Noninvasive localization of arterial occlusive disease: A comparison of segmental Doppler pressures and arterial duplex mapping

Transcription

1 Noninvasive localization of arterial occlusive disease: A comparison of segmental Doppler pressures and arterial duplex mapping Gregory L. Moneta, MD, Richard A. Yeager, MD, Raymond W. Lee, MD, and John M. Porter, MD, Portland, Ore. Purpose: The purpose of this study was to compare the abilities of arterial duplex mapping and segmental Doppler pressures to noninvasively localize hemodynamically significant lower extremity arterial occlusive disease. Methods: After angiographic controls were instituted, arterial duplex mapping and segmental Doppler pressures were blindly compared for their ability to localize a high-grade (50% to 100%) stenosis to the iliac or common femoral arteries, the superficial femoral artery, or the popliteal artery in 151 lower extremities from 79 patients. Results: Rates of sensitivity and specificity of arterial duplex mapping for identifying a high-grade stenosis at the three arterial levels were 88% and 97%, 95% and 100%, and 78% and 99%, respectively. Those for segmental Doppler pressures were 59% and 86%, 73% and 80%, and 48% and 53%, respectively. There was complete agreement between arterial duplex mapping and angiography in 82% of the limbs studied and between segmental pressures and angiography in 34% of the limbs (p < ). The presence of diabetes, kidney failure, or previous vascular surgery in the limb studied did not affect the accuracy of either test. Conclusion: Arterial duplex mapping is far superior to segmental Doppler pressures for localization of high-grade angiographic lesions from the iliac to the popliteal arteries. (J VASC SURG 1993;17: ) Optimal noninvasive evaluation of chronic lower extremity ischemia requires accurate quantitation of atherosclerotic arterial occlusive lesions. Simple pulse evaluation is well recognized as a poor measure of arterial insufficiency,1 Most vascular surgeons therefore routinely determine ankle/brachial systolic blood pressure indexes as a measure of overall blood supply to the foot. Many surgeons, however, also desire to know the general location of hemodynamically significant lesions because treatment decisions may, in many patients, be influenced by the level of the occlusive process. Four-cuff segmental Doppler pressures may therefore be used to localize lower extremity arterial From the Depamnents of Surgery and Radiology, Oregon Health Sciences University and Veterans Affairs Medical Center, Portland. Supported by a grant from the Research Advisory Group, Department of Veterans Affairs. Presented at the Sixth San Diego Symposium on Vascular Diagnosis, San Diego, Calif., Feb , Reprint requests: Gregory L. Moneta, MD, Department of Surgery, Division of Vascular Surgery (OP- 11), Oregon Health Sciences University, 3181 S.W, Sam Jackson Park Rd., Portland, OR /6/ occlusive disease to the iliac or common femoral arteries, the superficial femoral artery, the poplite~ artery, or the tibial vessels. Duplex scanning can now also be used to map occlusive lesions in lower extremity arteries. 2,3 Arterial duplex mapping can potentially provide more information than segmental Doppler pressures. Recent studies in our laboratory have shown that lower extremity arterial duplex mapping can reliably distinguish stenosis from occlusion, separately examine the deep femoral and superficial femoral arteries, and, in most cases, individually examine tibial arteries. 4,5 However, a prospective comparison of the ability of arterial duplex mapping and segmental Doppler pressures to localize iliofemoropopliteal occlusive disease has not been reported. Such a comparati~. evaluation should be useful to surgeons who have the option of using either or both examinations in the evaluation of their patients. We therefore compared segmental Doppler pressures and arterial duplex mapping in a recent cohort of our patients admitted to the Portland, Oregon, Veterans Affairs Hospital for treatment of chronic lower extremity ischemia. The results of this comparison form the basis for this report.

