Rapamycin has been shown to reduce anatomical evidence of cardiac allograft vasculopathy, but its effect on coronary artery physiology is unknown.

Twenty-seven patients without angiographic evidence of coronary artery disease underwent measurement of fractional flow reserve (FFR), coronary flow reserve (CFR), and the index of microcirculatory resistance (IMR) within 8 weeks and then 1 year after transplantation using a pressure sensor/thermistor-tipped guidewire. Measurements were compared between consecutive patients who were on rapamycin for at least 3 months during the first year after transplantation (rapamycin group, n = 9) and a comparable group on mycophenolate mofetil (MMF) instead (MMF group, n = 18).

At baseline, there was no significant difference in FFR, CFR, or IMR between the 2 groups. At 1 year, FFR declined significantly in the MMF group (0.87 ± 0.06 to 0.82 ± 0.06, P = .009) but did not change in the rapamycin group (0.91 ± 0.05 to 0.89 ± 0.04, P = .33). Coronary flow reserve and IMR did not change significantly in the MMF group (3.1 ± 1.7 to 3.2 ± 1.0, P = .76; and 27.5 ± 18.1 to 19.1 ± 7.6, P = .10, respectively) but improved significantly in the rapamycin group (2.3 ± 0.8 to 3.8 ± 1.4, P < .03; and 27.0 ± 11.5 to 17.6 ± 7.5, P < .03, respectively). Multivariate regression analysis revealed that rapamycin therapy was an independent predictor of CFR and FFR at 1 year after transplantation.

Early after cardiac transplantation, rapamycin therapy is associated with improved coronary artery physiology involving both the epicardial vessel and the microvasculature.