Comparative study of Doppler ultrasonography with arteriography in the evaluation of aortoiliac occlusive disease

Abstracts

Contexto: A arteriografia com contraste (AC) tem sido o exame tradicional de avaliação de pacientes com suspeita de doença oclusiva aorto-ilíaca (DOAI). Recentemente, métodos menos invasivos, como a eco-Doppler, têm sido usados com a mesma finalidade. Objetivo: Comparar prospectivamente a eco-Doppler com a AC e eventual manometria arterial direta (MAD) na avaliação pré-operatória de pacientes com suspeita de DOAI. Métodos: Foram submetidos a eco-Doppler e a AC 125 pacientes internados para tratamento de doença arterial oclusiva dos membros inferiores, avaliando comparativamente 552 segmentos da aorta infrarrenal e das artérias ilíacas comum e externa. As lesões encontradas foram classificadas em cinco categorias: 1) normal e estenose leve (0 a 19%); 2) estenose moderada (20 a 49%); 3) estenose significativa (50 a 79%); 4) estenose crítica (80 a 99%); e 5) oclusão total. A MAD foi usada em 19 segmentos de 15 pacientes para classificar lesões limítrofes entre duas categorias. Foram calculados índices de validade (sensibilidade, especificidade, valor preditivo positivo, valor preditivo negativo e acurácia) para distinguir lesões hemodinamicamente significativas de não-significativas e para distinguir estenoses críticas de oclusões. O padrão-ouro foi AC, complementado pela MAD. Foram também calculados coeficientes de correlação kappa entre arteriografias e eco-Doppler para o conjunto dos segmentos aorto-ilíacos. Resultados: Lesões clinicamente relevantes (estenoses de 50 a 99% e oclusões totais) foram observadas na eco-Doppler em 163 segmentos (29,5%) e na AC em 158 segmentos (28,6%). A eco-Doppler mostrou altos índices de validade para distinguir lesões hemodinamicamente significativas de lesões não-significativas em todos os segmentos (acurácia = 92%; kappa = 0,81) e para diferenciar estenoses críticas de oclusões (acurácia = 86%; kappa = 0,73). Os índices de correlação entre os resultados das eco-Doppler e das AC foram ótimos em todos os segmentos aorto-ilíacos. Conclusão: A eco-Doppler apresenta elevados índices de validade e ótimos coeficientes de correlação com a AC na avaliação de pacientes com suspeita de DOAI.

Aorta abdominal; artéria ilíaca; aterosclerose; angiografia; eco-Doppler

ORIGINAL ARTICLE

Comparative study of Doppler ultrasonography with arteriography in the evaluation of aortoiliac occlusive disease

Ricardo Cesar Rocha Moreira

Vascular Surgery Service, Hospital Universitário Cajuru (HUC), Pontifícia Universidade Católica do Paraná (PUC-PR), Curitiba PR, Brazil

Correspondence

ABSTRACT

Background: Contrast arteriography (CA) has been the traditional method of evaluation of patients with suspected aortoiliac occlusive disease (AIOD). Recently, less invasive methods, such as Doppler ultrasonography, have been used for the same purpose.

Objective: The present study prospectively compares Doppler ultrasonography with CA and direct arterial manometry (DAM) in the preoperative evaluation of patients with suspected AIOD.

Methods: A total of 125 patients admitted for treatment of arterial occlusive disease of the lower extremities underwent Doppler ultrasonography and CA, comparatively evaluating 552 aortic, common iliac e external iliac segments. The lesions found were classified into five categories: 1) normal and mild stenosis (0-19%); 2) moderate stenosis (20-49%); 3) significant stenosis (50-79%); 4) critical stenosis (80-99%); and 5) total occlusion. DAM was used in 19 segments of 15 patients to classify borderline lesions. Validity indexes (sensitivity, specificity, positive predictive value, negative predictive value and overall accuracy) were calculated to distinguish hemodynamically significant from non-significant stenosis and to discriminate critical stenosis from total occlusions. The gold standard was CA, supplemented by DAM. Correlation coefficients (kappa statistics) between arteriography and Doppler ultrasonography were also calculated for the whole sample of aortoiliac segments.

Results: Clinically relevant lesions (stenoses between 50-99% and total occlusions) were observed on Doppler ultrasonography in 163 segments (29.5%) and on CA in 158 segments (28.6%). Doppler ultrasonography showed high validity indexes to distinguish hemodynamically significant from non-significant lesions (overall accuracy = 92%; kappa = 0.81) and an overall accuracy of 86% (kappa = 0.73) to distinguish critical stenosis from total occlusion. Optimal correlation coefficients between the results of Doppler ultrasonography and CA were observed for all aortoiliac segments.

