N. J. Lalak, MB, BS, K. C. Hanel, MB, BS, FRACS, DDU, J. Hunt, RN, and A. Morgan, RN, RVT, DMU (vasc.), Kogarah, Australia

Transcription

1 Duplex scan surveillance prosthetic bypass grafts of infrainguinal N. J. Lalak, MB, BS, K. C. Hanel, MB, BS, FRACS, DDU, J. Hunt, RN, and A. Morgan, RN, RVT, DMU (vasc.), Kogarah, Australia Purpose: Surveillance protocols of infrainguinal vein bypass grafts have almost universal acceptance. To date corresponding studies of prosthetic grafts have not been carried out. We have performed a prospective 4-year duplex scan fouow-up on polytetrafluoroethylene grafts to assess the usefulness of a surveillance program of prosthetic bypass grafts in preventing graft failure. Methods: Over 4 years 69 infrainguinal polytetrafluoroethylene grafts in 56 patients were studied at six monthly intervals by our vascular laboratory. Full duplex scan mapping of the grafts and inflow and outflow arteries and standard ankle pressure measurements were performed. A midgraft peak flow velocity was also measured. Results: Over 4 years 27 (39.1%) grafts occluded without any predictive changes in the preceding duplex scan examination. Of the 42 (60.9%) grafts that remained patent, only four developed stenoses (three at the proximal anastomosis and one at the distal anastomosis) that were amenable to intervention. Changes in ankle pressures or midgraft flow velocity did not predict failure. Conclusions: The low yield of remediable disease does not justify the cost of duplex scan surveillance of infrainguinal prosthetic bypass grafts. (J VAsc SURG 1994;20: ) Numerous reports in the surgical literature support the role of the noninvasive vascular laboratory for postoperative surveillance of infrainguinal autogenous vein bypass grafts. 1"9 Serial surveillance with selective secondary intervention in both reversed vein grafts and in situ grafts is estimated to have improved patency rates by 10% to 15%. 2 The predominant disease detected is fibrotic strictures in the graft with 30% occurring within the first 2 years after operation, 1 and they are usually suitable for surgical or endovascular corrective procedures. However, many prosthetic grafts fail because of thrombotic occlusion, which is due to poorly understood interactions at the graft-blood interface, whereas a lesser number fail because of anastomotic stenoses similar to those seen in vein grafts. Unlike the vein graft surveillance programs of lower limb, prosthetic grafts have only been sporadically studied and reported. 9 Against a background of spiraling health costs and calls to justify medical treatment on a cost-efficient basis, n this prospective From St. George Hospital and Hurstville Community Vascular Laboratory (Messrs. Hunt and Morgan), Kogarah. Reprint requests: K. C. Hand, MB, BS, FRACS, DDU, 3/22 Belgrave St., Kogarah, NSW, Australia, Copyright 1994 by The Society for Vascular Surgery and International Society for Cardiovascular Surgery, North American Chapter /94/$ /1/57309 study assesses the role of a duplex scan surveillance program in a series of 69 femorodistal Gore-tex grafts* to determine its efficacy in preventing graft: failure. MATERIAL AND METHOD Between January 1989 and December 1992, 56 patients who had undergone 69 infrainguinal grafts with polytetrafluoroethylene material (Gore-tex) were entered into a surveillance program at the Hurstville Community Hospital Vascular Laboratory. Nine had bilateral procedures, and 29 had two or more prosthetic grafts inserted in the same leg. Two patients underwent three operations. All operations were performed by the same surgeon and are a consecutive series of patients with polytetrafluoroethylene grafts who were discharged from the hospital with a functioning graft. Fifty-eight patients were operated on within the 4 years of the study, whereas 11 were operated on in the 12 months before January 1989 and had patent grafts before inclusion in the program. The characteristics of the patients with regard to age, sex, and risk factors are outlined in Table I. The indications for surgical procedure are listed in Table II, and the details of the operative procedures are listed in Table III. Thirty-one (45%) ~Gore-tex is a trademark ofw. L. Gore & Associates, Elkton, Md. 637

