SAHPENOUS VEIN VIABILITY: A COMPARATIVE STUDY BETWEEN TWO SURGICAL SPECIALTIES HARVESTING HUMAN SAPHENOUS VEIN WITH A PORCINE SAPHENOUS VEIN MODEL EMULATING INTRAOPERATIVE MECHANICAL STRESS.

BACKGROUND: The human long saphenous vein (HSV) is the autologous conduit used most commonly for coronary (CABG) and peripheral vascular (PV) reconstructions. In spite of the shorter length of conduit and higher flow in CABG, numerous reports suggest that patency rates are higher in PV. This study was performed to determine the viability of the smooth muscle in HSV harvested for CABG and PV between two surgical specialties. We further used porcine saphenous veins to assess the impact of radial and longitudinal stress to model intraoperative mechanical handling of HSV.
METHODS: Remnants of HSV were collected in University of Wisconsin (UW) preservation solution and stored at 4°C. Rings were cut to 1mm thickness, lengths and weights were measured before suspension in a muscle bath where they were equilibrated in bicarbonate solution at 37°C. HSV rings were then exposed to potassium chloride (KCl, 110mM) to depolarize and contract the vascular smooth muscle and the amount of force generated over basal force was determined (Δg). Force was converted to stress (N/m²) to adjust for varying lengths and weights. Porcine saphenous veins (PSV) were similarly preserved. These were divided into two groups; each group endured either radial or longitudinal stress. Prior to application of stressor, a portion of each individual vein was preserved as control. To determine if mechanical trauma alters tissue viability, PSV was subjected to radial stress via manual distension (>300 mm Hg). Longitudinal stress was applied by manual stretch method which involved taking a sample of vein, clamping the two ends and stretching the vein to 200% its original size. PSV rings were then similarly prepared for muscle bath suspension and KCl challenge to calculate force and stress.
RESULTS: HSV harvested for PV produced significantly greater force (3.75g ± 0.8566) than HSV harvested for CABG (0.8466g ± 0.1809, Figure 1). When adjusted for tissue mass and length, HSV harvested for PV (0.1192 10⁵ N/m² ± 0.02776) also produced significantly greater stress than HSV harvested for CABG (0.04198 10⁵ N/m² ± 0.008128, Figure 2). Manual distension did not alter the smooth muscle responses of PSV (Figure 3). Longitudinal stress significantly decreased the force of PSV (Figure 4).
CONCLUSIONS: These data suggest that longitudinal mechanical stress during harvest as seen with minimally invasive or endoscopic harvesting techniques may affect functional viability of HSV smooth muscle. Manual distension did not appear to affect PSV viability. Since injury is one of the inciting events leading to intimal hyperplasia, avoiding longitudinal stress during harvest and preparation may improve patency of arterial bypass using HSV.