Significant mitral regurgitation is protective against left atrial spontaneous echo contrast formation, but not against systemic embolism.

The prevalence of left atrial spontaneous echo contrast (SEC) and the occurrence of systemic embolism were prospectively studied in 176 consecutive patients. All had significant mitral regurgitation (MR) and underwent transesophageal echocardiographic (TEE) studies. Left ventriculography was performed in all patients to document the severity of MR. The underlying causes of MR included rheumatic heart disease in 84 patients, ruptured chordae tendineae in 37, mitral valve prolapse in 18, infective endocarditis in 20, coronary artery disease in 8, congenital heart disease in 5, and dilated cardiomyopathy in 4. No patient was found to have left atrial thrombus. Left atrial SEC was observed in three patients (1.7 percent), all of whom had atrial fibrillation, concomitant mitral stenosis, and huge left atria. Color flow mapping revealed that left atrial SEC was prominent in regions where the turbulent flow of MR was not present. Systemic embolism occurred in ten patients (5.7 percent). The underlying disease was infective endocarditis, rheumatic heart disease, and dilated cardiomyopathy in 6, 3, and 1 patient, respectively. The sites of embolization involved the central nervous system in eight patients and the spleen in the remaining two. Three patients with rheumatic heart disease and the one with dilated cardiomyopathy were in atrial fibrillation and had dilated left atria (diameter > 45 mm) when systemic embolism occurred. Only one patient with rheumatic heart disease was found to have left atrial SEC. The remaining six, with infective endocarditis, all had sinus rhythm. In conclusion, left atrial SEC or thrombus detected by TEE is uncommon in patients with significant MR. Clinical conditions may be of help to identify the subsets of patients at higher risk for systemic embolism.