Influence of phlebographic abnormalities on the natural history of venous ulceration

Eighty-five limbs in 73 patients with a healed venous ulcer were assessed by ascending and descending phlebography, foot volume plethysmography and transcutaneous oxygen measurements. Forty-four limbs had post-thrombotic changes on ascending phlebography. In 24 (28 per cent) these extended into the femoral vein, while in 20 (24 per cent) only the calf veins were involved. In the 41 limbs (48 per cent) with normal deep veins on ascending phlebography, 11 had evidence of localized incompetence of the calf communicating veins, 14 had either long saphenous incompetence, deep vein reflux to the level of the knee or below, or both of these abnormalities, and 16 limbs had no phlebographic abnormalities. However all limbs had a decreased half volume refilling time on foot volume plethysmography. Limbs with post-thrombotic changes extending into the femoral vein were associated with a significantly longer history of ulceration and more ulcer recurrences than limbs with calf vein damage (P less than 0.05 for each) and limbs with normal deep veins (P less than 0.01 for each). However, these limbs did not have lower transcutaneous oxygen ratios or longer times to achieve ulcer healing. Ascending phlebography identified a group of limbs with extensive post-thrombotic changes in which there was a higher incidence of ulcer breakdown, but this was not associated with a delay in ulcer healing.     

Changes in the apparently normal limb in unilateral venous ulceration

Forty-seven patients with unilateral venous ulceration have been investigated to determine if any abnormalities were present in the contralateral limbs which had not had lipodermatosclerosis or ulceration. Ascending phlebography in the non-ulcerated limbs showed post-thrombotic changes in 28 per cent and incompetent lower leg communicating veins in 19 per cent. This incidence was not significantly different to the limbs with healed ulceration (45 and 23 per cent respectively, chi 2 test, P = 0.10). Half volume refilling time measured by foot volumetry suggested that 79 per cent of the non-ulcerated limbs had evidence of deep vein incompetence or incompetent lower leg communicating veins, which was again similar to the incidence in the previously ulcerated limbs (85 per cent). Transcutaneous oxygen readings, expressed as a ratio of a reading at a standard site in the gaiter region of the leg over a reading from the upper arm, were significantly lower in non-ulcerated limbs (mean 0.84 +/- 0.26 s.d.) than in a cohort of age and sex matched controls (mean 1.02 +/- 0.14, Student's t test, P less than 0.001), and significantly higher than in previously ulcerated limbs (mean 0.68 +/- 0.31, P less than 0.01). Abnormalities in venous anatomy and function have been shown, in conjunction with evidence of reduced oxygen diffusion, through the gaiter skin before overt skin changes develop.     

A rational approach to surgery of the chronic venous statis syndrome.

Ambulatory venous pressure (AVP) and ascending and retro-grade phlebography have been used to elucidate the precise pathogenetic factors in cases of venous stasis. On the bases of this information, procedures aimed at the correction of the particular pathophysiological alterations were carried out. Fifty-two lower extremities in 49 patients suffering from chronic venous statis were studied. The AVP was performed by having the patient walk in place for 15 seconds without tourniquet and with one or two tourniquets at different levels of the extremity. The per cent drop of pressure in a foot vein during exercise and the time to return to standing pressure were used to determine a venous sufficiency index. Four distinct factors or groupings could be distinguished: incompetent perforators (31), deep vein incompetence (14), incompetence of the saphenous vein (3), and obstruction of deep veins (4). Six types of surgical procedures were done: ligation of perforators (25), superficial femoral valvuloplasty (3), segmental venous transposition (1), ligation of the superficial femoral vein (1), cross femoral venous bypass (1) and high ligation and stripping of the long saphenous vein (3). Three patients had skin sloughing after perforator ligation, and one patient developed a hematoma requiring evacuation following segmental venous transfer. Post-operative AVP evaluation in 11 patients after perforator ligation, two patients following superficial femoral valvuloplasty, one patient after segmental venous transfer, and one patient after cross femoral venous bypass showed significant improvement. Early follow-up results are very satisfactory.     

Venous ulceration and continuous flow in the long saphenous vein.

