Hiroto Takeuchi

Leukocyte-Targeted Myocardial Contrast Echocardiography Can Assess the Degree of Acute Allograft Rejection in a Rat Cardiac Transplantation Model

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.

Potentiation of C-type natriuretic peptide with ultrasound and microbubbles to prevent neointimal formation after vascular injury in rats

OBJECTIVES Long-term intravenous infusion of high-dose C-type natriuretic peptide (CNP) is known to prevent neointimal formation after vascular injury. Ultrasound (US) irradiation during microbubbles (MBs) infusion (US/MBs) has been used for local delivery of bioactive agents. We examined whether short-term infusion of CNP could also inhibit neointimal development and whether combined US/MBs treatment at the beginning of the CNP infusion could enhance its effect. METHODS In the rat carotid artery-balloon injury model, the intima/media area (I/M) ratio 14 days after injury was compared among various short-term post-injury treatments. For combined US/MBs, a commercial echocardiograph (1.8 MHz, mechanical index 1.0) and albumin-coated octafluoropropane gas MBs were used. RESULTS Infusion of high-dose CNP (1.0 microg/kg/min) immediately after injury for only 24 h successfully reduced the I/M ratio (0.18+/-0.05) to 18% of the ratio in control rats (1.00+/-0.13) that underwent only balloon injury. Although low-dose CNP (0.1 microg/kg/min for 24 h) alone was not effective in reducing the I/M ratio (0.83+/-0.18), combined US/MBs treatment for the first 80 min of the infusion markedly reduced the I/M ratio (0.17+/-0.07), which persisted until 28 days after injury (0.16+/-0.04). CONCLUSIONS The effects of CNP on the events occurring early after arterial injury may be important in preventing subsequent neointimal development. Thus, intravenous infusion of CNP with US/MBs at its initiation may provide a clinically feasible anti-restenosis therapy applicable immediately after vascular interventions.

Quantitative assessment of coronary stenosis by harmonic power Doppler with a simple pulsing sequence and vasodilator stress in patients.

OBJECTIVES We examined whether myocardial contrast echocardiography (MCE) with harmonic power Doppler (HPD) employing a simple ultrasound pulsing sequence enables estimation of the severity of coronary artery stenosis in patients. BACKGROUND Contrast intensity (CI) during MCE with intravenous microbubble infusion is dependent on the myocardial blood flow velocity (MBFV) and pulsing interval (PI). METHODS Based on an in vitro experiment, we devised the MBFV index calculated as the reciprocal of the magnitude of CI decay produced by abrupt PI shortening during intermittent imaging. In 68 coronary artery territories from 49 patients, myocardial HPD images were acquired during intravenous infusion of Levovist, while the long PI with 1:10 electrocardiographic gating was shortened to 1:1, both at baseline and during adenosine triphosphate infusion. The MBFV index in each coronary territory and MBFV reserve as the ratio between hyperemia and baseline were compared with the severity of corresponding coronary artery stenosis assessed by quantitative coronary angiography (QCA) or by pressure guide wire as the fractional flow reserve (FFR). RESULTS Both the MCE-derived MBFV index during hyperemia and MBFV reserve exhibited significant negative correlations with the QCA-derived stenosis severity (r = -0.56 and r = -0.64, respectively). The MBFV reserve positively correlated with FFR (r = 0.89). By combining the cutoff values of the MBFV index during hyperemia and MBFV reserve, > or =75% of stenoses defined by QCA were determined, with a sensitivity of 77.3%, specificity of 93.4%, and accuracy of 88.3%. CONCLUSIONS Shortening of PI during intravenous MCE with intermittent HPD imaging under vasodilator stress enables assessment of coronary artery stenoses in patients.