We investigated 234 consecutive incident patients in whom IPAH was diagnosed at our institute between January 1, 2007 and September 30, 2009. All were inpatients and were diagnosed by right-sided heart catheterization according to standard criteria: a mean pulmonary artery pressure (mPAP) ≥ 25 mm Hg and PVR > 3 Wood units at rest in the presence of a normal pulmonary capillary wedge pressure (≤ 15 mm Hg).16 Patients with PAH associated with a definite cause, such as connective tissue disease and congenital heart disease, and those with portopulmonary hypertension, chronic pulmonary obstruction, chronic pulmonary thromboembolism, and pulmonary hypertension due to left-sided heart disease were excluded. We also excluded patients with coincident cardiac diseases; significant arrhythmias, including atrial fibrillation, Wolff-Parkinson-White syndrome, supraventricular tachycardia, atrioventricular block, or ventricular tachycardia; a pacemaker; or missing ECG data. In addition, patients receiving antiarrhythmic drugs were also excluded from the study because of their possible effects on ECG measurements.17 This left 212 patients for analysis. Details of these patients at the time of diagnosis were analyzed, including sex, age, history of any other concomitant disease and drug therapy, physical examination, echocardiography, 6-min walk test distance (6MWD), World Health Organization (WHO) functional classification, hemodynamic parameters, and blood tests for biochemical markers that are correlated with clinical severity and mortality in IPAH. The study protocol was reviewed and approved by the Shanghai Pulmonary Hospital ethics committee (K10-052).