Chapter 2: Sheaths, guide wires and catheters
Section I
I. Techniques of operation of sheaths
Sheaths can be divided into long sheaths and short sheaths according to their lengths. Short sheaths are generally used for simple imaging, and according to their therapeutic needs, there are also the Tumbledown sheaths for dealing with the contralateral lower extremity, the long Shuttle sheaths for dealing with the carotid artery, the Guiding sheaths for dealing with the renal artery, and the anti-fracture sheaths to. The sheaths have a side connection interface for intraoperative blood sampling, pressure monitoring, and injection of vasodilators or contrast media.
The guidewire is preferably placed so that the tip of the guidewire extends into the lumen of the puncture needle and is sufficiently far from the tip of the puncture needle to ensure that the softer part of the guidewire tip extends into the arterial puncture site. After the puncture, fluoroscopy is performed and the guidewire is introduced into the desired position. The puncture needle is then removed, and the puncture site is compressed during removal. The guidewire is preferably flushed with heparin saline.
Select a suitable sheath, soak the sheath and the accompanying dilator in heparin saline, and flush the lumen. To start the procedure, close the switch on the lateral arm of the sheath tube. The dilator base needs to be locked to prevent it from withdrawing during sheath entry. Check whether the skin puncture site requires pre-dilation and verify that the guidewire is stiff enough to allow entry of the sheath. Use a sheath-matched guidewire to ensure sheath entry. If the sheath is thicker and longer, or if there is scarring in the inguinal region, use a stiffer guidewire. Regardless of the type of guidewire used, ensure that the guidewire is long enough to ensure that the softer part of the tip of the guidewire is in the artery and the stiffer part of the main stem of the guidewire is in the arterial puncture needle.
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The operator uses one hand to gently compress the puncture site while the other hand pushes the arterial sheath down the guidewire into the skin and then into the artery. Continuous compression of the puncture site must be applied while the sheath is placed in the arterial Soap. The proximal part of the sheath must be pushed gradually into the artery to prevent bending of the sheath as it enters the tissue. Rotation of the sheath is required for both subcutaneous advancement and retraction of the sheath. The lateral tube of the sheath is placed in a convenient position, usually toward the operator, during sheath entry. If the base of the dilator loosens and withdraws while the sheath is being entered, the open end of the sheath can be forced into the tissue and may cause damage to the sheath itself and the artery. In this case, the sheath should be reassembled and reoperated. During this time, the arterial puncture site should be compressed until the sheath is felt to enter the artery, which will prevent subcutaneous bruising. After the tip of the sheath has entered the artery, reduce the amount of force used to enter. Resistance is felt when the sheath is pushed into the artery at the beginning, and subsequent entry is easy and smooth. If resistance persists, perhaps there is an error in the procedure and a fluoroscopy can be performed.
After the sheath is placed, it is flushed with heparin saline. The sheath lumen should be flushed frequently after imaging with a sheath tube. The lumen should be flushed immediately after any procedure. When working with large or tortuous vessels, it is best to secure the sheath to the skin with sutures to prevent possible slippage of the sheath in thicker or more tortuous vessels. If the catheter used is the same type as the sheath (e.g., a 5F catheter in a 5F sheath), the catheter will completely obstruct the lumen of the sheath and contrast and heparin saline cannot be injected through the lateral arm of the sheath. When entering the lumen, the tip of the sheath should be clearly positioned to prevent the balloon or stent from not extending out of the sheath and not being released. If the femoral artery puncture site is heavily calcified or has a lot of scar tissue around it, the guidewire may enter the artery easily, but the dilator or sheath may have great difficulty entering. In this case, the tip of the dilator may bounce back against the hard arterial wall and the entire puncture system, including the guidewire and sheath, may bend in the subcutaneous tissue. This is more likely to occur if the patient is obese and has scar tissue in the artery. The dilator should be introduced and the subcutaneous guidewire should be straightened. After the dilator is inserted, it may be necessary to change to a more rigid guidewire depending on the condition or the need to deliver the sheath.
