Computational and experimental simulations of the haemodynamics at cuffed arterial bypass graft anastomoses

The development of intimal hyperplasia at arterial bypass graft anastomoses is a major factor responsible for graft failure. A revised surgical technique, involving the incorporation of a small section of vein (vein cuff) into the distal anastomosis of polytetrafluoroethylene (PTFE) grafts, alters the distribution of intimal hyperplasia and improves graft performance. Numerical and in vitro flow visualization experiments have been conducted to identify the flow behaviour in the cuffed bypass model and to determine whether the improved performance of the cuffed system can be accounted for by haemodynamic factors. The flowfield at the cuffed anastomosis is characterized by an expansive recirculation. Separation occurs at the graft heel, and at the cuff toe as the blood enters the recipient artery. Wall shear stresses in the vicinity of the cuff heel are low, but high shear stresses and large spatial gradients in the shearing force act for a time on the artery floor. In the conventional model, a less disturbed flow prevails while the gradients of shear stress on the floor are smaller. Aspects of the anastomotic haemodynamics are worsened when the cuff is employed. The superior patency rates of cuffed bypasses may not be explained purely on the basis of local haemodynamic factors.

POSSUM and P-POSSUM overpredict mortality for carotid endarterectomy

OBJECTIVES

the aim was to test the predictive accuracy of POSSUM and P-POSSUM on patients undergoing CEA.

DESIGN

retrospective and prospective study.

MATERIALS

499 CEAs performed by four vascular surgeons from a single unit from 1992-99. The median age was 68 (range 38-86) and 60% were men.

METHODS

physiological parameters, operative parameters and the 30-day mortality were collected. Predicted mortality for each patient was calculated using POSSUM and P-POSSUM equations. Patients were stratified into risk groups and observed and predicted deaths were compared. Accuracy of the prediction was assessed using chi-squared analysis.

RESULTS

the observed 30-day mortality was 1.8% (9/499). The predicted deaths using POSSUM and P-POSSUM analysis were 49 and 25 respectively compared to nine observed deaths. There was significant evidence of lack of fit of both models in predicting mortality (chi-squared analysis, p<0.05).

CONCLUSIONS

POSSUM and P-POSSUM overpredict mortality and are unsuitable for comparative audit of CEA. Models developed specific for CEA might accurately predict mortality.

The use of impedance index in the surveillance of PTFE femorodistal grafts

BACKGROUND

Impedance is the equivalent in pulsatile flow of resistance in steady flow. The impedance index has been used successfully in the surveillance of vein grafts, but its use has not been reported in the context of PTFE femorodistal grafts.

METHODS

Twenty-eight patients (median age 68 years (IQR 59-73 years) and 20 men) undergoing 28 PTFE femorodistal grafts with a vein cuff were evaluated prospectively comparing the impedance index with standard duplex graft surveillance. All grafts were performed for critical ischaemia. At risk grafts were identified and treated appropriately after angiography.

RESULTS

The primary patencies at 1 and 2 years were 82% and 50% respectively. Duplex identified 11 at risk grafts of which 9 had an identifiable correctable lesion. Impedance analysis overpredicted at risk status when compared with duplex in the immediate postoperative phase and was unsuccessful in detecting inflow disease or low flow relating to cardiac failure. Using a threshold index of 0.5, impedance analysis has a sensitivity of 87%, specificity of 88%, with positive and negative predictive values of 76% and 94% respectively.

CONCLUSIONS

Impedance index is a non-invasive method of graft surveillance which is applicable to PTFE femorodistal bypasses and may be a useful alternative to duplex although formal validation studies will be required.

Long saphenous vein stripping and quality of life--a randomised trial

OBJECTIVES

To assess the quality of life of patients undergoing sapheno-femoral junction (SFJ) ligation and long saphenous vein stripping (LSV), using two different techniques.

DESIGN

Prospective, randomised trial.

