Atrial fibrillation substrate mapping with emphasis on voltage-based guidance

Voltage substrate mapping is a promising tool for the treatment of atrial fibrillation (AF). It is helpful to detect atrial fibrosis, which includes areas with low bipolar voltage, heterogeneous conduction properties, and shortened effective refractory period. The voltage amplitude is typically defined as the maximal peak-to-peak level within a specified time window of interest. Contemporary electroanatomic mapping platforms now enable many thousands of data points to be mapped, so that a geometric model of the atrial endocardium is constructable over a short period of time. This mapping procedure is often done with bipolar electrodes to cancel the far-field signal. The recording site coordinates are projected onto an atrial shell, with interpolation of the voltage data across the shell surface. The amplitude of the recorded bipolar electrogram depicted on the three-dimensional shell provides detailed information for substrate mapping. Wherever there are areas of low peak-to-peak voltage, it is thought to mark the presence of abnormal tissue properties and conduction. However, uncontrolled variables and environmental factors affecting voltage level include the oncoming electrical activation wavefront direction, the catheter incidence angle, the force applied to the catheter, and the region-variable shape and structure of atrial tissue. Techniques and settings to acquire atrial voltage data for AF analysis have not been standardized. Methods to characterize atrial electrograms are also presently limited. These factors affect quality and reproducibility of the mapping results. Herein, voltage substrate mapping and its variables pertaining to AF and radiofrequency ablation are described and discussed, with suggestions for future work efforts.