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Purpose: Cardiac resynchronization therapy (CRT) has been shown to improve left atrial function; however the effect on reverse electrical remodeling has been poorly evaluated. We hypothesized that CRT might induce reverse atrial electrical remodeling manifesting in the surface ECG as a shortening in P-wave duration.Methods: Patients with CRT and more than 92% biventricular pacing at minimum follow-up of 1 year were included in the analysis. Those with prior history of atrial fibrillation (AF) were excluded. Data were recorded for clinical, echocardiographic and ECG variables prior to implant and at least 12 months post implantation. Semiautomatic calipers and scanned ECGs at 300 DPI maximized × 8 were used to measure P-wave duration and diagnose advanced interatrial block (aIAB) during sinus rhythm. The occurrence of AF was assessed through analyses of intracardiac electrograms and clinical presentations.Results: 41 patients were included in the study with mean age of 67.4 ±9.6 years, 71% were male, left atrial diameter 41.1 ± 8.5 mm and LV EF 28.5 ± 6.5%. Over a mean follow up of 55 months, a significant reduction in P-wave duration (142.7 ms vs. 133.1 ms; p < 0.001) was noted. The presence of aIAB was significantly reduced (36% vs. 17%; p = 0.03). The incidence of new onset AF was 36%. Time to AF onset after CRT implantation was not influenced by a reduction in P-wave duration.Conclusion: CRT induces atrial reverse electrical remodeling manifested as a reduction in P-wave duration. Larger studies are needed to determine the impact on AF incidence after CRT implantation. [ABSTRACT FROM AUTHOR]