Formal Logic Based Heart-Model - Using Event-B for Critical Device Software Systems - page 150

Fig. 8.6 Time intervals and impulse propagation in the ECG signal (adapted from [ 30 ])

8.4.1 Heart Block

In this section, we explain the basic heart blocks in the heart conduction system.
We have formalised these basic heart blocks in the proposed methodology. Heart
block is the term given to a disorder of conduction of the impulse that stimulates
heart muscle contraction. The normal cardiac impulse arises in the SA node (A),
situated in the right atrium, and spreads to the AV node (B), whence it is con-
ducted by specialised tissue known as the Bundle of His (D), which divides into
the left and right bundle branches in the ventricles (see Fig. 8.4 (a)). Disturbances in
conduction may appear as slow conduction, intermittent conduction failure or com-
plete conduction failure. These three kinds of conduction failure are also known
as 1st, 2nd and 3rd degree blocks. We can show these different kinds of heart
block throughout the conduction network in terms of our set of landmark nodes
(see Fig. 8.7 ).