Stannius Ligatures

The spread of excitation and the inherent rhythmicity of cardiac muscle can be investigated by interrupting conduction between sinus venosus and atria (Stannius Ligature I), and between atria and ventricle (Stannius Ligature II).

Stannius Ligature I
A cotton ligature is positioned loosely between the sinus venosus and the atria. A few normal traces are recorded and then the ligature is tightened. Observation of the heart shows the sinus venosus to continue to beat normally, but atrial and ventricular contractions cease. After a period of time, which varies from 5-30 minutes, the atria and ventricle start to beat again.

The following trace was recorded 20 minutes after tying the first Stannius ligature, when the atrial and ventricular contractions resumed.

Task
You should compare the new rhythm of contraction with the control trace recorded in previous experiments.

Use the play/pause button to halt the display to enable you to take your measurements more easily.