The Value of Intravascular Ultrasound in the Treatment of Central Venous Obstructions in Hemodialysis Patients

Introduction

Central venous obstruction (CVO) remains a common problem in the hemodialysis population and is reported to occur in 25%-40% depending on the etiology (1, 2). Clinically, it becomes apparent by edematous upper extremities, collateral formation in the upper arm or chest region and in its most detrimental appearance, vena cava superior syndrome. Vascular access patency might also deteriorate due to fistula or graft thrombosis, secondary to outflow obstruction. International guidelines (K/DOQI) advocate percutaneous transluminal angioplasty (PTA), with or without stent placement as the preferred treatment approach to CVO (3). In fact, use of stents is recommended only when PTA fails. Similarly, The Society of Interventional Radiology Quality Improvement Guidelines, recommend bare metal stents be reserved for central vein lesions in which PTA has failed or that recur within 3 months after initially successful PTA (4). Early recurrence however, might very well be a direct result of suboptimal PTA in the first place. Therefore, accurate evaluation of PTA success directly after dilation of the central venous lesion is highly advisable. From iliofemoral vein stenting for compression syndromes or post-thrombotic syndrome, it has become clear that venography alone underestimates lumen reduction, and intravascular ultrasound (IVUS) was suggested superior for lesion evaluation. In the field of vascular access intervention, IVUS proved to be more sensitive in detecting intraluminal thrombus and vessel dissection after angioplasty for hemodialysis maintenance when compared to conventional angiography (5). In addition, IVUS was able to show intraluminal and wall abnormalities not identified by post-PTA angiography (6). Nevertheless, angiography continues to be the gold standard and IVUS has not been recommended in the international guidelines. Although IVUS might be obsolete in more distal oriented lesions because of multiplanar angiography and duplex accessibility, difficulties to evaluate central venous lesions may advocate the use of IVUS at this location. We report on the significance of IVUS to evaluate CVOs after PTA and suggest an important role in decision making during intervention for CVO.

Methods

Results

Distinct angiographic stenosis (>50% lumen reduction) in the frontal projection at subclavian/innominate vein level was present in 7 out of 10 on the right side and 1 out of 2 on the left side. In the other left-sided obstruction, a less obvious sign contrast translucency and lumen broadening were present. Angiographic proof of collaterals was seen in all patients with or without an angiographic significant stenosis. After PTA, persistent angiographic stenosis was observed in 3 out of 12 patients. Collaterals were still visible in 11 patients.

IVUS evaluation was performed in all patients from the femoral approach by manual pullback maneuver. All central venous lesions showed a minimal lumen reduction >50%. Thus, IVUS identified three additional significant lesions on the right side and one on the left. Concurrently, cross-sectional area was measured at the point of maximal stenosis. The median cross-sectional area before PTA was 24 ± 12 mm². In the four patients without obvious stenosis on angiography, the mean cross-sectional area was 56 ± 14 mm². After PTA, the median cross-sectional area increased to 37 ± 23 mm² (NS). IVUS examination additionally showed intraluminal fibrotic trabeculations in nine patients (Fig. 1). In two patients, the residual lumen reduction was <50% without significant intraluminal trabeculations visible and no further intervention was performed. In the other 10 patients, additional stent placement was performed. The sinus-Venous stent (Optimed GmbH, Ettlingen, Germany) was used in 100% of the cases, with diameters varying between 12 and 14 mm, and length between 60 and 100 mm, dependent on the anatomical location of the occlusion. The median minimal cross-sectional area post-stenting was 109 ± 20 mm². One patient showed a slightly <50% persistent compression on IVUS after stenting; however, angiography showed fast antegrade flow without visible collaterals, thus this result was accepted. Technical success of stenting for CVO was 100%. All patients who initially presented with arm swelling showed complete resolution within 7 days after stenting, and functional hemodialysis was achieved during the subsequent hemodialysis session.

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Fig. 1

(A) Angiography before PTA shows suggestive stenosis in the proximal right subclavian vein and collateral flow. (B) Angiography after PTA with a 14-mm balloon shows a better opacification of the subclavian and innominate vein, less collateral filling and <50% lumen reduction. (C) and (D). IVUS evaluation before (C) and after (D) PTA shows no clear increase of cross-sectional area. Further, intraluminal trabeculations remain present. (E) IVUS evaluation post-stenting with a 14-mm self-expandable stent shows an increased cross-sectional area without intraluminal trabeculations visible. The oval shape of the stent probably resembles unidentified outside compression.