OBJECTIVE: To determine the clinical significance of continuous flow in the long saphenous vein in limbs with venous ulceration. DESIGN: Retrospective review. PATIENTS AND METHODS: Review of 1608 consecutive limbs undergoing colour duplex scanning for venous disease over a 43 month period. RESULTS: Continuous flow in the long saphenous vein is seen in 8% of limbs with venous ulceration and in 37% of limbs with deep venous obstruction. Sixty-six per cent of ulcerated limbs with continuous flow in the long saphenous vein had deep venous obstruction, 27% had deep venous reflux with cellulitis and 7% had lymphoedema in addition to venous ulceration. CONCLUSION: Continuous flow in the long saphenous vein in patients with venous ulceration should alert the clinician to the possibility of deep venous obstruction. Such limbs should be treated by compression bandaging with extreme caution.     

Primary varicose veins: the sapheno-femoral junction, distribution of varicosities and patterns of incompetence.

OBJECTIVE: to determine the patterns of long saphenous vein (LSV) disease in primary varicose veins (VVs). DESIGN: a retrospective analysis of venous duplex scans performed on patients referred for treatment of primary VVs. METHODS: analysis was made of sapheno-femoral junction (SFJ) incompetence, non-SFJ incompetence, segmental and perforating vein incompetence, distribution of varicosities, deep venous insufficiency, and short saphenous incompetence. RESULTS: four hundred and eighty-one patients were assessed (median age 50 (range 12-98) years; male:female ratio 1:1.95), comprising 706 limbs. Forty-six per cent of limbs had a competent SFJ, 64% of which had no incompetent perforating vessels associated. Disease was more widespread when the SFJ was incompetent. Varicosities were most common in the calf, occurring at or below the level of incompetence within the LSV. Incompetent segments occurred most commonly above-knee. There was no obvious correlation between incompetent perforators and distribution of varicosities, or incompetent segments. Short saphenous incompetence and non-SFJ groin recurrence were associated more with a competent SFJ, the converse being true for the Giacomini vein. CONCLUSION: primary VVs develop in isolated segments of the superficial venous system (without connection to the deep system) at, or distal to, the underlying main trunk incompetence, suggesting a process of "spreading incompetence" from one focal point, producing varicosities (mainly in tributaries).     

Effect of Superficial Venous Surgery on Venous Function in Chronic Venous Insufficiency

Patients with chronic venous insufficiency often have combined superficial and deep venous incompetence. The aims of this study were to determine the effects of superficial venous surgery (SVS) on deep venous haemodynamics and on ambulatory venous pressure (AVP) and to determine if the AVP tourniquet test can predict the effect of SVS. Of 119 legs, 42 legs (32 subjects) with chronic venous insufficiency, healed ulceration, or active ulceration and with combined superficial and deep incompetence underwent preoperative duplex imaging and AVP measurement followed by appropriate SVS. Four months later, all underwent postoperative duplex imaging and AVP measurement. The pressure relief index (PRI) was calculated from the AVP measurement as an overall assessment of venous function. Seventeen of 119 (14%) showed no tourniquet improvement in PRI and were therefore excluded from SVS. Of those suitable for SVS, median (range) age was 56 (32-78) years. Twenty-two limbs underwent long saphenous surgery, four limbs short saphenous surgery, and 16 limbs both, based on duplex findings. Segmental deep incompetence resolved in 11/21 (52%) limbs after surgery compared to 6/21 (29%) with multisegment incompetence. Median (range) PRI improved from 319 (4-1,600) preoperatively to 1,300 (360-2,670) postoperatively (p < 0.001, Wilcoxon). PRI with thigh tourniquet correlated with postoperative PRI (r = +0.828, p = 0.01, Spearman), as did calf tourniquet (r = +0.996, p = 0.004) and both tourniquets (r = 0.535, p = 0.046). The majority of patients with combined superficial and deep incompetence can be selected for SVS on the basis of AVP measurement with tourniquets. SVS can improve segmental deep incompetence and PRI in those properly selected.Part of these data were presented as an abstract at the Venous Forum of the Royal Society of Medicine, Manchester, UK, March 2004.     

