BackgroundEchocardiographic TAPSE/sPAP ratio is a non-invasive surrogate for right ventricular-pulmonary arterial (RV-PA) coupling. It has been related to outcome in patients with moderate to severe pulmonary hypertension (PH). Research QuestionIs RV-PA coupling of prognostic relevance in patients with suspected PH but only normal or mildly elevated mean pulmonary arterial pressure (mPAP) and is it associated with impaired exercise capacity and exercise hemodynamics? Study Design and MethodsPatients with mPAP<25mmHg who underwent echocardiography and exercise right heart catheterization in our PH-clinic, were retrospectively analyzed. Mild PH was defined by mPAP 21-24mmHg and exercise PH (EPH) by a mPAP/cardiac-output (CO) slope >3mmHg/L/min. Multivariate analysis was performed to identify independent predictors for clinical worsening, defined by disease-related hospitalization, transplantation, or death. Results237 patients (female: N=155; median age: 64 (IQR 54-73) years, no PH N=147; mild PH N=90; EPH N=202) were included. During the observation time of 63 (IQR:29-104) months, 36 patients died and 126 events of clinical worsening occurred. TAPSE/sPAP ratio turned out as age- and sex independent predictor of mortality (HR 0.09 95% CI: (0.01 – 0.62) p=0.014) and clinical worsening (HR 0.05 95% CI: (0.35-0.78); p=0.002). TAPSE/sPAP was also significantly correlated to 6-minute walk distance (r= 0.33; p<0.001) and exercise hemodynamics (mPAP/CO slope: rρ=-0.56, p<0.001). The best multivariate predictive model for clinical worsening in this patient collective consisted of TAPSE/sPAP ratio (HR: 0.71 (0.53-0.95), p=0.021), NT-proBNP (HR 1.15 (0.99-1.34), p=0.065) and 6MWD (HR: 0.998 (0.995-1.00), p=0.042). InterpretationIn patients with suspected PH but normal or only mildly elevated resting mPAP, TAPSE/sPAP ratio is an independent predictor of outcome. In addition, it is significantly associated with exercise capacity and exercise hemodynamics and may be a helpful tool in the prediction of future clinical worsening of this patient population.