Basic sheath type
The diameter of the guidewire is in inches. “035” means that the diameter of the guidewire is 0.035 inch. The available guidewire diameters are “0 1 0, 0 1 4, 0 1 8, 025, 035 and 038”. Each guide wire diameter has a matching catheter. The most commonly used guidewire sizes are “0 1 4 and 035”.
The unit of catheter is “French”. This unit is a description of the circumference of the catheter. The “French” system is based on the circumference, which is the ratio of the circumference of a circle to the diameter of that circle. The “French” dimension of the catheter or sheath is divided by the circumference or by 3 to obtain the catheter or sheath tube circumference.
to obtain the diameter of the catheter or sheath tube. For example, the diameter of a 6F sheath is 2 mm and the diameter of a 24F sheath is 8 mm. Dividing by 3 converts the “French” dimension to the diameter of the arterial puncture site. Both dilators and catheters are described in terms of outer diameter (OD), while sheaths are described in terms of inner diameter (ID). The ID of a sheath indicates the size of the device that can pass through its lumen, e.g., a 5Fr sheath fits a 5Fr catheter. The standard 5Fr sheath sheath has an outside diameter of 6 or 7Fr, which is 1-2Fr larger than the vascular puncture site, but is of little practical clinical significance. Sheaths are available in a variety of diameters, commonly in the 4-6Fr range because of their size, and most diagnostic and ball expansion catheters fit this size. Sheaths of 6-8 Fr are usually required for stent placement, with 6-12 Fr being preferred for the iliac and superficial femoral arteries (SFA) and 22-25 Fr for the aorta.
Sheaths are available in various lengths: 3-5cm, 10-12cm, 22-25cm, 30-40cm and 90-lOOcm. 010-12cm is the standard length and is suitable for most peripheral vascular diagnostic and interventional procedures. 3-5cm is usually used for hemodialysis access. Medium lengths are suitable for the contralateral iliac or femoral artery and renal artery. These sheaths have a pre-formed head or are torsion resistant to facilitate access to the aortic bifurcation. Some manufacturers place radiopaque markers at the end of the sheath to facilitate fluoroscopic visualization. This is particularly important during interventions, for example, to know if the stent is fully extended before releasing the sheath. The longest sheaths can be used for both carotid and contralateral tibial artery interventions.
Precautions for the use of sheaths.
1. Before using the sheath, the sheath and dilator should be flushed and wiped with heparin saline.
2. Close the switch of the lateral sheath tube.
3. Confirm the sheath type repeatedly.
4.Lock the dilator completely or insert it to the base of the sheath tube.
5.Pre-dilate the skin entry point.
6.Check the type and position of the guidewire.
7.Pre-dilate the entry tunnel with the dilator.
8.The puncture point should be compressed when performing the sheath tube device exchange.
9.The sheath and dilator are delivered together to the body.
10.Deliver the guidewire.
11.Hold the main body of the sheath while inserting the sheath.
12.Rotate the sheath and gently enter the subcutaneous tissue.
13.Press the arterial puncture site until the tip of the sheath enters the artery.
14.The lateral tube of the sheath is oriented toward the operator.
15. Check the dilator on the sheath to confirm that it will not withdraw.
16. If there is resistance to delivery, stop immediately and check.
17.Insert the sheath up to its base.
18.After sheath placement is complete, the dilator is removed and the sheath is suctioned and flushed.
19.If there is blood oozing around the sheath, you can change to a larger sheath.
20.Never use the sheath tube alone without dilator to enter.
21.If the tip of the sheath tube is damaged or irregular, it needs to be replaced promptly.
22.Sew the sheath to the skin to prevent it from slipping out (usually not used).
23.If the catheter completely fills the lumen of the sheath tube, fluid should not be injected into the lateral tube.
24.The position of the sheath tip in the lumen of the vessel should be clarified.
Section 2
Guidewire
I. Structure and basic characteristics of guidewires Basic characteristics of guidewires include guidewire stiffness, maneuverability, suppleness, and smoothness. Understanding the existing design and basic structure of guidewires helps to select the appropriate guidewire to complete the procedure.
