Percutaneous transluminal dilatation of peripheral arteries: An analysis of factors predicting early success

Transcription

1 SYMPOSIUM Interventional Radiology EDITOR'S NOTE: This symposium comprises the papers presented at the combined breakfast program of the Society for Vascular Surgery and the International Society for Cardiovascular Surgery, North American Chapter, on June 18, 1983, at the scientific meeting in San Francisco. The subjects were selected by the Program Committee for their value in answering problems of practical clinical import. Percutaneous transluminal dilatation of peripheral arteries: An analysis of factors predicting early success Michael E. Lally, M.D., K. Wayne Johnston, M.D., and David Andrews, Ph.D., Toronto, Ontario, Canada Four hundred ninety-five patients undergoing peripheral arterial percutaneous transluminal dilatation (TLD) with the Gruntzig balloon catheter were studied prospectively to determine which factors could be used to predict a successful result from the procedure. Ten variables were recorded before the TLD. The procedure was considered a success at follow-up if both the clinical grade and the objective vascular laboratory results improved. The results of a logistic discriminant function analysis showed that three variables were associated with success of a TLD at 3 months: the site of the TLD, the severity of the lesion (i.e., stenosis or ocdusion), and the runoff. With these results, logistic regression analysis was used to estimate the chances of a successful result for all combinations of these significant variables. It is concluded that the early result ofa TLD is determined by the site of the TLD, the severity of the lesion, and the runoff. A table of the estimated chances of success for any combination of these variables has been constructed and accurately describes our patient population. (J VASC SURG 1984; 1: ) In spite of some skepticism, percutaneous transluminal dilatation (TLD) is becoming an increasingly popular method for managing selected patients with localized peripheral arterial occlusive disease. The low morbidity and complication rates associated with this procedure make it an attractive option in the treatment of selected patients with ischemic complaints, especially if the patient is a high operative risk or the symptoms are not disabling enough to warrant surgery. Despite these advantages, its overall success rate is lower than reconstructive surgery, and consequently it is desirable to determine which factors predict the result of the procedure. 1,2 The purposes of this article are to ascertain which variables are associated with the success of a From the Departments of Surgery and Biostatistics, The University of Toronto. Reprint requests: K. W. Johnston, M.D., Toronto General Hospital, 915 E-N Eaton Bldg., 200 Elizabeth St., Toronto, Ontario MSG 1L7, Canada. 704 TLD and to develop a mathematical model that will estimate the chances of success for all combinations of the significant variables. METHODS Patients. Data on 495 consecutive patients undergoing TLD at the Toronto General Hospital formed the basis for this study. The patients were included if they were referred for the procedure by one of the physicians or surgeons at the Toronto General Hospital or if their referring physiciarl agreed to allow us to assess and follow-up their patients objectively. Technique. The TLDs were performed by experienced vascular radiologists using the Gruntzig balloon catheter. The details of our technique are similar to Gruntzig's and have been described previ~ ously, a'4 For both iliac and femoral-popliteal dilatations, the catheter was usually introduced through the ipsilateral common femoral artery. Heparin, 5000 units, was given intra-arterially after the ca~ e-

2 Voiume 1 Number 5 September 1984 Percutaneous transluminal dilatation 705 ter was across the stenosis or occlusion and was not reversed at the end of the procedure. The patients received aspirin, 325 mg, and dipyridamole, 50 mg, orally three times daily starting 2 or 3 days prior to the procedure and continued for 1 month. No other long-term anticoagulation was used. Evaluation of results. The result of the TLD was determined with the use of a combination of subjective criteria and objective vascular laboratory measurements. 