Discussion

Endovascular management of CVO is well established and accepted and has been attempted by PTA, stainless steel stents, nitinol stents and covered stents. Initial success rates of PTA ranges between 70% and 90% (7). However, significant recurrent stenosis rates are high, especially after PTA without stent placement (8–10).

Partly, this might be the result of uncertainty about the morphology and etiology of the lesions treated. Pure neointimal lesions might respond well to PTA; however, fibrous obstructions and outside compression suffer from significant recoil. As we know, not all lesions can simply be qualified as neointimal hyperplasia and many should rather be seen as intravascular web formation, i.e., fibrosis (11). It has been concluded that such venous lesions can't be treated by PTA alone, and stent placement is important to maintain long-term patency (12). However, determining which lesion can principally be treated by PTA remains a problem. Digital subtraction angiography (DSA) of the central veins is still considered the gold standard to identify central venous disease and evaluate post-PTA results (9). Nevertheless, increasing data show that angiography is not capable of recognizing vein wall changes, significant dissections and intraluminal webs, and suggests IVUS as a superior alternative to evaluate these lesions (5, 13).

In our study, we specifically focused on CVOs since external ultrasound and angiography are less susceptible at the level of the proximal subclavian vein and anonymous vein. We showed that both recoil and persistent intraluminal webs not depicted by angiography were clearly identified by IVUS (Fig. 1). Thrombus, dissection and scar tissue (fibrotic trabeculations) can be easily distinguished with IVUS. For example, hard echoes resemble collagen-rich fibrous tissue (14). We found these fibrous flaps or trabeculations in nine of our cases. Although the significance of these trabeculations has never been established in CVO, the sole presence of intraluminal webs might be an indication for stenting. They might partly obstruct flow and/or cause flow disturbance thereby inducing thrombosis and/or intimal hyperplasia. The origin of recoil after PTA was not scrutinized in this study. Residual stenosis could be the results of outside compression; however, this was not indisputably noticed by IVUS. It might be argued that the oval shape of the vein is a normal finding, which is congruent with typical variations in venous blood pressure during inspiration. However, it has been shown that the vein wall can lose its flexibility and compliance due to collagen accumulation, i.e., fibrosis (15). Again, this might be an indication for stent placement in order to support the debilitated vein wall.

A valid argument against routine use of IVUS is the increased costs associated with the imaging catheter and purchase of the machine. Therefore, it is reasonable to implement IVUS only when other modalities are deemed insufficient. Although single plane angiography is not sufficient to identify and quantify venous lesions, the upper extremity vasculature can readily be imaged with angiography in multiple projections. Furthermore, the upper extremity outflow lesions are quite accessible for duplex ultrasound. Although duplex is operator dependent and is hampered by a lower image resolution, in combination with angiography most distal obstructions can be accurately assessed. However, central venous lesions are much more obscured to external imaging (16). Duplex ultrasound is less sensitive due to anatomic considerations, and angiography in multiple projections is cumbersome and mostly impossible. Furthermore, the additional costs associated with IVUS may be justified to differentiate between successful and insufficient PTA and make the judgment towards immediate stenting more accurate. Namely, it might be argued that the cost associated with early recurrence, e.g., repeated thrombectomy, angioplasty, access failure, etc., may be more pronounced.

IVUS might be valuable under other circumstances as well when diagnosing and treating venous outflow obstructions. If iodinated contrast medium is contraindicated in patients with contrast allergy and impaired renal function/residual kidney function in end-stage renal disease, IVUS imaging might be beneficial.

Altogether, there are growing data to at least suggest a role for IVUS in the diagnosis and treatment of CVO. Nevertheless, guidelines still state that angiography is the gold standard and IVUS should not routinely be used, mainly considering the costs. In order for IVUS to demand a more significant role in international guidelines, cost-efficiency studies are highly advisable. Considering the etiology and pathophysiology of central venous disease, evaluating this group specifically is most likely to yield a strong indication for this imaging modality.