The Electrophysiological Substrate of Early Repolarization Syndrome: Noninvasive Mapping in Patients

Objectives This study sought to map the epicardial electrophysiological (EP) substrate in early repolarization (ER) syndrome patients using noninvasive electrocardiographic imaging (ECGI), and to characterize substrate properties that support arrhythmogenicity. Background The ER pattern is a common ECG finding. Recent studies established a definitive clinical association between ER and fatal ventricular arrhythmias. However, the arrhythmogenic substrate of ER in the intact human heart has not been characterized. Methods Twenty-nine ER syndrome patients were enrolled, 17 of whom had a malignant syndrome. Characteristics of the abnormal EP substrate were analyzed using data recorded during sinus rhythm. The EP mapping data were analyzed for electrogram morphology, conduction, and repolarization. Seven normal subjects provided control data. Results The abnormal EP substrate in ER syndrome patients has the following properties: 1) abnormal epicardial electrograms characterized by presence of J waves in localized regions; 2) absence of conduction abnormalities, including delayed activation, conduction block, or fractionated electrograms; and 3) marked abbreviation of ventricular repolarization in areas with J waves. The action potential duration (APD) was significantly shorter than normal (196 ± 19 ms vs. 235 ± 21 ms; p < 0.05). Shortening of APD occurred heterogeneously, leading to steep repolarization gradients compared with normal controls (45 ± 17 ms/cm vs. 7 ± 5 ms/cm; p < 0.05). Premature ventricular contractions (PVCs) were recorded in 2 patients. The PVC sites of origin were closely related to the abnormal EP substrate with J waves and steep repolarization gradients. Conclusions ER is associated with steep repolarization gradients caused by localized shortening of APD. Results suggest association of PVC initiation sites with areas of repolarization abnormalities. Conduction abnormalities were not observed.