Impact of Different Hemodynamic Criteria for Stent Placement after Suboptimal Iliac Angioplasty

Impact of Different Hemodynamic Criteria for Stent Placement after Suboptimal Iliac Angioplastyl Alfons G. A. Kamphuis, MD Andries D. van Engelen, MD Eric Tetteroo, MD, PhD Maria G' M' Huninkr MD' PhD WillemP' T' M' MD' PhD Trial for the Dutch Iliac Study Group

I n d e x terms: Arteries, stents and prostheses. ~ l vessels, ~ ~ flow dynamics. d ~liac arteries, angioplasty Iliac arteries, stents and prostheses

JVIR 1999; 10:741-746 Abbreviations: DIST = Dutch Iliac Stent Trial, FDA = Food and Drug AdPSV = peak velOcity, PTA = percutaneous transluminal angioplasty

From the Department of Radiology (A.G.A.K.), Red Cross Hospital Beverwijk, Vondellaan 13, 1942 LE Beverwijk, The Netherlands; the Department of Radiology (A.D.vE., E.T., W.P.T.M.M.) University Hospital Utrecht, Utrecht, The Netherlands; the Department and Biostatitics, and Department of Radiology (M,G,M,H,) Erasmus Medical Center, Rotterdam, The Netherlands; and the Department of Health Policy and Management, Harvard school of Public Health, Boston, Massachusetts. Supported by grant OG-931001 from the Commission of Investigative Medicine of the D U ~ National C ~ Health Insurance Council and by a PIONIER award from the Netherlands Organization for Scientific Research. Received September 30, 1998; revision requested November 17; revision received February 1, 1999; accepted February 3. Address correspond e n c e t o A.G.A.K.

o SCVIR, 1999

PURPOSE: To investigate the consequences of different hemodynamic criteria as indications for stent placement after suboptimal iliac angioplasty. MATERIALS AND METHODS: One hundred thirty-six patients with intermittent claudication, on the basis of atherosclerotic disease of the iliac artery, underwent angioplasty. Intraarterial systolic and mean pressures were simultaneously recorded above and below the lesion, with and without vasodilation, and before and after percutaneous angioplasty. These data were used to estimate what proportion of the study population would be eligible for stent placement according to different criteria reported in the literature. Subsequently, the authors compared peak systolic velocity (PSV) ratios during follow-up in their patients, with and without indication for stent placement according to two different criteria. RESULTS: Applying the different thresholds reported in the literature to the patient group shows that stent placement would be indicated in anywhere from 4% to 87% of cases. No difference was observed when PSV ratios were compared in patients with a residual mean pressure gradient of r 5 and 5 10 mm Hg with patients with a residual mean pressure gradient of less than 5 mm Hg. CONCLUSIONS: Application of the various published thresholds as indications for secondary stent placement leads to a wide range in proportion of cases requiring stent placement. Lesions with a residual mean pressure gradient of > 5 and < 10 mm Hg fare as well as lesions with a residual mean pressure gradient of less than 5 mm Hg. The optimal criterion is still not clear.

ILIAC artery stent placement has become an accepted adjuvant treatment for suboptimal percutaneous transluminal angioplasty (PTA) (1-9). The Palmaz balloon-expandable stent was the first device to be approved by the Food and Drug Administration (FDA) for use in the iliac artery. The indications for stent placement include suboptimal results of iliac angioplasty based on hernodynamic measurements, angiographic residual stenosis, or an extensive intima1 dissection (10). The use of hemodynamic pressure gradients to define a successful

angioplasty result appears to be correlated with successful clinical improvement and seems superior to using angiographic criteria (11-18). However, authors use different hemodynamic pressure gradients as a definition of a significant residual stenosis and, therefore, as an indication for secondary stent placement. To date, no studies have been published comparing clinical results using different hemodynamic criteria and it remains unclear which pressure gradient is optimal. The aim of this study was to investigate the consequences of apply-

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Table 1 Baseline Characteristics Characteristic

