FORUM EKSPERTÓW
The evolution of the human heart and its relevance to congenital heart disease

The evolutionary history of the human heart is fascinating and highly relevant to an understanding of congenital heart disease. Our phylum Chordata goes back to ancient fish of the Ordovician and upper Devonian periods, 500 million to 345 million years ago.

These fish had a single ventricle, from which our left ventricle (LV) is derived.

Amphibia evolved 345 million to 325 million years ago during the Carboniferous period. They had lungs and so could breathe air, but they had no right ventricle. Some amphibia evolved into fully terrestrial animals, the Amniota, animals with an amniotic sac filled with amniotic fluid in which the embryo and fetus could float, like our piscine ancestors.

Some amniotes evolved into reptiles. Others evolved into birds – feathered reptiles like archaeopterix. Still others evolved into mammals – furry or hairy reptiles. Mammals evolved during the Jurassic period, about 180 million years ago. Although fish and amphibia do not have a right ventricle (RV), higher reptiles (crocodiles and alligators), birds, and mammals normally all do. The comparatively recently evolved RV is only about 36% as old as the LV (180 million vs. at least 500 million years old, respectively). Most human congenital heart diseases consist of anomalies of one or more of the four components that make up the RV. Malformations of the LV are relatively infrequent. Congenital heart disease is the commonest anomaly in live born infants (0.8%); it also accounts for more than 20% of all spontaneous abortions and for 10% of all still births.

Thus, we are still having trouble with our major cardiovascular evolutionary adaptations to air-breathing and permanent land-living: the development of the RV sinus (inflow tract), the embryonic aortic switch procedure, and septation to separate the systemic and pulmonary circulations. Recent molecular genetic data suggest that one or more mutations in the Nodal cascade may well be of great importance in anomalies of right-left asymmetry, such as the embryonic aortic switch process, and the heterotaxy syndromes. The embryonic first heart field gives rise to most of the myocardium of the cardiogenic crescent and the early heart tube and contributes only to the embryonic LV. The embryonic second heart field contributes to the “recently” evolved RV. The embryonic anterior heart field, which is a subdomain of the second heart field, contributes to the development of the subarterial outflow tract (conal) free walls, that are important in the development of normally and abnormally related great arteries. Empedocles, an ancient Greek pre-Socratic physicist who lived in the 5th century BC, understood and promoted the concepts of evolution, natural selection, and survival of the fittest 2300 years before their rediscovery by Charles Darwin and Alfred Russel Wallace in the mid-19th century (1858). The primacy of Empedocles is proved by the surviving work of Aristotle (384-322 BC), who quoted Empedocles at length in order to disagree with him.