Protective Effect of Severe Mitral Regurgitation Against Left Atrial Thrombus Formation and Systemic Embolism in Patients with Rheumatic Atrial Fibrillation

Atrial fibrillation (AF) and /or mitral stenosis (MS) have been documented to be associated with increased incidence of left atrial (LA) thrombus (T) formation and systemic embolism (SE), and severe mitral regurgitation (MR) has been documented to lower these risks. However, indications of anticoagulation in patients with AF concomittant with severe MR remained to be determined. The purpose of our study is to investigate the incidence of LAT within the main LA cavity and/or LA appendage in patients with AF who underwent valve replacement because of rheumatic MS and/or MR, and to asess the impact of severe MR on incidence of LAT and SE in patients with chronic AF. The study population comprised 979 Pts (F 636, M 343, mean age 40±14.5 yrs) operated for pure or predominant MS (n=517), pure MR (n= 388), and combined severe MS and severe MR (n= 74) in our institution between 1993 and 2001. Preoperative cardiac rhythm was AF in 530 patients (54.1%), and sinus rhythm (SR) in the remainder. History of SE before surgery was documented in 21.8% of the patients with MS, but in none of them with pure MR or MS concomittant with severe MR (MS+MR). Chronic anticoagulation was noted in 146 patients with history of SE and/or THR within the LA documented by echocardiography. Age, gender, and preop LA diameter were not different between patients with pure MS, MR, and MS+MR (p>0.05). Intraoperative assessment disclosed THR within the LA and/or LA appendage in 108 patients. In MS group incidence of LAT was higher in patients with AF as compared to patients with SR (31.3% vs 4.8%, p<0.001). In subgroup of MS with AF (n=310), thrombus was found to be located in the LAA in 51(16.4%), in the LA in 14(4.5%), and both in the LA and LA appendage in 31 (10.3%) patients. In subgroup of MS with SR (n=207), all of the LAT (n=10) was located in the LA appendage. However, none of the patients with severe MR had LAT. In MS + MR group, LAT was detected in one patient with AF in the LA appendage. Incidence of the LAT was lower in MR group irrespective of rhythm as compared to patients with MS with AF (p<0.001), and MS with SR (p<0.05). Patients with MS concomittant with severe MR had a lower incidence of LAT than patients with MS with AF (p<0.001) and MS with SR (p<0.05).
CONCLUSION
Results from clinical history and intraoperative assessment of our study provide further support for the protective effect of severe MR against SE and LAT formation in non-anticoagulated patients with chronic AF. The indications of anticoagulation in patients with chronic AF related to severe MR seem to need reconsideration.