Developmental Morphology of the Atrial Venous Component in the iv/iv Mouse

ABSTRACT

PURPOSE: Developmental processes of atria in embryos or fetuses of the iv/iv mouse were studied to find the differences between right and left atrial chambers and to identify the characteristics of atrial isomerism in the abnormal laterality syndrome. METHODS: Seventy-three embryos from SI/Col iv/iv mice (Jackson's laboratory, USA) or fetuses at the 10th-13th day were used. They were examined using stereomicroscope, scanning electronmicroscope, serial section, and thick slicing in the agar block. RESULTS: Thirty-three cases (45%) had usual arrangement but 40 cases (55%) had abnormal laterality, which included 29 cases of mirror-imaged appendages, seven with left isomerism, two with right isomerism and two with undeterminate appendages. Embryonic right atrium was initially composed of a large conspicuous appendage, which was a thin walled diverticulum and small venous component. As development progressed, venous valves and septum spurium became prominent. The embryonic left atrium was composed of the less conspicuous appendage but the major part of embryonic left atrium was the primitive atrium merging into the atrioventricular canal. The atrial chamber in the right isomerism had a bilateral big appendage and small venous component and the atrioventricular orifice was located in the center of the atrial outlet. Atrial chambers in the left isomerism had a bilateral small appendage and the central venous component was wide. CONCLUSION: The atrial morphology is the best marker in the determination of the atrial laterality. The appendages in hearts with isomerism had bilateral symmetrical arrangement of the appendages.