Kidney pulmonary hypertension: another road on the map?

Pulmonary hypertension (PH) is a serious disorder that worsens the course of chronic heart, lung or systemic diseases. However the need to discriminate PH, a pathophysiological condition, from pulmonary arterial hypertension (PAH), which is a rare clinical condition, has been recently stressed [1]. PH is defined as an increase in mean pulmonary arterial pressure (PĀP) > 25 mm Hg at rest, as assessed by right heart catheterisation. According to various combinations of values of pulmonary capillary wedge pressure (PCWP), pulmonary vascular resistance (PVR) and cardiac output, different hemodynamic types of PH can be identified. In the updated clinical classification of PH, 37 clinical conditions with PH are classified into six groups according to pathological, pathophysiological and therapeutic characteristics: PAH (group 1), pulmonary veno-occlusive disease (group 1’), PH due to left heart disease (group 2), PH due to lung disease (group 3), chronic thromboembolic PH (CTEPH, group 4) and PH with unclear and/or multifactorial mechanisms (group 5) [4]. In this issue of MRM, Bozbas et al. [2] report that pulmonary hypertension is not uncommon in patients with end stage renal disease (ESRD). They detected an increase of systolic pulmonary arterial pressure (sPAP) in 85 of the 500 (17%) patients undergoing pre-transplant evaluation. Moreover, a significant decrease was observed in mean sPAP values in an average of 53 months of postoperative follow up on 42 patients who had undergone both preand post-transplant echocardiographic examination compared to pre-transplant values [3]. As the authors acknowledge, their retrospective data have the important limitation of lacking direct hemodynamic assessment which would have readily diagnosed and classified PH occurring in ESRD. Accordingly, the correlation between echocardiographic estimate of sPAP and right heart catheterization is not absolute. Thus if we apply the PH echo probability criteria of ESC/ERS guidelines [4], we could find only 6 patients fulfilling PH high probability criteria. Nevertheless the potential role of PH as a cardiovascular complication of ESRD should be acknowledged. The death rate among U.S patients undergoing dialysis continues to exceed 20% per year during the first 2 years after maintenance dialysis has begun. Moreover, hospitalization rates have remained nearly constant, averaging almost 13 hospital days and two admissions per patient/year [5]. It has been suggested that dialysis-focused quality measures should also include an assessment of risk factors for cardiovascular disease which constitutes the major cause of hospitalization and death in the population receiving dialysis. Indeed while it is well known that cardiovascular diseases including ischemic heart disease, heart failure and arrhythmias are very common and are the most frequent causes of mortality in patients with ESRD, data on PH in patients with ESRD are limited. PH is a strong independent predictor of mortality in hemodialysis (HD) patients [6]. In a recent review, the prevalence of PH in ESRD patients was reported to be around 40-50% [7]. Its frequency has been reported to be higher in HD than in peritoneal dialysis (PD) patients due to the presence of arterio-venous fistula (AVF) [8]. The mechanisms involved in