Conclusion: Doppler ultrasonography has high validity indexes and optimal correlation coefficients with CA in the evaluation of patients with suspected AIOD.

Keywords: Abdominal aorta, iliac artery, atherosclerosis, angiography, Doppler ultrasonography.

Introduction

Contrast arteriography (CA) is the traditional examination for the diagnosis of aortoiliac occlusive disease (AIOD).¹ CA clearly shows the morphological changes caused by atherosclerosis in abdominal aorta and in iliac arteries, allowing treatment plan. Although established by tradition, CA has serious disadvantages as a diagnostic method: it is invasive, uncomfortable, has the risk of severe complications and high cost.² Over the past 2 decades, Doppler ultrasonography, an examination that gathers the image of a blood vessel by ultrasound and analysis of blood flow by Doppler effect within the same device, has been used in the initial assessment of occlusive arterial disease of the lower limbs.^3,4 Doppler ultrasonography has the following advantages in relation to CA: it is noninvasive; it provides anatomic and physiologic information; it is much cheaper and there is no risk of complications.⁵

The main disadvantage of Doppler ultrasonography is that it depends on the examiner's experience.⁶ For that reason, Doppler ultrasonography is still less used in the assessment of trunk vessels than in limb and neck vessels. Despite being widely used, there are doubts as to the accuracy of Doppler ultrasonography in patients with multiple atherosclerotic lesions.^7,8 Particularly clinical decision making based on ultrasound data is still controversial.⁹

This study aims at determining the validity indexes of Doppler ultrasonography and its correlation with CA in the evaluation of patients with suspicion of AIOD.

Methods

Patients admitted to the Vascular Surgery Service of Hospital Nossa Senhora das Graças and at Vascular Surgery of Hospital de Clínicas da Universidade Federal do Paraná (UFPR), both in Curitiba, Brazil, were prospectively recruited to participate in the study. All patients had been hospitalized with the diagnosis of lower limb ischemia for possible surgical or interventionist treatment. Initial clinical examination consisted of physical examination and assessment of lower limb arteries using a portable Doppler ultrasound flow detector.

A total of 125 suspected of having AIOD or multiple-level occlusive disease after initial clinical assessment were prospectively studied. The sample was comprised of 99 men (79.2%) and 26 women (20.8%), mean age 62±8 years. Associated diseases are described in Table 1.

Based on the initial examination, the patient was classified in one of the functional categories of occlusive arterial disease of the lower limbs according to the recommendation of the Joint Commission on Reporting Standards of the Society for Vascular Surgery and of the North American Chapter/International Society for Cardiovascular Surgery.¹⁰

In this study the abdominal aorta and iliac arteries were divided into three segments: infrarenal aorta (from origin at renal arteries to bifurcation); common iliac artery (from origin at the aorta until bifurcation) and external iliac artery (from bifurcation of the common iliac artery to the transition into the femoral artery, in the inguinal ligament).

Doppler ultrasound examinations were performed by two vascular ultrasonographers. All examinations were performed according to the protocol of Doppler ultrasonography examination.

Protocol of Doppler ultrasonography examination

Patient preparation:

- 12-hour fasting (exams scheduled for the morning period);

- Empty bladder, or at least as empty as possible, soon before starting the examination;

- Antiphysetics are not routinely used (when the amount of intestinal gases prevents a technically adequate examination, laxative and simethicone are occasionally used for 1 to 3 days and the examination is repeated);

- At least 30-minute rest before the examination.

Examination technique:

- Patients in a supine position on an appropriate bed;

- Extended lower limbs for the examination of the aortoiliac segment (note: for the proper examination of the aortoiliac segment it is sometimes necessary to adopt lateral decubitus position);

- Abduction and external rotation of the limb to assess the femoral arteries, cross-sectional, longitudinal and oblique screening and registers of interest.

B-mode image (black and white, conventional ultrasound image): enables to measure diameters, determine dilatations, identify thrombi, plaques, etc.

Color image (including use of power/angio mode): enables to determine presence or absence of flow, locate stenosis areas (by characteristics such as change in the color mosaic, turbulence, reduction in the colored section in angio mode, etc.).

Doppler flowmetry: enables accurate measurements of velocities (peak or maximal systolic, final diastolic and mean velocity) and to obtain indexes or times, such as resistance, pulsatility, acceleration, acceleration time indexes, etc.

