Vascular Intervention

Indication/Technique

Introduction

Angiography as a radiology procedure developed in the 1920s. Physicians were able to image vessels using a hollow needle, contrast agent and live radioscopy. Technical options at the time were limited to inserting the needle into a vessel and injecting contrast agent directly through the same needle. As a result, not all target vessels could be imaged effectively. 
This concept evolved in time, increasing the technical options.  Vessel imaging became more and more selective, also for less accessible vessels as in the abdomen.  In addition, more and more techniques were developed for endovascular treatment of pathologic processes. There is now a broad diversity of techniques based on this concept.  This article will address the basis of vascular interventions with a number of frequently used vascular procedures as an example.

Indications

Vascular intervention can be indicated for several reasons. This will be discussed in more detail hereafter. Patients are referred for intervention by other specialisms, in many cases surgery, who also inform their patients about the procedure. In some hospitals the radiology department also has outpatient consultations. In order to prepare for the procedure, renal function, coagulation status and allergies are tested. Adequate renal function is essential seeing the contrast agent used during the procedure is harmful to the kidneys. If renal function is reduced, additional measures are required to protect the kidneys (prehydration). Good coagulation status is important to prevent bleeding. A large proportion of the patients use anticoagulants, which should be discontinued well before the procedure. Protocols may differ among hospitals, but generally an INR of less than 2 is accepted for vascular procedures. Then finally, allergies are relevant because some patients may develop a severe reaction to the contrast agent or local anesthesia.  If this is known, anti-inflammatory agents and antihistaminics must be administered prophylactically.

Imaging 

When vascular pathology is suspected, the vasculature can be imaged in different ways. The least invasive and least expensive form is echo duplex, which is commonly used when there is a specific question about a limited section of the vasculature.  There are a number of drawbacks, however: assessment is subjective, time-consuming, assessibility also largely depends on the patient's physical characteristics. Especially the assessment of abdominal vessels can be challenging, e.g. due to overlying intestinal loops and excessive fat tissue.  Where necessary, CT or MR angiography is used to provide additional information.

Vascular interventions are performed in the angio room. It has a mobile table on which the patient is placed, an X-ray device (C arch) and a screen showing the radioscopy images (fig 1). This configuration can image the target area in the desired direction.  As opposed to X-rays, short videos are made, all procedures can be followed ‘live'.  Imaging of certain structures (blood vessels, urinary tract, bile ducts etc.) can be improved using contrast agents.

Figure 1. Intervention room.

General technique 

The initial procedures of vascular interventions are generally similar.
First, access to the vascular system must be obtained, usually with the Seldinger technique (fig. 2).

Figure 2. Seldinger technique. A needle is inserted into the blood vessel (1), the guide wire is advanced (2).  The hollow needle over the wire is then replaced by a sheath (3) and stable vascular access has been obtained (4).

In this procedure, a blood vessel (artery or vein) is punctured with a hollow needle containing a guide wire.  This can be guided by palpation, but usually ultrasound guidance is used in the radiology department.  The needle is then withdrawn, leaving the guide wire in the vessel. A kind of thick working tube, the sheath, can then be inserted over the guide wire. At the end (outside of the patient) of the sheath is a valve preventing leakage of blood through the sheath. The blood vessel generally used for access is the common femoral artery (Latin name a. femoralis communis – AFC). Access is relatively easy in view of its superficial position and large caliber.  The brachial artery is also used frequently. The popliteal artery or a crural artery is used only rarely. Other arteries, like the superficial femoral artery (a. femoralis superficialis – AFS) are less suitable in view of their deep position and because there is no underlying bone to press the vessel against when the needle or sheath is removed. If venous access is required, the common femoral vein or jugular vein is generally used. 
Once the sheath has been placed, this provides stable access to the vascular system allowing several types of guide wires and catheters to be passed through.  Using live radioscopy, these guide wires and catheters can be maneuvered to the target region. There is a broad diversity of guide wires and catheters. Guide wires may differ in length, tip curvature, flexibility and material. Flexible hydrophilic guide wires are generally used for navigation through the blood vessels. They are less traumatic, but their lack of stability is a drawback. The opposite is true in stiff guide wires. Stiff guide wires provide needed firmness when e.g. tough tissue must be penetrated to insert a sheath.  Flexible guide wires are less suitable in this setting as less “push” can be given.  Catheters also have various shapes and measures.  The greatest difference is in the tip, which can have several shapes (fig. 3). 

Figure 3. Various catheter types.

