High‐resolution in vivo imaging of the cross‐sectional deformations of contracting embryonic heart loops using optical coherence tomography

Abstract

The embryonic heart tube consists of an outer myocardial tube, a middle layer of cardiac jelly, and an inner endocardial tube. It is said that tubular hearts pump the blood by peristaltoid contractions. The traditional concept of cardiac peristalsis sees the cyclic deformations of pulsating heart tubes as concentric narrowing and widening of tubes of circular cross-section. We have visualized the cross-sectional deformations of contracting embryonic hearts in chick embryos (HH-stages 9 -17) using real-time high-resolution optical coherence tomography. Cardiac contractions are detected from HH-stage 10 onward. During the cardiac cycle, the myocardial tube undergoes concentric narrowing and widening while the endocardial tube undergoes eccentric narrowing and widening, having an elliptic cross-section at end-diastole and a slitshaped cross-section at end-systole. The eccentric deformation of the endocardial tube is the consequence of an uneven distribution of the cardiac jelly. Our data show that the cyclic deformations of pulsating embryonic heart tubes run other than originally thought. There is evidence that heart tubes of elliptic cross-section might pump blood with a higher mechanical efficiency than those of circular-cross section. The uneven distribution of cardiac jelly seems to prefigure the future AV and cono-truncal endocardial cushions. Developmental Dynamics 237:953-961, 2008.

In vivo imaging of the cyclic changes in cross‐sectional shape of the ventricular segment of pulsating embryonic chick hearts at stages 14 to 17: A contribution to the understanding of the ontogenesis of cardiac pumping function

“…4). The ventricular segment principally shows the same pattern of cardiac cycle-related deformations as described in previous studies Mä nner et al, 2008). The OCT-pictures obtained at stage 14, however, differ slightly from the previously described picture because the endocardial tube shows multiple spike-like ''appendages'' that radiate from the endocardial tube toward the myocardial mantle (Figs.…”

“…Careful re-examination of the data from our previous study discloses that short endocardial spikes are already present in the ventricular segment at stage 13 but cannot be detected at stages younger than stage 13 (see Fig. 6 in Mä nner et al, 2008). During stages 13 and 14, the tips of endocardial spikes do not reach the basal surface of the myocardial mantle but end within the cardiac jelly layer.…”

“…In view of this fact and in view of the fact that the blood supply of the embryonic myocardium comes exclusively from the endocardial lumen, it is tempting to speculate that the primary physiological ''purpose'' of the structural changes leading to the bell-shaped cross-section of the ventricular endocardial tube is to accomplish the steadily increasing energy demands of the ''generators'' of the cardiac pumping force. The bell-shaped crosssection of the ventricular segment, which still facilitates an almost complete occlusion of the ventricular lumen at end-systole, then might represent a structural compromise between (1) the optimization of the pumping efficiency of a tubular embryonic heart, which depends on the presence and spatial distribution of a relatively thick layer of cardiac jelly (Barry, 1948;Mä nner et al, 2008), and (2) the optimization of the energy supply of the ventricular myocardium, which tends to reduce the thickness of the cardiac jelly layer.…”

“…Using these new in vivo imaging techniques, we and others have recently shown that the cyclic deformations of the pulsating embryonic heart tube run other than traditionally thought Mä nner et al, 2008). According to the traditional view, the cyclic changes in its cross-sectional shape were described as concentric narrowing and widening of a tube of circular cross-section (e.g., Barry, 1948;Liebling et al, 2006).…”

Blood flow through the embryonic heart outflow tract during cardiac looping in HH13–HH18 chicken embryos

“…three to four cardiac cycles; n ¼ 10). The embryo was positioned so that the lumen completely filled the OFT at maximum expansion and made a slit-like shape in the centre of the OFT at maximum contraction [30,34]. A glass capillary tube standard was imaged to calculate a pixel to length conversion factor that was used in all structural analyses.…”