Angiographic classification in ischemic lower limb revascularization: can it define arterial outflow resistance?

Rossi, Fabio Henrique; Leão, Pedro Puech; Izukawa, Nilo Mitsuro; Prakasan, Akash Kuzhiparambil

doi:10.1590/S1677-54492009000300004

Abstracts

BACKGROUND: Angiography is often used as the only preoperative method to define the therapeutic approach for ischemic lower limb revascularization, either by transluminal angioplasty or surgery. Today its use is still controversial. OBJECTIVE: To compare a simple method of angiographic classification with hemodynamic preoperative and intraoperative studies of the ischemic arterial bed in order to verify its efficacy in defining arterial bed resistance. METHODS: We analyzed 68 cases of surgical revascularization of ischemic lower limbs performed from July 1999 to July 2004 at the Division of Vascular Surgery of Instituto Dante Pazzanese de Cardiologia. The characteristics of the graft recipient arterial runoff were studied and compared using the method of preoperative angiographic classification proposed by the authors, preoperative hemodynamic analysis by color duplex scanning, and intraoperative direct measurements of flow, pressure and resistance. RESULTS: Positive rates for Spearman correlation (p < 0.05) were observed between the preoperative angiographic classification proposed in this study and the preoperative ultrasound hemodynamic measurements of blood flow volume (p = 0.035) and direct intraoperative measurements of flow (p = 0.006), pressure (p = 0.037) and resistance (p = 0.006). CONCLUSION: The preoperative method of angiographic classification proposed can assess the resistance of the arterial bed to be revascularized and help to define the approach and prognosis of the revascularization of ischemic lower limbs.

Angiography; ischemia; lower extremity; ultrasound examination; color Doppler; resistance

CONTEXTO: A arteriografia é muitas vezes utilizada como único método pré-operatório para a definição da conduta terapêutica na revascularização do membro isquêmico, seja ela realizada através de angioplastia transluminal, ou de cirurgia convencional. Ainda hoje, sua utilização é assunto de debate. OBJETIVO: Comparar um método de classificação arteriográfica simples com estudos hemodinâmicos pré e intraoperatórios do leito arterial isquêmico a ser revascularizado, com o objetivo de verificar seu poder para definir a resistência desse leito arterial. MÉTODOS: Foram analisadas 68 cirurgias de revascularização de membros inferiores isquêmicos realizadas no período de julho de 1999 a julho de 2004 no Setor de Cirurgia Vascular do Instituto Dante Pazzanese de Cardiologia. As características do leito arterial receptor do enxerto foram estudadas e comparadas através de método de classificação arteriográfica pré-operatória proposto pelos autores, análise hemodinâmica pré-operatória por eco-Doppler colorido e intraoperatória por medidas diretas de vazão, pressão e resistência. RESULTADOS: Foram observados índices de correlação de Spearman positivos (p < 0,05) entre o sistema de classificação arteriográfica pré-operatória proposto e as medidas hemodinâmicas ultrassonográficas pré-operatórias de volume de fluxo sanguíneo (p = 0,035) e as medidas diretas intraoperatórias de vazão (p = 0,006), pressão (p = 0,037) e resistência (p = 0,006). CONCLUSÃO: O método de classificação arteriográfica pré-operatória proposto pode definir a resistência do leito arterial a ser revascularizado e auxiliar na definição da conduta e do prognóstico da revascularização do membro inferior isquêmico.

Angiografia; isquemia; extremidade inferior; ultrassonografia Doppler colorida; resistência

ORIGINAL ARTICLE

Correspondence

ABSTRACT

Background: Angiography is often used as the only preoperative method to define the therapeutic approach for ischemic lower limb revascularization, either by transluminal angioplasty or surgery. Today its use is still controversial.

Objective: To compare a simple method of angiographic classification with hemodynamic preoperative and intraoperative studies of the ischemic arterial bed in order to verify its efficacy in defining arterial bed resistance.

Methods: We analyzed 68 cases of surgical revascularization of ischemic lower limbs performed from July 1999 to July 2004 at the Division of Vascular Surgery of Instituto Dante Pazzanese de Cardiologia. The characteristics of the graft recipient arterial runoff were studied and compared using the method of preoperative angiographic classification proposed by the authors, preoperative hemodynamic analysis by color duplex scanning, and intraoperative direct measurements of flow, pressure and resistance.

Results: Positive rates for Spearman correlation (p < 0.05) were observed between the preoperative angiographic classification proposed in this study and the preoperative ultrasound hemodynamic measurements of blood flow volume (p = 0.035) and direct intraoperative measurements of flow (p = 0.006), pressure (p = 0.037) and resistance (p = 0.006).

