Vena cava backflow and right ventricular stiffness in pulmonary arterial hypertension

Abstract

Vena cava (VC) backflow is a well-recognized clinical hallmark of right ventricular (RV) failure in pulmonary arterial hypertension (PAH). Backflow may result from tricuspid regurgitation during RV systole or from impaired RV diastolic filling during atrial contraction. Our aim was to quantify forward and backward flow in the VC and to establish the main cause in PAH.

In 62 PAH patients, cardiac magnetic resonance measurements provided volumetric flows (mL·s⁻¹) in the superior and inferior VC; time-integration of flow gave volume. “Backward fraction” was defined as the ratio of backward and forward volume in the VC, expressed as percentage. Time of maximum VC backflow was expressed as percentage of the cardiac cycle. RV volumes and aortic stroke volume were determined. Right heart catheterisation gave RV and right atrial pressures. RV end-diastolic stiffness was determined with the single beat method.

The backward fraction was 12 (IQR:3–24)% and larger than 20% in 21 patients. Maximum backflow occurred at near 90% of the cardiac cycle, coinciding with atrial contraction. The backward fraction was associated with maximal right atrial pressure (Spearman's r=0.77), RV end-diastolic stiffness (r=0.65), RV end-diastolic pressure (r=0.77), and was negatively associated with stroke volume (r=–0.61; all p<0.001).

Significant backward flow in the VC was observed in a large group of PAH-patients and occurred mostly during atrial contraction as a consequence of impaired RV filling due to RV diastolic stiffness. Backward flow due to tricuspid regurgitation was of significance in only a small minority of patients.