Similarities and differences in the arrangement of the atrioventricular conduction axis in the canine compared to the human heart.

BACKGROUND: Subtle differences exist between dog and human, despite use of the dog as a model for cardiac surgical and electrophysiological research. OBJECTIVE: The purpose of this study was to investigate the differences in the atrioventricular conduction axis and adjacent structures between dogs and humans. METHODS: We prepared 33 human and 5 canine hearts for serial histologic sections of the atrioventricular conduction axis, making correlations with gross anatomic findings. We additionally examined and photographed 15 intact normal human hearts obtained from infants undergoing autopsy. Furthermore, we interrogated a computed tomographic dataset from a human adolescent and from 2 autopsied canine hearts, both with normal cardiac anatomy. RESULTS: All canine hearts lacked an inferoseptal recess, with the noncoronary leaflet of the aortic valve and the right fibrous trigone having direct attachments to the septal surface of the left ventricular outflow tract. This correlated with an extensive nonbranching component of the ventricular conduction axis, which skirted half of the noncoronary aortic sinus. This anatomic arrangement was observed in 2 of 15 of autopsied infant hearts. In the human hearts with an inferoseptal recess, the relatively shorter nonbranching bundle is embedded within the fibrous tissue forming its right wall. CONCLUSION: We found a major difference between canine and the majority of human hearts, namely, the presence or absence of an inferoseptal recess. When this recess is absent, as in the canine heart and in some human hearts, a greater proportion of the atrioventricular conduction axis is found within the circumference of the subaortic outflow tract.

Why do we break one of the first rules of anatomy when describing the components of the heart?

A rule of human anatomy is that all structures within the body should be described relative to the so-called "anatomical position." Along with those describing structures such as the skull and liver, those accounting for the components of the heart consistently break this rule, describing the organ as if removed from the body and positioned on its apex, the so-called "Valentine position." Although potentially appropriate to some animal species, this approach produces problems when used in human anatomy, even if the right and left ventricles are only viewed in truly right-sided and left-sided positions when assessed in the Valentine fashion. The names of the ventricles, of course, are never going to change. This is not necessarily the case with other cardiac components. Consider the artery that extends between the ventricles on their diaphragmatic surface. Blockage produces inferior myocardial infarction, which is to be expected, since the vessel is located in inferior and interventricular position. It is incorrect to describe the artery as being posterior and descending. Such infelicities are now the more obvious with the advent of techniques that, in clinical cardiology, show the components of the heart as it lies within the chest. In this review, we have assessed the frequency of use of the Valentine approach in popular textbooks used by students of human anatomy. We show that, using the conduction tissues as a model, this system also being incorrectly described in the majority of the textbooks, the situation can be improved by use of attitudinally appropriate description. Clin. Anat. 32:585-596, 2019. © 2019 Wiley Periodicals, Inc.

The independence of the infundibular building blocks in the setting of double-outlet right ventricle.

It has long been contentious as to whether the presence of bilateral infundibulums, or conuses, is a prerequisite for the diagnosis of double-outlet right ventricle. As the use of such a criterion would abrogate the so-called "morphological method", which correctly states that one variable entity should not be defined on the basis of another entity that is itself variable, it is now accepted that double outlet can exist in the setting of fibrous continuity between the leaflets of the atrioventricular and arterial valves. Although this debate has now been resolved, there are other contentious areas still requiring clarification in the setting of hearts unified because of the presence of this particular ventriculo-arterial connection - for example, it is questionable whether the channel between the ventricles should be described as a "ventricular septal defect", whereas it is equally arguable that the mere presence of fibrous continuity between the leaflets of the arterial valves does not necessarily place the channel in a doubly committed location. In this review, we describe a series of autopsied hearts in which the anatomical features serve to illuminate these various topics. We then discuss recent findings regarding cardiac development that point to the individuality of the building blocks of the ventricular outflow tracts, specifically the outlet septum, the inner heart curvature, or ventriculo-infundibular fold, and the septomarginal trabeculation, or septal band.