Pattern of changes over time in myocardial blood flow and microvascular dilator capacity in patients with normally functioning cardiac allografts

This study tests the hypothesis that myocardial blood flow and coronary mic rovascular dilator capacity vary as a function of time after orthotopic hea rt transplantation in humans. Positron emission tomography measurements of myocardial blood flow were obtained at rest and during adenosine in 24 pati ents between 1 and 86 months after heart transplantation. At the time of th e study all patients were clinically well and had angiographically normal e picardial coronary artery vessels. patients were divided into 3 groups base d on time from transplant to positron emission tomography measurement of my ocardial blood flow: group 1 to 12 months (n = 9); group 13 to 34 months (n = 8); and group greater than or equal to 37 months (n = 7). Basal myocardi al blood flow in group 1 to 12 months (1.86 +/- 1.01 ml/min/g) exceeded (p <0.05) that of group 13 to 34 months (1.17 +/- 0.73) and group greater than or equal to 37 months (0.98 +/- 0.34). In group 13 to 34 months, basal myo cardial blood flow and maximal dilator capacity (minimal coronary vascular resistance with adenosine 36 +/- 12 mm Hg/ml/min/g) were comparable to that of normal volunteers (1.01 +/- 0.20 and 37 +/- 9, respectively). In group greater than or equal to 37 months, maximal flow response to adenosine was reduced (2.54 +/- 1.25 vs 3.16 +/- 0.52, respectively, p = 0.06). Maximal d ilator capacity in group greater than or equal to 37 months (60 +/- 34) wet s impaired versus group 1 to 12 months (36 +/- 10) and group 13 to 34 month s (36 +/- 12; both p <0.05) as well as normals (37 +/- 9, p <0.05). During the first year after cardiac transplantation basal myocardial blood flow is elevated out of proportion to external determinants of myocardial oxygen d emand, but maximal dilator capacity of the coronary microcirculation is nor mal. Between 1 and 3 years both basal myocardial blood flow and microvascul ar function tend to normalize. After 3 years, although basal myocardial blo od flow is normal, microvascular dilator capacity is impaired. (C) 1998 by Excerpta Medica, Inc.