Extension of the inferior vena cava into the posteroinferior right atrium.

BACKGROUND: The inferior vena cava (IVC) is obliquely connected to the right atrium (RA), and often a low-voltage area is observed in the posteroinferior RA.

OBJECTIVES: The purpose of this study was investigate the size of the IVC extension into RA and its anatomic background.

METHODS: We investigated 30 human hearts [11 men and 19 women; mean age 79 +/- 10 years; 7 cardiac deaths (group A) and 23 noncardiac deaths (group B)]. After obtaining macroscopic measurements around the RA-IVC junction, serial sections were cut and examined histologically. We defined a horizontal baseline at the level of the cavotricuspid isthmus and measured (1) the length of IVC extension, which was defined as the distance from the baseline to the top of the RA-IVC junction, and (2) the width of the RA-IVC junction at the baseline level.

RESULTS: The top of the RA-IVC junction was always located in the posteroinferior RA. The mean length of the IVC extension was 17.6 +/- 6.6 mm, and the mean width was 29.6 +/- 7.5 mm. The IVC extension was wider in group A than in group B (35.8 +/- 9.0 mm vs 27.5 +/- 5.9 mm; P = .0277). The right and left borders of the RA-IVC junction corresponded to the reflection of the pericardium. Histologic examination showed no myocardium in the IVC extension.

CONCLUSION: The IVC extension into the posteroinferior RA always exists and varies in size. Because this area lacks myocardium, it is important to consider when analyzing catheter mapping from this area.