From June @ to July @ , @ patients with chronic atrial fibrillation and rheumatic heart disease were randomized : ( @ ) control group , patients underwent only valve replacement followed by amiodarone for rhythm control , ( @ ) left atrial group ( LA group ) , patients underwent valve replacement and left atrial mono-polar radiofrequency ablation , ( @ ) bi-atrial group ( BA group ) , patients underwent valve replacement and bi-atrial mono-polar radiofrequency ablation .