Number

Number of patients % Malememale Number of lesions Age (years i SD) History Tobacco use Diabetes mellitus Hypertension Cerebrovascular accident Cholesterol >6.5 mmol/L Clinical grade (SVSIISCVS classification) Category 1 Category 2 Category 3 Category 4 Category 5 ABI a t rest ABI after exercise Walking distance (m) Previous interventional procedure PTA Vascular surgery (bypass) Lesion characteristics Arterial segment Common iliac artery External iliac artery Angiographic stenosis grade < 50% diameter reduction 2 50% diameter reduction Total occlusion Patency of runoff vessels Occlusion superficial femoral artery Occlusion deep femoral artery

136 73127 169 60 i 10 128 (94) 15 (11) 37 (27) 9 (7) 36 (26) 37 (27) 69 (51) 18 (13) 11(8) l(1) 0.77 t 0.20 0.54 ? 0.26 224 +- 88 22 (16) 16 (12) 114 (67) 55 (33) 19 (11) 138 (82) 12 (7) 19 (11) 8 (5)

Note.-Plus-minus values are means +- SD; all other values are numbers of patients, with percentages given in parentheses. SVSIICSVS = Society of Vascular Surgery and International Society for Cardiovascular Surgery.

ing various hemodynamic criteria reported in the literature (1-9,18-22), in terms of numbers of lesions requiring stent placement. Subsequently, we compared peak systolic velocity (PSV) ratios during follow-up in patients with and without indication for stent placement according to two different published criteria.

MATERIALS AND METHODS Study Population This study was part of the Dutch Iliac Stent Trial (DIST), a multicenter randomized controlled trial. The DIST was initiated, among

other reasons, to analyze whether intraarterial pressure gradients across angioplasty sites may serve as an indication for secondary stent placement (18,191. Patients who presented with intermittent claudication or critical ischemia a t the vascular surgery department from November 1993 through November 1996 were contacted and requested to participate in the trial. Inclusion criteria were (i) typical clinical symptoms of intermittent claudication or ischemia, reduced ankle-brachial indices, and reduced pulsation of the femoral artery; and (ii) a hemodynamically significant lesion in the common or external iliac artery at angiography

(diameter reduction of more than 50% based on visual estimation) or at duplex examination (PSV ratio of more than 2.5). Exclusion criteria were comorbidity, such as malignancy and severe cardiac or cerebrovascular pathology; stenosis longer than 10 cm; occlusion longer than 5 cm; stenosis extending into the distal aorta; nonmedical factors, such as not being able to read or write the Dutch language; and anticipated poor compliance. Patients with multilevel disease or a history of vascular surgery of the iliac artery were not excluded. The study protocol was approved by the Institutional Review Boards of the participating centers, two university hospitals, and four large referral hospitals. All patients were informed about the background and procedures of the trial by means of both oral and written information, and all patients gave their written consent. Patients were randomly assigned to undergo either primary stent placement (n = 143) or primary PTA (n = 136). PTA was considered suboptimal in cases of a residual trans-stenotic mean pressure gradient of more than 10 mm Hg, with or without injection of vasodilators distal to the treated segment. In these circumstances, PTA was immediately followed by stent placement ( n = 59). In the present study, only data concerning the patients assigned to primary PTA, with or without subsequent stent placement, were evaluated. Baseline characteristics of this group are presented in Table 1. The treatment scheme, as well as the number of patients and lesions, is presented in the Figure.

Procedures The interventional procedure was described in detail previously (18,19). Briefly, in all patients, digital substraction angiography was performed with a 5-F pigtail catheter. Subsequently, extensive intraarterial measurement of systolic and mean pressures was performed, before and during pharmacologically induced vasodilatation, with a

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279 patients1356 lesions

Randomization

within the stenosis and in the adjacent nonstenotic region. After therapy, PSVs were recorded at the treated site and the adjacent region. PSV ratios were calculated by dividing the PSV in the stenosis or treated site by the PSV in the adjacent region. Data Acquisition and Analysis

Primary stent placement 143 patients1187 lesions

PTA 136 patients1169 lesions

IntraarteriaI pressure measurements

Selective stent placement 59 patients165 lesions Figure. Flow chart with the number of patients and number of lesions.