2 J'OURNAL OF VASCULAR SURGERY Volume 17, Number 3 Moneta et al. 579 METHODS Patients. All patients admitted to the vascular surgery service at the Portland, Oregon, Veterans Affairs Hospital for elective treatment of infrarenal arterial disease during the calendar year 1990 were eligible for participation in this study. The protocol was approved by the Human Subjects Committee of the Portland Veterans Affairs Hospital and informed consent was obtained from all patients. Consecutive patients were selected who were admitted for treatment of chronic lower extremity ischemia or who had ymptoms of lower extremity arterial occlusive disease as a significant component of their arterial disease. To ensure meaningful statistical analysis, patients were entered into this study until 150 extremities had been studied with angiography, segmental Doppler pressures, and lower extremity arterial duplex mapping. Particular note was made of the presence of conditions that could potentially impair the accuracy of either segmental pressures or arterial duplex scanning. Patients were therefore specifically evaluated for the presence of diabetes and chronic renal failure (serum creatinine level >2.0 mg/dl). These conditions may be associated with extensive medial calcification and impair the ability of arterial duplex to insonate a vessel or diminish vessel compressibility in the performance of segmental pressures. It was also noted whether the patient had undergone previous lower extremity vascular surgery because extensive periarterial scarring may also impair vessel compressibility. Angiography. All angiography was performed and interpreted without knowledge of the results of the segmental pressure or arterial duplex, mapping studies. Both digital subtraction and standard-cut film techniques were used. If the iliac arteries were angiographically normal, clearly highly stenosed, or only mildly diseased in the anteroposterior projection, only anteroposterior views of the iliac vessels were taken. Biplanar views of the iliac arteries were obtained when the anteroposterior views demonstrated moderate atherosclerosis but no obvious,2ow-restricting lesion and, at the discretion of the attending angiographer, of selected obviously highly diseased vessels. Most patients' angiographic studies included bilateral visualization ofrunoffvessels to the ankle and foot. Patients with previous above- or below-knee amputations and occasional patients with renal insufficiency and unilateral symptoms of chronic lower extremity ischemia tmderwent selective studies of the symptomatic extremity only. Angiograms of individual extremities were evaluated for the presence of a 50% to 100% stenosis in the following arterial segments delineated A, B, and C as follows: A, iliac or common femoral arteries; B, superficial femoral artery; and C, the popliteal artery. Evaluation of stenosis was based on the width of the contrast column immediately proximal to the lesion. When necessary, caliper measurements were used to grade the degree of stenosis. Segmental Doppler pressures. Segmental Doppler pressures were performed by one of two registered vascular technologists without knowledge of angiographic or duplex results. A four-cuff technique with 12 x 40 cm cuffs is used in our vascular laboratory. 6 In each lower extremity a high-grade iliac or common femoral artery (group A arterial segments) stenosis was diagnosed as present when the high thigh pressure was more than 20 torr less than the highest brachial artery pressure. An aboveknee pressure more than 20 torr less than high thigh pressure indicated a significant stenosis in the superficial femoral artery (group B arterial segments). Finally, a below-knee pressure more than 20 torr less than the above-knee pressure was interpreted as indicating a high-grade stenosis in the popliteal artery (group C arterial segments). Arterial waveform analysis was not employed in this study. Arterial duplex mapping. Lower extremity arterial duplex mapping studies were performed by two additional registered vascular technologists who were blinded to the results of the angiographic or segmental pressure studies. Both technologists have extensive experience in lower extremity duplex techniques and have participated in previous research protocols in our vascular laboratory. Our technique for arterial duplex mapping has been described in detail in a previous publication. 