 3. Method of detection of atrial electrical remodeling: 1. the measurement of surface electrocardiogram: the p-wave amplitude, P wave time duration and the p-wave duration dispersion dP Pmax- Pmin of the same 12 lead electrocardiogram in the same cardiac cycle.Two cardiologists measured the value separately.The investigators record the mean value. 2. Atrial effective refractory period AERP measured from the high right atriumHRA,the junction of superior vena cava and the right atrium , near the sinus node, low lateral right atriumLLRA,the junction of inferior vena cava and the right atrium,on the right atrium free wall side, coronary sinus electrode CS7.8, and CS1.2 at 3 basic drive cycle lengths CLs of 600, 500, and 400 ms. Pacing was performed using a pulse width of 2 ms and a current output of twice the local diastolic threshold. If the latter was 2.0 milliampere mA, the catheter was replaced and the threshold repeated. AERP was measured using an 8-beat drive train and a single extrastimulus incremented by 10 ms from a starting point of 170 ms. Every AERP was repeated 3 times, and the mean was taken. 3. At each CL, the dispersion of refractoriness was measured by subtracting the minimum from the maximum AERP across the 4 sites. 