A New Method to Evaluate Linear Block at the Left Atrial Roof. Objective: The present study aimed to evaluate a new method for validation of complete linear block at the left atrial (LA) roof. Background: Linear lesions at the LA roof have been reported to improve the success rate of catheter ablation of atrial fibrillation (AF). Methods: Complete linear block at the LA roof was evaluated in 31 patients after complete isolation of pulmonary vein antrum (PVA) using a simple method. We hypothesized that complete linear block of the LA roof could be confirmed during sinus rhythm if (1) a continuous line of double potentials could be recorded at the LA roof, and (2) the activation sequence along the posterior wall changed to caudocranial. The results of this method were compared with standard pacing techniques. Results: Thirty-nine lines were assessed using this method: 8 before and 31 after achievement of complete conduction block. After validation of complete linear block at the LA roof, double potentials with a mean interpotential interval of 60 ± 13 ms were recorded in 25 patients and electroanatomical mapping of the left atrium showed the activation sequence of posterior wall changed to caudocranial in all 31 patients during sinus rhythm. The sensitivity, specificity, positive and negative predictive values of this method for validating complete linear block were 100%, 88.9%, 96.8%, and 100%, respectively. Conclusion: A corridor of double potentials along the roof line and a caudocranial activation sequence along the posterior wall during sinus rhythm can indicate conduction block at the LA roof after PVA isolation. © 2010 Wiley Periodicals, Inc.