Pharmacologic relaxation of vein grafts is beneficial compared with pressure distention caused by upregulation of endothelial nitric oxide synthase and nitric oxide production

Vein graft preservation solutions, patency, and outcomes after coronary artery bypass graft surgery: follow-up from the PREVENT IV randomized clinical trial

IMPORTANCE

In vitro and animal model data suggest that intraoperative preservation solutions may influence endothelial function and vein graft failure (VGF) after coronary artery bypass graft (CABG) surgery. Clinical studies to validate these findings are lacking.

OBJECTIVE

To evaluate the effect of vein graft preservation solutions on VGF and clinical outcomes in patients undergoing CABG surgery.

DESIGN, SETTING, AND PARTICIPANTS

Data from the Project of Ex-Vivo Vein Graft Engineering via Transfection IV (PREVENT IV) study, a phase 3, multicenter, randomized, double-blind, placebo-controlled trial that enrolled 3014 patients at 107 US sites from August 1, 2002, through October 22, 2003, were used. Eligibility criteria for the trial included CABG surgery for coronary artery disease with at least 2 planned vein grafts.

INTERVENTIONS

Preservation of vein grafts in saline, blood, or buffered saline solutions.

MAIN OUTCOMES AND MEASURES

One-year angiographic VGF and 5-year rates of death, myocardial infarction, and subsequent revascularization.

RESULTS

Most patients had grafts preserved in saline (1339 [44.4%]), followed by blood (971 [32.2%]) and buffered saline (507 [16.8%]). Baseline characteristics were similar among groups. One-year VGF rates were much lower in the buffered saline group than in the saline group (patient-level odds ratio [OR], 0.59 [95% CI, 0.45-0.78; P < .001]; graft-level OR, 0.63 [95% CI, 0.49-0.79; P < .001]) or the blood group (patient-level OR, 0.62 [95% CI, 0.46-0.83; P = .001]; graft-level OR, 0.63 [95% CI, 0.48-0.81; P < .001]). Use of buffered saline solution also tended to be associated with a lower 5-year risk for death, myocardial infarction, or subsequent revascularization compared with saline (hazard ratio, 0.81 [95% CI, 0.64-1.02; P = .08]) and blood (0.81 [0.63-1.03; P = .09]) solutions.

CONCLUSIONS AND RELEVANCE

Patients undergoing CABG whose vein grafts were preserved in a buffered saline solution had lower VGF rates and trends toward better long-term clinical outcomes compared with patients whose grafts were preserved in saline- or blood-based solutions.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00042081.

In vivo human lower extremity saphenous vein bypass grafts manifest flow mediated vasodilation

OBJECTIVE

As in arteries, venous endothelium modulates vessel homeostasis and tone. The effect of an arterialized environment on venous endothelial function remains poorly understood. In particular, regulation of saphenous vein graft (SVG) blood flow and lumen caliber remains undefined. We hypothesized that mature SVGs would exhibit endothelium-dependent, flow-mediated vasodilation (FMD). We further hypothesized that endothelium-derived nitric oxide (NO) was an important mediator.

METHODS

Patients with femoral to popliteal artery SVGs that had maintained primary patency and were at least 1 year from surgery were enrolled. High-resolution, B-mode ultrasound scans were used to measure vein graft diameter before and 1 minute after reactive hyperemia (RH) to determine FMD. RH was created through application of 220 mm Hg to the calf for 5 minutes with a sphygmomanometric cuff. After a 10-minute recovery period, nitroglycerin-mediated, endothelium-independent vasodilation was measured 3 minutes after administration of nitroglycerin 0.4 mg sublingually. Brachial artery FMD was determined by validated techniques. L-N(G)monomethyl arginine (L-NMMA; 1 mg/kg infusion over 10 minutes) was used in a subset of patients (n = 6) to competitively inhibit endothelial NO synthase.

RESULTS

Nineteen subjects were enrolled. The median age of the SVGs was 34.6 (21.0-49.7) months. SVG flow-mediated, endothelium-dependent vasodilation was measured at 5.28% +/- 3.1% mean change in lumen diameter (range, 1.99%-9.36%; P < .0001 for diameter change). Nitroglycerin-mediated vasodilation was 3.7% +/- 1.0%, (range, 16%-10.04%; P < .005). Intravenous administration of L-NMMA abolished SVG FMD (5.7 +/- 1.4% before L-NMMA vs 0.01 +/- 0.01% during L-NMMA infusion; P = .0088) and attenuated brachial artery FMD (7.54% +/- 1.0% vs 5.7 +/- 1.4; P = .05).

CONCLUSION

SVGs manifest flow-mediated, endothelium-dependent, and nitroglycerin-mediated endothelium-independent vasodilation. Vein graft endothelium-dependent FMD is likely mediated by NO. Further investigation will be required to determine the role of endothelial function in vein graft patency.

Arterialization of a vein graft promotes cell cycle progression through Akt and p38 mitogen-activated protein kinase pathways: impact of the preparation procedure

BACKGROUND

Vein arterialization following bypass surgery often leads to graft occlusion, but the underlying cellular mechanisms have been poorly studied.

OBJECTIVES

Cell cycle progression and the activation of proliferation signalling were compared in arterialized grafts prepared either according to the conventional procedure or using pharmacological relaxation with the native vein.

METHODS

Using the porcine carotid-jugular bilateral interposition graft model on one side, a segment of porcine jugular vein was prepared for grafting using the conventional procedure, with pressure distention at 300 mmHg; the segment grafted on the other side was treated with a combination of pharmacological vasodilators. Both veins were grafted into the carotid artery for two weeks.

RESULTS

On the immunolabelling of proliferation cell nuclear antigen, a greater number of proliferating cells was found in the conventionally prepared grafts compared with pharmacologically prepared grafts. Cyclin D1 expression and phosphorylation of retinoblastoma increased after implantation, coinciding with nuclear accumulation of beta-catenin, activation of the Akt and mitogen-activated protein kinase cascades, and upregulated phosphatase and tensin homologue phosphorylation. Replacement of distention with pharmacological relaxation reduced the increase in cyclin D1 expression, phosphorylation of retinoblastoma, Akt-Thr(308), glycogen synthase kinase 3 beta and p38, but not extracellular signal-regulated kinases. This technique preserved the active phosphatase and tensin homologue, as well as the expression of cyclin-dependent kinase inhibitor p21(Cip1), while elevating the expression of p27(Kip1).

CONCLUSIONS

It was concluded that two-week arterial implantation stimulates proliferation signalling and promotes the cell cycle in vein grafts. Replacement of the conventional preparation procedures with pharmacological vasorelaxation restricts the activation of proliferation and cell cycle progression, and can be beneficial for improving vein graft patency.