1"4 For a TLD to be called a success, the following criteria had to be satisfied: the patient's symptoms improving by at least one clinical grade; the ankle/brachial systolic pressure index increasing by at least 0.10; the Doppler pulsatility index increasing by more than 20%; monophasic Doppler waveforms becoming biphasic or triphasic; and the treadmill exercise distance doubling. Variables. Based on the resuks of previous vascular follow-up studies, we hypothesized that the following 10 variables might be related to the success of the procedure, and they were recorded prospectively: age, sex, presence and severity of diabetes, history of previous TLD at the same site, clinical indication for the procedure, site of the dilatation, ankle/brachial pressure ratio before the procedure, severity of the lesion (i.e., stenosis or occlusion), severity of arterial occlusive disease distal to the TLD (i.e., runoff), and occurrence of a complication. The subcategories of these variables are shown in Table I. Data analysis and statistical methods. The patient data were stored on a microcomputer and updated after each patient follow-up visit. The microcomputer was used to tabulate a frequency distribution of the characteristics of the patient population ~d to calculate the long-term results of TLDs by the life-table analysis method. In this study a larger computer was used for the logistic discriminant function analysis and the logistic regression analysis. A logistic discriminant function analysis was performed with the use of the SAS FUNCAT (SAS Institute, Inc., Cary, N.C.) subroutine to identify the variables associated with success. First, the program was used to determine which of the variables most significantly affected the result of the TLD. Second, to assure that none of the remaining variables had significance that might have been concealed in the initial discriminant analysis, the following procedure was adopted. The designated group of significant variables was combined with one of the remaining variables one by one and the FUNCAT procedure repeated. This procedure was repeated with each of the remaining variables, Table I. Variables and characteristics of the study population Variable Patients Subcategories and codes (%) Age (yr) < > Sex Male 65.1 Female 34.9 Diabetes Nil 80.1 Diet controlled 4.3 Oral hypoglycemics 8.3 Insulin dependent 7.3 Previous TLD No 92.9 Yes 7.1 TLD indication Claudication 82.2 Limb salvage 12.5 Other 4.3 Site Common iliac Common and external iliac 8.9 Femoral-popliteal 26.2 Other 8.4 Complications Nil 88.5 Death 0.6 Minor 10.3 Major 0.6 Ankle-pressure ratio < > Severity lesion Stenosis 79.6 Occlusion 20.4 Runoff No distal disease 46.0 <50% stenosis or 1-vessel 13.1 occlusion 50%-99% stenosis or vessel occlusion Complete occlusion or vessel occlusion and the significance of the added variable was assessed. Logistic rcgression analysis was used to estimate the chances of a successful result for all combinations of the significant variables. The success of the procedure dcpends on thc selected variables and logistic rcgression analysis gives estimates of this dependence in the form: L = K + KI~VARIABLE 1 + K2*VARIABLE 2 (1) +... Kn~VARIABLE n where K is a constant and K1, K2,... Kn are the coefficients associated with each ofthc variables and * represents multiplication. A variable may represent the presence of a particular condition. The probability of success of the TLD for each of the combinations of the variables is given by: Probability success = (c~+~l)/ (1 + e**l) (2) where e~+*l represents e raised to the Lth power.

3 706 Lally, Johnston, and Andrews Journal of VASCULAR SURGERY Table. Distribution of patients according to three significant variables < 50% Stenosis or 1 Vessel Occlusion 50-99% Stenosis or 2 Vessel Occlusion Occlusion or 3 Vessel Occlusion Common External Gommon Femorallilac Ilia and popliteal External Iliac -- S~enosis % successful TLDS D% Failed TLDS Height of each box is ~" # TED Patients Fig. 1. Results of logistic discriminant function analysis showing the three variables: site of the TLD, severity of lesion, and runoff. Heights of shaded areas are square root of number of failures; clear areas, square root of number of successes. (This format was used for purposes of scaling in figure.) Forty-one of the 495 procedures were excluded from the analysis because the site of the TLD was uncommon and there were insignificant numbers in the groups to be meaningful. In this study the factors determining early success (defined as success at 3 months) were analyzed. RESULTS Frequency distribution of variables. The characteristics of the study population are shown in Table I. Specifically, the frequency distribution of each of the variables and subcategories are listed. Logistic discriminant function analysis. The logistic discriminant function