The association of low voltage atrial electrograms and the myocardial substrate for atrial fibrillation

Abnormal human atrial muscle has elevated resting membrane potential, depressed maximal amplitude of the action potential, and decreased upstroke velocity. These electrical abnormalities are histologically correlated to degenerative changes of the atrial muscle structure. Investigations based on the recording of abnormally prolonged and fractionated atrial endocardial electrograms during sinus rhythm have provided important knowledge about the electrophysiological properties of the pathological atrium. Human atrial tissues, where fractionated electrograms are recorded, consist of muscle fibers that are widely separated and their orientation distorted by connective tissue. These histological changes results in decreased intercellular connections, which might increase resistance to current flow, and thereby slow conduction. The potential clinical significance is that detection of abnormal atrial endocardial electrograms during sinus rhythm in patients with atrial vulnerability may help to identify those with greater atrial conduction defects and higher incidence of induced and spontaneous episodes of AF. 3D electroanatomic mapping (EAM) has been utilized in clinical electrophysiological studies for substrate description in atrial arrhythmias. Using this 3D EAM system low bipolar endocardial voltage can be identified and localized for guiding catheter ablation. Voltage mapping with 3D electroanatomic mapping is based on the correlation of the registration of low-voltage areas (<0.5 mV) in the left atrium with endocardial scar and/or structural defects as an atrial substrate. These low-voltage zones are the target for individualized substrate ablation or modification. Patients with low-voltage substrate have lower success rates after pulmonary vein ablation. However, this low success rate can be significantly improved by targeting atrial substrate zones with low voltage areas. Although more clinical evidence should be further generated, patient specific substrate ablation targeting atrial fibrosis estimated by bipolar voltage mapping is a promising alternative strategy for additional substrate modification beyond PVI ablation for AF. 1-