Which catheter is used depends on which blood vessel needs to be catheterized. Abdominal arteries separate from the aorta at a rather sharp angle, requiring a catheter with a sharper curve than in a relatively straight blood vessel such the leg arteries. 
Navigation through the blood vessels is always achieved using a (flexible hydrophilic) guide wire in front with a catheter as support. This is very important seeing guide wires are less traumatic to the vessels. If a catheter is inserted first, there is a much higher risk of complications such as dissection or even perforation of a vessel. When the target area has been reached, the wire is withdrawn from the catheter and various materials may be administered through the catheter, e.g. contrast agent for imaging, medication, or embolization material.

After the intervention, the sheath must be removed from the patient. This is not a simple procedure, because the sheath leaves a large hole behind in the vessel. By prolonged compression with the fingers followed by a pressure bandage, the hole can be closed.  In recent years, vascular closure devices have also been developed. See figure 4 as an example. The idea is that they reduce the risk of secondary bleeding, are less unpleasant for patients and that patients are more easily mobilized when a closure device has been used. As an additional benefit, prolonged pressing is not required, making the angio room available sooner for the next patient.

Figure 4. Example of a closure device. The sheath is removed, the guide wire is left behind (1) and the closure device is advanced (2).  When the closure device is withdrawn, the vessel is closed with an anchor and collagen against / in the vessel wall (3 & 4). There are many types of closure devices. In addition to devices using a collagen plug, there are also devices using a clip or suture.

Normal anatomy

The vascular wall consists of 3 layers: from inside out the intima, media and adventitia (fig. 5).

Figure 5. Anatomy of the vascular wall.

The intima consists of a layer of endothelial cells that are in direct contact with the circulating blood.  Behind it is another layer of connective tissue and elastic tissue. The intima is a hormonally active layer that secretes certain hormones under stress and can induce proliferation of endothelial cells and fibroblasts. The media is a muscular layer that provides firmness and can react quickly to hemodynamic changes by vasoconstriction and dilatation.  The outer layer, adventitia, is a strong layer consisting of connective tissue.  The vasa vasorum are in between the media and adventitia.  Sometimes one of these layers can rupture, causing a dissection (fig. 6).

Figure 6. Dissection.

This can happen spontaneously, usually secondary to underlying vascular wall pathology (atherosclerosis, connective tissue disease). In isolated cases it occurs in vascular procedures also. It is assumed that the anatomy of the entire arterial vascular system is known (fig. 7).

Figure 7. Anatomy of the vascular system.

Checklist

Tip for reviewing radioscopy images (if you were not present during the procedure): always review the images chronologically; reviewing the first and the very last images in particular gives a good idea what exactly has been achieved during the procedure. 
Also scroll through the images using your mouse wheel.

Pathology

  • General

  • Peripheral vascular disease

  • Abdominal vascular disease

  • Dialysis shunts

  • Abdominal bleeding

General

Vascular interventions can roughly be subdivided into interventions to improve blood flow and interventions to reduce blood flow (embolization).  As described above, the initial procedures of all vascular interventions are basically similar: after the insertion of a sheath, several guide wires and catheters can be maneuvered to the target area. There is a broad diversity of vascular interventions and it is beyond the scope of this article to describe them in detail. The following describes a number of frequently used interventions.

Peripheral vascular disease

Most patients eligible for vascular intervention have a form of stenosing/occlusive vascular disease that causes ischemic symptoms.  Usually this occurs in the lower extremities. In the great majority of cases, it is caused by atherosclerosis.  There are many risk factors for the development of atherosclerosis including age, smoking, diabetes mellitus, and hypertension. Other causes for stenosing/occlusive vascular disease include thromboembolic processes, vasculitides, external compression, etc.
Symptoms resulting from peripheral vascular disease are subdivided according to the Fontaine classification (fig. 8):

  1. Asymptomatic
  2. Intermittent claudication (2a > 200 meters walking; 2b < 200 meters)
  3. Rest pain or nocturnal pain
  4. Ischemic ulcers or gangrene 

Figure 8. Fontaine classification.

