Reduction of intimal thickening in canine coronary bypass vein grafts with dipyridamole and aspirin.

The potential benefit of platelet inhibitor drugs on coronary arterial bypass vein grafts was assessed in dogs with magnification-corrected angiographic luminal measurements and quantitative histologic evaluation of the vein grafts. There were 11 control animals and 11 animals treated with dipyridamole, 55 mg/day, plus aspirin, 325 mg/day. Eighteen animals with patent grafts were studied when electively killed 2, 4 or 6 months after grafting. At 14 days, there was greater angiographic narrowing in the most distal 1 cm of vein grafts in control than in treated dogs (P less than 0.01). This same angiographic narrowing persisted in control dogs until they were killed (P less than 0.03). Computer-assisted measurements of the entire area of intimal thickening were done on vein graft cross sections taken 1 cm from the distal anastomosis. The circumference of the vein grafts at the intimal-media junction was measured from the same section and the potential maximal luminal area calculated. The calculated luminal narrowing due to intimal thickening was greater in control than in treated dogs (P less than 0.03). These data correlate well with the demonstrated angiographic narrowing. The findings indicate that the degree of early intimal thickening that persists 2 to 6 months postoperatively in canine coronary bypass vein grafts may be reduced by the platelet inhibitor combination of dipyridamole plus aspirin.

Hemodynamic response to positive end-expiratory pressure following right atrium-pulmonary artery bypass (Fontan procedure).

Thirteen patients were studied in the early postoperative period to determine the hemodynamic response to increasing levels of positive end-expiratory pressure (PEEP) following right atrium-pulmonary artery bypass (Fontan procedure). Hemodynamic data and arterial oxygen and carbon dioxide tensions were measured without PEEP and with PEEP = 3, 6, 9, and 12 cm H2O. Cardiac index decreased progressively with increasing levels of PEEP compared to PEEP = 0 (cardiac index = 2.7 +/- 1.2 L/min/m2), and the decrease was significant at PEEP = 9 (cardiac index = 2.2 +/- 0.8 L/min/m2, p less than 0.05) and 12 cm H2O (cardiac index = 2.0 +/- 0.7 L/min/m2, p less than 0.05). Both arterial oxygen tension and pulmonary vascular resistance index increased significantly at all levels of PEEP studied compared to PEEP = 0. Significant positive trends were demonstrated for arterial oxygen tension and pulmonary vascular resistance index and a significant negative trend was shown for cardiac index with increasing PEEP. Heart rate, right atrial pressure, left atrial pressure, mean arterial blood pressure, and arterial carbon dioxide tension did not change significantly nor consistently with increasing PEEP. From these data it appears that PEEP is an effective means of raising arterial oxygen tension after right atrium-pulmonary artery bypass. A progressive fall in cardiac index occurs with increasing PEEP, and the fall becomes significant at PEEP greater than 6 cm H2O. The fall in cardiac index appears to be mediated by a significant rise in pulmonary vascular resistance index.

Noninvasive radioisotopic technique for detection of platelet deposition in coronary artery bypass grafts in dogs and its reduction with platelet inhibitors.

At 8 and 32 hours after saphenous vein bypass graft surgery in six dogs, in vivo images of the graft were obtained with a gamma camera after intravenous injection, 2 hours postoperatively of autologous platelets labeled with indium-111. Platelet deposition in the grafts could be imaged in vivo from the scintiphotos. In vitro images of the excised heart showed saphenous vein graft uptake confirming the in vivo image. In vitro determination of radioactivity in the graft averaged 17 +/- 14 times greater than in blood and 33 +/- 26 times greater than in the lung. Under identical conditions, in eight dogs treated with dipyridamole (55 mg/day) plus aspirin (325 mg/day), the grafts appeared to have considerably less platelet deposition as estimated by imaging. In vitro determination of radioactivity in the graft averaged 5 +/- 2 times greater than in blood and 8 +/- 4 times greater than in the lung (p less than 0.01). This noninvasive technique may be a promising tool for a better understanding of the role played by platelets in the process of occlusion of saphenous vein bypass grafts in man and its prevention with platelet inhibotors.