MATERIALS AND METHODS

Eighty patients were recruited and randomised to either Perforate Invagination (PIN) stripping (43) or Conventional stripping (37). Patients completed the Short Form 36 (SF-36) and EuroQol (EQ) questionnaires preoperatively, and postoperatively at 6 weeks and 6 months.

RESULTS

Bodily pain, role function and physical summary were significantly improved at 6 months in the PIN stripping group. In the Conventional group, bodily pain and physical function were similarly improved, but not role function. EQ global quality of life was significantly and progressively improved at 6 weeks and 6 months in the PIN group (global score p<0.003; self-rated score p <0.001). In the Conventional group there was no overall improvement in global score or self-rated health.

CONCLUSIONS

Primary varicose vein surgery is associated with significant and progressive improvements in quality of life scores. Whilst overall quality of health does improve in the Conventional group, this appears to be to a lesser extent than in the PIN group.

Do Patients with Critical Limb Ischaemia Undergo Multiple Amputations after Infrainguinal Bypass Surgery?

BACKGROUND

it has been suggested that an aggressive policy of bypass for limb salvage in critical ischaemia may result in patients subsequently undergoing multiple amputations. The aim of this study was to test this suggestion in the context of a dedicated Vascular Surgical Unit in a U.K. teaching hospital.

METHODS

three hundred and sixty-eight patients undergoing lower limb bypass operations for critical limb ischaemia between April 1991 and March 1999 were studied retrospectively. Their median age was 69 years (IQR 64--75) and 243 (66%) were men.

RESULTS

seventy-five operations were followed by one or more amputation (20%). Only 2% were multiple amputations. Age and sex had no effect on amputation rates, but emergency bypass operations led to a higher rate of amputation in those with critical limb ischaemia.

CONCLUSION

patients with critical limb ischaemia who undergo lower limb bypass surgery rarely have subsequent multiple amputation.

Cyclist's iliac syndrome: temporary relief by balloon angioplasty

External iliac stenosis due to endofibrosis is a rare condition that predominantly affects top level cyclists. Short term symptomatic relief is reported in an Olympian after percutaneous transluminal angioplasty, which was performed to allow the patient to return to training without delay.

An unusual cause of femoral embolus

Acute lower limb ischaemia is associated with high morbidity and mortality. The authors describe an unusual cause of arterial occlusion two weeks following aorto-coronary bypass surgery. This case should make vascular surgeons aware of the possibility of prosthetic materials acting as emboli. Furthermore, they should also be mindful that the presenting symptom may be at a site and time remote from the original intervention.

Surgical Management of Leg Ulcers Associated with Pulsatile Varicose Veins and Tricuspid Regurgitation

Design:

Case report.

Setting:

Vascular Surgery Department, Hull Royal Infirmary, UK.

Patients:

A 79-year-old man with a history of right leg ulcer and pulsatile veins.

Investigations and interventions:

Clinical examination revealed findings of tricuspid regurgitation. Investigations included duplex scans, CT scan, arteriography and both trans-thoracic and trans-oesophageal echocardio-graphy. These all proved inconclusive. High sapheno-femoral ligation and stripping of long saphenous vein ligation procedure resulted in healing of his ulcers within six months

Conclusion:

Pulsatile veins in the leg may be due to tricuspid regurgitation or AV malformation. Echocardiogram, duplex scan and angiograms can help to differentiate between the two diagnoses. In this case, the above investigations were misleading and clinical examination here played the key role.

Axial flow fields in cuffed end-to-side anastomoses: effect of angle and disease progression

OBJECTIVE

to visualise the axial flow fields in standard and cuffed end-to-side anastomoses (ESA).

DESIGN

in vitro experiments using a flow rig, custom-built glass models and frame-by-frame video analysis of flow patterns in standard and cuffed ESA.

SUBJECTS

glass models of standard or cuffed (1 cm or 2 cm high) ESA of angles 15, 30, 45 and 60 degrees.

