Mitral Isthmus anatomy: Detailed examination and classification proposal

Abstract

Aim

The aim of this study was to investigate the anatomical features of the mitral isthmus (MI) line, the vessels located there and their localisation in the MI line.

Methods

MI length and wall thickness were measured in a total of 65 autopsied fresh hearts. The distances of the vessels at the level of MI to the left inferior pulmonary vein (LIPV), mitral annulus (MA), endocardium surface (ES) and lateral adipose tissue (LAT) were recorded.

Results

The mean linear length of MI and left atrial wall thickness were 49.6 ± 9.9 mm and 3.9 ± 1.2 mm, respectively. GCV and LCx are approximately 1 cm from MA, 4 cm from LIPV, 5-6 mm from ES and 7 mm from LAT. Great cardiac vein (GCV) was found to be located in the MI line in 100 %, left circumflex artery (LCx) in 60 %, and vein of Marshall (VOM) in 63.1 % of cases. Presence of only GCV was recorded as Type-1 (18.5 %), GCV and LCx as Type-2 (18.5 %), GCV and VOM as Type-3 (21.5 %) and presence of all three as Type-4 (41.5 %). LCx located below the GCV was recorded as Type-A (59 %), above the GCV as Type-B (25.6 %), and at the same level but with LCx on the endocardial surface as Type-C1 (12.8 %) and on the epicardial surface as Type-C2 (2.6 %).

Conclusion

This study proves that the anatomy of MI is far from standardised and helps to raise awareness of the vascular pattern that may be encountered prior to ablation intervention.