2 638 Lalak et al. JOURNAL OF VASCULAR SURGERY October 1994 Table I. Patient details Table II. Indications for surgical procedure No. Percent No. Percent Patients 56 Men 22 Women 34 Grafts 69 Age range (yr) Mean age (yr) 70.5 Diabetes mellitis (%) Ischemic heart disease (%) Hypertension (%) Cerebrovascular disease (%) Current smokers (%) Lapsed smokers (%) Secondary procedures (%) procedures were for disabling claudication, and 38 (55%) were for rest pain or gangrene. Most distal anastomoses were at the above-knee popliteal level (40 of 61), with only seven tibioperoneal anastomoses. LABORATORY PROCEDURES Patients were seen 1 month after the operation and thereafter at 3 months and then at six-monthly intervals. Only grafts found patent at the first interrogation were retained in the study. A continuous wave Doppler resting ankle systolic pressure index (ASPI) was derived, and treadmill exercise studies were performed, if possible. The grafts were then studied with duplex scanning with an Acuson 128 (Acuson 128 Computed Sonography, Mountain View, Calif.) color-coded scanner. The inflow arteries, the total graft, and the adjacent outflow vessels were serially scanned and mapped, looking for increases in peak systolic flow velocity and other morphologic criteria for stenosis. A sudden increase in peak systolic flow velocity greater than 50% was taken as the minimal criteria for a significant stenosis. +'9 A single reading, the peak systolic flow in the mid part of the graft, was noted and defined the midgraft flow velocity (MFV) per Bandyk's study) 2 Graft failure was always confirmed by duplex scanning and/or angiography, if appropriate, either at the routine surveillance scanning session or at an unscheduled scan, if the patient presented with clinical symptoms of an occluded graft. Changes in ASPI greater than 0.15 between successive studies were noted as an abnormal finding, l'2"s7'9'lz'z316 as was an MFV of less than m/see. 7-9'12 All results are expressed as the mean with the 95% confidence intervals. Data have been analyzed by the Mann-Whitney nonparametric test. Claudication Rest pain Gangrene A p value less than 0.05 has been taken as being significant. RESULTS Sixty-nine grafts were inserted in 56 patients. The mean age of patients was 70.5 years, with an age range of 45 to 88 years. The mean number of studies of individual grafts during the 3 years of the survey was 3.7, with a range ofl to 11. No patients were lost to follow-up before the termination of the study or until graft occlusion and/or intervention. Secondary bypass procedures with polytetrafluoroethylene were reentered into the surveillance program as new cases. During the 3 years of the study 27 (39.1%) grafts occluded. Fifteen of these patients had significant symptoms, whereas 12 patients had no symptoms or mild symptoms not severe enough to seek urgent medical attention, and the diagnosis of an occluded graft was made during routine surveillance scanning. Of the remaining 42 (60.9%) grafts that remained patent throughout the course of the study, only four had stenoses detected that were considered to place the grafts at risk of occlusion. Three had stenoses at the proximal anastomoses and one at the distal anastomosis (Table IV). These anastomotic lesions had the characteristic appearance of neointimal hyperplasia. No instances occurred where significant progressive atherosclerosis in the inflow or outflow arteries was found. Two of the grafts with proximal stenoses underwent balloon angioplasty, and one had a patch angioplasty, whereas the one with a distal stenosis was anticoagulated with warfarin. All remained patent. The hemodynamic parameters before and after intervention are outlined in Table IV. Patients 3 and 4 with proximal stenoses had an interval decrease in ASPI of greater than 0.15, with only one significantly improving after angioplasty. Two of the three with proximal stenoses had an improvement in MFV after angioplasty. These numbers are too small for any statistical evaluation. All 27 grafts that occluded had had a full duplex interrogation within the preceding 6 months without any remediable disease detected. Five of the failed

3 JOURNAL OF VASCULAR SURGERY Volume 20, Number 4 Lalak et al. 639 grafts had had a normal scan result less than 1 month before occlusion. In the study before occlusion the mean MFV for the 27 occluded grafts was 0.56 m/sec (95% confidence interval 0.47 to 0.66), which compared to the MFV of the 42 patent grafts of 0.57 m/see (95% confidence interval 0.50 to 0.65). This finding was not statistically significant. Nine (33.3%) of the 27 occluded grafts had an MFV of less than 0.45 m/see compared with 10 (23.8%) out of the 42 patent grafts (not statistically significant). No abnormal changes in ASPI were seen in any of the occluded grafts in the studies before occlusion. The outcome of the occluded grafts is outlined in Table V. We have defined significant symptoms as those in patients presenting with acute ischemia and mild/nil symptoms as those detected at routine Doppler follow-up with symptoms not severe enough to