RESULTS

the cross-sectional area of standard ESA is much smaller than that of ESA between graft and cuff. The size of the vortex in the anastomotic zone of both standard and cuffed ESA increased with increasing ESA angle and cuff height, but did not change with flow rate. The presence of the vortex maintains a zone of flow separation and low shear at the heel of standard and graft/cuff anastomoses.

CONCLUSIONS

the observations explain the clinical findings of intimal hyperplasia (IH) at the heel of PTFE/cuff anastomoses. The improved patency rates of cuffed ESA may be due not to decreased IH, but to an increased ability of the cuff to accommodate IH before causing a significant stenosis.

Endovascular stent-grafts for superficial femoral artery disease: results of 1-year follow-up

PURPOSE

To document a preliminary study to assess the deployment and outcomes of endoluminal stent grafting in the superficial femoral artery (SFA) with use of a prototype device.

MATERIALS AND METHODS

Twenty patients with lifestyle-limiting intermittent claudication were selected for treatment with a balloon-mounted expansive polytetrafluoroethylene graft. All patients had angiographically proven SFA disease (median length, 17 cm) with normal arterial inflow and at least two calf vessels patent to the ankle. Follow-up was by means of ankle brachial pressure index (ABPI), duplex ultrasound, and angiography.

RESULTS

Fourteen patients were successfully treated. Six patients were excluded: five by the study protocol and one because the procedure was a technical failure. ABPI rose from 0.6 before treatment to 1.0. The treated limbs became asymptomatic. Twelve-month primary, primary assisted, and secondary patency rates of treated patients were 29%, 50%, and 64%.

CONCLUSION

Endovascular stent grafting of SFA lesions is technically feasible, but the patency rates obtained with this design are inferior to those obtained with conventional surgical bypass.

Measuring serum total cholesterol: do vascular surgeons know what they are doing?

Raised serum total cholesterol (TC) is an accepted risk factor for both coronary and peripheral vascular disease and three landmark trials have shown the benefit of lowering TC using statins. Vascular surgeons tend to measure TC, but little is known about how they manage hypercholesterolaemia or whether they believe treatment will be of benefit. A questionnaire was sent to listed members of the Vascular Surgical Society of Great Britain and Ireland seeking responses to a range of questions on the measurement and management of raised TC. In all, 374 questionnaires were sent out. The response rate was 67%. Over 90% of respondents said they measured TC and considered a level below 5.5 mmol/l as normal. The cut-off for initiating drug therapy, referral to a dietician or to a lipid specialist varied from 5.5 to 7.5 mmol/l. Most (62%) believed that lowering TC improved coronary mortality, but fewer (26%) that it prevented worsening of claudication. Although most vascular surgeons check for raised TC, the level at which treatment begins and the form it takes varies; in many cases being at odds with recommendations. Few surgeons are convinced of the benefits of lowering TC for claudication and nearly one-fifth do not believe it improves coronary mortality.

Impedance index measurements of in vitro PTFE end-to-side anastomoses: effect of angle and Miller cuff

OBJECTIVE

To measure non-invasively the impedance index of a range of geometries of PTFE end-to-side anastomoses (ESA).

DESIGN

In vitro experiments using a custom-built flow rig.

SUBJECTS

Anastomoses constructed at each angle. (15 degrees, 30 degrees, 45 degrees, 60 degrees, 90 degrees, 120 degrees) for both standard and cuffed ESA.

RESULTS

The impedance index of each ESA increased non-linearly with flow rate. The impedance index at a given flow rate was reduced by decreasing the anastomotic angle and further reduced by the addition of a Miller cuff.

CONCLUSIONS

The reduction in impedance index achieved with a Miller cuff may help to explain the improved patency rates of femoropopliteal grafts incorporating a cuff.

Polytetrafluoroethylene (PTFE) femorodistal grafts with a distal vein cuff for critical ischaemia

OBJECTIVE

To analyse the results of PTFE femorodistal bypass grafts using a distal anastomotic vein cuff in the treatment of critical ischaemia.

DESIGN

Prospective study of consecutive patients under the care of a single Vascular Surgeon.

