Pulmonary to Systemic Flow Ratio in Precapillary Pulmonary Hypertension Without Left-to-Right Shunts: A Prognostic Implication of the Fick Method.

Objective: We routinely calculate the pulmonary to systemic (Qp/Qs) ratio to avoid missing any left-to-right shunts in patients with precapillary pulmonary hypertension (PH). However, the pulmonary artery oxygen saturation (SpaO2) was lower than the mixed venous oxygen saturation (SmvO2) calculated using the formula; hence, the Qp/Qs ratio was calculated as less than "1" in some patients despite the absence of any detectable shunt. We hypothesized that this observation might have prognostic significance; however, to the best of our knowledge, it has not been investigated yet. Therefore, we aimed to examine the prognostic value of the Qp/Qs ratio in precapillary PH without left-to-right shunts. Methods: In this retrospective cohort study of 173 consecutive patients, hospital files were scanned for clinical, echocardiographic, and hemodynamic data including the Qp/Qs ratio calculated using the Fick method. Results: During a median follow-up of 25 months, 74 patients died. Nonsurvivors had lower Qp/Qs ratio than survivors (0.76±0.19 vs. 1.02±0.07 p<0.001). The multivariate logistic regression analysis showed that a decreased Qp/Qs ratio and poor functional capacity (World Health Organization class III-IV) were independent predictors of mortality. The receiver operating characteristic curve analysis revealed that the optimal cutoff value of the Qp/Qs ratio for predicting mortality was 0.90 with a sensitivity of 76% and specificity of 98%. Conclusion: The Qp/Qs ratio calculated using the Fick method was an independent predictor of mortality. This prognostic implication was based on the difference between SpaO2 and SmvO2 calculated using the formula. Nevertheless, this result might be a reflection of a potential intrinsic methodological flaw of the Fick method. [ABSTRACT FROM AUTHOR]