special 5-F double-sensor catheter (Sentron, Roden, The Netherlands), which allowed simultaneous measurement of intraarterial pressures both proximal and distal to the lesion. This catheter employed a monorail system and was introduced over a 0.025-inch guide wire. After initial calibration, the signal from the Dressure catheter was recorded through a special interface on both a dieital readout and a channel recoQder. Vasodilation was induced by either 25 mg of papaverine (8% of cases), 40 mg of tolazoline (33%),or 100 pg of nitroglycerin (59%),to mimic exercise conditions. The systolic and mean pressures were recorded when the online intraarterial pressure reached a minimum, which occurred 20-40 seconds after vasodilator injection. Balloon dilation was performed according to standard techniques. After completion of the dilation, the balloon catheter was exchanged for the pressure catheter, and again systolic and mean pressures were measured proximal and distal to the treated site, before and during vasodilation. In cases with a resid-

ual translesional mean pressure gradient of more than 10 mm Hg, with or without vasodilation, a Palmaz balloon-expandable stent was placed (Johnson & Johnson Interventional Systems, Warren, NJ) across the lesion. After stent placement, translesional pressures were again recorded before and during vasodilation. In 148 of the 169 (88%)lesions assigned to primary PTA, complete pressure recordings could be obtained. In the remaining 21 lesions, not all measurements could be recorded because of patient-related complications, such as cardiac problems or hypotension, a long duration of the procedure in elderly patients, or because of technical problems such as the presence of an occlusion or subtotal stenosis preventing pressure measurement with the double-sensor pressure catheter. Duplex measurements were performed in all patients before intervention, and at 3 and 12 months after intervention with standard ultrasound machines equipped with color Doppler. Before PTA, PSVs were recorded at the jet stream

A search of the English-language literature published since 1990 was performed to identify articles reporting on stent placement after suboptimal iliac angioplasty. Studies in which suboptimal angioplasty was described in terms of residual intraarterial pressure gradients were further analyzed (1-5,7-9, 18-22). The range of hemodynamic criteria found in the literature was applied to our patient group. We calculated the percentage of lesions eligible for stent placement using these different thresholds as a measure of a significant pressure gradient. In the DIST, hemodynamic significance was defined as a residual mean pressure gradient of more than 10 mm Hg, with or without pharmacologically induced vasodilation. Because vasodilation increases the translesional pressure gradient, lesions with a gradient of more than 10 mm Hg without vasodilation ( n = 19) did not undergo additional pharmacologic testing and were assumed to also have a gradient of more than 10 mm Hg with vasodilation. This assumption allowed us to also consider these lesions in the calculation of the total number of lesions eligible for a stent when applying criteria with vasodilation. After pharmacologically induced vasodilation, another 41 lesions revealed a mean pressure gradient exceeding 10 mm Hg. Thus, use of vasodilation tripled the number of lesions needing stents at the 10 mm Hg threshold. Although the DIST was not initiated to determine the optimal pressure gradient as an indication for subsequent stent placement, it was possible to compare the treatment results of two different protocols: we

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Table 2 Different Residual Translesional Pressure Gradients as an Indication for Stent Placement

Author Palmaz (1,2) Murphy (8) Martin (21) Long (22) Henry (9) Hausegger (5) Cikrit (7) Tetteroo (18,19) Hausegger (20) Zollikofer (4)

Hemodynamic Criterion Proportion of Lesions (systolic/mean pressure Eligible for gradient [mm Hg]" Vasodilation? Stent Placement (%) 5 (mean) 5 (mean) 2 5 (systolic)" 2 5 (mean)*' 2 5 (systolic)" 2 5 (mean)'" > 5 (systolic) 2 10 (mean) 2 10 (mean) 2 10 (mean) >10 (mean) >10 (mean) > 20 (systolic)" > 20 (mean)"; 2

2

Yes Yes No No Yes Yes No No Nof Yesf Yes No No No

77 77 76 36 87 77 70 13 13 48 41 13 18 4

Note.-The right column shows the percentages of lesions in our patient group eligible for stent placement, using these different translesional residual pressure gradients. * When not specified by the author, the criterion was applied to both mean and systolic gradients. f When not specified by the author, both methods (with and without vasodilatation) were calculated.

