Effects of long-term beta-blocker therapy on P-wave duration and dispersion in patients with rheumatic mitral stenosis.

BACKGROUND: P-wave dispersion (PWD), has been defined as the difference between maximum and minimum P-wave duration. Prolonged P-wave duration and increased PWD have been reported to be related with increased risk for atrial fibrillation (AF). AF is the most common sustained arrhythmia encountered in patients with rheumatic mitral stenosis (MS). Beta-blockers are the mainstay of therapy in patients with rheumatic MS to control ventricular rate both during sinus rhythm and AF. In the present study, we aimed to evaluate the effect of long-term beta-blocker therapy on P-wave duration and PWD in patients with rheumatic MS.
METHOD: Study population includes 46 patients (group I, 8 men, 38 women, mean age = 34+/-8 years) with newly diagnosed moderate-to-severe rheumatic MS who have not taken any medication before and prescribed oral beta-blocker therapy and 46 healthy control subjects without any cardiovascular disease (group II, 8 men, 38 women, mean age = 35+/-7 years). Mitral valve area, maximum and mean diastolic mitral gradients, left atrial diameter, and systolic pulmonary artery pressure were evaluated by transthoracic echocardiography before initiation of beta blocker therapy and repeated at the end of the first month. Baseline maximum and minimum P-wave duration and PWD were determined on 12-lead electrocardiogram recorded for each patient and control subject and repeated at the end of the first month after initiation of beta-blocker therapy in patient group.
RESULTS: Maximum P-wave duration and PWD were found to be significantly higher in patients with MS than those in control subjects (Maximum P-wave duration: 128+/-7 ms vs. 104+/-4 ms and PWD: 52+/-6 ms vs. 27+/-3 ms, p < 0.001 for both). Both groups had comparable minimum P-wave duration (75+/-4 ms vs. 76+/-4 ms, p = 0.093). Maximum P-wave duration and PWD were found to be significantly decreased by long-term beta blocker therapy (Maximum P-wave duration; 128+/-7 ms vs. 122+/-6 ms, p < 0.001, PWD; 52+/-6 ms vs. 47+/-5 ms, p < 0.001). However, there was no significant difference between the values of minimum P wave duration measured before and at the end of the first month of beta-blocker therapy (75+/-4 ms vs. 75+/-3 ms, p = 0.678). Statistically significant decrease were detected on maximum and mean mitral gradient and systolic pulmonary artery pressure and resting heart rate at the end of the first month of beta-blocker therapy. However, only the change in resting heart rate was found to be significantly correlated with the decrease in maximum P-wave duration and PWD (Maximum P-wave duration: r = 0.327, p = 0.026, PWD: r = 0.378, p = 0.01).
CONCLUSION: We have shown for the first time that long-term beta-blocker therapy causes a significant decrease in maximum P-wave duration and PWD in patients with rheumatic MS.