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 IMRs and IMRc 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.