Development of the atrioventricular junctional area in the human heart.

The structure of the heart has been the subject of many observations since the beginnings of medical research. The first information regarding the existence of the conduction system of the heart was described by Purkinje and regarding the a-v node by Tawara. From the history regarding this structure it seems that this special system, so relevant to today's invasive cardiologist, is not understood in full. With regards to the interventional electrophysiology on the basis of histological study we decided to evaluate in detail the morphology and the topography of the various portions of the a-v junction. In order to confirm this hypothesis we made observations on the autopsy material of 100 normal human hearts, both sexes from 16 weeks of foetal life to 105 years of age, in which no pathological changes or inborn faults were found. Sections were done containing the heart's septum, stained using Masson's method with Goldner's modification. This research proves that the atrioventricular junction is a stable structure occurring in all hearts, undergoing involutionary changes with age, in which two main parts can be differentiated: the node and the bundle. The morphology of the node is very complex, because it is composed of three zones: the prenodal, the perinodal and the main, differing in cell structure and position. The topography of the node is generally stable, as it lies in the interatrial septum and always above the septal leaflet of the tricuspid valve. The structure of the bundle, in contrast to the node, is more stable and consists of the following parts: the penetrating, the non-branching and the branching. Its topography is also stable, as it lies in the membranous septum, mainly below the septal cusp of the tricuspid valve.

Anterior region of the atrioventricular perinodal area in relation to radiofrequency ablation procedures.

Atrioventricular nodal reentry tachycardia base on reentry circulation in nodal-perinodal area. The radical treatment of choice is radiofrequency ablation. Procedure approached from the anterior-superior (fast) region sufficient a few seconds of energy delivery for success, however this can result in A-V block. The possibility that arrhythmias substrate may lie very superficially (success of ablation) and damage the normal structures (complication) in the perinodal region must be considered. In order to confirm this hypothesis we examined the autopsy material of 100 normal hearts, both sexes from 18 to 105 years of age (control) and 50 hearts with A-V total block 45-95 years of age (block). We paid attention to the morphology of the nodal artery (NA), atrial inputs (AI) and transitional inputs (TI). It was observed that NA at the level of the central fibrous body was positioned in 94% in the central and in 6% in the inferior part of Koch's triangle. It was removed from the endocardium 3-6 mm in control and 2-5 mm in block group respectively (NS). In the perinodal area we distinguished AI that directly joined the A-V compact node: superficial (right part of the interatrial septum) or deep (left part). The former occurred in 100% of controls and in 80% of block groups (NS), and the latter in 80% of control group and in 34% in block respectively (p < 0.05). The real substrate of arrhythmia in anterior-superior region lies very superficially and far from the conduction tissue; NA in examined hearts was lying deep beneath the endocardium; ablation close to the node could result in A-V block.

Histologic evaluation of the atrioventricular nodal artery in healthy humans and in patients with conduction disturbances.

The anatomy of the conduction system of the heart so relevant in the contemporary invasive cardiology is not fully understood. It has turned out that ablation procedures bring new information as to its structure and function, but in some cases can result in complete a-v block. Atrioventricular nodal artery located within the nodal-perinodal tissue can probably be damaged during the ablation procedures. Therefore, we decided to explore in detail the morphology and the topography of the atrioventricular nodal artery in healthy humans and in patients with clinical traits of a-v conduction disturbances requiring permanent pacing. The microscopic study was carried out on 30 normal human hearts specimens (17 F, 3 M) from 17 to 86 years of age, and on 20 hearts with conduction disturbances (11 F, 9 M) from 39 to 85 years of age. We found that the number of the atrioventricular node arteries is different and independent of the extent that induces block causing conduction disturbances. The topography of the artery in perinodal zone was consistent in normal hearts, yet in hearts with conduction disturbances we observed about 2% of deviations in its location. It might be the reason for generation of iatrogenic complications after invasive cardiological procedures. The morphology revealed changes in 50% of the examined hearts and their vessel walls, which was declared to be connected with ageing. This correlated with certain stages of atherosclerosis as well as hypertension characteristic of elderly patients. We observed that in 33% of hearts from control group small parietal thrombi were detected and in 60% of paced group respectively. Hence, it seems that the procedures in perinodal zone should be performed in its proximal part because of a minor probability of direct and indirect (through nodal artery) damage of the atrioventricular structure of the junction.

Morphology of the tendon of Todaro within the human heart in ontogenesis.

The tendon of Todaro, found in the right atrium of the heart, has considerable clinical importance in the fields of both cardiac surgery and invasive cardiology. The goal of this study was to examine the occurrence and degree of development of the tendon of Todaro in humans. Research was conducted on material consisting of 160 human hearts of both sexes from the age of 14 Hbd to 87 years of age. Classical anatomical methods were used and histological sections were prepared from 100 hearts of various age groups stained with Masson's method in Goldner's modification. The tendon of Todaro occurred in all examined hearts. In foetal hearts, in the area typical of the course of the tendon of Todaro, a very well-developed, white structure was observed, convexed into the lumen of the atrium. Histologically, this was young fibrous tissue with a characteristically large number of fibroblasts. Evenly in infants and newborns, a visible convex structure was also observed extending into the lumen of the right atrium, however, to a lesser degree than in foetuses. In the group of hearts of young adults, it was also possible to follow the course of the tendon of Todaro macroscopically. However, the older the heart was, the less the convex was visible, and in older adults it was completely invisible. In histological sections, it was observed that with ageing the number of connective tissue cells decreased, and fibres forming the lining increased. In the hearts of older adults the tendon of Todaro formed very small ribbons of connective tissue. Histologically, only small numbers of cellular elements were noticed. In the adult heart the examined tendon was located the deepest and did not connect to the endocardium. We can conclude that the tendon of Todaro is a stable structure, occurring in all examined hearts even when it is not macroscopically visible. Due to the morphological changes that affect the tendon of Todaro in human ontogenesis, for the cardiac surgeon, its relevance as an important topographical structure in the hearts of older adults is minimal.