Rotors are a spiral form of reentry which can drive atrial fibrillation, unlike the leading circle reentry in which there is a circular circuit. In leading circle reentry, the wavefront follows with wavetail without much of an excitable gap. The core of the circle is rendered refractory by centripetally spreading wavelets. But in a rotor, the wavefront and wavetail meat at a focal point which is called phase singularity. The wavefront near the phase singularity has the highest curvature and very slow velocity. Hence it is not able to penetrate the core tissue in the centre of the tissue. The tissue is not truly refractory, but it is not activated in the process. Waves moving away from the rotor can get fragmented in different parts of the atrium when functional or anatomical obstacles are encountered. This leads to multiple chaotic atrial activation which is characteristic of atrial fibrillation . Unlike fixed reentrant circuits, rotors can meander along the atrium.
Focal Impulse and Rotor Modulation (FIRM) mapping has demonstrated has demonstrated the presence of rotors in human atrial fibrillation . The recording system uses 64 pole basket electrodes. The electrodes are introduced through the femoral vein into the right atrium and into the left atrium across the interatrial septum. These are direct mapping electrodes and good contact is confirmed by both fluoroscopy and electroanatomic mapping. This technique employs wide area mapping which can be done both during spontaneous and induced AF. Once the rotors driving atrial fibrillation are identified, they can be targeted for ablation. This localized form of ablation has been shown to be useful, especially when combined with pulmonary vein isolation, improving long term success rates.