Acute coronary syndrome: Short-term effects of early intravenous metoprolol on maximum P wave duration and P wave dispersion

In patients with acute coronary syndrome (ACS), the presence of atrial fibrillation (AF) results in worse inpatient outcomes than in those without AF. Two electrocardiographic markers, maximum P wave duration (P_maximum) and P wave dispersion (P_dispersion), have been assessed because they reflect conduction abnormalities in patients with paroxysmal AF. β blockers are known to have beneficial effects in patients with ACS. This prospective study was conducted to investigate whether early intravenous (IV) metoprolol injection acutely decreases P_maximum and P_dispersion in patients with ACS. This study involved 100 consecutive patients with ACS who were divided into 2 groups according to whether or not they received early IV metoprolol. Group 1 consisted of 19 patients who received IV metoprolol within 3 h after onset of symptoms, and group 2 consisted of 81 patients who did not receive IV metoprolol within 3 h after symptom onset because of late admission. P_maximum and P_dispersion were measured on admission and again at 2 h after admission. Two-dimensional echocardiographic examination was also performed. For patients who received early IV metoprolol, P_maximum and P_dispersion, measured 2 h after admission, were shorter than values at admission (P<.001). Conversely, P_maximum and P_dispersion, measured 2 h after admission, did not differ significantly from values at admission in patients who did not receive early IV metoprolol (P=.292 andP=.236, respectively). IV administration of metoprolol reduced values for P_maximum and P_dispersion, measured 2 h after admission, among patients with ACS who were admitted within 3 h after onset of symptoms.