4 We depend on point-to-point examination of lower extremity arteries with the Doppler portion of a color-flow duplex scanner (Acuson-128; Acuson, Inc., Mountain View, Calif.) to assess stenosis. Arterial segments with no color filling on the color-flow portion of the examination and no detectable Doppler signal are judged occluded. For iliofemoropopliteal arteries a focal increase in peak systolic velocity greater than 100% of that in the immediately preceding arterial segment is considered indicative of a 50% to 99% stenosis at that point when the angle ofinsonation is 70 degrees or less. 2 In addition, in the common iliac arteries any velocity recording with a peak systolic velocity greater than 200 cm/sec at an angle ofinsonation less than 70 degrees is interpreted as a 50% to 99% stenosis. 3 To ensure that the two noninvasive tests were

3 580 21/Ioneta et al. March 1993 Table I. Comparison of segmental Doppler pressures versus arterial duplex mapping for detection of 50% to 100% stenoses in 151 lower extremities: Arterial segments with correct (true positives and negatives) and incorrect (false positives and negatives) findings Correct findings (n) Incorrect findings (n) Arterial segment SDP ADM SDP ADM p Value Iliac/CFA (n = 151) < SFA (n = 151) < Popliteal (n = 151) < SFA/Popliteal (n = 151) < SDP, Segmental Doppler pressure; ADM, arterial duplex mapping; CFA, common femoral artery; SFA, superficial femoral artery. subject to the same accuracy requirements and because segmental pressures cannot be expected to distinguish stenosis from occlusion or to localize lesions precisely, the results of the duplex studies were scored in a fashion similar to those used for segmental pressures. The duplex mapping results were therefore evaluated as to whether they indicated a 50% to 100% stenosis in A, B, or C arterial segments as defined above without regard to the precise location of the lesion within the arterial segment evaluated. Data analysis. The abilities of segmental pressures and arterial duplex mapping to detect a high-grade stenosis in arterial segments A, B, and C were tabulated as sensitivities, specificities, and positive and negative predicative values with an anglographic 50% to 100% stenosis used as the control definition of a high-grade arterial lesion. A separate analysis was performed combining arterial segments B and C because precise localization of an arterial stenosis about the knee may be of little practical clinical significance. The relative accuracies of segmental pressures and arterial duplex mapping were compared for their ability to identify or exclude the presence of a 50% to 100% angiographic stenosis with McNemar's test from a readily available statistical software program. 7 With comparisons of proportions from the same statistical package, the sensitivities and specificities of the two noninvasive tests were also analyzed for the effects of diabetes, renal failure, and previous lower extremity vascular surgery on their ability to identify or exclude a high-grade angiographic lesion. 7 RESULTS Patients/extremities. Seventy-nine consecutive patients with symptomatic chronic lower extremity ischemia were entered into the study. In these patients 151 lower extremities were studied with angiography and therefore could be used for a comparison of segmental Doppler pressures and arterial duplex mapping. All but two patients were men. Mean age was years. The indication for angiography was ischemic rest pain in 43%, ulceration or pedal gangrene in 28%, and shortdistance claudlcation in 23% of patients. Five patients (6%) with chronic lower extremity ischemia had other primary indications for arterial reconstruction. The median ankle/brachial systolic blood pressure ratio of all the 151 legs available for study was 0.59 (range 0.0 to 1.08). This included the limbs with ischemic rest pain, gangrene, and short-distance claudication, as well as contralateral mildly symptomatic or asymptomatic lower extremities studied angiographically as part of a routine runoff study. Thirty percent of patients were diabetic and 3% had chronic renal failure. Twenty-eight percent of the study extremities had previously undergone vasculk~,~ surgery. Angiography. Fifty-eight of the limbs (38.4%) had group A arterial segments with a high-grade (50% to 100%) angiographic stenosis. High-grade angiographic lesions were present in 92 (60.9%) of group B arterial segments and 63 (41.7%) of group C arterial segments. Arterial duplex mapping versus segmental pressures. Arterial duplex mapping was statistically superior to segmental Doppler pressures