Development and Validation of a Noninvasive Model of Mixed Venous Oxygen Saturation in Heart Failure

Mixed venous oxygen saturation (SvO₂), measured with right heart catheterization, is a crucial prognostic tool in patients with heart failure. The prognostic significance of SvO₂ estimated noninvasively using cardiovascular magnetic resonance (CMR) from the T2 of intracardiac blood pools remains unknown.

The objective of the study was to develop a CMR model of mixed venous saturation (imaging-derived SvO₂ [iSvO₂]), and establish if it is associated with future adverse events in heart failure.

The iSvO₂ was modeled in the discovery cohort (N = 30), who underwent CMR T2 mapping and invasive right heart catheterization, by linear regression. The validation cohort of 628 patients with recently diagnosed heart failure underwent clinical assessment, CMR, and follow-up (median 3 years [IQR: 1.5-4.8]) for a primary endpoint of all-cause mortality or heart failure hospitalization.

Significant positive correlation was found between the ratio of right ventricular blood pool T2/left ventricular blood pool T2 and invasive mixed venous oxygen saturation (R = 0.82; 95% CI: 0.66-0.91; P < 0.001), giving the equation: iSvO₂ = 95·(RV-T2_BP/LV-T2_BP). In the validation cohort, there was a strong association between iSvO₂ and the primary endpoint (HR: 0.66 for 10% change in iSvO₂; 95% CI: 0.54-0.81; P < 0.001), which remained significant after adjusting for age, sex, left ventricular ejection fraction, right ventricular ejection fraction, N-terminal pro-B-type natriuretic peptide, NYHA functional class, and diabetes.

The CMR iSvO₂, measured from simple T2 maps of left and right ventricular blood pool, allows accurate estimation of the invasive SvO₂. In a real-world heart failure registry, iSvO₂ is an independent predictor of mortality and heart failure hospitalization.