Subintimal obliterative proliferation in saphenous vein grafts. A cause of early failure of aorta-to-coronary artery bypass graft

Arginine vasopressin enhances sympathetic constriction through the V1 vasopressin receptor in human saphenous vein

BACKGROUND

Arginine vasopressin (AVP) not only acts directly on blood vessels through V1 receptor stimulation but also may modulate adrenergic-mediated responses in animal experiments in vivo and in vitro. The aim of the present study was to investigate whether AVP can contribute to an abnormal adrenergic constrictor response of human saphenous veins.

METHODS AND RESULTS

Saphenous vein rings were obtained from 32 patients undergoing coronary artery bypass surgery. The vein rings were suspended in organ bath chambers for isometric recording of tension. AVP (3x10[-9] mol/L) enhanced the contractions elicited by electrical field stimulation at 1, 2, and 4 Hz (by 80%, 70%, and 60%, respectively) and produced a leftward shift of the concentration-response curve to norepinephrine (half-maximal effective concentration decreased from 6.87x10[-7] to 1.04x10[-7] mol/L; P<.05). The V1 vasopressin receptor antagonist d(CH2)5Tyr(Me)AVP (10[-6] mol/L) prevented the potentiation evoked by AVP. The selective V1 receptor agonist [Phe,2 Orn8]-vasotocin (3x[-10]-9 mol/L) induced potentiation of electrical stimulation-evoked responses, which was also inhibited in the presence of the V1 receptor antagonist (10[-6] mol/L). In contrast, the V2 receptor agonist desmopressin (10[-9] to 10[-7] mol/L) did not modify neurogenic responses, and the V2 receptor antagonist [d(CH2)5, D-Ile,2 Ile,4 Arg8]-vasopressin (10[-8] to 10[-6] mol/L) did not prevent the potentiation induced by AVP. The dihydropyridine calcium antagonist nifedipine (10[-6] mol/L) did not affect the potentiating effect of AVP.

CONCLUSIONS

The results suggest that low concentrations of AVP facilitate sympathetic neurotransmission and potentiate constrictor effects of norepinephrine in human saphenous veins. These effects appear to be mediated by V1 receptor stimulation and are independent of calcium entry through dihydropyridine calcium channels. Thus, AVP may contribute to vascular mechanisms involved in acute ischemic syndromes associated with venous grafts, particularly if the sympathetic nervous system is activated.

State of the vein grafts, native coronary arteries, and myocardium and principal cause of death in patients dying after aortocoronary bypass grafting

Fifty five patients with 108 coronary bypass saphenous vein grafts were studied at necropsy. The mean duration of the grafts was 153 days (SD 516). The luminal narrowing of the native coronary arteries proximal to, at, and distal to the vein graft anastomoses and the narrowing of the non-grafted arteries were evaluated planimetrically. Twenty nine per cent of coronary arteries distal to graft anastomoses showed at least 76% narrowing and 50-75% occlusion was seen in 39% of such arteries. Fifty three per cent of non-grafted arteries showed at least 76% luminal narrowing and 26% had 50-75% narrowing. Six patients (11%) had surgically induced dissection of coronary arteries. Seventy seven vein grafts (71%) showed no appreciable luminal narrowing. Problems related to operative technique caused 30% of the deaths.

Use of saphenous vein allografts for aortopulmonary artery anastomoses in neonates with complex cyanotic congenital heart disease

A saphenous vein allograft was used to create an aortopulmonary communication in 16 infants with cyanotic congenital heart disease and ductus-dependent pulmonary blood flow. These grafts measured from 3 to 8 mm in diameter and were placed between the aorta and main pulmonary artery in eight patients, between aorta and right pulmonary artery in eight, and between aorta and left pulmonary artery in one (one child had two grafts). Before heparin was used, early in the series, four of these grafts occluded and three of the four infants died during attempted revision. Another infant died early from renal failure. Late mortality has claimed four: one from cerebral hemorrhage, two from hypoxia, and one at open-heart surgery for repair. There are eight late survivors (50%). Most of the allografts were used before small diameter Gore-Tex was available; in more recent patients, 4- to 6-mm Gore-Tex grafts have been used. In our most recent patient, however, the attempt to place a Gore-Tex graft was unsuccessful, but the more pliable saphenous vein graft was readily placed and an adequate shunt obtained. Both the saphenous vein graft and the Gore-Tex have the advantage of providing pulmonary flow without the higher risk of congestive failure or pulmonary hypertension seen in patients with a Waterston or Potts anastomosis. They are easier to perform, require less anesthesia time than the Blalock-Taussig shunt, last as long as the Blalock-Taussig when done under similar conditions, and are easy to take down at the time of total repair.

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.

