Background Pulmonary hypertension (PH), a mean pulmonary artery pressure ≥25 mm Hg, is generally classified as either precapillary (PRE) or postcapillary in origin, with critical diagnostic and therapeutic implications. However, a less characterized subset of patients demonstrates a mixed type (MIX) of PH. The hypotheses of this study were that patients with MIX would have greater hemodynamic and functional changes than PRE and that the groups could be distinguished by a novel index, the echo-determined pulmonary artery to LA diameter ratio (PAd/LAd)⇓.
Methods We retrospectively analyzed right heart catheterization, echo, and clinical data in 124 patients referred to the Pulmonary Hypertension Clinic at University Hospitals Case Medical Center within a one-year period. Patients were divided into groups based on pulmonary capillary wedge pressure (PCWP) and the transpulmonary gradient (TPG); thus, PRE was defined as PCWP≤15 mm Hg with TPG>12, while MIX was defined as PCWP>15 with TPG>12. The number of patients with postcapillary PH (PCWP>15 and TPG≤12) was small and not considered in this analysis. Right ventricular (RV) function was assessed by the RV myocardial performance index (RIMP) and the tricuspid annular tissue velocity (RV S'). Functional impairment was assessed by the six minute walk test (6 MW) and indirectly by log10 Nt pro-BNP levels.
Results Compared to precapillary PH (n=73), the mixed group (n=35) had higher PA and PCWP pressures, lower pulmonary vascular resistance (PVR) but similar TPG and cardiac index; a larger right ventricular basal diameter (RVD) and borderline larger right atrial area but similar RV function. While LV mass and E/E'(data not shown) were greater in MIX, the PAd/LAd ratio was significantly lower in MIX than PRE (table) Functionally, the percent predicted on 6MW was significantly lower (0.75±0.36 vs. 0.93 MIX than PRE 0.40, p<0.05) and the log10Nt-BNP tended to be higher (3.04±0.66 vs. 2.73±0.79, p=0.059) in MIX than PRE.
Conclusions Patients with mixed PH have more pronounced abnormal hemodynamics, right heart dimensions and functional impairment than patients with precapillary PH. The PAd/LAd ratio may be a simple method of identifying mixed PH noninvasively and should be studied prospectively.