SummaryDiscrimination between paroxysmal and persistent atrial fibrillation (PAF and persistent AF) is important for determining the therapeutic strategy in patients with new-onset AF. We evaluated various clinical factors and P wave morphology to discriminate PAF and persistent AF patients in patients with new-onset AF.The study population consisted of 79 patients with new-onset AF (70.3 ± 10.8 years, female:male 33:46) who were retrospectively selected from 8,632 AF patients in the Kitasato University Hospital ECG storing system. PAF (n = 38) and persistent AF (n = 41) patients were diagnosed by whether the initial PAF episode continued for 1 week. The P wave morphologies were analyzed using the most recent 12 lead-ECG recording of sinus rhythm. P wave dispersion was defined as the difference between the maximum and minimum durations of all leads. Along with these data, various clinical factors were evaluated and compared between PAF and persistent AF patients.Multivariate analysis identified P wave dispersion (56.6 ± 14.8 versus 66.5 ± 12.8 msec, P = 0.002) and left atrial dimension (LAD: 40.2 ± 7.0 versus 47.7 ± 8.2 mm, P < 0.001) as independent factors for discrimination between PAF and persistent AF patients. Combining these two parameters achieved a specificity of 88.9%, a positive predictive value of 81.8%, a sensitivity of 95.3%, and a negative predictive value of 88.9%.In patients with new-onset AF, P wave dispersion and LAD were independent factors for discrimination between PAF and persistent AF. (Int Heart J 2016; 57: 573-579) Key words: P wave I n clinical practice, identification of the clinical stage of atrial fibrillation (AF) is an important issue to enable clinicians to determine a therapeutic strategy, especially in patients with new-onset AF, in whom it is important to determine the indication of antiarrhythmic agents or catheter ablation.1-3) When considering catheter ablation for AF, it is important to identify the early stage of AF, ie, paroxysmal atrial fibrillation (PAF), because the efficacy of catheter ablation is higher in PAF patients, and the ablation procedure itself can be simplified. 4,5) Recently, we have reported that P wave analysis in the 12-lead ECG of sinus rhythm is useful in determining the emergence of AF in clinical cases. 6) We have shown that the P wave amplitude in lead II or V1 was higher, and P wave dispersion, ie, the dispersion of P wave duration, was larger in patients with new-onset AF compared with control patients without AF.6) Therefore, we hypothesized that the clinical stage of AF may also be identified by P wave analysis, as well as with the other clinical parameters. In the present study, we retrospectively identified patients with new-onset AF in the digital ECG profiling system of our hospital. Patients were classified into PAF and persistent AF by their clinical course in accordance with the definitions in the AHA/ACC/ESC guidelines and JCS guidelines.7,8) P waves in the preceding sinus rhythm state were analyzed as the precursor state for new-onset ...