Background: Atrial fibrillation (AF) may be triggered from arrhythmogenic foci originating from atrial muscular sleeves that extend into the caval veins (CVs). The aim of this anatomic study was to evaluate both the extent and arrangement of atrial myocardial fibers in CVs in subjects with and without a history of AF.
Methods and results: Twenty-five human autopsied hearts (15 men; mean age, 65.5+/-12 years; range, 39 to 80 years) were studied. Seven subjects had a previous history of AF. The presence and morphology of atrial myocardial extensions were studied microscopically in both CVs. Such extensions were found in 38 of 50 CVs (76%). Their average length in the superior vena cava reached 13.7+/-13.9 mm (maximum, up to 47 mm) and in the inferior vena cava, 14.6+/-16.7 mm (maximum, up to 61 mm). The thickness of atrial myocardium extending into the CVs was 1.2+/-1.0 mm (maximum, 4 mm) for the superior vena cava and 1.2+/-0.9 mm for the inferior vena cava (maximum, 3 mm). The majority of myocardial extensions revealed discontinuous and circular patterns. Degenerative changes were found in approximately half of the subjects. There was no significant difference between patients with and without a history of AF.
Conclusions: Atrial myocardial extensions into both CVs are present in the majority of human beings, both with and without a history of AF. The extensions are localized on the outer side of venous adventitia. Arrangement, length, and thickness of myocardial sleeves onto the CVs vary individually, and many of them contain degenerative changes.