Alteration of reactivity of native arteries induced by venous graft placement.

Occlusion of aortocoronary venous grafts can be due to thrombosis, atherosclerosis, or vasospasm. Investigations have focused on properties of the graft itself, and little is known about the vascular reactivity and function of the native arteries proximal and distal to the vein graft, although spasm of the native artery distal to the graft site has been observed in patients. We hypothesized that the function of the endothelium of the native arteries may be altered after surgery. Autogenous venous grafts were placed in femoral arteries of rabbits to study the reactivity of the native arteries after grafting. Four weeks after graft implantation, the vein graft, ipsilateral vein, and native artery proximal and distal to the graft were removed for in vitro studies. Morphological evaluation by scanning electron microscopy and fluorescence microscopy after labeling with acetylated low density lipoprotein labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate indicated the presence of an intact, metabolically active endothelial layer. There was no alteration in the contractile responses to phenylephrine of the arteries, vein grafts, or veins. Precontracted vein grafts, veins, and arterial segments proximal to the grafts relaxed when exposed to endothelium-dependent vasodilators (acetylcholine, arachidonic acid, and substance P), but the native arteries distal to the grafts did not. In bioassay cascade experiments, the distal artery did not release any measurable relaxing factor when exposed to acetylcholine. We conclude that the endothelium of the distal artery did not function normally. The extent and reversibility of altered endothelial function remain to be determined. This observation may help to explain the occurrence of myocardial infarction after aortocoronary bypass grafting in some patients.

Removal of venous endothelium with air.

Much research on the activity and half-life of endothelium-derived substances has entailed the removal of endothelium from arteries by mechanical or enzymatic processes. It has been observed that the technique used for the removal of arterial endothelium may profoundly affect smooth muscle function and release of prostanoids by the vessel wall. The function and patterns of regeneration of arterial endothelium have been extensively described, but there is a relative paucity of information about the venous endothelium, due in part to the difficulty of its removal. We developed a technique for removal of the endothelium of rabbit femoral veins by passing a stream of air through the lumen of the vessel to dry and remove the endothelium. The effectiveness of endothelium removal was verified by the lack of in vitro reactivity to endothelium-dependent relaxing substances, examination of frozen sections of vessels, labeled with fluorescent-tagged acetylated low-density lipoprotein, with fluorescent light microscopy and scanning electron microscopy of vessel segments. Air drying effectively removed the endothelium and abolished mechanical responses to endothelium-dependent vasodilators but did not affect the function of the smooth muscle. We propose the use of air to remove endothelium from veins to be used to study endothelium-derived factors since this method achieves complete removal of endothelium without causing detectable damage (morphological or functional) to the remainder of the vessel wall.

The de-endothelialized rat carotid arterial graft: a versatile experimental model for the investigation of arterial thrombosis.

A novel model of arterial thrombosis was developed. A mechanical endothelium-denuding injury was created (using a scalpel blade) on harvested, freezer-stored rat carotid arteries. Vessel length of 5 mm. were grafted into the femoral arteries of recipient Sprague-Dawley rats using microvascular anastomotic technique. Patency rates in untreated animals were compared with those in animals receiving systemic aspirin or heparin. The control group patency after 2 hours of flow was 15%, while grafts in aspirin- and heparin-treated animals achieved 35% and 95% patency rates, respectively. Uninjured non-frozen carotid grafts in untreated animals yielded a 95% patency rate, while frozen grafts achieved an 80% patency. Therapeutic levels of aspirin, heparin, and urokinase were confirmed through tail bleeding and whole blood clotting tests, as well as platelet aggregation studies and scanning electron microscopy of the graft lumenal surfaces. A long-term series using syngeneic grafts placed in recipients (Lewis-to-Lewis) and employing systemic heparinization demonstrated maintenance of patency for 4 weeks. Scanning electron microscopy revealed good re-endothelialization, well advanced by one week. Histology confirmed the regrowth of endothelial cells, but showed sparse cellular repopulation of medial and adventitial layers. The mechanical injury model was compared to enzymatic de-endothelialization (using trypsin or collagenase), for which patency rates were similar (10% and 0%, respectively). Trypsin de-endothelialized vessels were tested in vitro for the amount of active trypsin remaining bound to the lumenal surface; no detectable activity was found when trypsin inhibitor was applied following trypsin treatment. The versatility of allowing both in vitro evaluation and in vivo patency assessment demonstrates the uniqueness and value of this new model, offering an avenue toward more direct investigations of surface-mediated thrombotic processes.

Free flap transfer of the cutaneous maximus muscle in the rat: comparison to the latissimus dorsi muscle flap.

A new rat model of free muscle flap transfer is presented. Microvascular transplantation of the cutaneous maximus muscle flap is performed at the groin site, with anastomosis of the axillary vessels to the appropriate femoral vessels. This muscle flap has many useful attributes for experimental manipulation. It has a high success rate following transplantation, the anatomy is consistent, the dissection is straightforward, the length of pedicle is relatively long (10 mm), the vessels for repair are of sufficient size (1.0-1.35 mm diameter), and the microsurgical procedure can be performed in a relatively short period. The donor site deficit causes minimal impairment to animal mobility, and no evidence of limb ischemia is noted after ligation of the axillary vessels. The cutaneous area adjacent to the muscle is perfused by muscular perforators supplied by the flap pedicle; thus a skin island may be used to monitor the flap or to create a composite myocutaneous transfer. The cutaneous maximus muscle has mixed muscle types and anatomic dimensions similar to those of the latissimus dorsi muscle, and it provides ample tissue for pharmacological and biochemical studies, yet it presents easier dissection and microanastomoses than the latissimus flap, with more potential for versatility in application. The advantages of this muscle flap make it a very useful experimental model for flap transfer research.

A survey of microsurgery training in the United States.

The increasing use of clinical and experimental microsurgical techniques has created a need for standardized, high-quality training programs in microsurgery. Toward this end, we conducted a study of the microsurgery instruction available in the United States. The data were collected from responses to surveys mailed to 55 microsurgery training centers across the country. Survey questions asked for a general characterization of each training program and its participants and for a specific description of course content. The results indicated that, even though training programs differed considerably, there were common elements. Total course length ranged from less than 40 hours to 80 hours, with a range of 32-40 hours devoted to basic microsurgery techniques. Forty percent of instructional programs were not certified for continuing medical education (CME) credit. Half of all reported trainees were residents in training. The basic microsurgery techniques common to most programs included instruction in microvascular end-to-end and end-to-side anastomoses of femoral arteries and veins in rats. Instruction in peripheral nerve repair was not offered. We conclude that, although there are merits to a diverse curriculum, it is time to institute a minimum level of standardized basic microsurgery training.

The incredible T vein graft: developing increased microsurgical skill through a competitive student exercise.

We developed an exercise to encourage microsurgery students to practice technically difficult procedures. The incredible T exercise uses the contralateral femoral vein of the rat as an interpositional graft into the femoral vein and the inferior epigastric vein as an end-to-side anastomosis into the graft. The technically difficult procedure requires students to practice and improve their surgical technique, thereby gaining skill and self-confidence. Friendly competition helps to make the learning process more enjoyable.