Cardiac cycle

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

Tissue Doppler gated (TDOG) dynamic three-dimensional ultrasound imaging of the fetal heart.

Abstract: Dynamic three-dimensional (3D) ultrasound imaging of the fetal heart is difficult due to the absence of an electrocardiogram (ECG) signal for synchronization between loops. In this study we introduce tissue Doppler gating (TDOG), a technique in which tissue Doppler data are used to calculate a gating signal. We have applied this cardiac gating method to dynamic 3D reconstructions of the heart of eight fetuses aged 20-24 weeks. The gating signal was derived from the amplitude and frequency contents of the tissue Doppler signal. We used this signal as a replacement for ECG in a 3D-volume reconstruction and visualization, utilizing techniques established in ECG-gated 3D echocardiography. The reliability of the TDOG signal for fetal cardiac cycle detection was experimentally investigated. Simultaneous recordings of tissue Doppler of the heart and continuous wave (CW) spectral Doppler of the umbilical artery (UA) were performed using two independent ultrasound systems, and the TDOG signal from one system was compared to the Doppler spectrum data from the other system. Each recording consisted of a two-dimensional (2D) sector scan, transabdominally and slowly tilted by the operator, covering the fetal heart over approximately 40 cardiac cycles. The total angle of the sweep was estimated by recording a separate loop through the center of the heart, in the elevation direction of the sweep.3D reconstruction and visualization were performed with the EchoPAC-3D software (GE Medical Systems). The 3D data were visualized by showing simultaneous cineloops of three 2D slices, as well as by volume projections running in cineloop. Synchronization of B-mode cineloops with the TDOG signal proved to be sufficiently accurate for reconstruction of high-quality dynamic 3D data. We show one example of a B-mode recording with a frame rate of 96 frames/s over 20 seconds. The reconstruction consists of 31 volumes, each with 49 tilted frames. With the fetal heart positioned 5-8 cm from the transducer, the sampling distances were approximately 0.15 mm in the beam direction, 0.33 degrees approximately 0.37 mm azimuth and 0.45 degrees approximately 0.51 mm elevation. From this single dataset we were able to generate a complete set of classical 2D views (such as four-chamber, three-vessel and short-axis views as well as those of the ascending aorta, aortic and ductal arches and inferior and superior venae cavae) with high image quality adequate for clinical use.

Electrical Stimulation and Digitalis Drugs Repetitive Response in Diastole.

Abstract: SummaryIn the nondigitalized animal, a unipolar stimulus to the endocardium or myocardium discharged during diastole resulted in a single response unless energies greater than 5 J were used. During digitalization employing ouabain, the diastolic threshold energy for a repetitive ventricula response (RVR) was reduced by 6 orders of magnitude. RVR was first noted after 70% of the toxic dose of ouabain had been given and consisted of 2 ventricular ectopic beats. With advancing degrees of digitalization, a single stimulus evoked paroxysms of ventricular tachycardia. The most sensitive part of the cardiac cycle followed immediately after inscription of the T wave. As toxicity was approached, the zone of lowered threshold extended throughout most of the diastolic interval.

High-frame rate four dimensional optoacoustic tomography enables visualization of cardiovascular dynamics and mouse heart perfusion

Abstract: Functional imaging of mouse models of cardiac health and disease provides a major contribution to our fundamental understanding of the mammalian heart. However, imaging murine hearts presents significant challenges due to their small size and rapid heart rate. Here we demonstrate the feasibility of high-frame-rate, noninvasive optoacoustic imaging of the murine heart. The temporal resolution of 50 three-dimensional frames per second provides functional information at important phases of the cardiac cycle without the use of gating or other motion-reduction methods. Differentiation of the blood oxygenation state in the heart chambers was enabled by exploiting the wavelength dependence of optoacoustic signals. Real-time volumetric tracking of blood perfusion in the cardiac chambers was also evaluated using indocyanine green. Taken together, the newly-discovered capacities offer a unique tool set for in-vivo structural and functional imaging of the whole heart with high spatio-temporal resolution in all three dimensions.

Modulation of left atrial function by ventricular filling impairment.

Abstract: Left atrial function is an important determinant of ventricular filling. Assessment of the complex role that the atrial cavity exerts in the ventricular filling process can be made noninvasively. Computing the net instantaneous difference between mitral and pulmonary venous flow is an approach which permits the construction of the left atrial volume curve throughout the cardiac cycle (as well as the left ventricular volume curve during diastole), and to quantify the 3 different functions that the cavity performs. In particular, increasing degrees of ventricular filling impairment are met by mechanical left atrial adaptations which basically rely on the Starling mechanism, with the reservoir/pump complex activated to the limit of the preload reserve of the cavity. At end-stage left ventricular dysfunction, however, the atrial reservoir and the booster pump function decline and conduit takes precedence, suggesting afterload mismatch, impaired atrial compliance and, perhaps, depressed atrial contractility. Increased wall stiffening and reduced elastic recoil induced by chronic atrial distension might explain the additional power of atrial size in stratifying prognostically patients with left ventricular dysfunction.