Introduction
Pulmonary hypertension is a rare disease that can have many long term consequences including significant disability and death1. Traditionally, echocardiography has been used to identify patients with this disease because of its non-invasive nature. Various indirect parameters demonstrated with echocardiography can indirectly help quantify right ventricular systolic pressure (tricuspid regurgitant velocity, ventricular septal defect velocity) or mean pulmonary artery pressure (patent ductus arteriosus velocity, early pulmonary regurgitation velocity); however for many patients, these jets are insufficient or absent for quantification. In particular, the tricuspid valve regurgitant velocity cannot be obtained in 30-54% of pediatric echocardiograms performed for assessment of pulmonary hypertension2-6. Qualitative assessment of the position of the interventricular septum has been used to gauge whether a right ventricle is “sub-systemic, half-systemic, or supra-systemic”7-10. In patients with normal right ventricular systolic pressures (RVSP), the septum bows towards the right ventricle and the left ventricle is rounded in short axis during systole (Figure 1B); whereas, in those with elevated RVSP, the septum is flattened and can even bow into the left ventricle in suprasystemic RVSP conditions. While used frequently, this qualitative assessment may yield significant inter-reader and intra-reader variability11. Another recently published echocardiographic measure, the eccentricity index, which is the ratio of the LV dimension parallel to the septum to the LV dimension perpendicular to the septum is limited by dependence upon a normal left ventricular geometry, precise placement of a perpendicular line through the septum, and precision in timing the measurement within the cardiac cycle12. Catheter-based measurements are the gold-standard for assessment of RVSP because of their direct measurements, however these procedures are invasive and have known and potentially catastrophic complications13.
Given that septal position is frequently the only available method for non-invasive assessment for elevated right ventricular pressures in many children, a quantitative assessment of that curvature could be useful to assist in the diagnosis and medical management of patients with pulmonary hypertension. Some quantifications of septal position like the left ventricular end-diastolic eccentricity index12and the septal flattening angle14 have been compared with other echocardiographic measures of right ventricular systolic pressure such as the tricuspid regurgitant jet velocity. The only other quantifications of septal position to compare with gold-standard catheterization direct-pressure measurements is the normalized septal curvature9 and the eccentricity index12.
The aim of this study was to create a novel semi-quantitative measurement of septal positioning that was easy to perform, reproducible, and accurate in identifying significant pulmonary hypertension.