Prospectively randomized clinical trial to compare in situ and reversed saphenous vein grafts for femoropopliteal bypass

Two hundred and fifteen femoropopliteal bypass procedures using autologous saphenous vein grafts were randomly allocated to either the reversed or in situ technique. Eleven veins (5 per cent) were rejected at operation on the basis of their small size, nine in the reversed group and two in the in situ group, and there were two (2 per cent) perioperative deaths in each group, leaving 102 reversed and 98 in situ grafts for further study. The cumulative patency at 3 years of the reversed grafts was 77 per cent and that of the in situ grafts was 68 per cent (n.s.). The patency of all grafts was affected adversely by small veins (P less than 0.005), long grafts (P less than 0.05), low volume of blood flow in the grafts (P less than 0.001) and poor run-off (P less than 0.05). These factors influenced the outcome of the in situ and reversed operations to a similar degree and there was no statistically significant difference between them within any subgroup. The mean compliance of the in situ grafts measured 3 months or more after operation with an ultrasonic echo-tracking system was 0.024 +/- 0.01 per cent/mmHg (+/- s.d.) compared with 0.017 +/- 0.01 per cent/mmHg for the reversed grafts (t = 2.43, P less than 0.02). The incidence of fibrous stricture formation as shown by intravenous digital subtraction angiography was 29 per cent in both the reversed and the in situ grafts. The results of the study to date indicate that reversed and in situ vein grafts are equally effective for femoropopliteal bypass.     

Ambulatory venous pressure revisited

PURPOSE: The purpose of this study was to describe a method for measuring the deep venous pressure changes in the lower extremity and compare it with those obtained in the dorsal foot vein. METHODS: After cannulation of the posterior tibial vein, a catheter with a pressure transducer in its tip was inserted and placed at the knee joint level. The dorsal foot vein was also cannulated. Pressures were recorded simultaneously at both sites during toe stands and repeated with the probe in the upper, middle, and lower calf. RESULTS: The study was performed in 45 patients with signs and symptoms of chronic venous insufficiency. Duplex Doppler scanning and ascending and descending venography performed before pressure measurements revealed saphenous vein incompetence in 11 lower extremities, incompetent perforators in 11 extremities (eight were combined with saphenous incompetence), and marked compression of popliteal vein with plantar flexion in 28 extremities. No significant deep axial reflux was observed on duplex Doppler examination or descending venography. No morphologic outflow obstruction was detected. The mean deep pressure at the knee joint level fell during toe stands, -15% +/- 27 (SD), and the mean dorsal foot vein pressure drop was even more marked, -75% +/- 22 (SD). Although the exercise pressure in the dorsal foot vein decreased in all patients (range, 13-90% drop), the popliteal vein pressure increased (4-72%) in nine limbs, decreased only marginally if at all in 15 limbs (0-15%), and fell more markedly in 21 extremities (22-65%). Deep vein recovery time was considerably shorter overall as compared with the findings by the dorsal vein measurement. In the comparison of limbs with and without superficial reflux, the recovery times in the deep system were significantly shorter in limbs with superficial incompetence. CONCLUSION: Ambulatory dorsal foot venous pressure is not always accurate in detecting changes in the pressure of the tibial and popliteal veins. Although dorsal foot venous pressure may be normal, deep venous pressure may decrease to a lesser degree or even increase.     

Investigation and significance of short saphenous vein incompetence.

In this study, 186 limbs with varicose veins or venous skin changes were examined using duplex ultrasonography. Limbs were classified on the basis of short saphenous or popliteal venous incompetence and the number of limbs with venous ulceration (active or healed) recorded. Short saphenous incompetence did not produce a significant increase in the incidence of ulceration, whereas popliteal reflux produced an increase in the risk of ulceration which was statistically significant when compared with limbs without reflux in these two veins (chi 2 = 4.55, P = 0.003). There was no significant difference in the proportion of limbs with concomitant long saphenous reflux between these two groups. Short saphenous reflux is not important in the pathogenesis of venous ulceration. Popliteal reflux is an important factor in the pathogenesis of venous ulceration. More attention should be paid to the surgical correction of popliteal reflux when present in limbs with venous ulceration that fail to heal by conservative measures.     

