Shocks administered within a second of the fibrillation are nearly 100 percent effective. If we can understand why, we will be one step closer to preventing fibrillation. Roth is using a mathematical approach called the bidomain model. The model describes how electrical impulses move through the heart, which is different from the way they travel through skeletal muscles. In skeletal muscles, electrical signals move down wiry nerve cells in a linear fashion from point A to point B to specific regions of the muscle.
Signals can activate different regions independently or all at once.
In this way the electrical signals can control whether part or all of the muscle contracts. Only part of the biceps may be called upon to raise a piece of paper, but the entire muscle may be enlisted to pick up the end of a desk. The heart is different. Electrical signals move down cardiac fibers to make the atria, or upper chambers, contract before the ventricles, or lower chambers. The signal fans out in all directions, skipping from muscle cell to muscle cell so that every cell in the heart responds by contracting.