Pathogenesis of various forms of double outlet right ventricle in mouse fetal trisomy 13.

The pathogenesis of double outlet right ventricle with or without pulmonary infundibular atresia in mouse fetal trisomy 13 was studied at the organ level using microdissection and scanning electron microscopy. Altogether, 394 karyotyped trisomic embryos were collected between 11 days and 16 hours of gestation (presence of a vaginal plug = day 1) and 15 days of gestation at intervals of 8 hours, and at 16 days of gestation. The hearts were perfusion-fixed, microdissected, and prepared to be observed in scanning electron microscope in the following standardized orientations: frontal, right or left profile, septal and parietal halves of the right ventricle and outflow tract (conotruncus). Comparison of 276 trisomic hearts with their normal counterparts described previously has shown that: the first pathognomonic feature is the abnormal anterior position of the proximal part of the parietal outflow tract ridge or of both ridges (at 12 days and 16 hours of gestation); the abnormal anterior fusion of these ridges ("coalescence") results in a mesenchymal mass behind which is deviated the pulmonary part of the outflow tract lumen; from 14 days and 16 hours of gestation on, this lumen is either obstructed, resulting in a supravalvar stenosis of the pulmonary trunk and subsequently evolving into double outlet right ventricle with pulmonary infundibular atresia; or, in a minority of cases, this lumen is not obstructed and the heart develops into double outlet right ventricle without pulmonary infundibular atresia. The pathogenesis of these malformations differs from most of the known hypotheses based on deductions from human malformed hearts, as well as from observations of the pathogenesis of similar outflow tract malformations, such as those found in the Keeshond dog or rats treated with trimethadione.