Jonathan E. Hasson

Effect of compliance mismatch on vascular graft patency

The hypothesis that a mismatch in compliance between a vascular graft and its host artery is detrimental to graft patency was tested by implanting paired arterial autografts, prepared with differential glutaraldehyde fixation of carotid arteries in the femoral arteries of dogs. These grafts differed only in circumferential compliance: they were 100% (compliant) vs. 40% (stiff) as compliant as the host artery. Their flow surfaces were equivalent, as determined by physicochemical measurements and scanning electron microscopy; both lacked viable cells, as determined by in vitro cell culture. In 14 dogs, eight stiff and two compliant grafts became occluded within 3 months, the latter doing so within 24 hours after their contralateral counterparts. Cumulative patencies were 85% and 37% for compliant and stiff grafts, respectively (p less than 0.05) and 100% and 43%, excluding the two dogs with bilateral graft failures (p less than 0.01). We conclude that even with near optimal flow surfaces, compliance mismatch is deleterious to graft patency.

Increased compliance near vascular anastomoses

Mismatch in mechanical properties (compliance mismatch) between host artery and prosthetic graft has been suggested as a cause of graft failure, but no mechanism linking the two has been identified. With the use of a simplified model based on isocompliant arterial grafts, pulsed ultrasound was used to generate detailed longitudinal profiles of diameter and compliance near the anastomoses. These longitudinal profiles revealed that although arterial diameter decreases monotonically to a minimal level at an anastomosis, arterial compliance first increases by approximately 50% before decreasing to 60% of the control value. This para-anastomotic hypercompliant zone (PHZ) is centered 3.6 mm from the anastomosis. PHZ also occurs in the artery adjacent to compliant or stiff grafts and is probably caused by transmitted effects of the suture line on the arterial wall. PHZ adds to any mismatch in compliance that already exists between artery and graft and can produce a compliance mismatch even between an artery and a nominally isocompliant prosthetic graft. It is hypothesized that PHZ, a region of increased cyclic stretch, promotes subintimal hyperplasia near anastomoses and may thus be a link between the mechanical properties of arteries and the failure of bypass grafts.

Suture technique and para-anastomotic compliance***

We previously described a para-anastomotic hypercompliant zone (PHZ), located 3 to 4 mm from end-to-end continuous anastomoses in canine femoral arteries, in which arterial compliance first increases approximately 50% above adjacent reference values before falling to a minimum at the anastomosis. To determine if PHZ is affected by suture technique, 16 interrupted and 21 continuous end-to-end anastomoses were studied. Pulsed ultrasound was used to obtain detailed longitudinal profiles of compliance and diameter vs. distance, at 1 mm intervals within a 2 cm region centered at the anastomoses. Both compliance and diameter at the anastomosis were lower in continuous compared with interrupted anastomoses (p less than 0.003). The PHZ was present in 86% of continuous but in only 50% of interrupted anastomoses (p less than 0.03). The site of peak compliance averaged 3.8 +/- 1.2 mm from the anastomosis and was independent of suture technique. The increase in peak compliance at the PHZ, when normalized to adjacent references values, was the same in continuous and interrupted anastomoses. PHZ augments any preexisting compliance mismatch between artery and graft, which may contribute to the development of para-anastomotic subintimal hyperplasia. Interrupted anastomoses, which create a smaller compliance mismatch than do continuous and have a lower incidence of PHZ, may be preferred in certain settings.

Mural degeneration in the glutaraldehydetanned umbilical vein graft: Incidence and implications*

After discovering an aneurysm in a glutaraldehyde-tanned umbilical vein (GTUV) graft that resulted in graft thrombosis, we reevaluated all patients from our institution who had GTUV grafts implanted for more than 2 years. Of 60 patients identified, 14 of 15 patients with patent grafts were recalled and had either digital subtraction or standard angiographic studies. Angiographic changes in the grafts were graded on a scale of 0 to 3, from normal (grade 0) to frank aneurysmal degeneration (grade 3). Eight grafts (57%) had frank aneurysmal (grade 3) changes, and three other grafts (21%) had preaneurysmal (grade 2) changes. Only one graft was angiographically normal. GTUV grafts undergo aneurysmal degeneration in a significant percentage of implants. Symptomatic aneurysms have presented with thrombosis and limb-threatening ischemia as well as rupture. GTUV aneurysms should be treated by complete graft resection, as segmental resection of diseased portions of grafts resulted in metachronous aneurysm recurrence. Because of the high incidence of GTUV degeneration, the clinical indications for the use of GTUV grafts should be seriously reevaluated, and we recommend that all patients with patent GTUV grafts for more than 2 years be evaluated for the presence of aneurysmal degeneration.

