Spatial relationship of blood vessels within the mitral isthmus line

Aims: The aim of this study was to assess the spatial relationship of blood vessels and the thickness of the atrial wall within the mitral isthmus line. Methods and results: A total of 200 randomly selected autopsied adult human hearts (Caucasian) were examined. The mitral isthmus line was cut longitudinally and the thickness of the left atrial wall was measured. The blood vessels within the isthmus were identified and their relationship with the endocardial surface (ES), mitral annulus (MA), and the left inferior pulmonary vein (LIPV) ostium was assessed. The mean myocardial thickness in the upper, middle, and lower 1/3 of the mitral isthmus section were 1.9 ± 1.0, 3.0 ± 1.5, and 2.7 ± 1.3 mm, respectively. The great cardiac vein (GCV) was present within the isthmus in 98.0%, the left circumflex artery (LCx) in 57.0%, and the Marshall vein in 35.0% of all hearts. The GCV was located 4.5 ± 2.2 mm from the ES, 7.3 ± 5.3 mm from the MA, and 24.3 ± 7.3 mm from the LIPV. The LCx was situated 3.8 ± 2.3 mm from the ES, 7.9 ± 5.1 mm from the MA, and 25.3 ± 8.0 mm from the LIPV. We were able to detect eight different patterns of GCV and LCx mutual arrangement within the mitral isthmus line. Conclusion: The myocardium is the thinnest in the upper 1/3 sector, and the blood vessels are mainly located in the middle and lower 1/3. In 49.1%, the LCx is situated at a distance of less than 3 mm from the ES. In 55.3%, the LCx is located between the GCV and ES of the left atrium.