compared treatment results of lesions without an indication for stent placement according to the DIST protocol, but with an indication for stent placement according to the FDA criteria (ie, a post-PTA mean pressure gradient during vasodilation of 2 5 mm Hg and 5 10 mm Hg [group A]), with the results of lesions without an indication for stent placement according to both protocols (ie, < 5 mm Hg [group BI). Lesions with a gradient of more than 10 mm Hg would have had stents placed according to both protocols and were, therefore, excluded from this subgroup analysis. When the 5 mm Hg criterion is the optimal threshold, one would expect that the treatment results of group A would be less favorable than those of group B. However, if the 10 mm Hg criterion were to suffice, results would not differ between the two groups. Treatment results after 3 and 12 months were evaluated using PSV ratios because it is the best noninvasive method to quantify iliac artery stenosis and has been suggested as a follow-up method

after PTA (23,24). The KruskalWallis test was used to determine the statistical significance of differences between group A and B with respect to the PSV ratios.

1 RESULTS Table 2 illustrates the lack of uniformity of the hemodynamic criteria reported in the literature as an indication for stent placement. Variation exists in the magnitude of the gradient, the type (mean or systolic) pressure used, and in the process of vasodilation. Use of the various thresholds described in the literature would have led to stent placement in 4%-87% of the lesions in the DIST patient population (Table 2). Group A consisted of 46 patients with 52 lesions. These would have been treated with a stent using the FDA criteria, but were denied stent placement according to the DIST protocol. There were 34 lesions (in 31 patients) without indication for stent placement, according to both

the FDA and DIST criteria (group B). Table 3 shows the treatment results of both groups with regard to PSV ratios at 3- and 12-month follow-up. Not all follow-up information was available for logistical reasons, technical failures, and noncompliance. At 3 months, PSV ratios were available in 85% of group A and in 91% of group B. At 12 months, follow-up was available in 54% of group A and 59% of group B, respectively. The PSV ratios during follow-up do not differ significantly between the two groups.

I DISCUSSION In 1992, the Palmaz balloon-expandable stent received FDA approval for use after suboptimal iliac angioplasty. Previous studies demonstrated the incapability of angiography in identifying a suboptimal angioplasty result, and the use of intraarterial pressure gradients was advocated (17,18,25). Until now, however, authors disagree as to which pressure gradient is relevant-systolic or mean-the necessity of vasodilation, and the threshold pressure gradient considered significant as criterion for suboptimal angioplasty. Also, the technique of intraarterial pressure measurement is not uniform. Some authors use a two-transducer catheter system, with one catheter in the aorta and a second catheter in the femoral or external iliac artery. Some investigators use the unilateral pullback technique, whereas others measure the femoral pressure via the side port of the introducer sheath and the systemic arterial blood pressure by a catheter in the aorta (17). We used a double-sensor catheter positioned across the stenotic segment. The presence of a 5-F catheter may lead to additional narrowing of the luminal area and, therefore, to higher pressure gradients. Applying the different thresholds reported in the literature to our patient group suggests that stent placement would be indicated in anywhere from 4% to 87% of cases. This wide range suggests that cer-

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Table 3 Treatment Results as Determined with Color Duplex US (PSV ratio) at 3 and 12 Months Residual Mean Pressure Gradient Time

2

preprocedure 3 month 12 month

Group A 5 and 5 10 mm Hg 4.2 ? 2.5 ( n = 52) 1.4 t 0.6 ( n = 44) 1.6 t 0.7 ( n = 28)

Group B <5mmHg

P Value*

5.2 ? 2.8 ( n = 34) 1.2 2 0.6 ( n = 31) 1.8 t 1.0 ( n = 20)

.10 .37 .58

" By Kruskal-Wallis test. tain thresholds must be inadequate as an indication for stent placement. However, these observations do not clarify which threshold is the optimal one. In our opinion, the best way to solve this problem is a trial in which patients are only treated with angioplasty, and not stent placement. A meticulous registration of the intraarterial pressure gradients before and after PTA, and thorough follow-up of all patients may clarify the relationship between certain pressure thresholds and clinical decline of the patient. Given that current

practice dictates stent placement for suboptimal PTA results, however, such a trial will probably never be performed. In the DIST, a study concerning patients with mild claudication on the basis of an iliac artery stenosis, stent placement was performed if the residual mean pressure gradient exceeded 10 mm Hg after vasodilation. Therefore, investigation of a possible correlation between pressure gradients of more than 10 mm Hg and follow-up results was impossible. However, it was possible to compare the treatment results

