Congenital Heart Defects

The foundations of cardiac development are established within the first 8 weeks following fertilization. During these critical 8 weeks precardiac cells replicate, migrate, aggregate, differentiate and associate to form a chambered pump. Anything that interferes with the timely completion of these processes can result in cardiac defects.

Parents, family and patients often seek to identify the cause of congenital defects. Genetics, maternal exposure to disease and teratogens have been often suspected, but the exact underlying cause of a congenital defect is rarely determined. However, a recent study by Sadia Malik et al. has found a dose related association between maternal tobacco smoking anytime during the period from one month before conception to the end of the first trimester with septal cardiac defects. They also found that women who smoked 25 or more cigarettes a day were more likely to birth infants with right-sided obstructive cardiac defects. This study highlights the possibility of prevention through behavioral change.

Advances in the science of embryologic development are also raising hope for prevention. Today, molecules that trigger and direct development at the cellular level are being identified. Understanding the composition and chronology of these molecules will surely lead to effective early interventions.

Day 15

Precardiac cell migrate and aggregate in the caudal end
of the embryonic plate.

Day 20

Endocardial tubes form and begin to move centerline.

Day 22
Endocardial tubes fuse to form a single pulsatile tube.

Day 24

Tube lengthens and loops to the right.

Day 28

Separation of the folded single chambered pump by endocardial cushions and septae begins the formation of the four chambers.

Day 33

Septum primum is completed. Foramen secundum is formed.

Day 37

Foramen ovale is formed by completion of the septum secundum.

Day 50

By day 50 the arterial and venous tracts are complete.

You may find that the important developmental landmarks pictured above are useful as patient education tools.

For information on specific cardiac anomalies visit the Cincinnati Children's Hospital Medical Center web site. This web site is an incredibly generous graphic resource.