in detecting the presence (true positive) or absence (true negative) of a high-grade angiographic lesion in all three groups of arterial segments (p < ; Table I). Sensitivities, specificities, and positive and negati\:, predictive values were considerably higher for arterial duplex mapping than for segmental Doppler pressures at all three levels (Table II). If levels B and C are combined, the sensitivities of the two tests for detecting a high-grade lesion somewhere in either the superficial femoral or popliteal artery become more compatible (85% for segmental pressures and 93% for duplex mapping; Table II). However, the low specificity of segmental pressures when levels B and

4 Volume 17, Number 3 A/loneta et al. 581 Table II. Sensitivities, specificities, and positive and negative predictive values for detection of a 50% to 100% stenosis by segmental Doppler pressures and arterial duplex mapping in suprageniculate arterial segments from 151 lower extremities Sensitivity (%) PPV (%) Specificity (%) NPV (%) Arterial segment SDP ADAr~ SDP ADM SDP AD~/I SDP ADA/I Iliac/CFA SFA Popliteal SFA/Popfiteal SDP, Segmental Doppler pressure; AD_M, arterial duplex mapping; PPV, positive predictive value; NPV, negative predictive value; CFA, 3mmon femoral artery; SFA, superficial femoral artery. Table III. Comparison of percentages of 50% to 100% stenoses in suprageniculate arterial segments of 151 lower extremities (79 patients) missed by segmental Doppler pressures and arterial duplex mapping in patients/limbs with and without diabetes, renal failure, or previous lower extremity vascular surgery Segmental pressures Duplex mapping Arterial segment I (%) 17 (%) p Value I (%) 1I (%) p Value Iliac/CFA SFA Popliteal I and 17, With and without diabetes, renal failure, or previous lower extremity vascular surgery; CFA, common femoral artery; SEA, superficial femoral artery. C are combined (Table II) still results in a large..number of incorrect findings. Segmental pressures merefore remain inferior to arterial duplex mapping in terms of the total number of correct and incorrect findings in combined levels B and C (Table I). Overall, there was complete agreement between angiography and arterial duplex mapping as to the presence and location ofhemodynamically significant occlusive disease in 82% of the limbs studied. Complete agreement between segmental Doppler pressures and angiography occurred in only 34% of the limbs (p < ). The presence of diabetes, chronic renal failure, or previous extremity vascular surgery did not, at any level, influence the number of missed lesions by either arterial duplex mapping or segmental Doppler press~es (p = to 0.889; Table III). DISCUSSION Our results indicate that arterial duplex mapping is superior to segmental Doppler pressures for detection and localization of a 50% to 100% angiographic stenosis in the iliofemoropopliteai arteries. The relatively poor performance of segmental Doppler pressures in this study is not surprising. Using common femoral artery pressure measure- ments as controls, Flanigan et al.8 noted that four-cuff segmental pressure measurements detected significant iliofemoral occlusive lesions with a sensitivity of only 71% and a specificity of 73%. In the 100 patients studied there were also 22 false-positive test results. 8 In a review of the role of pressure measurements in the evaluation of vascular disease, Carter 9 noted that, although a pressure gradient of less than 20 torr between two contiguous sites is normal, measurement artifacts frequently affect the measurement of segmental pressures and thus apparent pressure gradients. These problems may be particularly acute in areas of long-standing arterial obstruction with extensive collateral formation. At such sites an excellent collateral blood supply may lead to underestimation of axial artery disease. This may contribute to the poor ability of segmental pressures to localize high-grade lesions to the popfiteal artery (Tables I and II). Other sources of measurement error such as vessel incompressibility may also lead to false-negative examinations. 6 However, the presence of diabetes, renal failure, or periarterial surgery, conditions that would appear to render an artery less compressible, did not affect the ability of segmental pressures to detect proximal arterial lesions in our patients (Table

