High prevalence of atrial fibrosis in patients with dilated cardiomyopathy

Objectives. We examined the extent of fibrotic changes in the left atrium of cardiomyopathic human hearts and investigated the relation of mechanical overload caused by left ventricular dysfunction to fibrosis of the left atrium. Background. Left atrial dysfunction in dilated cardiomyopathy may contribute to progression of heart failure. In contrast to fibrosis of the left ventricle, atrial fibrosis has not been extensively studied in cardiomyopathic hearts. Methods. The extent of fibrosis in the left atrium and left ventricle was determined by an automatic image analyzer in 38 autopsied hearts obtained from 9 patients who died of noncardiac illness (control group), 16 patients with dilated cardiomyopathy, 6 patients with hypertrophic cardiomyopathy with features mimicking dilated cardiomyopathy and 7 patients with previous myocardial infarction. Transverse sections were obtained at the upper margins of the foramen ovale and left auricle in the left atrium and the median level of the left ventricle. Results. There were no significant differences in extent of left atrial dilation, left ventricular dysfunction or duration of illness among the three groups with cardiac disease. Percent are of left atrial fibrosis (mean ± SD) was significantly greater in the specimens from patients with dilated cardiomyopathy (13.1 ± 6.1%, p < 0.01) and hypertrophic cardiomyopathy mimicking dilated cardiomyopathy (26.5 ± 9.5%, p < 0.01) than in those from patients with an old myocardial infarction (3.8 ± 1.1%). Percent are of left ventricular fibrosis in hearts from patients with dilated cardiomyopathy (12.9 ± 8.6%) was significantly smaller than that in hearts from patients with hypertrophic cardiomyopathy mimicking dilated cardiomyopathy (35.8 ± 11.9%, p < 0.01) and previous myocardial infarction (38.4 ± 8.0%, p < 0.01). Percent are of atrial fibrosis was significantly correlated with left ventricular ejection fraction in the group with previous myocardial infarction but not in the other groups. Conclusions. There was high degree of fibrotic change in the left atrium in the groups with dilated cardiomyopathy and hypertrophic cardiomyopathy mimicking dilated cardiomyopathy. Our findings suggest that atrial fibrosis in these patients may not have been related to mechanical overload of the left atrium but to some other, still unknown mechanisms.