analysis identified the following three variables as being jointly significant and associated with early (3 months) success of a TLD: the site of the dilatation, the severity of the lesion (presence of stenosis or occlusion), and the status of the runoff. None of the other variables, when added to these three variables, were found to be significant. The distribution of the patients based on these variables is shown in Table. Fig. 1 summarizes the results of the discriminant analysis and demonstrates the interrelationship of the site of the TLD, the severity of the lesion, and the runoff. For each combination of these three significant variables, the height of each histogram is the square root of the number of cases. The shaded area represents the number of failed TLDs and the clear area the number of successes. This figure visually Site (No.) (No.) Common iliac I I I I I I laemoral-popliteal I I I = no runoff disease; = <50% distal stenosis or one- fibial artery occlusion; I = 50%-99% distal stenosis or two- tibial artery occlusion; = occlusion distal stenosis or three-tibial displays the data that have been used for the logistic regression analysis. Logistic regression analysis. With the use of logistic regression analysis, the values of the coefficients K, K1, K2... were determined for the significant variables. For each combination of site,' severity of lesion, and status of runoff; the percentage chance of success of a TLD was calculated by using equation 2. Table IA is a table of the estimated probabilities of success of a TLD for the different combinations of site, severity of lesion, and runoff. Table IB shows the 5% and 95% confidence limits for these estimates. In regard to site, for the different combinations of the variables, this table shows that the best chance for a successful TLD is at the external iliac site, although the common iliac and femoral-popliteal sites have results at 3 months that were nearly identical. When attempts are made to dilate multiple iliac lesions (i.e., a combined common and external iliac lesion), the chance of success is lower. For all combinations of variables, dilatation of a stenotic lesion consistently has a 20% to 25% greater chance of success than dilatation of an occluded artery, and the chances of success are progressively worse as the runoff became poorer. As illustrated in Table, the logistic regression

4 Volume 1 Number 5 September 1984 Percutaneous transluminal dilatation 707 Table IA. Chance of successful TLD at 3 months Site (%) (%) Common iliac I I I I I I Femoral-popliteal I I I = no runoff disease; = <50% distal stenosis or one-tibial artery occlusion; I= 50%-99% distal stenosis or two- tibial artery occlusion; = occlusion distal stenosis or three-tibial equation accurately predicted the probabilities of a successful dilatation. For each combination of variables, the number of TLDs predicted as being successful by the regression analysis closely agreed with the actual number of successful cases. DISCUSSION Transluminal dilatation is an alternative to vascular reconstructive surgery for the treatment of selected patients with peripheral arterial occlusive disease. Its advantages include low morbidity, low mortality, lower cost, short hospital stay, repeatability, low complication rate, and high patient acceptability. Also, TLD can be used as an adjunct to surgery to improve the inflow, thus limiting the extent of the operative procedure, and to treat postoperative complications of saphenous vein bypass grafts or progression of the occlusive disease. Since the mid-1970s, when TLD with the Gruntzig balloon catheter first became popular in North America, most investigators have reported only small retrospective series and have rarely used objective criteria for evaluating the results of the procedure. In contrast, our series is a prospective study of 495 TLDs, and the procedure was considered a success only if there was improvement of both the patients' symptoms and the objective measurements in the vascular laboratory. Table IB. 95% confidence limits of estimated chance of success at 3 months Site (%) (%) Common iliac I I I I I I Femoral-popliteal I I I = no runoff disease; = <50% distal stenosis or one-tibial artery occlusion; I= 50%-99% distal stenosis or two- tibial artery occlusion; = occlusion distal stenosis or three-tibial From a review of the literature it is difficult to determine which factors were important determinants of success; however, the following seem to be important. Site of the TLD. Most authors agree that the best results are obtained in the iliac segment, where success rates at 1 year are 76% to 93% and at 2 years 66% to 92%. 