Reactive hyperemia test: placement of a cuff on the patient's thigh, inflated up to 50 mmHg above systolic pressure. The cuff is maintained inflated for 3-5 minutes and quickly deflated, with new flow record analyzing the wave form in the femoral artery after 30 seconds.

Ultrasound criteria to classify lesions are presented in the Appendix.

Detected lesions were classified into five categories, according to the parameters observed and measured in the color Doppler ultrasound (Table 2).

All patients were submitted to CA, according to specific protocol of the arteriographic study, which included at least two contrast injections and video recording in different sections.

Protocol of the arteriographic examination

Patient preparation:

- 4-6 hour fasting;

- Examinations preferentially scheduled for the morning period;

- Trichotomy of inguinal regions (and occasionally of the right axillary region).

Examination technique:

- Patients in supine position (and later oblique position) on the radiographic examination table;

- Extended lower limbs;

- Preparation of the anatomic region to be punctured with stain or topic solution of 2% pyrrolidone-iodine and sterilization;

- Puncture site: right femoral artery. If the right femoral pulse is not palpable: left femoral puncture. If both femoral pulses are not palpable: puncture of the right axillary artery;

- Puncture with needle and stylet, 20 G;

- Obtaining pulsatile flow through the needle and introduction of 0.035 guide-wire;

- Passage of guide-wire until the abdominal aorta under fluoroscopic control;

- Introduction of a multipurpose 5 or 7F catheter 140 cm long;

- Placement of catheter, leaving its tip at the level of renal arteries;

- Connection of catheter to the injecting pump;

- Injection of iodinated contrast (approximately 60 mL);

- Obtaining images of the aortoiliac segment in anteroposterior and right or left anterior oblique projections;

- New injection of iodinated contrast for lower limb images from the femoral arteries. If images are satisfactory, catheter is removed;

- Manual compression of puncture site for at least 10 minutes;

- If there are still doubts as to the hemodynamic meaning of a stenosis, proceed to direct arterial manometry (DAM).

All CA were performed in radiologic devices with digital subtraction images. DAM was performed in the examinations that had doubts as to the hemodynamic meaning of any lesion.

DAM protocol

Cases of stenosis ipsilateral to the catheter:

- Catheter arteriography in at least two sections (AP and one oblique projection);

- Connection of the catheter to a transducer of membrane pressure, attached to an electronic monitor that provides real-time pressure curve;

- DAM in the abdominal aorta, proximally to any lesion;

- Gradient measurement through stenotic lesion by slow catheter removal and observation of pressures throughout the artery;

- Injection of papaverine (30 mg) distally to the stenotic lesion and new DAM 2-3 minutes later.

Cases of stenosis contralateral to the catheter:

- Puncture of the contralateral femoral artery with needle or short catheter, such as Jelco 18 F.

- DAM in the abdominal aorta through the catheter (as described above);

- Connection of the needle/short catheter to the transducer;

- Contralateral DAM at rest;

- Measurement of DBP after injection of papaverine (30 mg) through needle or short catheter placed on the lumen of the contralateral femoral artery.

A gradient higher than 15 mmHg between the proximal and distal segment to a stenosis was considered hemodynamically significant. Examinations were interpreted by the vascular ultrasonographer, who provided the report based on images and DAM.

Lesions were classified into the same five categories of the Doppler ultrasound examination according to stenosis degree. Lesions classified as significant stenosis (degree 3), critical stenosis (degree 4) and occlusion (degree 5) were considered clinically relevant. In this study, clinically relevant means that the lesion was causing ischemia or reduction in inflow to the limb, which could compromise the results of arterial reconstruction distal to the lesion.

The following were excluded from comparative analysis:

- Iliac segments proximal to an amputated lower limb because they are clinically irrelevant;

- Contralateral iliac segments apparently normal in patients with unilateral ischemia. Due to ethical reasons, additional contrast injections or DAM were not justified in such segments. Therefore, it was not possible to determine a gold standard in such segments that enabled comparison with Doppler ultrasonography;

- Iliac segments where it was not possible to perform a satisfactory ultrasound examination due to technical reasons (extensive arterial calcification, intestinal flatulence).

Doppler ultrasonography was performed before CA in 95 patients; the order of examinations was the opposite for the remaining 30 patients. Mean interval between both examinations was 2.5 days (15 days maximum). Ultrasonographic report was only included in the patient's record after the arteriographic examination had been performed and vice versa. Thus, both ultrasonographers and vascular radiologists were not aware of the comparative examination.

