Histologic changes in saphenous vein aorta-coronary bypass grafts

Endothelial nitric oxide synthase (eNOS) mediates neointimal thickness in arteriovenous fistulae with different anastomotic angles in rats

BACKGROUND

It is known that the anastomotic angle can influence neointimal hyperplasia and patency in arteriovenous fistulae (AVF). Endothelial nitric oxide synthase (eNOS) is released from the vascular endothelium and can inhibit neointimal hyperplasia. Therefore, here, we aimed to test the hypothesis that the manipulation of eNOS expression could influence neointimal thickness in a rat AVF model with different anastomosis angles.

METHODS

Rat carotid artery (inflow, CA) and jugular vein (outflow, JV) AVF were created with acute, blunt, or end-to-end (ETE) anastomosis angles. Aspirin was used to increase eNOS expression in the acute angle group, while N(G)-nitro-L-arginine methyl ester (L-name) was used to decrease eNOS expression in the obtuse angle group. The rats were sacrificed on day 21, and tissues were harvested and analyzed histologically and with immunostaining.

RESULTS

A larger anastomosis diameter (p < 0.016) and smaller neointimal area (p < 0.01) were observed in the obtuse and end-to-end (ETE) groups compared to in the acute group. In the acute angle group, there were more proliferating cell nuclear antigen (PCNA) and α-actin dual-positive cells (p < 0.0001) and fewer phospho (p)-eNOS-positive endothelial cells (p < 0.0001) in the neointima than in the obtuse and ETE angle groups. On treating the acute angle and blunt angle groups with aspirin and L-name, respectively, no significant differences in the neointima/lumen rate were observed (p = 0.6526) between the groups; however, there were fewer von Willebrand factor (vWF) and p-eNOS dual-positive cells in the obtuse angle group treated with L-name (p = 0.0045).

CONCLUSIONS

We demonstrated that eNOS plays an important role in neointimal hyperplasia in AVF with different anastomosis angles; further, eNOS could potentially be used as a therapeutic target in patients with AVF in the future.

Improving Patency of Coronary Conduits "Valveless" Veins and/or Arterial Grafts

BACKGROUND

Veins used for coronary artery bypass operation have a well-documented limited long-term patency. Internal thoracic artery (ITA) grafts have shown exceptional "durability." Assumptions were made that other arterial conduits have similar characteristics.

AIM OF THE STUDY

The purpose of this article is to compare different conduits long-term patency including saphenous veins to other available arterial conduits: inferior epigastric artery (IE), right gastroepiploic artery (RGEA), and radial artery (RA).

METHODS

Recent studies have shown that radial artery bypasses have lower patency rate than saphenous veins. Flow patterns, physiological flow characteristics are reviewed including native vessel disease and area of myocardium supplied. In the case of venous bypasses, the primary culprit of failure seemed to be the quality of the vein itself and the reverse venous valves in the conduit resulting in: (a) trapping-hypertension, (b) thrombosis, (c) turbulence, (d) intimal damage, (e) mismatching in size.

RESULTS

Clinical follow-up of our patients up to 8 to 11 years (average 8.9 years) have proved the superior characteristics of the so-called "good veins." In a retrospective study of 436 patients sequential, valveless veins patency was 88.6% versus 72% of reversed valvular segments (p < 0.01). Patients' survival seemed to be significantly improved if these veins were combined with ITA grafts. Patients' survival with one valveless limb HS + ITA was 78% versus HS + SV 52% (p < or = 0.0017) and HS + ITA versus HS + ITA + SV (p < 0.0057).

CONCLUSION

Selective decision-making of the surgeon at the time of the operation is required to choose the best conduit to be able to perform the best operation with the best long-term result.

CorLink™ sutureless aortic anastomotic device: results of an animal study

BACKGROUND

The CorLink Automated Anastomotic Device (AD) was developed to create a sutureless vein-to-aorta anastomosis without the need to clamp the aorta. This study examined the effectiveness and safety of this device in an animal model.

MATERIALS AND METHODS

Forty-seven vein-to-aorta anastomoses using the AD and 27 control hand-sutured anastomoses were constructed in 28 sheep. The distal part of these grafts were connected either to the main pulmonary artery (40 AD, 20 control), or to the sheep's brachiocephalic trunk (7 AD, 7 control). Procedural details focusing on deployment, leakage, and early patency rates were examined. Sheep were sacrificed after periods ranging from 1 to 180 days. Specimens were examined grossly and histologically.

RESULTS

All but three attempts to construct an anastomosis were successful (2 AD, 1 control). All anastomoses were patent immediately after their construction. There was no difference between control and AD anastomoses in respect to flow rates at the end of operation and before sacrifice. No metal breaks were detected. Fourteen of the 47 AD anastomoses and 6 of the control anastomoses (29.8% versus 22.2% P = ns) were occluded at autopsy. Histological findings characteristic of the healing process, were evenly distributed between AD and control anastomoses in both models. Intimal thickening was found in a notable number of anastomoses, but without any significant difference between the AD and control sutured (44.7% versus 40.7% P = ns).

CONCLUSIONS

The AD proved safe and effective for the construction of proximal vein-to-aorta anastomoses as compared to control hand-sutured anastomoses.