1'2"5-s The reported success rates for femoral-popliteal disease are 51% to 80% at i year and 46% to 75% at 2 years. 1-a'~'8-11 In the series reported here the cumulative success rates for all iliac TLDs at 1 year and 2 years was 71.1 _+ 2.9% (mean +_ 1 SE) and %, respectively, and for the femoral-politeal segment was 56.I +_ 4.8% and %. The results of dilatation of the profunda femoris artery, the common femoral and the tibial arteries have been less satisfactory. Severity of lesion. Some authors are reluctant to dilate occluded vessels because of the potential risk of arterial perforation; however, in our experience this concern is unfounded)7 In the femoralpoptiteal segment, Waltman et a12 reported a success rate of 87.5% for stenoses and 76% for occlusions. In our previous study we noted a 60% cumulative success rate at 1 year for stenoses and 40% for occlusions. Although the same trend has been re-

5 708 Lally, Johnston, and Andrews Journal of VASCULAR SURGERY Table. Number of TLDs predicted successful by logistic regression analysis/actual number of successful results Site (No.) (No.) Common lilac I 73/73 14/16 12/12 1/2 I 13/11 1/1 27/26 1/1 I 37/35 3/2 13/12 1/1 I 15/17 0/0 1V 27/28 1/1 I 14/17 3/4 2/2 1/0 I 2/0 0/0 8/8 1/0 FemoralTopliteal I 34/34 15/13 13/13 9/9 I 12/13 8/8 7/7 7/8 I = no runoff disease; = <50% distal stenosis or one- tibial artery occlusion; I = 50%-99% distal stenosis or two- tibial artery occlusion; = occlusion distal stenosis or three-tibial ported in the iliac segment, we have had excellent results with dilatation of occluded iliac arteries. 4'7 Runoff. There is general agreement that the results following vascular surgery are less satisfactory if the runoff is poor. The same has been reported with TLD, although some have suggested that the adequacy of the runoff is of little or no importance. 5"8"11'12 This divergence of opinion is likely due to the fact that the runoff has not been evaluated very critically. Other variables. Although we previously reported that the success rate was higher in patients with an ankle/brachial systolic blood pressure ratio higher than 0.35, 4 our present results and those of others have not observed a difference between the pre-tld pressure measurements in the successful and unsuccessful cases. 13 In general, it is to be expected that the results will be better when the indication for the procedure is claudicarion and lower when the patient has more severe disease and ischemic rest pain, ulceration, or gangrene are present. In the iliac segment Spence et al. 8 reported that the results were better if the indication was claudication compared with salvage, but in the femoral-popliteal segment the indication did not seem to be a factor. Freiman et al.12 noted an overall early success rate of 91.8% for claudication compared with 83% for sal- vage. In our previous analysis we found the presence of diabetes did not adversely affect the results. 1"4 In the iliac segment Spence et al. s reported that the results were the same in diabetics and nondiabetics, but in the femoral-popliteal area the 1-year success rate was 85.4% for nondiaberics and 53.5% for diabetics. Schmidtke et al.14 reported that age had little effect on the results, although we previously reported that patients younger than 55 years had a statistically better long-term result than the older patients. 1,4 The studies reported above have not clearly identified the factors associated with success of a TLD. Furthermore, they have not considered the important interrelationships between variables. When the effect of an individual variable on the outcome is assessed independently of the other variables, their interrelated effects are disregarded. In fact, it is to be expected that all of the significant variables will have interrelated effects, and consequently the effect of each individual variable on the result of the TLD will be confounded by the presence of other significant variables. This distortion in the estimate of the chances of a successful TLD can be handled by using logistic discriminant function analysis to identify the variables associated with success and logistic regression analysis to estimate the probabilities of success for a specific combination of significant variables. '~ In this study of the 10 variables analyzed the logistic discriminant function analysis identified only three as being associated with success at 3 months: the site of the TLD, the severity of the lesion, and the runoff. With