BACKGROUND: Cardiac index is an important determinant of outcome in patients with idiopathic pulmonary artery hypertension (IPAH). An implantable hemodynamic monitor (IHM) [Chronicle; Medtronic; Minneapolis, MN; a system limited to investigational use only] that records right ventricular (RV) pressure waveforms continuously may increase our understanding of IPAH and improve therapeutic selections and outcomes. The aim of this study was to investigate whether the RV pressure waveform utilizing an IHM can be used to estimate the magnitude of pressure wave reflection and cardiac index in patients with IPAH in acute settings. METHODS: In eight patients with pulmonary arterial hypertension, RV pressure waveforms were recorded utilizing the IHM, and breath-by-breath cardiac index was recorded during acute IV epoprostenol infusion at 3, 6 and 9 ng/kg/min. Late systolic pressure augmentation and cardiac index were estimated using the RV pressure waveforms and correlated with direct measurement of cardiac index. RESULTS: At baseline, the cardiac index was 2.1 +/- 0.2 L/min/m(2), total pulmonary resistance index was 38 +/- 2 Wood U/m(2), and RV systolic pressure was 92 +/- 4 mm Hg. Wave reflection accounted for 29 +/- 1 mm Hg of the RV systolic pressure. During epoprostenol infusion, total pulmonary resistance index and wave reflection decreased (- 15 +/- 4 Wood U/m(2), p < 0.001, and - 5 +/- 2 mm Hg, p < 0.05, respectively). The breath-by-breath cardiac index correlated with the RV pressure waveform cardiac index estimates (r(2) = 0.95). CONCLUSIONS: RV pressure waveform analysis provides continuous hemodynamic assessments including cardiac index in acute settings. Once confirmed in long-term settings, this information may prove useful in optimizing a treatment regimen in patients with IPAH.