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AIMS The atrioventricular (AV) septal junction includes the coronary sinus (CS) and the compact part of the AV node and its posterior extensions. It has been recognized as the target site for ablation therapy of the AV nodal reentrant tachycardia and its variant forms. Despite the clinical significance of this region, the arrangement of the musculature in the AV septal junction, including the CS, has not fully been elucidated. We tried to explore the histological muscular diversity within the AV septal junction. METHODS AND RESULTS Sixteen autopsied human hearts (seven women), mean age 59.8 years, without structural anomalies, were studied. We removed the whole AV septum, including the CS opening after the macroscopic measurements, and prepared serial sections parallel to mitral and tricuspid annuli (short-axis style) to elucidate the positional relationships between the compact AV node and the CS musculature. Out of 16 hearts, the CS musculature extended deeply into the AV septal junction in eight hearts. In the other eight hearts, the CS musculature was located above the AV septal junction. In the former group, we found that the offset of both annuli was wide (mean 3.8 +/- 1.4 vs. 2.4 +/- 1.1 mm), the distance between CS opening and membranous septum was long (mean 14.8 +/- 1.6 vs. 12.3 +/- 2.2 mm), and the CS opening level was lower and closer to the His bundle level (mean 2.8 +/- 1.9 vs. 5.8 +/- 2.9 mm) (P < 0.05). CONCLUSION The deep extension of CS musculature into the AV septal junction seems to increase the tissue non-uniformity in this area.

A 68-year-old woman with idiopathic dilated cardiomyopathy suffered from drug-resistant monomorphic ventricular tachycardia (VT). Electrophysiological study revealed a re-entrant VT circuit located just beneath the inferior mitral valve annulus. The VT was considered to be related to the mitral valve isthmus and was abolished by radiofrequency ablation. The patient died 2 years after the ablation due to worsening of heart failure and an autopsy was performed. Pathological examination revealed ablation scar tissue on the localized myocardial bundle running parallel to the mitral valve annulus. Therefore, this bundle appeared to comprise the slow conduction area of the re-entrant VT in this case.

We report a case, which we believe to be rare, of adenosine-sensitive atrial tachycardia (AT) originating from the mitral valve annulus. The patient, a 73-year-old woman, died of unrelated cause 4 years after radiofrequency (RF) ablation therapy. Histologically, fibrous replacement of atrial musculature by mature collagenous tissue produced by the RF current was observed at the left inferior atrioventricular junction. In serial sections that included the coronary sinus, two distinct nodal structures containing small, pale myocytes within the fibrous tissue matrix were identified around the region of the ablation lesion. Our case appears to be a unique representation of tissue that was associated with the occurrence and maintenance of AT.

Aims Recent clinical observations suggest that the right atrial posterolateral wall structures originate ectopic beats and function as anatomical obstacles. Because atrial arrhythmias increase in incidence after middle age, we investigated histological diversity and age-related changes in right atrial posterolateral wall. Methods and results Twenty-six autopsied hearts (mean 65.2 years, 16 men and 10 women) were studied. The entire posterolateral right atrium was cut serially. We determined the distribution of the sinoatrial node and localized it in relation to the crista terminalis and sinus venosus. We also compared histopathological changes in these tissues between three groups consisting of 31- to 50-year-old, 51- to 70-year-old and 71- to 90-year-old hearts. Total mean length of the crista terminalis, the sinoatrial node, and the sinus venosus was 46 mm, 21 mm and 29 mm, respectively, and showed no age-related changes, but the distribution of the sinoatrial node was varied. Mean muscular volume of the sinus venosus was significantly reduced in the two older groups, though that of the crista terminalis showed no age related-changes. Conclusion Histological diversity of the sinoatrial node and age-related changes in the sinus venosus beneath the sinoatrial node may enhance histological heterogeneity and hence arrhythmogenicity.