Conclusion: The preoperative method of angiographic classification proposed can assess the resistance of the arterial bed to be revascularized and help to define the approach and prognosis of the revascularization of ischemic lower limbs.

Keywords: Angiography, ischemia, lower extremity, ultrasound examination, color Doppler, resistance.

Introduction

Revascularizations of ischemic lower limbs have well-established clinical indications and surgical techniques.^1-4 However, half of these procedures may fail within a 1-year clinical follow-up period.^1,5,6

The definition of anatomic characteristics of the distal bed can contribute to the establishment of the best therapeutic approach and it is a crucial step for the indication of the treatment and the surgical approach to be followed.

Inadequate indications for revascularization can cause early graft occlusion and threaten limb patency, exacerbating pain, increasing the rate of amputations and making rehabilitation more difficult. Moreover, it can place at risk the life of the patient, who usually has severe comorbidities, and it can increase costs with medical and hospital services.

Several studies based on different methods showed that the outflow resistance in the ischemic bed can affect patency and limb salvage outcomes.^7-26

Despite being the gold standard and the more common method, preoperative angiography may fail to predict the outcome of revascularization.²⁷ On two occasions, the Society for Vascular Surgery and the North American Chapter of the International Society for Cardiovascular Surgery suggested a scoring system that could improve the use of angiography in establishing prognosis.^28,29 Despite their effort and the complexity of the angiographic scoring systems recommended, studies that used them showed contradictory results in terms of their ability to predict graft patency.^27,30,31

Arterial blood flow can be studied with color Doppler ultrasound. The preoperative study of the hemodynamic flow of the artery to be revascularized on the ischemic lower limb may define its outflow resistance and graft prognosis.^32-34

Intraoperative direct measurements of flow, pressure and runoff resistance may define graft resistance and prognosis.^10-15

In the present study, the authors aimed at observing the efficacy of a simplified and intuitive preoperative angiographic classification system that includes the site for distal anastomosis, the number of patent lower limb arteries and characteristics of the pedal arch artery in order to establish its outflow resistance; this system was compared with two hemodynamic methods, the preoperative non-invasive use of color Doppler ultrasound and the intraoperative direct measurement of flow resistance.

Methods

Sixty eight preoperative angiographies for revascularization surgeries performed from July 1999 to July 2004 at the Division of Vascular Surgery of Instituto Dante Pazzanese de Cardiologia were retrospectively assessed.

Considering that the angiographic scoring system recommended by the Society for Vascular Surgery is complex, a simple classification system was designed to assess only the arterial bed distal to the site of anastomosis.

Items considered for scoring within the angiographic system proposed by the authors were:

- Site of distal anastomosis: supragenicular popliteal artery, infragenicular popliteal artery; lower limb artery.

- Angiographic characteristics of patent lower limb arteries: anterior tibial artery; posterior tibial artery; fibular artery.

- Pedal arch integrity.

Within this system, higher scores were assigned to distal beds best suitable for surgery, which were theoretically associated with lower outflow resistance. The highest score was assigned when the site of distal anastomosis was the supragenicular popliteal artery, with all patent lower limb arteries and an intact pedal arch.

For lower limb arteries, the highest score (4) was assigned when the artery for distal anastomosis was patent, along with an intact pedal arch (Table 1).

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The patients underwent preoperative color Doppler ultrasound examination. At the site of distal anastomosis, blood flow volume was measured. To calculate this volume, the largest inner diameter of the artery (mean of three measurements performed on the same site) was measured in a cross sectional image (B-mode) and the pulsed Doppler spectrum was obtained in a longitudinal section on the same site of diameter measurements. The Doppler angle was corrected, aligned with the blood flow at up to 60º (considering the longitudinal axis of the vessel under study) and integral velocity of the Doppler velocity curve for this sample was calculated: volume (mL/min) = area (πr²) x velocity (cm/s) x 60.^34,35

After the choice of the recipient artery, defined with the methods described above, patients underwent surgery. The arterial bypass used was a reversed vein graft in 42 cases (61.8%), in situ graft in six cases (8.8%) and translocated saphenous vein graft in one case (1.5%); prosthesis (6 mm polytetrafluoroethylene) was used in 19 cases (27.9%). Distal anastomosis of the arterial graft was performed on the supragenicular popliteal artery in 20 cases (29.4%), on the infragenicular popliteal artery in nine cases (13.2%), on the anterior tibial artery in 14 cases (20.6%), on the fibular artery in 16 cases (23.5%), on the posterior tibial artery in eight cases (11.8%) and on the tibial-fibular trunk in one case (1.5%).

