Viscosity-corrected pulmonary vascular resistance: a prognostic marker in left ventricular assist device candidates

Despite being a significant clinical marker in heart failure, pulmonary vascular resistance (PVR) is not an important predictor of outcome in left ventricular assist device (LVAD) candidates. Based on the Hagen-Poiseuille law, PVR is also influenced by blood viscosity which is mostly determined by hematocrit (HCT); however, it is not taken into account in the clinical practice. Accordingly, we aimed to examine the changes and the prognostic role of HCT-adjusted PVR (aPVR) in a single center cohort of patients before LVAD implantation. Of the 101 LVAD implants, 96 patients prior to surgery (53±10 years old, 84% male) were enrolled. We collected clinical characteristics, preprocedural and early postoperative laboratory and right heart catheterization data. The aPVR was calculated using previous experimental data and PVR was adjusted to a reference HCT of 0.45. Our outcome was 365-day mortality, reached by 20 patients (21%). Adjustment to HCT resulted in a mean 35% relative change of aPVR compared to PVR, with more pronounced relative difference in patients with clinically relevant HCT-abnormality (62% change). Notably, adjustment resulted in frequent reclassification of pulmonary vascular disease severity compared to PVR (Figure 1). PVR was not a predictor of outcome, while aPVR was significantly associated with poor prognosis (HR: 1.183 [1.014-1.379], p=0.03). The prognostic value of aPVR remained significant even when other clinically and statistically significant predictors, such as RVAD support or the HM3 Survival Risk Score were added to the model. Corresponding blood viscosity should not be neglected in the assessment of PVR: aPVR significantly reclassifies the severity of pulmonary vascular disease in LVAD candidates, moreover, aPVR is an independent predictor of survival.