seek urgent medical attention. All patients who on clinical grounds had occluded grafts greater than 4 weeks' duration underwent graft replacement, if their symptoms warranted it. Urgent limb-threatening ischemia and occlusions that on historic evidence had occluded within 4 weeks initially had an open graft thrombectomy followed by graft replacement, if the thrombectomy was unsuccessful. Ten patients required replacement grafts, whereas four of the thrombectomies were successful. The two patients with occluded grafts who had angioplasties had percutaneous tranluminal angioplasties of stenosed deep femoral arteries. The 10 patients not undergoing intervention because of acceptable symptoms or medical contraindications either underwent anticoagulation or were observed. DISCUSSION The identification of remediable stenoses in vein bypass grafts is justified by the resuks of studies showing that the secondary patency after intervention is almost as good as the primary patency. 13 The surgical literature is replete with reports supporting the role of surveillance programs of infrainguinal arterial vein autografts. 19,14,1s The classic study by Szilagyi in 1973,1 who used angiography to study 377 reversed vein grafts, characterized the disease leading to failure in these grafts. It popularized the policy of aggressive surgical prophylactic intervention to maintain patency. Angiography, however, is expensive and invasive, rendering it unsuitable for following large number of grafts. The development of the noninvasive vascular laboratory and more recently duplex scanning has provided a suitable alternative to angiography, with the duplex scan Table III. Operative details Femoropopliteal - above knee 41 Femoropopliteal - below knee 21 Tibioperoneal trunk 1 Anterior tibial 5 Peroneal 1 Total 69 reported to be as accurate in detecting graft stenosis as angiography, s Before the advent of the vascular laboratory, traditional follow-up was by clinical examination supplemented by continuous wave Doppler-derived ankle pressures. However, recent studies have shown that up to 40% of grafts fail without a premonitory change in ASPI, 6,7'16 and recurrence of symptoms and decrease in ASH usually indicates a failed graft and one not suitable for surgical or endovascular intervenfion, s'13 We also found in this series of prosthetic grafts that the ASPI was not helpful in detecting grafts at risk. Recent reports have also shown that duplex scan surveillance may detect up to 15% to 24% of stenosis in in situ grafts and 6% to 10% in reversed vein grafts. 2,3 Remediable intervention can improve patency rates by up to 15%. 2 Duplex scan surveillance of autologous vein grafts has been shown in one study to be worthwhile for only the first year after operation, during which time approximately 25% of femorodistal grafts will develop stenoses. 3 For surveillance to be effective in this time period it should be conducted immediately before discharge from hospital, followed by 4 to 6 weeks, 3 months, 6 months, and 9 months after the operation. In this way up to 95% of stenoses would be detected. 24 Increasing the frequency of surveillance of prosthetic grafts to three monthly intervals may improve the detection of disease. However, the fact that five grafts in this series occluded within 1 month of a completely normal duplex study contradicts this view. In an effort to improve the cost benefit of noninvasive surveillance of vein grafts, Bandyk et al.s,s,12 and Mills et al.7 have shown that full duplex: scanning of the graft and adjacent arteries may not be necessary and that MFV is accurate in identifying grafts at risk of failure. An MFV of less than m/see is highly predictive of graft failure and is a less expensive alternative to duplex scanning. Using Bandyk's criteria of MFV of m/see, we found no difference in occluded versus nonoccluded grafts. The role of peak systolic flow in prosthetic grafts, which have a uniformly larger (6 mm) diameter compared with that of autologous vein grafts

