Introduction: During pulmonary vein isolation (PVI) of atrial fibrillation (AF), electroanatomic mapping (EAM) is used to characterize voltage characteristics of the left atrium, identifying low voltage areas (LVA) as ≤0.5 mV. Posterior wall (PW) LVAs have been used as ablative targets in patients with persistent AF, showing mixed results. Methods and Results: We compared the mapping performance and PW LVA characterization between the novel 8-spline high-resolution Octaray catheter versus the 5-spline Pentaray catheter. An analysis of registry patients from ALPINE (Adjunctive Left atrial Posterior Isolation Efficacy Study), a single-center, prospective, randomized control trial evaluating outcomes in index PVI +/- PW isolation in patients with >10% PW LVA, was performed. EAMs of initial registry patients were performed with Pentaray (January – May 2022) and were compared with later EAMs mapped with Octaray (May 2022 – August 2023) to determine differences in procedural metrics and PW LVA characterization. EAMs of 273 patients (87 with Pentaray, 186 with Octaray) were analyzed. There were no differences in baseline characteristics. Mapping with Octaray resulted in increased mean normal PW voltage (97.05% vs 93.78%; p=0.002), and less mean PW LVA (2.64% vs 4.36%; p<0.01) than Pentaray. Octaray resulted in significantly lower mapping time (13 vs 16 minutes; p<0.01) and greater number of Fast Anatomic Mapping (FAM) points collected (8081 vs 2939; p<0.001). When adjusted for baseline confounders, a multivariable linear regression analysis revealed that use of Octaray did have an independent, significant association corroborating these findings. Conclusion: To our knowledge, our study contains one of the largest groups of patients with increased normal PW voltage, and less PW LVA, when using Octaray compared to Pentaray. It is possible the higher density mapping capability of the Octaray leads to more mapped points, improved contact, and less voltage interpolation than prior catheter technology, with resultant decreases in LVA characterization. The mapping catheter’s role in quantifying LVA is significant due to its treatment implications with respect to pursuing adjunct PW modification in AF ablation. Further investigation of the mapping performance, voltage characteristics, and procedural outcomes of the Octaray would be beneficial.