Spontaneous Left Cardiac Isomerism in Chick Embryos: Case Report, Review of the Literature, and Possible Significance for the Understanding of Ventricular Non-Compaction Cardiomyopathy in the Setting of Human Heterotaxy Syndromes

The outer shape of most vertebrates is normally characterized by bilateral symmetry. The inner organs, on the other hand, are normally arranged in bilaterally asymmetric patterns. Congenital deviations from the normal organ asymmetry can occur in the form of mirror imagery of the normal arrangement (situs inversus), or in the form of arrangements that have the tendency for the development of bilateral symmetry, either in a pattern of bilateral left-sidedness (left isomerism) or bilateral right-sidedness (right isomerism). The latter two forms of visceral situs anomalies are called “heterotaxy syndromes”. During the past 30 years, remarkable progress has been made in uncovering the genetic etiology of heterotaxy syndromes. However, the pathogenetic mechanisms causing the spectrum of cardiovascular defects found in these syndromes remain poorly understood. In the present report, a spontaneous case of left cardiac isomerism found in an HH-stage 23 chick embryo is described. The observations made in this case confirmed the existence of molecular isomerism in the ventricular chambers previously noted in mouse models. They, furthermore, suggest that hearts with left cardiac isomerism may have the tendency for the development of non-compaction cardiomyopathy caused by defective development of the proepicardium.

Spontaneous Left Cardiac Isomerism in Chick Embryos: Case Report, Review of the Literature, and Possible Significance for the Understanding of Ventricular Non-Compaction Cardiomyopathy in the Setting of Human Heterotaxy Syndromes

Except for a few species, the outer shape of vertebrates normally is characterized by bilateral symmetry. The inner organs, on the other hand, normally are arranged in bilaterally asymmetric patterns, which are of special importance for the normal function of the cardiovascular system of lung-breathing vertebrates. Deviations from the normal organ asymmetry can occur in the form of mirror imagery of the normal arrangement (situs inversus), or in the form of arrangements that have the tendency for development of bilateral symmetry, either in a pattern of bilateral left-sideness (left isomerism) or bilateral right-sidedness (right isomerism). The latter two forms of visceral situs anomalies are called “heterotaxy syndromes”. During the past 30 years, remarkable progress has been made in uncovering of the genetic etiology of heterotaxy syndromes. However, the pathogenetic mechanisms causing the spectrum of cardiovascular defects found in these syndromes remain poorly understood. In the present report, a spontaneous case of left cardiac isomerism found in a HH-stage 23 chick embryo is described. The observations made in this case suggest that hearts with left cardiac isomerism may have the tendency for development of a non-compaction cardiomyopathy caused by defective development of the proepicardium.

The Story of Dr Stella (1927-2006)

A life of professional caring, research, teaching, and inspiration—this is the legacy of Dr Stella Zacharioudaki Van Praagh, MD. Among her many outstanding contributions, only a few are recorded here: (1) a new surgical operation for closing apical muscular ventricular septal defects, (2) a newly discovered form of anomalous pulmonary venous drainage and its surgical repair, (3) a new understanding of sinus venosus defects and their surgical repair, (4) the realization that the concept of atrial-level isomerism (mirror-imagery) in the heterotaxy syndromes of asplenia, polysplenia, and single right-sided spleen is erroneous, (5) the understanding that it is possible to diagnose the atrial situs in the majority of cases of the heterotaxy syndromes, and (6) the fact that the concepts of evolution, natural selection, and survival of the fittest were described by Empedocles, an ancient Greek philosopher, in the fifth century bc, and that these concepts were not discovered and published for the first time by Charles Darwin and Alfred Russell Wallace in the 19th century (1858 ad). Dr Stella was conversant with ancient Greek and read it frequently in an ancient Greek study group that she headed. Dr Stella translated from ancient Greek into English a portion of Aristotle’s The Physics in which Empedocles’ understanding is cited at length. There is no doubt about what Empedocles thought.

Heterotaxy syndrome: This is the left, right?

Heterotaxy syndrome is a rare and complex disorder of the chest and abdominal organ arrangements, and presents a diagnostic challenge to the radiologist. This article describes the morphological characteristics of heterotaxy and situs abnormalities, in particular left and right atrial isomerism, and suggests an approach in evaluating the spectrum of abnormalities associated with heterotaxy syndromes, using appropriate imaging modalities.