the use of logistic regression analysis, a table of the estimated probabilities of success of a TLD at 3 months was constructed for the different combinations of site, severity of the lesion, and runoff. These analyses show that these three factors are strongly interrelated. The probability of early success of a TLD is high if the vessel is stenosed and the runoff is good. If the other factors are equal, common lilac, external iliac, and femoral-popliteal dilatations all have a high probability of early success, but the results are less sarisfactory when multiple iliac dilatations of both the common and the external iliac arteries are performed. The mathematical model appears to be quite accurate since the calculated number of successful dilatations closely agrees with the actual number of successes. Nonetheless the estimated probabilities of success in Table I were calculated based on the population of patients studied at the Toronto General Hospital. Therefore they apply only to this or a

6 Volume 1 Number 5 September 1984 Percutaneous transluminal dilatation 709 similar population. One should be cautious in applying this data to unknown or unrelated populations. The table of estimated probabilities have been developed to predict early success (3 months). In the future, with larger numbers of patients available for follow-up at 1 and 2 years, similar analyses will be performed to determine the variables that predict the long-term results. CONCLUSIONS By using discriminant function analysis we have dctcrmined which variables were associated with succcss of a TLD and have developed a table of predicted success rates for the different combinations of site, severity of the lesion, and runoff. No factor can be selected as being more important than the other two in predicting the result of the TLD. Rather, all three variables combined consistently have a significant effect on the result. We wish to acknowledge the financial support of Cook Inc., the assistance of Mrs. Maureen Rae who coordinated the follow-up study, and Mrs. Susan Ungaro and Mrs. Marilyn Bleach who performed the vascular laboratory studies. REFERENCES 1. Johnston KW, Colapinto RF. Peripheral arterial transluminal dilatation: Early results. Can J Surg I982; 25: Johnston KW. A surgeon's view of peripheral arterial transluminal dilatation. In: Bergan JJ, ed. Clinical surgery international, vol 7. New York: Churchill Livingstone, Gruntzig A, Kumpe DA. Technique of percutaneous transluminal angioplasty with the Gruntzig balloon catheter. AJR I979; i32: Johnston KW, Colapinto RF, Baird RJ. Transluminal dilatation--an alternative? Arch Surg 1982; 117: Neiman HL, Bergan JJ, Yao JS, Bran& TD, Greenberg M, O'Mara CS. Hemodynamic assessment of transluminal angioplasty for lower extremity ischemia. Radiology 1982; 143: Neiman IlL, Brandt TD, Greenberg M. Percutaneous transluminal angioplasty: an angiographer's viewpoint. Arch Surg 1981; 116: Roberts B, Ring EJ. Current stares of percutaneous transluminal angioplasty. Surg Clin North Am 1982; 62: Spence RK, Freiman DB, Gatenby R, Hobbs CL, Barker CF, et al. Long-term results of transluminal angioplasty of the iliac and femoral arteries. Arch Surg 1981; 116: Waltrnan AC, Greenfield AJ, Novelline RA, Abbott WM, et al. Transktminal angioplasty of the iliac and femoropopliteal arteries. Current status. Arch Surg 1982; 117: Gnmtzig A, Zeitler E. Coopcrative study of results of PTR in 12 different clinics. In: Zeitler E, Gruntzig A, Schoop W, eds. Percutaneous vascular recanalization. Berlin: Springer- Verlag, 1978: Lu CT, Zarins CK, Yang CF, Sottiurai V. Long-term arterial occlusion: Percutaneous transluminal angioplasty. AJR 1982; 138: Freiman DB, Spence R, Gatcnby R, Gertner M, Robcrts B, Berkowitz HD, et al. Transluminal angioplasty of the iliac and femoral arteries: Follow-up results without anticoagulation. Radiology 1981; 141: Kaufman SL, Barth KH, Kadir S, Williams GM, Smith GW, et al. Hemodynamic measurements in the evaluation and follow-up of transluminal angioplasty of the iliac and femoral arteries. Radiology 1982; 142: Schmidtke I, Zeitler E, Schoop W. Late results ofpercutaneous catheter treatment (Dotter's technique) in occlusion of the femoro-popliteal arteries, Stage. In: Zeitler E, Gruntzig A, Schoop W, eds. Percutaneous vascular recanalization. Berlin: Springer-Verlag, 1978: Anderson S, et al. Logit analysis. In: Anderson S, Auquier A, Hauck WW, Oakes D, Vandaele W, Weisberg HI, eds. Statistical methods for comparative studies. Techniques for bias reduction. New York: John Wiley & Sons, Inc, 1980:7-17,