Relationship of venous reflux to the site of venous valvular incompetence: implications for venous reconstructive surgery

To evaluate the relationship of the site of venous valvular incompetence to the severity of venous reflux, legs of 71 patients with suspected chronic venous insufficiency were evaluated with Doppler ultrasonography and photoplethysmography. A venous recovery time (VRT) of less than 20 seconds after calf muscle exercise was considered indicative of significant reflux. Average VRTs were brief in 15 legs with stasis changes (10 +/- 7 seconds), longer in 42 legs with edema (26 +/- 23 seconds), and normal in 64 asymptomatic legs (37 +/- 24 seconds) and 16 legs with pain (53 +/- 19 seconds). Average VRTs in limbs with incompetent saphenous veins were abnormal. In limbs with competent superficial veins, only those with incompetent distal deep veins (popliteal and posterior tibial) had abnormal VRTs (14 +/- 10 seconds). VRTs in limbs with no detectable valvular incompetence and in those with incompetence limited to the proximal deep veins (common and superficial femoral) were normal (47 +/- 23 and 42 +/- 27 seconds, respectively). When superficial veins were incompetent, an ankle tourniquet normalized VRTs in 63% of legs with proximal deep venous incompetence and in only 33% of legs with distal deep venous incompetence. It is concluded that venous reflux is largely determined by saphenous and distal deep valvular function and that competence of the proximal valves has little effect. Decreased venous reflux would not be expected after proximal valvular reconstruction.     

Venous ulcer healing by four-layer compression bandaging is not influenced by the pattern of venous incompetence

BACKGROUND: Previous studies have related deep venous incompetence to reduced venous ulcer healing rates. The aim of this study was to determine the relationship between the pattern of venous incompetence and ulcer healing. METHODS: A total of 198 legs with venous ulceration were investigated with colour venous duplex imaging to determine the presence and site of venous incompetence. All were treated initially with the four-layer bandage technique. RESULTS: At 6 months, 74 per cent of the venous ulcers had healed using the four-layer bandage technique. There was no significant correlation between the pattern of incompetence and the healing rate of the ulcer. Previous deep vein thrombosis (DVT), increased size of the ulcer and previous episodes of ulceration were associated with a poor healing rate. CONCLUSION: The four-layer bandage technique achieved an ulcer healing rate of 74 per cent after 6 months, irrespective of the pattern of venous incompetence. Patients with a large ulcer, previous DVT or previous episodes of ulceration had delayed healing, supporting the previous literature.     

Recurrent varicose veins following high ligation of long saphenous vein: a duplex ultrasound study

Duplex scanning was used to study recurrent varicose veins in 244 limbs with previous high ligation of the long saphenous vein. The recurrent varicose veins were classified into two types according to the presence or absence of a residual long saphenous vein. Varicose veins with a residual long saphenous vein (type I) occurred in 168 limbs (68.9%). A residual long saphenous vein with an incompetent saphenofemoral junction was present in 125 limbs and one without any residual saphenofemoral junction in 43 limbs. Besides the presence of an incompetent long saphenous vein in this group, an incompetent short saphenous vein was detected in 26 limbs, incompetent perforating vein(s) in 45 limbs and incompetent deep veins in 26 limbs. Varicose veins without a residual long saphenous vein (type II) occurred in 76 limbs (31.1%). An incompetent short saphenous vein was demonstrated in 44 limbs, incompetent perforating vein(s) in 18 limbs and incompetent deep veins in 32 limbs. Of the total 244 limbs with recurrent varicose veins, long saphenous vein incompetence was involved in 168 (68.9%), short saphenous vein incompetence in 70 (28.7%), perforating vein incompetence in 63 (25.8%) and deep venous incompetence in 58 (23.8%). Although saphenofemoral junction incompetence was found to be the main source of recurrence, a segment of incompetent residual long saphenous vein, an incompetent short saphenous vein, perforating vein and deep venous system incompetence are other common sources of recurrence. A precise assessment to identify underlying venous incompetence is important for the management of recurrent varicose veins.     

Mechanism of action of external compression on venous function.

Compression stockings and bandages have been shown to improve venous haemodynamics and may act by reducing venous reflux. The aim of this study was to assess the mechanism of action of compression therapy on venous function and to determine whether such treatment may correct valvular incompetence. Both lower limbs of 36 patients (median age 59 (interquartile range 45-65) years) were assessed by duplex ultrasonographic scanning. There were 17 limbs with popliteal vein reflux, 19 with long saphenous vein (LSV) reflux and 21 with short saphenous vein (SSV) reflux. A water-filled adjustable pressure cuff was applied around the knee and inflated gradually, while continuously assessing the veins for reflux using ultrasonographic imaging. The external pressure applied by the cuff was noted when reflux was abolished or when the vein was completely occluded. In four (24 per cent) of 17 popliteal veins, eight (42 per cent) of 19 LSVs and three (14 per cent) of 21 SSVs reflux was abolished before occlusion of the vein. The cuff pressures required to achieve restoration of valvular function were significantly lower than those required to occlude the veins. It is possible, in some refluxing veins, to correct valvular dysfunction by external compression therapy. Coaptation of valvular cuffs to restore valvular competence may be the mechanism of action of compression therapy in venous disease.     

