Qualitative and quantitative analyses of the morphological-dynamics of early cardiac pumping function using video densitometry and optical coherence tomography (OCT)

Introduction: During the initial phase of its pump action, vertebrate embryonic hearts are seen as valveless tubular pumps. It was traditionally thought that these tubular hearts generate unidirectional blood flow via peristalsis. Recently, however, the pumping mechanism of early embryonic hearts has become a matter of dispute.

Uncovering of the pumping mechanism of tubular embryonic hearts requires detailed information about the hemodynamics as well as morphological dynamics of the pump action. We have analyzed the morphological dynamics of cardiac pump action in chick embryos (HH-stage 16) using densitometric analyses of high-speed video recordings and M-mode optical coherence tomography (OCT) recordings.

Materials and Methods: White leghorn chick embryos (HH-stages 16) were grown in shell-less culture. Examinations were carried out in an environmental incubator, that provided stable physiological conditions during examination of the embryos. The high-speed video camera (120 frames/s) and the probe of the OCT system (4000 A-scans/s, 5.1μm axial pixel spacing) were integrated into the environmental incubator.

Hearts were examined in frontal views. For this purpose, the embryos were rotated rightward around their cranio-caudal axis. During examination this position was stabilized by using clips made of tungsten wire. Results: Utilizing OCT M-modes we have recorded striking differences in the contraction behavior (e.g. contraction speed, duration of systolic occlusion of heart lumen) of the embryonic heart segments (common atrium, AV-canal, embryonic ventricles, outflow tract).

Video densitometric M-mode curves show remarkable similarities to OCT M-mode recordings. OCT M-mode recordings can only be taken at one site at a time whereas video densitometry allows simultaneous recordings at any site. Moreover, we show, for the first time, the pump action of tubular embryonic chick hearts in frontal views, which provide a much better understanding of early cardiac pump action than the traditional right or left lateral views.

Summary: OCT M-mode recordings and video densitometric analyses show striking differences in contraction behavior of different heart segments of the tubular embryonic heart. These findings are important for the understanding of the pumping mechanism of the developing valveless embryonic heart.