1.Structure
The basic structure of a guidewire consists of a stiff inner spool and a tightly wound outer spring coil. The internal axis of the guidewire is called the spool, which ensures the hardness of the guidewire, and it tapers toward the tip, making the tip softer. The outside of the spool is made of a stainless steel spring coil. The guide wire contains a thin safety wire that connects the shaft wire to the tip of the external spring ring to prevent separation. The wire is usually coated with a hydrophilic polymer, such as PTFE, to increase its smoothness. This property facilitates guidewire advancement and catheter/guide wire exchange.
The shape of the head of the guidewire plays a major role in its passage performance. A “J” shaped head is the least traumatic and is less likely to cause entrapment or perforation, but this shape makes it difficult to pass through severely stenotic lesions. The head of the guidewire can be shaped to the desired shape, and the shaped head allows easy access to the branch vessels. The guidewire is equipped with a twisting device that provides a 1:1 rotation ratio.
2. Classification
According to the shape of the head end, the guidewire can be divided into different types such as “J” shaped head, straight head, and angled head. According to the diameter of the guide wire can be divided into 0.035 inch, 0.038 inch, 0.018 inch, and 0.014-0,018 inch micro-guide wire, etc. According to the role of the guide wire can be divided into puncture guide wire, selective guide wire for guide wire, etc.. Each type of guidewire has different length specifications (such as 80cm. 145cm. 180cm. 260cm. 300cm, etc.).
260cm. 300cm, etc.). The standard length of cross-Q guidewire is 145cm to 300cm. 145cm long guidewire can be used to deliver catheter for routine imaging. 180cm long guidewire is used for aortic bifurcation for hill-turning operation and can deliver catheter to the contralateral superficial femoral artery. 260-300cm long guidewire is used for long distance operation such as aortic arch, carotid angiography and aortic stent placement.
(Bentson guidewires (Cook, Inc., U, S. A.) are an ideal choice, with a soft tip, a toughened body, a diameter of 0.035 inch, and a standard length of 145 cm. Longer guidewires are also available for special lesions.
(2) The selective guidewire has good maneuverability and is coated with a hydrophilic surface. Hydrophilic coated guidewires are useful when passing through stenotic or irregular lesions, where they can follow the blood flow path. Hydrophilic-coated guidewires are very smooth when exposed to water, giving the operator the impression that the guidewire will slide forward during manipulation, when in fact it is very stable. When it is necessary to exchange different catheters through hydrophilic guidewires, it is best to choose a stiffer guidewire that does not slide easily.
(3) Exchange guidewires have a strong inner core and are therefore stiffer than other guidewires. The use of a cross-Q guidewire will ensure a safe operation. If the access to the endoluminal device is tortuous or if the device is large, then an exchange guidewire should be considered. Amplatz, Rosen and Lunderquist are some of the more suitable exchange guidewires. Stiffened guidewires should not be used during initial passage through the lesion because of the potential for damage to the vascular lumen. Stiffened guidewires can be very helpful when performing complex endoluminal maneuvers such as complex, multi-stent revascularization or release of the graft vessel.
II. General principles of guidewire manipulation
Manipulation of the guidewire should first clarify the interrelationship between the head end of the guidewire and the lesion site under fluoroscopic imaging. Patiently observe the morphological changes of the guidewire in the vascular lumen and its route of travel.
1. Soak the guidewire with heparin saline to make the guidewire function better. The guidewire with hydrophilic coating must be soaked in heparin saline before use. When each exchange of the guidewire is completed, wipe the guidewire with heparin saline.
2. Increase the stiffness of the soft tip of the puncture guidewire so that it can pass smoothly through the puncture needle and through the arterial access point.
3. Standard, non-flexible guidewire tips can be shaped with fingers and hemostatic forceps to make the tip curved.
4.If the guidewire cannot pass through the puncture needle, it should be replaced promptly.
If the tip of the guidewire is close to the lesion but has not yet passed through the lesion, fluoroscopy must be performed intermittently to ensure that the tip of the guidewire has not migrated or impinged on the lesion. Blind delivery of the guidewire may lead to vascular damage.
6. If the guidewire is bent a few centimeters at a time, the delivery device may be difficult and the guidewire must be replaced. Do not apply force to the guidewire.