Valvular incompetence in superficial, deep and perforator veins of limbs with varicose veins

Venous valvular incompetence was investigated with Doppler technique in 296 limbs with untreated primary varicose veins. Partial or complete insufficiency of the long saphenous vein was found in 95%. Six patterns of incompetence of this vein could be distinguished. Insufficiency of the short saphenous vein was present in 15% of the limbs and perforator incompetence in 45%. Femoral and/or popliteal vein reflux was found in 20% of the limbs. In eight limbs (2.7%) with verified primary deep venous insufficiency there was a moderate or severe degree of femoral and popliteal venous reflux. Skin changes secondary to the venous disease were present in 18% of the limbs, mainly those with incompetence of perforator and long saphenous veins. Doppler investigation of varicose limbs give valuable information and can be recommended as a standard pre-treatment test.     

Differences in pressures of the popliteal, long saphenous, and dorsal foot veins

PURPOSE: The purpose of this study was to examine the relationship among pressures obtained simultaneously in the popliteal, long saphenous, and dorsal foot veins. METHOD: Eight limbs were studied. One limb had an isolated popliteal vein reflux, and two had moderate long saphenous vein incompetence. No perforator or short saphenous vein insufficiency was detected. Pressures and recovery times of the popliteal/tibial and long saphenous veins were obtained with cannulation at the ankle level and insertion of catheters with a pressure transducer tip. The dorsal foot vein pressure was measured with the insertion of a scalp needle (14-gauge) connected to an external transducer. During 10 toe stands, recordings were simultaneously made in the three veins at the level of the knee joint, in the middle third of the calf, and 5 to 7 cm above the ankle with all the transducers at the same level (ie, same reference point). RESULTS: In one limb the popliteal/tibial pressure increased at all calf levels, whereas pressures decreased in both saphenous and dorsal foot veins. The pressures decreased in all three systems in the remaining seven limbs. There was no statistical difference between the pressure drop in the long saphenous vein and the deep vein. However, the decrease of the dorsal foot venous pressure was significantly more marked compared with the other two veins at all levels. The recovery time was significantly increased in the long saphenous vein compared with the deep vein; recovery time was further prolonged in the dorsal foot vein. CONCLUSION: The dorsal foot, long saphenous, and popliteal/posterior tibial veins clearly exhibit different pressure waveforms in response to calf exercise. The postexercise pressure, the percentage pressure drop, and the recovery times are widely different, which indicates that the three veins behave hydraulically as separate compartments in limbs without significant venous insufficiency.     

Evaluation of non-invasive and invasive methods in the assessment of short saphenous vein termination

Surgery of the short saphenous vein is associated with a high recurrence rate because of variations in the anatomy or inadequate clinical examination. To prevent this, accurate definition of the pattern and level of termination of the saphenopopliteal junction and flush ligation is necessary. Clinical examination, Doppler ultrasound, duplex scanning and peroperative venography have been compared to assess the level of termination of the short saphenous vein. In all, 64 limbs of 46 patients were examined. In 39 limbs there was primary short saphenous incompetence, in 13 limbs there was recurrent short saphenous incompetence; in ten of these there was incompetence of the gastrocnemius vein. In 12 limbs a duplex scan did not demonstrate incompetence of the short saphenous vein or gastrocnemius vein. The accuracy of these methods when locating incompetence of the short saphenous vein to within 2 cm of the saphenopopliteal junction was 56 per cent for clinical examination, 64 per cent for Doppler ultrasound and 96 per cent for duplex scanning. When there was no saphenopopliteal junction (9 per cent), duplex scanning correctly detected the pattern of the incompetent vein. The apparent success of clinical examination was because the vein was not felt above the femoral intercondylar groove and 52 per cent of the veins terminated at this level. Duplex scanning is a non-invasive technique which is almost as accurate as venography and provides additional haemodynamic information about the incompetent veins by demonstrating the presence and extent of reflux.     

