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Published on: May 13, 2016
Changing activation sequence in the embryonic chick heart. Implications for the development of the His-Purkinje
E T Chuck1, D M Freeman, M Watanabe
1Department of Pediatrics, Case Western Reserve University, Cleveland, Ohio, USA.
Insights
The embryonic chick heart transitions from base-to-apex to apex-to-base contraction, indicating the His-Purkinje system (HPS) begins functioning around stages 29-31, shortly after ventricular septation.
Area of Science:
- Developmental Biology
- Cardiovascular Physiology
- Electrophysiology
Background:
- The mature heart relies on the His-Purkinje system (HPS) for efficient apex-to-base contraction.
- Embryonic hearts contract without a specialized conduction system, starting as a simple myocardial tube.
Purpose of the Study:
- To determine the developmental stage at which the His-Purkinje system (HPS) initiates function in the embryonic heart.
- To map the ventricular depolarization sequence during embryonic heart development.
Main Methods:
- Recorded microvolt-level electrograms from embryonic chick myocardium using 50-micron extracellular electrodes.
- Employed high-gain amplification and advanced signal-processing techniques to analyze ventricular activation.
- Utilized immunohistochemistry to track the expression of HPS biochemical markers.
Main Results:
- Observed a developmental shift in ventricular activation sequence from base-to-apex to apex-to-base patterns.
- Early stages (HH 25-28) showed a base-to-apex pattern (20/33 hearts).
- Late stages (HH 33-36) exhibited an HPS-like apex-to-base pattern (12/17 hearts).
- HPS marker expression paralleled the transition to the mature activation pattern.
- The mature ventricular activation pattern emerged between Hamburger-Hamilton stages 29 and 31.
Conclusions:
- Ventricular activation sequence in chick embryos matures between stages 29-31.
- Preferential conduction via the His-Purkinje system likely begins shortly after complete ventricular septation.
Abstract:
In the mature heart, impulse propagation through the His-Purkinje system (HPS) is required for efficient ventricular contraction in an apex-to-base direction. However, the embryonic heart begins to contract as a myocardial tube without a specialized conduction system. To identify the developmental stage when the HPS begins to function, we mapped the ventricular depolarization sequence from microvolt-level electrograms recorded from embryonic myocardium using 50-micron extracellular electrodes, high-gain amplification, and signal-processing techniques. Analysis of left ventricular activation in 99 embryonic hearts revealed a transition in the activation sequence that was dependent on developmental stage. As the heart develops, a transition in the activation sequence occurred from the primitive base-to-apex pattern (in 20 of 33 hearts) at early stages (Hamburger-Hamilton stages 25 to 28) to the HPS-like apex-to-base pattern (12 of 17 hearts) late in development (stages 33 to 36). Immunohistological experiments (n = 10) also confirm that the expression pattern of two biochemical HPS markers changes in parallel with the change to the mature ventricular activation pattern. These data indicate that the ventricular activation sequence in the chick heart develops to a mature pattern at stages 29 to 31, suggesting that preferential conduction through the HPS begins shortly after ventricular septation is complete.