Intraoperatively, after exposure and arteriotomy of the artery selected for distal anastomosis, an urethral catheter was inserted distally, a bag of saline solution was placed 120 cm above the level of arteriotomy and it was connected to the catheter; intermediating them was a device to measure central venous pressure (CVP). As the system was opened, the saline solution flow during 1 minute was measured. When the CVP equipment was full with saline solution to the height of 120 cm as measured in the scale, it was opened and, for approximately 1 minute, the column of saline solution was observed to gradually reduce until it was balanced with the pressure in the catheterized artery. Considering that pressure and flow variables tend to interfere with graft function, the index of outflow resistance was also observed¹⁵ (Figure 1).

To analyze the efficacy of the angiographic scoring system proposed here in defining hemodynamic characteristics of the recipient artery and predicting graft patency, studies on the correlation of this method with preoperative and intraoperative hemodynamic methods previously mentioned were performed. Spearman correlation was used because a non-normal distribution was observed in the angiographic scoring system proposed.

Results

The highest angiographic scores coincided with distal beds with the highest blood flow volume according to preoperative Doppler ultrasound studies (Figure 2).

The same was observed for intraoperative flow (Figure 3), pressure (Figure 4) and resistance (Figure 5) measurements in the distal bed.

A positive correlation was observed between the angiographic scores and intraoperative measurements of pressure, volume and resistance with preoperative blood flow volume measured with color Doppler ultrasound. (Table 2)

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Discussion

In the surgical revascularization of a ischemic limb, graft patency can be affected by several factors. Resistance of the recipient artery can cause early graft failure.^1-6

Traditionally, preoperative angiography has been the most commonly used method to establish the treatment and the surgical approach for the revascularization of the ischemic limb. However, for several reasons, this method can fail to define the characteristics of the distal arterial bed. For the contrast agent to be visualized in the artery under study, it should overcome the flow resistance that led to insufficient perfusion of the ischemic limb. Moreover, the techniques for dilution, injection rate and volume and the definition of radiographic parameters can affect the final results. A low cardiac output, which frequently affects patients with severe diffuse atherosclerosis, can markedly decrease the blood flow. The presence of multiple occluded arterial segments, increased blood viscosity, underdeveloped collateral circulation and dehydration are other factors that can negatively impact on the flow of blood and contrast agent to the ischemic limb.¹⁸

These factors may have influenced the conflicting results of the analysis on the efficacy of angiography in defining graft patency after revascularization of ischemic limbs.

Several new concepts arose from non-invasive analysis of the blood flow in ischemic lower limbs. An investigation conducted by the first author of this article in 2006 and published in his Ph.D. dissertation showed that preoperative Doppler ultrasound examination could define the hemodynamic characteristics of the recipient artery and predict graft patency. Measurements of flow volume, with Doppler ultrasound in the distal arterial bed, were compared to intraoperative direct flow, pressure and resistance measurements in the same artery, with a method widely recognized in predicting graft patency, and a positive correlation was revealed.^34,35

Despite this positive correlation, some factors should be highlighted. The estimation of the blood flow volume with preoperative Doppler ultrasound involves an important technical limitation. A precise measurement of the arterial diameter may be difficult, particularly for leg arteries. A small variation in the diameter measurement in these small arteries can represent a considerable difference in the estimated volume flow. In relation to intraoperative direct measurements, it should be borne in mind that, because it is an invasive method, factors such as arterial spasm, patient position and the characteristics of the arterial wall may affect measurement results.

Preoperative angiographies performed in the present study were classified with the method described above according to the characteristics of the arterial bed distal to the site for anastomosis. This system was found to be simple, intuitive and easily implemented, since only the graft recipient artery is analyzed.

Despite the few cases studied, there seems to be a proportional relation between the scores in our angiographic system and the flow volume measured with Doppler ultrasound and the intraoperative direct flow, pressure and resistance measurements observed in the figures above. There also seems to be a positive correlation between the angiographic scores in our system and the preoperative and intraoperative hemodynamic measurements with methods previously mentioned, which both were efficient in establishing resistance and predicting graft patency.^15,34,35

Conclusion

Preoperative angiography, within the angiographic scoring system presented in this study, can be used to define characteristics of the graft recipient artery in the ischemic lower limb and, potentially, to predict graft patency. Thus, multicenter studies with long-term follow-up are suggested to investigate the clinical applicability of this new angiographic classification.

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