5 582 Moneta et al. March I993 III). Perhaps the advanced arterial disease present in most of our patients, nearly three fourths of whom were studied for limb-threatening ischemia, overwhelmed our ability to detect an effect of these risk factors on the accuracy of segmental pressures. It may be argued that segmental pressures and arterial duplex mapping are not measuring the same parameters and therefore should not be compared at all. By directly examining the arteries under study, arterial duplex mapping should have better correlation with angiographic controls, whereas segmental pressures may be more of a physiologic measure of overall arterial inflow to a particular portion of the extremity. However, although this reasoning is sound, the practical point is that both techniques are usually evaluated in comparison with angiography 9 and decreases in segmental pressures are regarded as indicative of progression of arterial disease. ~ Researchers involved in clinical evaluation of atherosclerotic risk factors need to understand that segmental pressures are inadequate for monitoring the atherosclerotic process and an alternative, more accurate, technique exists. We have also previously demonstrated the ability of duplex scanning to accurately distinguish stenosis from occlusion and to separate a greater than 50% from a less than 50% stenosis in the iliofemoropopliteal arteries, and that the results are independent of occlusive disease in proximal arterial segments. ~ Physicians also must appreciate the comparative accuracies and advantages and disadvantages of segmental pressures and arterial duplex mapping so the proper technique is used to answer their clinical or research questions. The present data suggest that if the physician only wishes to document the presence of a significant occlusive lesion somewhere in the superficial femoral or popliteal artery, arterial duplex mapping holds no major advantage over four-cuff segmental Doppler pressures because the two techniques have similar sensitivities for detecting such a lesion somewhere in the thigh. If, however, it is believed necessary to localize the lesion to above or below the knee, document the absence of a flow-restricting lesion in the superficial femoral or popliteal artery, evaluate the lilac arteries, or distinguish stenosis from occlusion, 4 arterial duplex mapping would be the preferred test. Such situations may be encountered in selecting patients for possible endovascular therapies or in research studies monitoring the progression of atherosclerosis in lower extremity arteries. Unfortunately, neither mode of testing provides information on the suitability of a vessel for a surgical anastomosis. We therefore believe angiography is still required for optimal preoperative planning. We acknowledge the technical assistance of Robert DePew, RVT, and John Kazmar, RVT, in performance of the segmental pressure examinations and Cary A. Cummings, RN, RVT, and John D. Caster, RN, RVT, ~ performance of the duplex studies. Ruza Antonovic, MD, aided in angiogram interpretation. Gary J. Sexton, PhD, provided advice on statistical analysis. REFERENCES 1. Yao JST, Hobbs JT, Irvine WT. Ankle systolic pressure measurements in-arterial disease affecting the lower extremities. Br J Surg 1969;56: Kohler TR, Nance DR, Cramer MM, Vandenburghe N, Strandness DE Jr. Duplex scanning for diagnosis of aortoiliac and femoropopliteal disease: a prospective study. Circulation 1987;6: Cossman DV, Ellison JE, Wagner WH, et al. Comparison of contrast angiography to arterial mapping with color-flow duplex imaging in the lower extremities. J VASC SURG 1989;10: Moneta GL, Yeager RA, Antonovic R, et al. Accuracy of lower extremity arterial duplex mapping. J VAsc SURG 1992;15: Caster JD, Cummings CC, Moneta GL, Taylor LM Jr, Por'~-,r JM. Accuracy oftibial artery duplex mapping (TADM). J Vasc Technol 1992;16: Bridges RA, Barnes RW. Segmental limb pressures. In: Kempczinski RF, Yao JST, eds. Practical noninvasive vascular diagnosis. 2nd ed. Chicago: Year Book, 1987: Glautz SA. Primer of biostatistics: the program. Computer software. New York: McGraw Hill, Flanigan DP, Gray B, Schuler JJ, Schwartz JA, O'Connor JA, Williams LR. Utility of wide and narrow blood pressure cuffs in the hemodynamic assessment ofaortoiliac occlusive disease. Surgery 1982;92: Carter SA. Role of pressure measurements in vascular disease. In: Bernstein EF, ed. Noninvasive diagnostics in vascular surgery. St. Louis: CV Mosby, 1985: Rosenbloom MS, Flanigan DP, Schuler JJ. Risk factors affecting the natural history of intermittent claudication. Arch Surg 1988;123: Submitted March 4, 1992; accepted May 11, 1992.