Abstract Body (Do not enter title and authors here): Background
Right atrial pressure (RAP) is estimated noninvasively by sonographic evaluation of inferior vena cava (IVC) size and collapsibility. We evaluated a new internal jugular vein (IJV) based approach for RAP estimation.

Methods
Sixty-nine patients underwent right heart catheterization and sonographic evaluation of IVC and right IJV. Both IVC long axis (LA) – IVC(LA) and short axis (SA) - IVC(SA) images were analyzed for RAP. SA images of right IJV were obtained at the clavicular level at 0°and clavicular and mandibular levels at 45° & 90° (60° if the patient is unable to sit upright) (Figure 1). Cine images were recorded during free breathing, sniff, and valsalva maneuvers at each location, in each posture. IJV was classified as distended (D), pulsatile (P), or collapsed (C). Models were developed to grade noninvasive RAP (niRAP) based on IJV classification in these images – IJV(c) and combined IJV & IVC imaging – IJV+IVC (Figure 2). A simple model IJV(s) using only 45° posture was also analyzed. The invasive RAP (iRAP) was categorized as 3 (<5 mm Hg), 8 (5-10 mm Hg), and 15 (>10 mm Hg) and compared with the niRAP from IJV(c), IJV(s), IVC(LA), IVC(SA) and IJV+IVC.

Results
IVC(LA) was nondiagnostic in 3 patients and IVC(SA) in 8 patients. In comparison, both IJV(c) and IJV(s) were diagnostic in all patients. The correct niRAP category was identified in more patients by IJV (c-54%, s-54%) than by IVC imaging (LA-39%, SA-46%). IVC(SA) performed better than the traditional IVC(LA). While both IJV(c) and IJV(s) had an overall similar performance, IJV(c) was better when iRAP>10 and the IJV(s) was better when iRAP ≤10. Combined IJV+IVC identified RAP category correctly in most patients (64% overall, 84% if iRAP >10) (Table 1).

Discussion:
While IJV was diagnostic in all patients, IVC imaging was nondiagnostic in some. IJV correctly identified the RAP category more often than IVC and combined IJV and IVC had the best performance. IJV imaging was easier to perform and more comfortable for patients. A simpler 45° only evaluation of IJV had a performance similar to comprehensive IJV imaging. While IVC(SA) was nondiagnostic in more patients, its classification was more accurate than IVC(LA).

Conclusion
Sonographic imaging of IJV is potentially better than IVC imaging in noninvasive evaluation of RAP. Combined IJV and IVC imaging is better than IJV or IVC alone. When IVC only imaging is done, short axis or biplane imaging is preferable to long axis alone.