Depending on severity, Fontaine 2 is amenable to conservative treatment with mobilization. This stimulates the body to form collateral vessels. If symptoms are very debilitating or if conservative treatment fails, an invasive procedure is opted for: percutaneous transluminal angioplasty (PTA, also known as Dotter procedure) or surgery. In many hospitals, the selection of treatment is discussed in multidisciplinary consultations.  The decision to opt for a treatment modality is guided by the location and extent of the vascular abnormalities and by any previous therapies. 
Patients generally have one or more stenoses or occlusions causing symptoms.  These stenoses and occlusions in the vasculature may be at different levels, from the aorta down to the lower leg. The lesions may be approached in different ways, depending on their exact location. The sheath in the AFC is of course always placed in the direction of the lesion, so iliac lesions against the blood stream (retrograde), and femoral and crural lesions with the blood stream (antegrade).  Procedures are generally performed more conveniently when the sheath is placed at the ipsilateral side.  However, sometimes there is not enough room to place the sheath because the stenosis is too close to the puncture location. In these cases, contralateral and retrograde positioning of the sheath is also possible, creating a small detour as it were (‘over the bifurcation') (fig.  9). 

Figure 9. Cross-over.

Guide wires and catheters must then be passed through the stenosis or occlusion. This is generally done intraluminally. However, especially in longstanding occlusions, it can be very difficult to recanalize via the lumen. In these cases, subintimal recanalization is frequently opted for.  Either a dissection is created deliberately using the guide wire and catheter to get past the occlusion or stenosis.  It this setting, it is important to return to the correct location in the lumen: the re-entry. Once the stenosis has been passed, a balloon can be inflated allowing the placement of a stent (fig. 10 and 11). When restenosis occurs in a patient, the decision can be made to repeat PTA / stent placement or switch to surgical intervention.

Figure 10a. PTA of a stenosis.

Figure 10b. Stenosis treated with PTA + stent.

Figure 11a. Occlusion of right common iliac artery (a. iliaca communis or AIC). The catheter is in the distal aorta. Injection of contrast agent reveals absent filling of the right AIC. Note also extensive collateral formation.

Figure 11b. Passing the occlusion in the right common iliac artery (AIC).

Figure 11c. Patency restored in the right AIC.

The above pathology is a chronic process. Sometimes patients present with (sub)acute symptoms in the leg secondary to arterial thrombosis.  The symptoms consist of the well-known ‘5 p's’ (pain, pallor, paresthesias, paralysis, pulselessness). These are in many cases patients who received a bypass or stent in the past, where thrombosis developed in that exact region. In acute occlusion, the occluding material is frequently still soft thrombus, which allows for relatively easy recanalization.  In acute occlusion, treatment may consist of the placement of a catheter with various side holes in the thrombus allowing for continual administration of a thrombolytic, such as urokinase. After a few hours follow-up angiography is performed to ensure patency of the vessels in question.  In many cases, when the thrombus has dissolved, a stenosis is observed which caused the thrombosis.  It is then treated with PTA or stent placement.

Abdominal vascular disease

As in peripheral vascular disease, the abdominal arteries may be affected also. Think of abdominal angina secondary to stenoses in the splanchic arteries or renal insufficiency / uncontrolled hypertension secondary to renal artery stenoses. CT or MR angiography is performed to accurately image these vessels. If significant stenosis is found, PTA and possibly stent placement may be considered. The procedure is highly similar to that in peripheral vascular disease. However, a different material is used as these vessels have different curvatures and calibers. Sometimes these vessels cannot be catheterized effectively through the AFC because of the angle of the vessels to the aorta. In these cases, access through the brachial artery is opted for. Though rare, a sample PTA procedure of a renal artery in a patient with fibromuscular dysplasia is shown below (fig. 12/13).

Figure 12. Patient with hypertension secondary to renal artery stenoses in fibromuscular dysplasia. Characteristic string of pearls configuration.

Figure 13. Patency has been restored and blood pressure normalized after PTA.

Dialysis shunts

There are several ways to dialyze, e.g. using a shunt (arteriovenous (AV) fistula or AV graft), through a large-caliber central venous catheter or by peritoneal dialysis. Dialysis through an AV fistula is preferred as this is the most durable way and causes the fewest complications. In an AV fistula, the artery is connected directly to an adjacent vein (usually in the arm).  After some time, the vein becomes hypertrophic and has a high flow volume, allowing for easy withdrawal and return of blood. The shunt can be placed at several levels (fig. 14). The most common are the radiocephal (lower arm) shunt and the brachiocephal shunt (upper arm).

Figure 14. Brachiocephal shunt and radiocephal shunt.

