Atrial fibrillation (AF) is the world’s most common cardiac arrhythmia effecting millions of people worldwide, yet the disease has resisted a full mechanistic explanation for over one hundred years. When the heart is beating normally, each contraction is carefully coordinated by a planar electrical wavefront passing through the muscle from top to bottom. However, these wavefronts can be spontaneously disrupted resulting in the chaotic motion of wavefronts and a loss of heart coordination. Mapping studies have pointed towards AF originating from both ectopically beating focal points in the heart, and from rotors – points where electrical wavefronts indefinitely spiral around themselves. However, theoretical models have struggled to explain both observations from a single underlying phenomenon.
New clinical work by Hansen et al.  has given early evidence for a potential unifying mechanism of AF, as noted by a recent Nature Review . The work shows that both ectopic focal points and rotational activity can be explained by micro-anatomical re-entry circuits forming in the heart muscle wall with variable orientation. These circuits are structures formed from adjacent muscle fibres that are poorly connected, and as a result, electrical signals can continuously move around the circuit emitting ectopic electrical activity. In one orientation, the signals emitted by the circuit might look like a focal point source, in another orientation it may appear as rotational activity.
In previous work, we have introduced the first 2d model of atrial fibrillation that spontaneously generates AF from micro-anatomical re-entry circuits using a simple cellular automata [3,4]. However, in the 2d model, circuit orientation is fixed and as such, the model cannot be used to study the recent clinical findings. We have now extended the model to 3d and present our results here. The model successfully reproduces the findings by Hansen et al. and demonstrates that a unifying mechanism of micro-anatomical reentry can emerge from very simple principles with diverse and complex consequences.