Myointimal hyperplasia: pathogenesis and implications. 2. Animal injury models and mechanical factors

Arterial wall injury either by balloon catheter, drying, or scraping results in a denudation of endothelial cells (EC) and a subsequent proliferation of smooth-muscle cells (SMC). The degree of SMC proliferation appears to be dependent on the degree of initial injury and not to the loss of the overlying endothelium. Successful reendothelialization of denuded areas depends on the size of the denuded segment as well as SMC-EC interactions. Prolonged exposure of SMC to serum substances results in inhibition of EC regrowth, the production of prostacyclin by SMC, and the development of a thromboresistant surface. Heparin appears to inhibit SMC proliferation in vivo (as well as in vitro), an effect that is independent of platelet SMC interaction. EC-derived heparin in vivo may also result in inhibition of SMC proliferation. Platelets may play an important role in the early response to arterial injury and development of myointimal hyperplasia (MIH), but their long-term role appears to be minor. Antiplatelet agents have widely varying species-dependent effects on platelets and platelet-vessel wall interactions, but in specific circumstances they may inhibit MIH. The precise role of steroid drugs and immunosuppression on MIH in arterial injury models awaits further study. The role of lipoproteins in MIH is unclear; however, the inhibition of MIH by omega-3 fatty acids in vivo as well as their inhibition of platelet-derived growth factor production by EC in vitro implies a regulatory role. Acute hypertension results in a marked proliferation of EC and SMC in vivo and enhances the proliferative response to injury as well. Low wall shear stress, turbulence, and boundary layer separation all increase EC turnover, a likely influence on EC growth factor production. The compliance mismatch resulting from graft-artery anastomoses, injury, and endarterectomy results in locally increased cyclical stretch, which may predispose to SMC proliferation.

Intimal thickenings of jugular veins after application of a stimulus known to be sclerogenic in arteries

The present study examined the intimal reactions of rabbit jugular veins to a stimulus known to elicit arteriosclerotic alteration in the artery wall. Repeated transmural electrical stimulation was applied to external jugular veins of both normo- and hypercholesterolaemic rabbits. Endothelial permeability, as well as changes in intimal architecture, were investigated by electron microscopy. Initially, the veins responded to electrical stimulation with an increased transendothelial transport of horseradish peroxidase (40,000 daltons). After application of the stimulation program for 4 weeks, intimal fibrous thickening (33%), cellular fibrous proliferation (50%), and organized mural thrombi were observed. The fibrous thickening was characterized by an abundance of connective tissue matrix and paucity of subendothelial cells. The cellular fibrous proliferate predominantly consisted of myocytes with few interspersed monocytes/macrophages and granulocytes. It resembled intimal plaques induced in carotid arteries by the same method. However, the venous thickenings showed limited size and a more pronounced fibrous response when compared with the arteriosclerotic lesions. The morphological similarities between the observed venous intimal thickenings and the different types of phlebosclerotic manifestations described in the literature, especially intimal proliferations in vein grafts, render the model of electrical stimulation suitable for the elucidation of underlying pathogenic mechanisms.

Extrinsic arterial supply of the great saphenous vein: an anatomic study

The extrinsic arterial supply to the great saphenous vein was studied by dissection following latex injection, diaphanisation and contrast roentgenograms. Arterial supply arises from the external pudendal, superficial femoral, superior genicular and posterior tibial arteries. These branches ensure the irrigation of the vasa vasorum. The role they play in the outcome of bypass with the great saphenous vein is a further argument pleading in favor of the in situ technique.

Morphologic changes in long-term saphenous vein bypass grafts

A retrospective autopsy study was performed in 56 patients who had undergone saphenous vein bypass graft (SVBG) surgery 12 to 168 months prior to death. Twenty-five grafts had atherosclerosis, 66 grafts had fibrointimal proliferation, and 26 grafts were fibrotic with total occlusion. No significant differences were noted among the three morphologic groups with regard to age of the patient or number of native coronary arteries severely narrowed. Vein grafts with fibrointimal proliferation occurred with greater frequency in patients with systemic hypertension (p less than 0.001), and atherosclerotic grafts were more prevalent in patients with hypercholesterolemia (p less than 0.02). Therefore, the presence of risk factors may determine the type of change that occurs in saphenous vein bypass grafts: systemic hypertension leads to fibrointimal proliferation, whereas hypercholesterolemia leads to atherosclerotic change.

Ruptured atheromatous plaques in saphenous vein coronary artery bypass grafts: a mechanism of acute, thrombotic, late graft occlusion

Although early occlusion of saphenous vein coronary artery bypass grafts is usually thrombotic, late occlusion is most often a result of progressive intimal fibromuscular proliferation or atheroma formation in the implanted vain. We describe another mechanism of late graft occlusion: atheromatous plaque rupture with superimposed occlusive thrombosis. Four men, ages 48-67 years underwent repeat bypass surgery for recurrent angina. Six of eight vein grafts excised 5-8 years after original bypass showed complete luminal occlusion by recent thrombus superimposed on ruptured atheromatous plaques. Similar findings were present at autopsy in two of three vein grafts from a 66-year-old man who died 7 years after bypass. These lesions are indistinguishable from those that occur in native coronary arteries of many patients with acute myocardial infarction. Unlike previously described graft occlusions, the present lesion represents a mechanism of acute, thrombotic, late graft occlusion. If recognized early, it may be amenable to nonsurgical intervention by angioplasty or thrombolysis.

Changes in saphenous veins used as aortocoronary bypass grafts

This report describes morphologic changes in saphenous veins used as aortocoronary bypass conduits, and discusses the relative contribution of various factors to these changes. The three primary changes are: (1) medial fibrous replacement, (2) adventitial fibrous proliferation, and (3) intimal fibrous proliferation. Medial fibrous replacement is caused by vein wall ischemia with loss of smooth muscle cells; adventitial fibrous proliferation is the result of organization of fibrin deposits and repair of ischemic injury; and intimal fibrous proliferation results from some stimulus, probably fibrin deposition on injured intima, which causes stimulation of smooth muscle cells to become fibroblasts or "myointimal cells". Although all grafts show some changes, the degree and severity of these three changes is variable along the length of the grafts and among separate grafts in the same patient.