Table 4 Baseline Characteristics Characteristic Number of patients Number of lesions Malememale ABI at rest ABI after exercise Walking distance (m) Previous interventional procedure PTA Vascular surgery (bypass) Lesion characteristics angiographic stenosis grade < 50% diameter reduction 2 50% diameter reduction total occlusion Patency of runoff vessels occlusion superficial femoral artery occlusion deep femoral artery

2

Group A 5 and 5 10 mm Hg 40 46 29111 0.79 2 0.21 0.58 t 0.25 234 2 84 6 (15%) 7 (17.5%) 2 (4%) 44 (96%) 0 (0%) 5 (12.5%) 4 (10%)

Group B

< 5 mm Hg 25 28 1916 0.74 t 0.19 0.52 2 0.31 238 5 84 2 (8%) 3 (12%) 3 (12%) 21 (84%) 1(4%) 7 (28%) 2 (8%)

Note.-Plus-minus values are means 2 SD; all other values are numbers of patients or lesions, respectively, with percentages given in parentheses. Six patients had both a lesion with a mean pressure gradient between 5 and 10 mm Hg, as well as a lesion with a pressure gradient of less than 5 mm Hg. Therefore, these patients were not included in this table.

and follow-up of lesions with a residual mean pressure gradient of 2 5 and I10 mm Hg, with those of lesions with a residual mean pressure gradient of less than 5 mm Hg, both measured with vasodilation. The first group of lesions would have received a stent according to the FDA criteria, but were denied stent placement according to the DIST protocol. In the second group, there was no indication for stent placement according to both protocols. We found no significant differences between the two groups with regard to PSV ratios at 3- and 12-month follow-up. Therefore, our results demonstrated no significant benefit of using the FDA criteria, suggesting that the more conservative approach of the DIST was appropriate. Unfortunately, the question whether the 10 mm Hg criterion is optimal cannot be resolved with this study. An even more conservative approach (eg, using as criterion an intraarterial mean pressure gradient of 15 or 20 mm Hg, with or without vasodilation) may even be better. This question can only be resolved by comparing the follow-up of patients treated with a stent on the basis of different hemodynamic criteria in a randomized trial. A major limitation of this analysis is the small sample size, implying that a significant difference between the two groups may have been missed. The estimated power of the study, however, was 81% to detect a difference in PSV ratio of 0.5. Therefore, although the study population was fairly limited, it was sufficient to detect clinically significant differences. Another limitation of this study is the difference in baseline characteristics across the two subgroups that we compared. Although the DIST randomly assigned patients to primary stent placement versus PTA followed by selective stent placement, the subgroups with specific pressure gradients after PTA analyzed in this study were clearly not randomly selected. In fact, the two groups demonstrated differences in some baseline characteristics, such as former vascular interventions, per-

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centage occlusions, a n d quality of runoff vessels (Table 4). W e conject u r e d that these baseline differences would not invalidate the comparison of PSV ratios d u r i n g followup, which is a hemodynamic meas u r e pertinent to the lesion, b u t could very well have affected more general follow-up outcomes pertin e n t to t h e limb o r patient, such a s t h e ankle-brachial indices a n d quality-of-life indices. Therefore, for t h e of this subgroup analysis, w e restricted o u r focus to t h e PSV ratio. I n conclusion, o u r analysis shows that t h e r e i s a lack of uniformity of hemodynamic criteria reported i n t h e literature a s a n indication for s t e n t placement. Applying these different criteria, t h e indication for secondary s t e n t placement varies from 4% to 87% of lesions. Because of o u r studv d e s i m . w e w e r e not able to ide&ify tie'optimal threshold. However, comparison between a threshold of 5 m m H g o r more (FDA criterion) a n d a threshold of more t h a n 10 m m Hg (DIST criterion), both with vasodilation, did not show a n y benefit of t h e first criterion. Prospective studies, w i t h meticulous registration of t h e intraarterial pressure gradients a n d thorough follow-up of all patients o r randomized trials w i t h different pressure gradients as a n indication for s t e n t placement and long-term follow-up, a r e needed t o clarify the relations h i p between residual pressure gradients a n d t h e clinical situation of t h e patient. Such studies c a n ultimately define t h e most efficient criterion for s t e n t placement.

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