The role of air plethysmography in monitoring results of venous surgery.

The development of an objective, noninvasive method to assess the hemodynamic effects of venous surgery has long been awaited. Previous methods used to evaluate the results of surgery for varicose veins and venous stasis ulceration have been limited in their quantitative assessment. Now, by use of air plethysmography (APG), we can accurately quantify the effectiveness of corrective venous surgery. Twenty-five extremities that had evidence of venous insufficiency were examined with use of APG before and after venous surgical procedures. Surgery was directed at specific sites of venous incompetence as defined by physical examination and high-resolution duplex imaging. Twenty-one extremities underwent ligation and stripping of the greater saphenous vein. In these patients, APG showed an improvement in venous reflux as demonstrated by a decrease in the venous filling index from 6.6 +/- 0.7 ml/sec to 1.8 +/- 0.3 ml/sec (p = 0.0001) and venous volume from 177.1 +/- 14.5 ml to 139.2 +/- 8.9 ml (p = 0.0008). In addition, these patients showed a mild improvement in calf muscle pump function as noted by an improvement in ejection fraction from 45.8 +/- 2.0% to 50.8% +/- 2.5% (p = 0.07). The residual volume fraction decreased from 45.0% +/- 3.4% to 42.0% +/- 3.7%, a difference that was not statistically significant (p = 0.4). Four extremities with grade III chronic venous insufficiency underwent popliteal vein valve transplantation with use of an autogenous axillary vein valve.(ABSTRACT TRUNCATED AT 250 WORDS)     

Repair and replacement of deep vein valves in the treatment of venous insufficiency

Venous insufficiency is a widespread condition, the prevalence of venous ulceration being 0.5-1.0 per cent in Western populations. A principal abnormality causing venous insufficiency is deep venous reflux, usually resulting from post-thrombotic valve destruction. Patients undergoing treatment for venous insufficiency should have all venous abnormalities investigated, defined and corrected where possible. Although treatment for superficial and communicating vein incompetence is available, correction of deep vein reflux has been neglected until recently. Deep vein valve physiology, the selection of patients for deep vein valve surgery and methods of valve repair and replacement are reviewed.     

Role of B-mode venous mapping in infrainguinal in situ vein-arterial bypasses

Two hundred and eighty patients underwent B-mode mapping (B-map) of their saphenous vein over a period of 3 years (1984-1987) before lower limb revascularization. B-map deemed that 229 veins were suitable for bypass, 26 were questionable and 25 were unsuitable. A successful bypass was achieved in 97.8 per cent of the suitable group (all in situ), 85 per cent of the questionable group (in situ and composite vein), and 80 per cent of the unsuitable group (composite vein). At a minimum follow-up period of 1 year the overall patency rate was 95.0 per cent with a revision rate of 15.8 per cent. There was no correlation between revision rate and vein complexity or calf vein diameter. Calf vein diameter greater than 2.5 mm was correlated with a successful bypass (P less than 0.001). It is concluded that B-map is the investigation of choice for saphenous vein assessment before infrainguinal bypass surgery.     

Vein compliance: a preoperative indicator of vein morphology and of veins at risk of vascular graft stenosis.

Compliance measurements of 53 long saphenous veins before femorodistal bypass have been performed using a duplex scanner with venous occlusion for distension. These have been compared with the histological features of the veins. There was significantly more moderate or severe focal hyperplasia and circular muscle hypertrophy in distal long saphenous vein than in its proximal counterpart (P < 0.01 and P < 0.05 respectively). The mean (95 per cent confidence interval) compliance of distal vein with moderate or severe hyperplasia was 0.16 (0.13-0.19) compared with 0.29 (0.22-0.36) for that with no, minimal or mild hyperplasia (P = 0.001). The mean compliance of distal vein with moderate or severe muscle hypertrophy was 0.19 (0.17-0.21) and of vein with no, minimal or mild hypertrophy 0.25 (0.21-0.29) (P = 0.14). The mean lowest compliance in seven patients who developed stenosis was 0.10 (0.07-0.13) compared with 0.21 (0.16-0.26) in the rest (P < 0.001). Preoperative measurement of vein compliance can be used to identify vein with marked pre-existing intimal hyperplasia and as a predictor of future graft stenosis.