LAUSR

Combined postand pre-capillary pulmonary hypertension (CpcPH) caused by left heart disease (PH-LHD) has an undoubtedly worse prognosis compared with isolated post-capillary (IpcPH),1 yet how to best distinguish these two groups is still a matter of great debate. The diastolic pulmonary gradient (DPG), defined as diastolic pulmonary artery pressure (dPAP) minus pulmonary artery wedge pressure (PAWP), should be less affected by left heart failure-induced changes in vascular compliance,2 and, as a result, during the Fifth World Symposium on Pulmonary Hypertension it was proposed that a DPG ≥7 mmHg alone should define CpcPH.3 Since then, studies exploring the prognostic value of DPG have yielded mixed results4–9 and more recent guidelines have reincorporated pulmonary vascular resistance (PVR) into the CpcPH definition.10 Perhaps surprisingly these studies, as well as earlier ones,11 report a relatively high rate of negative DPG values. However, it remains unclear if a negative DPG is physiologically plausible or whether these values are simply a result of measurement error or catheter artefact.4 In this issue of the Journal, Nagy and colleagues12 attempt to answer this very intriguing question as well as define the prognostic significance of a negative DPG. Of the 316 subjects who were evaluated haemodynamically with right heart catheterization and echocardiography, a high proportion (n= 256, 84.5%) met criteria for PH-LHD and were analysed further. Of these, 162 were initially referred to the Karolinska University Hospital in Stockholm, Sweden for evaluation of heart failure and 94 were referred for percutaneous transvenous mitral commissurotomy for mitral valve stenosis at the Sri Sathya Sai Institute in Bangalore, India. Subjects with mitral valve stenosis had significantly worse haemodynamics including higher pulmonary pressures, higher PVR and lower cardiac index compared with the cohort of PH-LHD. When these cohorts were combined, a negative DPG was calculated in almost half of all subjects (48%). A negative DPG was associated with a more favourable haemodynamic