The diaphragm affects echocardiographic measurement of inferior vena cava diameter to predict right atrial pressure.

Abstract

It is recommended in current guidelines that the inferior vena cava (IVC) diameter should be measured at 1.0-2.0cm from the junction with the right atrium. However, right atrial pressure (RAP) is underestimated in some patients who have a small IVC diameter (IVCD) because of a high-echo structure compressing the IVC from the back at that portion. The aim of this study was to identify the structure behind the IVC and to evaluate its influence on RAP. We retrospectively studied 116 patients who underwent right-heart catheterization. We reviewed computed tomography (CT) scans and analyzed the relation between RAP and IVCD measured by echocardiography not only in the way recommended in the guidelines, but also in a way that avoided the structure. CT scans revealed that the diaphragm, not the vertebra, was located just behind the IVC in most patients. Sixteen patients (13.8%) had RAP ≥ 10mmHg. In those patients, when IVCs were measured in a way that avoided the diaphragm, IVCDmax diameter was larger and IVC collapsibility index (IVCCI) tended to be smaller than those when IVCDs were measured according to the guideline methods. The sensitivity of IVCD to predict RAP ≥ 10mmHg (IVCDmax > 21mm, IVCCI < 50%) increased from 31.3% to 68.8% with our method. The high-echo structure pushing the IVC from the back is the diaphragm in most patients. It might be better to measure IVCD using a method that avoids the diaphragm to accurately estimate RAP.