7.When the tip of the guidewire touches the lesion, the operator must be alert.
8.When using selective guidewires, it is best to use a torsion device. The torsion device provides a 1:1 rotation ratio for the guidewire.
9.When exchanging the guidewire and catheter, the guidewire is kept flat and tightened externally to prevent relaxation and advancement of the guidewire in the catheter.
10.When delivering the intraluminal treatment device through the guidewire, the position of the guidewire must be clarified first.
11.When operating on the hydrophilic guidewire, the guidewire should be fixed (with the thumb and index finger) to
prevent the guidewire from sliding forward or backward.
12.After withdrawing the guidewire, the guidewire should be rotated to its original state to prevent confusion on the instrument table. Place a piece of gauze on the guidewire outside the body to prevent the guidewire from slipping under the operating table.
13. If the guidewire is contaminated, the operator must use a new guidewire for the operation. If the end of the guidewire is contaminated, the end of the guidewire can be removed, and the original position of the guidewire is maintained, without abandoning the guidewire access until the operation is completely finished.
14. The placement of catheters or sheaths can increase the support and pushing force of the guidewire.
Third, the general principle of choosing a guidewire
The appropriate guidewire should be selected before the operation begins, and it should be clear that if this guidewire does not solve the problem, what should be done next. A 0.035-inch guidewire is generally preferred. The common guidewire used for coronary interventions is the 0.014 guidewire. Primary branch vessels such as the carotid, renal, cervical, and distal lower extremity arteries can be treated with both types of guidewires, but the technical trend is to attempt silicone revascularization of all branch arteries with 0.014 guidewires. 0.014-inch guidewires are more commonly used in conjunction with single-track systems for branch arteries.
When selecting the length of the guidewire, the length of the guidewire inside the patient must reach and exceed the lesion to ensure that the exchange catheter can reach the lesion; the length of the guidewire outside the patient must ensure that it can support the longest catheter and that the tail of the guidewire extends beyond the catheter after catheter introduction to facilitate the operator’s manipulation of the guidewire. The length of the guidewire usually ranges from 145 cm to 300 cm, with the option of longer guidewires when dealing with specific lesions. Monorail systems require less extracorporeal guidewire length than coaxial systems because the length of the guidewire within the catheter of a monorail system is only a small fraction of the overall catheter length, usually 20 cm to 30 cm.
Section III Catheter
I. Classification
L. Contrast catheter: a long, thin hollow tubular structure with thin walls, the end of the catheter can be connected to a syringe or high-pressure syringe. Catheter materials are mainly used polytetrafluoroethylene, polyurethane, polyethylene or nylon. The hydrophilic coating of the catheter increases the ability to follow up, and the mid-wire braiding structure of the tube wall increases the strength, folding resistance and torsional control of the catheter. The roles of contrast catheters are: injection of contrast agent to observe vessel morphology; pressure measurement to obtain hemodynamic information: transport and release of drugs or embolic materials; acting as a guiding catheter, etc. Contrast catheters are generally divided into non-selective contrast catheters and selective contrast catheters according to their uses. The former are mainly pigtail catheters and tennis racket catheters, which are mainly used for non-selective imaging of large vessels (such as aorta, pulmonary artery, vena cava), and the multi-lateral holes at the distal end of the catheter allow high speed and high flow rate of contrast injection), and straight catheters with multiple side holes can also be classified as non-selective catheters for selective imaging of carotid artery, iliofemoral artery, inferior vena cava, etc., which can increase the flow rate and flow rate accordingly. Selective contrast catheters are available in a variety of shapes, including preformed catheters with a single bend and reverse bend, with a single end hole, for selective vascular cannulation and selective catheterization of specific aortic branches. Selective catheters typically have lower contrast flow and flow rates than non-selective catheters. Commonly used selective contrast catheters include Ve]al catheters (vertebral artery catheters), Headhunter catheters (Hunter head catheters), Simmon series catheters, Cobra catheters (cobra catheters), Shepherd catheters (shepherd catheters), Mikaelsson ventral catheters, Bentson JB2 catheters, Vitek catheters Mani catheter, RDC catheter (renal double bend catheter), etc.