4 640 Lalak et al. JOURNAL OF VASCULAR SURGERY October 1994 Table IV. Hemodynamic parameters Preoperative Postoperative Preoperative PSFV Postoperative Disease Treatment ASPI ASPI MFV at stenosis MFV Proximal stenosis Patch angioplasty 0.81 (0.89) Distal stenosis* Anticoagulated Proximal stenosis PTA 0.57 (0.89) Proximal stenosis PTA 0.83 (1.00) Numbers in brackets correspond to in study before development of stenosis. ASH, Ankle systolic pressure index; M.FV, midgraft flow velocity; PSVF, peak systolic flow velocity (m/see); PTA, percutaneous transluminal angioplasty. *No active treatment. Table V. Outcomes and interventions of occluded grafts Symptoms Significant (presenting with acute symptoms) Mild/nil (detected on follow-up) Replacement graft 6 4 Thrombectomy 4 0 Amputation 1 0 Angioplasty 0 2 No treatment 4 6 > 4 ram) and in situ vein grafts ( < 4 ram), needs to be defined, because flow velocity is directly related to diameter of the conduit. We suggest that the observations in vein studies cannot be extrapolated to prosthetic grafts in similar anatomic sites. M1 the previously mentioned studies have applied to autologous vein grafts. Sporadic mention is made of prosthetic grafts in some studies that have included both vein and prosthetic infrainguinal grafts. No studies have been made, however, of a homogenous series of prosthetic grafts. This study has attempted to define the role of the various modes of surveillance (e.g., ASPI, MFV, and serial duplex mapping) in a consecutive series of Gortex infrainguinal bypass grafts. With neointimal hyperplasia at proximal and distal anastomoses, a well-recognized cause of failure of prosthetic grafts, one would expect the duplex scan to be an ideal mode of detecting these lesions. However a contrary result was obtained, with most grafts failing because of acute thrombotic occlusions with no predictive, morphologic, or hemodynamic changes being found in the preceding scans. Only four out of a total number of 255 duplex scans detected a lesion suitable for remediable intervention. No premonitory changes were found in ASPI or MFV that correlated with graft occlusion, and even total interrogation with duplex scans of the inflow and outflow arteries and the entire graft, with special attention to the anastomoses, was helpful. We postulate that the well-recognized pathologic entity of neointimal hyperplasia is a less common cause of failure than acute thrombosis. The thrombosis is duc to a complex relationship between blood coagulability, graft surface thrombogenicity, and the rate of flow through the graft. This relationship has not been addressed in this study and begs further evaluation. We conclude that routine vascular laboratory surveillance in the postoperative management of infrainguinal Gore-tex bypass grafts is still not proven. REFERENCES 1. Berkowitz HD, Hobbs CL, Roberts B, Freiman D, Oleaga J, Ring E. Value of routine vascular laboratory studies to identify vein graft stenosis. Surgery 1981;90: Moody P, Gould DA, Harris PL. Vein graft surveillance improves patency in femoro-popliteal bypass. Eur J Vasc Surg 1990;4: Taylor PR, WoVe JHN, Tyrrell MR, Nicolaides AN, Houston RE. Graft stenosis; justification for 1-year surveillance. Br J Surg 1990;3: GriggMJ, Nicolaides AN, Wolfe JHN. Detection and grading of femorodistal vein graft stenoses: duplex velocity measurements compared with angiography. J VAsc SURG 1988;8: Bandyk DF, Seabrook GR, Moldenhauer P, et al. Haemodynamics of vein graft stenosis. J VAsc SURG I988;8: McShane MD, Gazzard VM, Clifford PC, Httmphries KN, Webster JHH, Chant ADB. Duplex ultrasound monitoring of arterial grafts; prospective evaluation in conjunction with ankle pressure indicies after femorodistal bypass. Eur J Vasc Surg 1987;I: Mills JL, Harris EJ, Taylor LM, Beckett WC, Porter IM. The importance of routine surveillance of distal bypass grafts with duplex scanning: a study of 379 reversed vein grafts, l VASC SURG 1990;],2:37% Bandyk DF, Kaebnick HW, Bergamini TM, Moldenhauer P, Towne lb. Haemodynamics of in situ saphenous vein arterial bypass. Arch Surg 1988;123:

5 JOURNAL OF VASCULAR SURGERY Volume 20, Number 4 Lalak et al Green RM, McNamara J, Ouriel K, De wees e JA. Comparison of infrainguinal graft surveillance techniques. J VASC SURG 1990;2: Szilagyi DE, EUiott JP, Hegeman IH, et al. Biologic fate of autogenous vein implants as arterial substitutes. Ann Surg I973;178: Harris PL. Vein graft surveillance-all part of the service. Br J Surg 1992;79: Bandyk DF, Cato RF, Towue JB. A low flow velocity predicts failure of femoropopliteal and femorotibial bypass grafts. Surgery 1985;98: I3. Barnes RW, Thompson BW, MacDonald CM, et al. Serial noninvasive studies do not herald postoperative failure of femoropopliteal or femorotibial bypass grafts. Ann Surg i989;210: Wyatt MG, Muir RM, Tenant WG, Scott JA, Baird RN, Horrocks M. Impedance analysis m identify the at risk femorodistal graft. J VASC SURG 1991;13: Turnipseed WD, Acher CW. Postoperative surveillance-an effective means of detecting correctable lesions that threaten graft patency. Arch Surg 1985;120: Dolgin C, Collins R, Martin E, Voorhees AB, Nowygrod R, The prognostic value of the noninvasive vascular laboratory in autogenous vein bypasses of the lower extremities, l Cardiovasc Surg i983;24: Submitted Jan. 19, 1994; accepted May 2, 1994.