Patients were informed of the observational nature of the study, and that the ultrasound examination would not bring any risk for their health. A written authorization was obtained from all patients to perform arteriographic examinations. The study protocol was approved by the Research Ethics Committees of Hospital Nossa Senhora das Graças and Hospital de Clínicas (UFPR).

Results were statistically analyzed using two methods: Validity indexes and kappa correlation coefficient. Validity indexes: sensitivity, specificity, positive predictive value and negative predictive value and accuracy were calculated for each segment and for the whole sample. Kappa correlation coefficients between the results of CA and Doppler ultrasonography were calculated for each segment. Such index enables to correct any influence of chance on the results of correlation between both examinations.

Results

All 125 patients were classified into functional categories of occlusive arterial disease of the lower limbs, as described in Table 3.

In patients with bilateral ischemia the limb with the most severe degree of ischemia was considered. Of 125 patients, 33 (26.4%) had symptoms of right lower limb ischemia; 50 (40.0%) had left lower limb ischemia and 42 (33.6%) had bilateral lower limb ischemia. Thus, 167 ischemic limbs and 83 non-ischemic limbs with some degree of stenosis in the aortoiliac territory were included in the study.

Of 125 patients, 625 aortoiliac segments were potentially comparable. Throughout the study 73 segments were removed from analysis because they had one of the exclusion criteria described in the previous section.

- Six patients (12 segments) had previous amputation of the contralateral lower limb;

- Twenty-four patients (48 segments) with unilateral ischemia had normal contralateral lower limb;

- In 13 iliac segments, the ultrasound examination report was not conclusive due to technical reasons.

In total, 552 arterial segments were comparatively evaluated. Hemodynamically significant stenoses were detected by CA in 62 segments (11.2%) and by Doppler ultrasonography in 63 segments (11.4%). Segmental occlusions were observed in CA in 96 segments (17.4%) and in Doppler ultrasonography in 100 segments (18.1%). Therefore, clinically relevant lesions were observed in CA in 158 segments (28.6%) and in Doppler ultrasonography in 163 segments (29.5%).

Arteriographic and ultrasound findings of varied segments are listed in Table 4. The last column shows the number of examinations in which there was agreement between CA ad Doppler ultrasonography results (same stenosis degree).

Table 5 summarizes the statistical analysis of the results. There were high levels of validity in all arterial segments. Kappa tests showed excellent correlation coefficients between both examinations in all segments. Table 6 summarizes the analysis of Doppler ultrasonography validity to distinguish critical occlusion stenoses.

Discussion

Initial diagnosis of patients with AIOD is based on clinical examination. Complementary examinations aim at confirming clinical diagnosis, locating the pathological process and evaluating its physiopathological changes. Therefore, complementary examinations are evaluation examinations that enable to plan treatment of the pathological process.^1,7,11,12 CA has traditionally been used as the gold standard, that is, it is the examination that best evaluates occlusive disease and enables to make therapeutic decisions.^1,7,10-12 However, arteriography had major limitations as the gold standard in AIOD. In this discussion, the term limitations does not refer to method disadvantages (being invasive, uncomfortable, expensive and with risk of severe complications), but to the inability CA has of showing arterial anatomy and hemodynamic changes caused by AIOD. CA limitations are due to several factors:

- Distribution of contrast in the arterial lumen;

- Spasm caused by catheter or by contrast injection;

- Difficulty to show atheromatous plaques in arterial ostia;

- Difficulty to interpret degree of stenosis, even in good quality CA;

- And especially due to the fact that CA is a morphological examination, which does not provide physiological information.^7,13

Clinical decision making in POAD is based on the hemodynamic meaning of the lesions found in imaging examinations.^1,7,10-13 A stenosis cannot change perfusion pressure and distal flow in rest conditions. However, in conditions that require increased flow (such as exercise), stenosis becomes hemodynamically significant, causing reduction in perfusion distally to the lesion. Experimental and clinical studies established that a 50% reduction in artery diameter (which corresponds to about 75% of the arterial lumen cross section) is the limit from which a lesion becomes hemodynamically significant.^14-18 In both extremes (a normal or totally occluded iliac artery), arteriographic images are sufficient for clinical decision making. However, CA usually shows atherosclerotic lesions that cause 30-70% reduction in artery diameter, or shows two or more serial stenoses in the same arterial segment. The difficulties to evaluate degree of stenosis by CA have led some researchers to use DAM as a method to evaluate the hemodynamic importance of aortoiliac atherosclerotic lesions.^15,19-21 DAM is currently considered as the most accurate method to evaluate the hemodynamic meaning of a stenosis in the aortoiliac segment.^19-23 However, it has been little used in practice due to its technical difficulties.²⁴

