Conal contribution to the electrocardiogram of chick embryo hearts.

Contraction of the conus arterisus (conus) is visibly delayed in the tubular heart of the chick embryo, and since the electromechanical coupling interval of isolated conal segment is similar to other areas of the embryonic heart, the delayed contraction of the conus indicated an impedance in the spread of the depolarization wave across the ventriculo-conal (VC) junction. A surface electrode placed on the conus of hearts obtained from the 72-hour chick embryo records a deflection, termed the C wave, appearing between the QRS complex and the T wave. To establish that the C wave arose from below the atrioventricular sulcus, atria were removed from a series of hearts from 96-hour embryos and the electrogram revealed a C wave without a P wave.