Role of procurement-related injury in early saphenous vein graft failure after coronary artery bypass surgery

Antegrade cardioplegia as a possible cause of acute saphenous vein endothelial damage in patients undergoing on pump coronary artery bypass surgery

Background

The administration of antegrade cardioplegia through vein grafts after the completion of each distal anastomosis is a common practice. However, the cardioplegic solution may disrupt the vein endothelium and contribute to late vein graft atherosclerotic disease. This study aimed at evaluating the possible impact of the cardioplegic solution on vein graft endothelium.

Methods

Total of 52 patients (16 women and 36 men) aged 68±8.5 years old that underwent on pump coronary revascularization with at least one vein graft were enrolled. Sections of grafts from the greater saphenous vein were obtained prior to and after delivery of potassium antegrade cardioplegic solution through them. These sections were then examined histologically with immunochemical stain and CD34 index. The endothelial damage and length of vein specimens of both graft sections were evaluated.

Results

The endothelial damage of vein specimens appeared to be increased significantly with exposure to antegrade cardioplegia in male and female patients (P from Wilcoxon tests <0.001, for both genders). The increase in the length of vein specimens was significant too (P from Wilcoxon test <0.001 for men and P=0.001 for women).

Conclusions

Antegrade cardioplegia delivered through vein grafts causes substantial damage on vein endothelium. This may have an adverse effect on long-term graft patency.

Traditional graft preparation decreases physiologic responses, diminishes viscoelasticity, and reduces cellular viability of the conduit: A porcine saphenous vein model

Traditional methods of intraoperative human saphenous vein preparation for use as bypass grafts can be deleterious to the conduit. The purpose of this study was to characterize acute graft preparation injury, and to mitigate this harm via an improved preparation technique. Porcine saphenous veins were surgically harvested (unprepared controls, UnP) and prepared using traditional (TraP) and improved preparations (ImP). The TraP used unregulated radial distension, marking with a surgical skin marker and preservation in heparinized normal saline. ImP used pressure-regulated distension, brilliant blue FCF-based pen marking and preservation in heparinized Plasma-Lyte A. Rings from each preparation were suspended in a muscle bath for characterization of physiologic responses to vasoactive agents and viscoelasticity. Cellular viability was assessed using the methyl thiazolyl tetrazolium (MTT) assay and the terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay for apoptosis. Contractile responses to potassium chloride (110 mM) and phenylephrine (10 µM), and endothelial-dependent and independent vasodilatory responses to carbachol (0.5 µM) and sodium nitroprusside (1 µM), respectively, were decreased in TraP tissues compared to both UnP and ImP tissues (p ⩽ 0.05). TraP tissues demonstrated diminished viscoelasticity relative to UnP and ImP tissues (p ⩽ 0.05), and reduced cellular viability relative to UnP control (p ⩽ 0.01) by the MTT assay. On the TUNEL assay, TraP tissues demonstrated a greater degree of apoptosis relative to UnP and ImP tissues (p ⩽ 0.01). In conclusion, an improved preparation technique prevents vascular graft smooth muscle and endothelial injury observed in tissues prepared using a traditional approach.

Incidence of residual clot strands in saphenous vein grafts after endoscopic harvest

OBJECTIVE

: Strands of clot are frequently flushed out of saphenous vein grafts (SVG) during preparation for grafting, particularly those that are endoscopically harvested. However, saline distention at uncontrolled pressures increases graft thrombogenicity and the risk of early failure after coronary artery bypass grafting. The purpose of this prospective investigation was to define the incidence of intraluminal clot within endoscopically harvested SVG and the effect of attempted removal by saline distention.

METHODS

: Endoscopically harvested SVG were intraoperatively prepared for grafting by using saline distention at uncontrolled pressure (n = 24) or without distension (n = 20). Optical coherence tomography, a catheter-based infrared imaging system, was used to identify and characterize intraluminal clot strands in surplus SVG segments (average length for analysis, 4.9 ± 2.6 cm). These segments were also assessed for luminal tissue factor activity and percent endothelial integrity by CD31-directed immunohistochemistry.

RESULTS

: Clot strands were observed in 45.4% (20 of 44) of imaged SVG segments (severity of observed clots: 54%, mild; 32%, moderate; 14%, severe). Compared with grafts distended with saline, vein segments that were not distended displayed significantly higher endothelial integrity (60.1% ± 27.2% versus 24.7% ± 24.1%, P < 0.05) and lower tissue factor activity (1.28 ± 0.95 versus12.3 ± 5.5 U/cm, P < 0.001) despite having a higher incidence of clot stands (65.0% versus 29.1%, P < 0.02, Fisher exact test). Static flow was observed in veins during endoscopic harvest.

CONCLUSIONS

: Clot strands of varying severity are a common finding after endoscopic vein harvest. Saline distention is not completely effective in removing clot strands and increases overall graft thrombogenicity. Therefore, prevention of clot or less traumatic methods of removing clot are indicated.