From the Guidelines
Ostium primum defects are primarily caused by incomplete fusion of the endocardial cushions during embryonic heart development, and are strongly associated with Down syndrome (trisomy 21) and other congenital heart defects, such as atrioventricular canal defects and mitral valve abnormalities 1. The aetiology of ostium primum defects is closely linked to the embryonic development of the heart, specifically the formation and fusion of the endocardial cushions. This process typically occurs between weeks 4-8 of embryonic life, and any disruptions can lead to defects in the atrial septum. Some key associations with ostium primum defects include:
- Down syndrome (trisomy 21), with approximately 40% of individuals having some form of congenital heart defect, including ostium primum defects
- Atrioventricular canal defects
- Mitral valve abnormalities, particularly cleft mitral valve
- Tricuspid valve abnormalities
- Ventricular septal defects in more complex cases The genetic basis for these defects involves abnormalities in the genes controlling endocardial cushion formation and fusion, with chromosomal abnormalities like trisomy 21 disrupting normal cardiac development 1. Patients with ostium primum defects typically require surgical repair, with timing dependent on symptom severity and associated cardiac anomalies, as per the 2018 AHA/ACC guideline for the management of adults with congenital heart disease 1. In terms of management, the 2018 AHA/ACC guideline recommends surgical closure for adults with primum ASD, sinus venosus defect, or coronary sinus defect, causing impaired functional capacity, right atrial and/or RV enlargement, and net left-to-right shunt sufficiently large to cause physiological sequelae, unless precluded by comorbidities 1. It is essential to note that the management of ostium primum defects should prioritize reducing morbidity, mortality, and improving quality of life, and should be guided by the most recent and highest-quality evidence, such as the 2018 AHA/ACC guideline 1.
From the Research
Aetiology of Ostium Primum Defect
- Ostium primum defect is a congenital malformation involving the atrial septum contiguous with the atrioventricular valve annulus, accompanied by abnormalities in the development of the endocardial cushions 2.
- The basic deficiency in the 'ostium primum' defect is best understood as a product of defective atrioventricular septation, rather than an atrial septal defect 3.
- The defect occurs at the base of the interatrial septum and is the result of failure of fusion of the septum primum with the endocardial cushions 4.
Associations
- Ostium primum defect is often associated with abnormalities in the development of the atrioventricular valves, resulting in malformations such as mitral cleft 2, 5.
- The severity of mitral regurgitation seems to relate not only to the size of the cleft but also to the systolic configuration of the anterior mitral leaflet 5.
- Masked subaortic stenosis can be recognized and treated in patients with ostium primum atrial septal defect and a cleft mitral valve 6.
- The characteristic diastolic "goose-neck" deformity during left ventricular systole in atrioventricular canal defects is diagnostic of a potential or actual subaortic obstruction 6.