Composite indices of upstream pulmonary vascular impedance and capacitance do not help in identifying patients who should undergo pulmonary endarterectomy in chronic thromboembolic pulmonary hypertension

Abstract

Background Chronic thromboembolic pulmonary hypertension (CTEPH) is potentially curable by surgical pulmonary endarterectomy (PEA). Patient selection for PEA is crucial and depends mainly on discriminating between those with proximal accessible disease and distal disease. In this study we evaluated the value of composite indices such as upstream resistance (Zup) and capacitance (Cp) for partitioning of pulmonary vascular resistance and surgical outcome.Methods We retrospectively reviewed data from 30 patients who underwent PEA between 2007 and 2012. Zup, defined as the ratio between the mean pulmonary artery pressure (PAPm) minus diastolic pulmonary artery pressure (PAPd) and PAPm minus pulmonary artery occlusion pressure (POAP), was computed preoperatively as was the Cp, defined as the ratio of stroke volume over pulse pressure. We assessed the use of these indices to predict pulmonary haemodynamics after PEA.Results Postoperatively, total pulmonary vascular resistance (tPVR) was > 400 dynes•s•cm-5 in 11 patients (37%); nine patients were treated with an endothelin receptor antagonist (ERA) and had unsatisfactory surgical results. Preoperative Cp was identical in both groups (0.9945 ± 0.06867 vs. 1.348 ± 0.1961, P= 0.14). Zup was higher in the group with better haemodynamic outcomes (50.29% ± 3.266) than in the ERA group (38.59% ± 2.86) (P < 0.05). In multivariate analysis, the relation of Zup and outcome was not statistically significant when adjusted for tPVR.Conclusions The composite indices Cp and Zup were not useful for distinguishing between CTEPH patients who were good candidates for PEA versus patients with substantial distal vasculopathy with PVR values that remained elevated after surgery.