Acute temperature effects on function of the chick embryonic heart

Area of Science:

• Cardiovascular Physiology
• Developmental Biology
• Biophysics

Background:

• The embryonic heart's response to thermal stress is crucial for development.
• Understanding temperature effects on cardiac electrophysiology aids in predicting developmental anomalies.

Purpose of the Study:

• To investigate the effects of acute temperature variations on chick embryonic heart rate, conduction, and calcium dynamics.
• To compare in vitro and in ovo responses to thermal changes.
• To identify temperature-sensitive cardiac segments and potential causes of arrhythmias.

Main Methods:

• High-speed calcium optical imaging and videomicroscopy were used to analyze isolated ED4 chick hearts in vitro and in ovo.
• Experiments involved temperature changes (34°C, 37°C, 40°C) and artificial stimulation.
• Arrhythmia incidence, particularly atrioventricular block, was recorded and analyzed.

Main Results:

• A decrease in temperature (37°C to 34°C) reduced heart rate by 22% (in vitro) and 25% (in ovo) with unchanged Ca(2+) transient amplitude.
• An increase in temperature (37°C to 40°C) elevated heart rate by 20-23% but decreased Ca(2+) transient amplitude significantly (-35% atrium, -38% ventricle).
• Atrioventricular block was the most common arrhythmia (57% in vitro), likely due to hypoxia rather than tachycardia.

Conclusions:

• The pacemaker and atrioventricular (AV) canal are the most temperature-sensitive regions in the embryonic heart.
• Conduction is critically impaired at the junction of the ventricular trabecular network and the AV canal.
• Hypoxia, not tachycardia, is suggested as the primary cause of AV block under thermal stress.