Because the vein is not accustomed to the high arterial pressures, intimal hyperplasia may develop, which may lead to stenosis. Also frequent needling of the vessel may cause scarring and eventually stenosis. Common locations of stenosis are close to the anastomosis and at the level of the needle sites, but stenoses may develop also more proximally and centrally. Stenoses reduce blood flow, making dialysis more difficult.  Eventually thrombosis may develop in the shunt and it may be lost. It is therefore important to detect and treat stenoses in an early stage. Stenoses are detected when measured blood flow during dialysis is low. Subsequent echo duplex can then confirm a stenosis. Treatment is again similar to that of peripheral vascular disease: a sheath is introduced into the vein in the direction of the lesion. The lesion is passed with a guide wire and catheter.  PTA is then performed. If there are multiple lesions, it may be necessary to insert 2 sheaths in opposite directions (fig. 15).

Figure 15a. A stenosis at the level of the anastomosis of the brachiocephal shunt (left arm). A sheath is inserted proximal of the anastomosis in the cephalic vein. A catheter has been inserted through the sheath past the anastomosis proximal in the brachial artery. Contrast agent is administered from the brachial artery. No blood flow is visible in the cephalic vein due to the stenosis and the catheter blocking the remaining lumen. The stenosis is removed by PTA; when contrast agent is injected into the brachial artery, patency has been restored at the level of the anastomosis. A second stenosis is seen in the cephalic vein proximal of the sheath (see also fig. 15b).

Figure 15b. A second sheath is inserted into the cephalic vein. The sheath is pointed towards the stenosis proximal in the cephalic vein.  Blood flow is improved after PTA of the stenosis.

After the procedure, the sheaths may be left in place if followed immediately by dialysis. Dialysis is also possible through the sheaths. Once stenosis develops in a shunt, patients generally return very regularly with recurrent disease.

Abdominal bleeding

Intra-abdominal hemorrhages may occur in various situations, e.g. after trauma of surgery.   Hemorrhage may also occur 'spontaneously’, e.g. in diverticula, aneurysms, anticoagulation, tumor, etc.  When a hemorrhage is suspected, CT is usually performed first. After administration of intravenous contrast agent, multiple-phase scans are made: phase in which only the arteries are filled with contrast agent (arterial phase), phase in which the parenchymal organs are homogeneously enhanced (portal venous phase, after the arterial phase). Arterial hemorrhage can be seen when contrast agent escapes from the vessels in the arterial phase (contrast extravasation / blush), and increases in the portal venous phase (fig. 16). Usually a preliminary scan without contrast is performed in order to distinguish between abdominal calcification or iatrogenically introduced material and actual contrast extravasation. 

Figure 16. Patient with a large abdominal hematoma after coronary angiography. The hemorrhage is from a branch of the right inferior epigastric artery (the guide wire may have damaged the vessel). CT examination in the arterial and portal phase. Maximum Intensity Projection (MIP) reconstructions of a transversal slice at the level of the external iliac artery (AIE). There is clear contrast extravasation/blush which increases in the portal phase.

Hemorrhages may occur into the abdominal space, in a parenchymal organ or in a hollow organ or digestive tract.  The patient's condition may vary markedly, from fully stable with only few symptoms to impending shock. If the patient's condition allows, the hemorrhage can be stopped by an endovascular procedure (embolization). As in most procedures, the AFC is in principle used as access. A sheath is inserted through which the guide wire and catheter are maneuvered towards the site of the hemorrhage. 
Once in place, embolization may be performed using e.g. coils, gel foam or small particles. Coils are short metal wires that curl up once they are released from their cover or catheter. Apart from the fact that by their shape they block the blood flow, they are also coated with material with an additional thrombogenic effect. It is vital to place coils both proximal and distal of the hemorrhage (fig. 17a/b).

Figure 17a. This is the same patient as in figure 16. Angiography of the right external iliac artery (AIE). Contrast extravasation/blush in a branch of the inferior epigastric artery. AFC = a. femoralis communis.   

Figure 17b. Selective catheterization of the inferior epigastric artery. Coils are then placed in all adjacent arterial branches. AIE = a. iliaca externa. AFC = a. femoralis communis.

If coils are only placed proximally, there is a high risk that blood flow at the distal side will in time reverse and the hemorrhage recurs.  If this happens, it is very difficult to reach the bleeding site again because the proximal part has now been coiled!

Sources

  • J.A. Kaufman et al; Vascular and Interventional Radiology: The Requisites, 2nd Edition (2014)

Author

  • Text:
    drs. B. Ortega,MSc (Fellow interventional radiology, LUMC)
    dr. R. van der Meer (interventional radiologist, LUMC)

  • Image editing:
    drs. A van der Plas

13/02/2016 (translated 14/3/2017)

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