Change of P-wave duration in patient with acute myocardial infarct before and after percutaneous coronary intervention (PCI) Atrial fibrillation (AF) is a most common arrhythmia in clinical practice and is a frequent complication of acute myocardial infarction (AMI), with a reported incidence of 7–18%. The incidence of congestive heart failure, in-hospital mortality, and long-term mortality is higher in AMI patients with AF than in those without AF. The p-wave duration (PWD) and late potential (LP) on signal averaged electrocardiogram (SAECG) are a non-invasive markers of intra-atrial conduction disturbances, which are believed to be the main electrophysiological cause of AF. Lorsatan treatment significantly decrease the PWD and LP incidence and improves atrial electrical conduction disturbance. The aim of this study was to investigate the change of PWD and LP on SAECG before and after percutaneous coronary intervention (PCI) in patient with acute myocardial infarct. Also whether lorsatan can be reduce the PWD in short-term follow-up after PCI A total of 21 first attack AMI patients were enrolled in the study. All patient was performed PCI. Almost patient with AMI was performed primary PCI. The P-wave SAECG was recorded at first visit (before PCI) and at first short-term follow-up visit (9 ~ 21 days after PCI). Almost SAECG before PCI was recorded within 30 minutes after emergency department visit. SAECG recordings of P wave were performed using a MAC 5500 ECG machine (GE Medical Systems, USA). Echocardiographic and clinical characteristics was recorded during admission. The mean first follow-up visit after PCI in patient with AMI is 13 days. The p-wave duration on the SAECG was significantly shortened in the post-PCI status than in the pre-PCI status ; 122.7 짹 38 versus 143.1 짹 22 milliseconds (p = 0.03). The p-wave late potential (LP) was reduced after PCI than before PCI ; 4 patient (19 %) versus 6 patients (29%). However, there was no significant change in consecutive groups with or without treatment of lorsatan. PWD on SAECG measured in a very early period of AMI is shortened after PCI and p-wave late potential incidence is reduced after PCI. The PWD shortening is associated improving of atrial electrical conduction disturbance. These were suggested that coronary reperfusion in patient with AMI may reduce the post AMI AF development.