Establishment of a gold standard method should be the first step in the execution of comparative studies. In the present study, all arteriographies were performed in at least two sections (anteroposterior and oblique). Angiographic findings were quantified using an accurate measurement of stenoses in radiographic images. Questions regarding some lesions were clarified either applying new contrast injections in the suspicious segment or by DAM through angiographic catheter. Complete accordance with protocols enabled CA (with the occasional aid of DAM in 19 segments) to be considered as the gold standard for this study.

Many studies using slightly different methodologies compared Doppler ultrasonography with CA, showing high sensitivity and specificity rates (80 and 95%) for Doppler ultrasonography in the aortoiliac segment.^8,25-37 In this study, accuracy to distinguish a hemodynamically significant lesion from a non-significant lesion was 92%. Therefore, Doppler ultrasonography proved to be highly accurate to confirm presence of AIOD (high sensitivity) and to exclude AIOD in cases where degree of suspicion was low (high specificity). Such results are in agreement with the literature.^8,25-37

High accuracy rates have two implications: one is that Doppler ultrasonography enables safe identification of patients with mild to moderate lesions of the aortoiliac segment, which do not cause ischemic symptoms nor reduction in inflow for a distal arterial reconstruction.³⁸ Second, Doppler ultrasonography enables to select patients with more severe lesions, but better located, which are candidate to catheter interventionist therapy.^39-52 Traditionally, candidates to such form of therapy have to be submitted to two arteriographic examinations: a diagnostic examination and a second examination, during which the intervention is performed. When a stenosis or short segmental occlusion in the iliac artery is identified by Doppler ultrasonography, percutaneous interventionist treatment can be directly indicated, as recommended by TASC II.¹¹

The most frequent criticism to Doppler ultrasonography is that it is a diagnostic examination whose results are examiner-dependent. In Doppler ultrasonography, differently from other imaging methods, the examiner is the only person that "sees" the images obtained during the examination and chooses those that will be included in the report. In the USA and Europe, technicians (called vascular technologists) perform the examinations, collecting images and physiological data that are deemed important for subsequent interpretation by a physician, who signs the report. Thus, the examination is dependent on skill and experience of a technician, who is not the only person responsible for the report issued by the laboratory. In Brazil, ultrasound examinations are performed by specialized physicians, who perform the examination, interpret it and sign the report.^5,6 Such form of performing vascular ultrasonography makes the Brazilian examination more reliable than in other countries. However, the fact that the examiner's experience and dedication are as important as the quality of the ultrasound device remains valid.

The argument is that Doppler ultrasonography is excessively dependent on the examiner can be contested by the counterargument that CA is also examiner-dependent. A quality arteriography, for example, depends on the patient's proper placement on the examination table, on a precise insertion of the catheter in the artery lumen, on contrast injection using proper volume and concentration, and on obtaining images at the right moment after injection. All such stages depend on the examiner's skill and experience.^13,41 Therefore, the fact that Doppler ultrasonography is examiner-dependent cannot be used as an argument against such examination. What is new in Doppler ultrasonography is that the specialist has to make clinical decisions based on an examination that they cannot interpret and must trust in the report provided by another physician. Such new situation brings trouble to many vascular surgeons, who request other examinations with which they are more familiar, to confirm the finding obtained by Doppler ultrasonography.

Conclusion

In this study, Doppler ultrasonography had high rates of validity and correlation with arteriography in the evaluation of patients with suspicion of AIOD. This conclusion is in accordance with nearly all studies in the literature.^{8,25-37,39-54} Doppler ultrasonography can be used in primary investigation of AIOD, avoiding preintervention angiography by any method (catheter angiography, computed tomography and magnetic resonance) in most patients with suspicion of AIOD.

Acknowledgements

To Dr. Enrique Vidal, Dr. Aguinaldo de Oliveira and Dr. Graciliano José França, for their excellence in the Doppler ultrasounds that were used in this study, and to Dr. Jeferson Freitas Toregiani, for his invaluable aid in statistical study.

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Publication Dates

• Publication in this collection
  29 May 2009
• Date of issue
  Mar 2009

History

• Accepted
  12 Dec 2008
• Received
  19 Nov 2007