Comparison of simplified and comprehensive methods for assessing the index of microvascular resistance in heart transplant recipients

Objectives The objectives of the present study were to compare a simplified and a comprehensive method of estimating the index of microvascular resistance (IMR) and assess the changes from 7–11 weeks to 1 year after heart transplant (HTx). Background he IMR is specific to the microvasculature and reflects the status of the microcirculation in cardiac patients and can be estimated via a simplified method (IMR s ) or a comprehensive method (IMR c ). The calculation for the latter includes coronary wedge pressure and central venous pressure. Methods Consecutively transplanted patients ( n  = 48) underwent left and right heart catheterization including physiological evaluation at two time points post‐HTx. The agreement between the values of IMR obtained using the IMR s and IMR c methods were assessed using Bland–Altman analysis. The agreements and differences were assessed using mixed model analysis. Results The mean bias between IMR s and IMR c was 1.3 mm Hg·s (95% limits of agreement: −1.2, 3.8 mm Hg). Between 7–11 weeks and 1 year post‐HTx there was a significant decline in IMR s values ( P  = 0.03) but a smaller and statistically nonsignificant decline in IMR c values ( P  = 0.13). The significant difference ( P  = 0.04) between IMR c and IMR s 7–11 weeks post‐HTx was no longer present at 1 year ( P  = 0.24). Conclusions The IMR s method resulted in slightly higher IMR estimates and exhibited a somewhat larger change over the 10‐month follow‐up period than the IMR c method. However, the differences between the methods were small and unlikely to be of clinical importance. © 2015 Wiley Periodicals, Inc.