Background--Repetitive endomyocardial biopsies are necessary to monitor the effects of immunosuppressants after cardiac transplantation. Contrast ultrasound with microbubble targeting of leukocytes detects acute leukocyte infiltration. We examined whether leukocyte-targeted myocardial contrast echocardiography (MCE) could provide for the quantitative assessment of acute cardiac rejection.

Methods and Results--Hearts from Brown Norway rats or Lewis rats were transplanted into other Brown Norway rats. Isografts and groups of allografts either untreated or treated with cyclosporin A (CsA) at a low dose (3 mg · kg^-1 · d^-1) or high dose (10 mg · kg^-1 · d^-1) from 3 days before transplantation were compared at posttransplantation day 3. Echocardiography-derived left ventricular wall thickening was comparable among the 4 groups. Myocardial blood flow assessed with MCE, relating pulsing intervals with signal intensity (SI), was slightly decreased only in untreated allografts. However, myocardial SI (in gray levels) obtained after a 10-minute period allowing microbubble-leukocyte interactions after contrast injection exhibited a clear gradient in these groups (12±2 in untreated allografts, 9±5 in allografts treated with low-dose CsA, 6±3 in allografts treated with high-dose CsA, and 2±1 in isografts, P<0.001). The pattern of difference in SI among the groups agreed well with that in ED-1-positive cell (macrophage) count (25±7, 12±4, 5±3, and 1±0 cells per high-power field, respectively, P<0.001), which correlated with CD3-positive cell (T lymphocyte) count (33±5, 22±5, 9±4, and 1±0 cells per high-power field, respectively, P<0.001).

Conclusions--Leukocyte-targeted MCE can noninvasively assess the degree of rejection in transplanted hearts by directly revealing the magnitude of intramyocardial infiltration of macrophages and T lymphocytes.