolumic relaxation (tau), a regional chamber stiffness constant (Kp), and maximum segment lengthening velocity during rapid ventricular filling (dL/dtE) and atrial systole (dL/dtA). On 3 separate days, a CaCl2 infusion at 1.25, 2.5, or 5 mg.kg-1 x min-1 was administered. Hemodynamics and ventricular pressure-length loops were recorded after a 20-min equilibration at each dose in the conscious state or during halothane or isoflurane anesthesia. RESULTS In conscious dogs, CaCl2 produced a significant (P < .05) and dose-dependent increase in contractility as evaluated by Mw. In the presence of halothane anesthesia, CaCl2 increased contractility (Mw of 26 +/- 5 mmHg to 78 +/- 10 mmHg during the high dose of CaCl2), enhanced isovolumic relaxation (tau of 57.9 +/- 4.2 ms to 41.1 +/- 1.9 ms during the high dose of CaCl2), improved rapid ventricular filling (dL/dtE of 11.8 +/- 1.4 mm/s to 20.2 +/- 1.6 mm/s during the high dose of CaCl2), and reduced regional chamber stiffness (Kp of 0.70 +/- 0.18 mm-1 to 0.38 +/- 0.04 mm-1 during the high dose of CaCl2). Similar findings were observed when CaCl2 was administered to dogs anesthetized with isoflurane. CONCLUSIONS Although CaCl2 produced positive inotropic effects in both the conscious and anesthetized states, CaCl2 did not alter diastolic function in conscious dogs. In contrast, CaCl2 reversed halothane- and isoflurane-induced negative lusitropic actions. The results of the present investigation suggest that improvement of left ventricular performance by CaCl2 during volatile anesthesia may be related to actions in diastole as well as systole.

Optimization of cardiac resynchronization guided by Doppler echocardiography: haemodynamic improvement and intraindividual variability with different pacing configurations and atrioventricular delays

Abstract: Aims Cardiac resynchronization therapy (CRT) improves symptoms in heart failure patients with intraventricular conduction delay (IVCD). Different pacing modalities produce variable activation patterns and are likely to result in different haemodynamic changes. The objective of this study was to demonstrate acute haemodynamic changes with different CRT configurations. Methods and results In 26 patients (left ventricular ejection fraction 22.7±6.1%, QRS 176±29 ms, New York Heart Association III/IV 18/8), a CRT device was implanted. An optimization procedure was performed including left (LVPEI) and right ventricular pre-ejection intervals, interventricular mechanical delay (IVD), left ventricular filling fraction (FTc), and myocardial performance index (MPI) during left and biventricular pacing with three different atrioventricular (AV) delays. An optimal mode and AV delay were defined. LVPEI changed from 166±27 to 139±25 ms, IVD from 49±19 to 6±18 ms, MPI from 0.98±0.25 to 0.62±0.22, and FTc from 0.42±0.08 to 0.51±0.08 ( P <0.001 for all comparisons). The variability was 39±20 ms for LVPEI, 55±24 ms for IVD, 0.11±0.07 for FTc, and 0.35±0.18 for MPI. Conclusion Optimized resynchronization in heart failure patients with IVCD produces marked acute improvement of the altered cardiac cycle timing. The variability of Doppler parameters with different CRT modalities underlines the necessity of individualized settings and suggests that the patients' benefit may be jeopardized without optimization.

Body surface Laplacian mapping of cardiac electrical activity.

Abstract: Cardiac electrical activity is distributed over the 3-dimensional volume of the myocardium. Ideally one would like to be able to map the 3-dimensional distribution of cardiac electrical activity in the heart at each point in time during the cardiac cycle. The conventional electrocardiogram and vectorcardiogram provide a highly degenerate representation of cardiac electrical activity. The body surface potential map (BSPM) involves the measurement of the potential at many points on the body surface in an attempt to characterize the distributed nature of cardiac electrical activity. 1–7 Although the BSPM has been shown by a number of investigators to reliably identify major single cardiac events, 8 its ability to resolve spatially separated bioelectrical events is limited 4–6 because of the smoothing effect of the torso volume conductor. 9,10 The fundamental limitation to interpreting the BSPM in terms of cardiac electrical events is the nonuniqueness of the electrocardiograph inverse problem. 11 One can generally represent the heart as a bioelectrical source in terms of a 3-dimensional distribution of electrical dipoles. One can prove that any given body surface potential distribution does not uniquely specify a specific 3-dimensional electrical dipole source distribution. Whereas the epicardial potential distribution has been estimated from the BSPM, 12,13 such inverse calculations require detailed geometric information 14 and are mathematically ill-posed. Furthermore, the epicardial potential distribution itself does not specify the distribution of bioelectrical sources within the heart. The ability to image cardiac electrical activity noninvasively from the body surface could greatly enhance our ability to diagnose a wide range of cardiac abnormalities, specifically ischemia, infarction and cardiac rhythm disturbances. We have developed a new approach to mapping spatially distributed cardiac electrical events noninvasively by measuring the 2-dimensional Laplacian of the potential on the body surface. 15,16 The 2-dimensional Laplacian of the potential is the second spatial derivative of the electrical potential on a surface and provides a 2-dimensional-type projection image of the 3-dimensional distribution of cardiac electrical sources onto the body surface. 16 The 2-dimensional Laplacian of the potential map may also be interpreted as an equivalent charge density distribution. A depolarization wavefront perpendicularly approaching a point on the chest wall will generate a positive equivalent charge density at that point; a depolarization wavefront tangential to the chest wall will generate a parallel double layer of positive and negative equivalent charge density overlying the wavefront. The purpose of the present study is to investigate body surface Laplacian maps (BSLMs) during normal and abnormal cardiac beats in humans and to test the hypothesis that body surface Laplacian mapping can relate body surface recordings to regional myocardial events.