The evolution of morphologic and biomechanical changes in reversed and in-situ vein grafts.

A comparative study of experimental reversed (RV) and in-situ (INS) vein grafts with respect to the evolution of morphologic and compliance characteristics was done in a canine model. In addition, the compliance characteristics in a series of human INS vein grafts were recorded as a function of time after operation. At 6 months after implantation, all experimental grafts displayed well-developed intimal hyperplasia. There was no significant difference in either absolute intimal thickness (INS 0.133 +/- 0.09 mm vs. RV 0.085 +/- 0.06 mm; NS) nor in the percentage of the total wall thickness occupied by the intima when experimental INS grafts were compared with RV grafts after 6 months. Similarly, compliance values of INS and RV vein grafts were similar at all time intervals examined up to 6 months after operation. Thirty-three human INS vein grafts had a mean compliance value of 1.74 +/- 0.72 (percent radial changes per mmHg X 10(-2) at a median postoperative interval of 14 weeks. This value did not differ significantly from those measured in the INS vein grafts. Although all vein grafts examined retained their native viscoelastic properties, this study suggests that functioning human INS vein grafts are less compliant than previously suspected on the basis of prior ex-vivo and clinical studies of RV saphenous vein grafts. The purported clinical superiority of the INS vein graft cannot be explained on the basis of superior biomechanical performance or failure to develop intimal hyperplasia.

Penetrating duodenal trauma.

Ten cases of penetrating injuries to the duodenum are presented. Six injuries were treated with primary repair, retrograde decompressing jejunostomy, and feeding jejunostomy. There was no postoperative duodenal leak in any patient treated with primary repair and retrograde decompressing jejunostomy. In a review of 563 cases of penetrating duodenal trauma, the superiority of primary repair of duodenal injuries with decompression of the suture line by a tube inserted in a remote site of the bowel (stomach or jejunum) was demonstrated. This technique afforded the lowest mortality and incidence of postoperative duodenal fistulae. When applicable, primary repair with retrograde decompressing jejunostomy and feeding jejunostomy is a rapid, simple, and safe method for the treatment of penetrating duodenal injuries.

Compliance changes in glutaraldehyde-treated arteries

Glutaraldehyde tanning of carotid arteries was used to develop a model for studying the effects of compliance on arterial graft performance, independent of other graft parameters. Canine carotid segments were filled with dilute phosphate-buffered glutaraldehyde (0-0.5%, pH 7.4), maintained at physiological pressure, and then immersed in either saline or 10.0% glutaraldehyde for up to 1 hr. After rinsing with saline, compliance was measured in vitro. All vessels which were immersed in 10% glutaraldehyde exhibited a significant reduction in compliance compared to native artery control [C = 11.8 +/- 1.3 (mean +/- SEM), % radial change/mm Hg X 10(-2), measured at 100 mm Hg], but maximum stiffness (C = 1.1 +/- 0.3) required that the lumen be specifically exposed to at least 0.025% glutaraldehyde in addition to simple immersion of the vessel segment in 10% fixative. Exposing the artery to 0.5% glutaraldehyde internally, without immersion of the entire structure, caused a decrease in compliance similar to that obtained after immersion in 10% glutaraldehyde, with only saline present in the lumen. Matched pairs of stiff and compliant grafts were generated by exposing the lumen to 0.025% glutaraldehyde and immersing the vessels in 10% fixative or saline, respectively. Light and scanning electron microscopy, internal reflection spectroscopy, and measurements of critical surface tension revealed nearly identical wall morphology and lumenal surface chemistry for these matched pairs. Differential tanning of the internal and external surfaces of carotid arteries thus provides a good model of arterial prostheses, wherein a substantial compliance mismatch can be studied without the complicating influences of varying diameter or differing flow surface properties.