SETTING

A dedicated Vascular Surgical Unit in a University teaching hospital.

SUBJECTS

Fifty-one consecutive femorodistal PTFE grafts were performed on 50 patients (median 74 years, range 58-94 years, 25 men; median ankle:brachial index 0.4). In 28 (55%) a common ostium arteriovenous fistula (AVF) was fashioned at the distal anastomosis.

RESULTS

The 30-day postoperative mortality was 8%, with 10 (21%) major complications. The 1 and 2 year primary patency was 64% and 51%, respectively, with corresponding limb salvage rates of 85% and 80%. The presence of an AVF did not significantly affect graft patency or patient survival, but appeared to hinder limb salvage. The latter effect may be due to bias in patient selection.

CONCLUSION

PTFE femorodistal grafts with a distal vein cuff are a suitable alternative to autogenous saphenous vein in distal reconstructions for critical ischaemia. No conclusions can be made about the efficacy of an AVF in this context.

Polytetrafluoroethylene femorodistal grafts: can the use of a vein collar offer patients a reasonable chance of success?

The growing number of patients with critical ischemia who lack a suitable autogenous vein for grafting pose a particular problem for the vascular team. In such patients the use of a polytetrafluoroethylene graft with a distal anastomotic vein cuff or patch has been advocated as an alternative to primary amputation. The use of such adjunctive techniques is reviewed through a 3-year retrospective study of 50 patients under the care of one surgeon. Data analyzed include patient demographics, risk factors, and presenting symptoms. All patients were included in a Duplex graft surveillance program. The cumulative patency rates at 1 and 2 years were 56% and 55%, respectively, with limb salvage rates of 85% and 80%. The data support a reconstructive approach to maintain the quality of the patient's life.

Comparison of POSSUM and the Portsmouth predictor equation for predicting death following vascular surgery

BACKGROUND

The Physiological and Operative Severity Score for enUmeration of Mortality and morbidity (POSSUM) scoring system has been proposed as an accurate predictor of death which takes account of case mix. It appears to overpredict death, and may have drawbacks which prevent accurate individual or subgroup analysis. An alternative system, the Portsmouth predictor equation for mortality (P-POSSUM) may have overcome these problems, but its apparent advantage could be related to inappropriate analysis of POSSUM predictions.

METHODS

Some 312 patients having arterial procedures were studied. POSSUM and P-POSSUM scores were used to predict death and compared with actual outcomes. The observed:predicted (O:E) mortality ratios were calculated by two methods for each of the scoring systems. First the analysis devised by the inventors of POSSUM was used and second the method devised for P-POSSUM.

RESULTS

The O:E ratio for POSSUM using its recommended 'exponential' method of analysis was 1.14, but it was 0.59 if the P-POSSUM 'linear' analysis was used. The O:E ratio for P-POSSUM using its correct method of analysis was 0.89, but it was 0.67 if the method of analysis devised for POSSUM was used.

CONCLUSION

The O:E ratios for POSSUM and P-POSSUM were close to unity when the appropriate analysis was performed. Both POSSUM and P-POSSUM overpredicted death if the incorrect analysis was used.

Analysis of renal artery geometry may assist in the design of new stents for endovascular aortic aneurysm repair

BACKGROUND

Endovascular repair of infrarenal aortic aneurysms is a feasible technique, but up to 30 per cent of patients may be excluded on the basis of a short proximal aortic neck.

METHODS

A dissection study was performed on 65 cadavers to measure the distance between the superior mesenteric and renal artery ostia, and to document the points of origin of the renal arteries.

RESULTS

The interostial distance did not differ significantly between aneurysmal and non-aneurysmal aortas (P = 0.90 for the left renal artery; P = 0.72 for the right). The median distance was 0.7 cm. The renal arteries originated between 2 and 4 o'clock on the left and between 9 and 10 o'clock on the right.

CONCLUSION

The relative consistency of the anatomy in this region may allow the development of a new stent which would increase the number of patients suitable for endovascular repair.