Status of the grafts and the native coronary arteries proximal and distal to coronary anastomotic sites of aortocoronary bypass grafts

The status of the native coronary arteries at necropsy in the vicinity of the coronary anastomoses of saphenous vein aortocoronary bypass grafts in 20 patients with severe coronary heart disease is presented. Of the 37 graft systems (graft plus coronary artery into which graft inserted) analyzed, the lumina of 44% of the native coronary arteries within the first 2 cm distal to the anastomoses were greater than 75% narrowed in cross-sectional area by atherosclerotic plaques, and the native coronary artery at the site of the anastomosis was greater than 50% narrowed in cross-sectional area already by atheroclerotic plaque in 25% of the graft systems. The mean coronary arterial size distal to the site of the coronary graft anastomosis, even after correction for heart weight, was greater in the 13 men than in the seven women. The residual luminal areas squared per gram of heart weight, however, were similar in both men and women. These results suggest that 1) relative coronary vessel size is greater in men than women; 2) the luminal area squared per gram myocardial mass (a relative estimation of flow) is the same in the two groups of patients; and 3) less atherosclerotic plaque is necessary in women then in men to produce similar limitation to coronary flow. Thus, vessel size alone cannot account for the higher reported frequency of unsuccessful aortocoronary bypass procedures in women.

Aortocoronary bypass graft in dogs: late histological changes

Late histological changes occurring in aortocoronary bypass vein grafts were studied by lignt and electron microscopy in three dogs killed one, two and three years after grafting. The changes consisted of intimal thickening due to a proliferation of modified smooth muscle cells (myointimal hyperplasia) and replacement of most of the medial smooth muscle by fibrocytes. Serial angiography in the dogs did not reveal progression of the intimal thickening after one month.

The structural study of the saphenous vein

From November, 1971, to September, 1974, 1,179 patients received aortocoronary saphenous vein bypass grafts at the Cleveland Clinic Hospital. Segments of saphenous vein from each patient were sent for microscopical analysis. These vein segments were classified as normal or abnormal (phlebosclerotic). Four hundred ninety-six normal vein grafts in 295 patients were restudied and had a patency of 87.9%. One hundred forty-four abnormal vein grafts in 86 patients were restudied and showed 89.5% patency. This study suggests that histopathological identification of an abnormal (phlebosclerotic) vein segment does not constitute a determining factor as far as late patency is concerned in a vein segment that is not grossly sclerotic.

Intimal hyperplasia. A cause of radial artery aortocoronary bypass graft failure

Autogenous radial artery grafts have been advocated for those situations in which adequate saphenous vein is not available for aortocoronary bypass procedures. It was anticipated that autogenous artery would demonstrate less predilection to develop the intimal proliferative changes seen with vein grafts in the arterial system. Early clinical experience with 79 patients receiving one or more radial artery grafts has shown that the radial artery is not spared occlusive intimal proliferative changes. Although early restudy of 6 patients was encouraging, late restudy in 29 patients showed 22 of 34 radial artery grafts (64.7%) to be unsatisfactory. Recovered grafts from 3 patients who required a second operation revealed severe generalized intimal hyperplasia. On the basis of this experience we no longer consider the radial artery an alternative conduit for aortocoronary bypass.

Internal mammary artery versus autogenous vein for coronary artery bypass graft

Aortocoronary venous graft (ACVG) and internal mammary artery graft (IMAG) are currently the two most popular choices for coronary artery bypass. The morphologic alteration and susceptibility to atheromatous degeneration of the IMAG were compared with the ACVG. Six of 12 surviving dogs with IMAGs were fed a hyperlipidemic diet and six were placed on a regular diet. All dogs were sacrificed 3-15 months after surgery. Twelve of 28 long-term surviving dogs with ACVGs were also on hyperlipidemic diets, and all were sacrificed 3-18 months after surgery. Arteriography and electron microscopy were performed in selected cases, and histology was performed in all cases. All long-term IMAGs remained patent; 83 percent (5/6) "regular" diet arteries were normal, with no intimal proliferation, while 33 percent (2/6) "hyperlipidemic" IMAGs had diffuse atheroma. Eighty-two percent of ACVGs revealed significant atherosclerosis. Severity of arteriosclerotic involvement of the ACVG was far greater than that of the native coronary circulation; this was not true for the IMAG.

It may be concluded that (1) in the normolipidemic condition the IMAG undergoes significantly less severe histologic change than the ACVG, (2) both the IMAG and the ACVG are more susceptible to atheromatous change than the native coronary circulation. In these series, patency was not influenced by severity of histologic changes, and no grafts were occluded by virtue of the arteriosclerotic process.

Biologic fate of autogenous vein implants as arterial substitutes: clinical, angiographic and histopathologic observations in femoro-popliteal operations for atherosclerosis

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New surgical approaches to coronary heart disease

Coronary heart disease is now the principal cause of death in the Western world. In recent years a new surgical approach to the problem has been developed with encouraging results. The operation of aorto-coronary bypass grafting with autogenous vein relieves angina in the majority of patients. Whether or not the long term prognosis is improved is not yet known. A European multi-centre controlled trial has been organised to answer this question.