Catheter specifications are generally divided into outer diameter, commonly used for 4F-7F outside diameter, general imaging is generally used for small diameter catheters, usually 4F and 5F catheters. The end-hole catheter is generally used for selective angiography; the side-hole function, in addition to increasing the flow and flow rate of the angiogram, is also contraindicated, especially in high-pressure injection angiography, to avoid high amplitude oscillation of the catheter to damage the vessel wall. The catheter length for abdominal aorta localization angiography is typically 60-80: while in the thoracic aorta and carotid region a catheter of 00-120 length is required for the door. Catheters should always be kept moist and should be flushed before entering the body: intermittent intraoperative flushing can extend the life and reduce the formation of blood clots at the catheter tip.
2.Guidance catheter: Guidance catheter is an important channel for interventional device delivery, with functions such as delivery, support, pressure measurement and contrast injection. The appropriate guiding catheter is an important guarantee for the successful completion of balloon dilation and stentoplasty. The guiding catheter is similar to but different from the contrast catheter in shape and knot. The special requirements are that the guiding catheter must have sufficient internal lumen to deliver the interventional device, and that the outer diameter of the catheter should not be too large to avoid complications at the puncture site. Therefore, the design, material selection, and structure of the guidewire catheter are more important than those of the imaging catheter because of its “small outer diameter and large inner lumen”, while taking into account the important properties of the guidewire catheter such as fracture resistance, torsional control, and support. Basic structure: The wall is composed of three layers, the outer layer is made of polyethylene, which determines the shape and hardness of the catheter and has a smooth outer surface to prevent intimal damage and thrombosis: the middle layer is a woven mesh of stainless steel wire, which is the backbone of the guidewire catheter and makes the catheter less likely to collapse and deform and resists fracture and transmits torsional control forces to the tip of the catheter: the inner layer is made of nylon or polytetrafluoroethylene for lubrication. Reduce the friction between the post-interventional device and the lumen of the guiding catheter, and prevent thrombosis.
The outer diameter of the guiding catheter: according to the size of the outer diameter is divided into 5F to 9F, the most commonly used outer diameter is 6F and 7F, while 8F is mainly used for carotid stents. The larger O.D. guiding catheters provide better support and have a correspondingly larger I.D., so they are suitable for the treatment of lesions requiring strong support (e.g., type II or type III aortic arch during carotid stenting, severely twisted abdominal aorta during renal stenting) and for more complex lesions requiring multiple devices (e.g., anastomotic balloon dilation at the opening or bifurcation) and special devices (e.g., cutting balloon and rotary grinding). The large OD guiding catheter is the appropriate choice for more complex lesions that require multiple devices (e.g., opening or bifurcation balloon dilation) and special instruments (e.g., cutting balloons and rotary lapping). However, large OD guidewire catheters also cause more damage to the vessel and increase local complications at the puncture site.
3.Thrombolytic catheter: The standard thrombolytic catheter is a straight-ended multi-lateral hole catheter with a tip end hole that can be inserted into the thrombus through a guidewire. Both ends of the perfusion segment are marked with opaque X-rays to precisely show the length and location of the perfusion segment, and the side holes of the perfusion segment are mainly used to increase the contact area between the thrombolytic drug and the thrombus. The length of the perfusion segment ranges from F 5 to 20 cm, and the number of corresponding side holes varies from 10 to 20. The length of the perfusion segment that contacts the thrombus should be selected according to the length of the thrombus occlusion. During thrombolysis, the end hole is blocked by the guidewire, and the thrombolytic solution flows out through the side holes and penetrates evenly into the thrombus. The inner diameter is generally 3F, which can accommodate the perfusion guidewire to form a word axis system to expand the thrombolytic area.
Fogarty catheters are single-lumen or double-lumen balloon catheters, which are inserted through direct visual dissection of the peripheral vessels and traverse the thrombus to its distal end. Afterwards, the balloon is filled with physiological saline or dilute contrast and pulled back from the vascular incision to remove the thrombus. The disadvantage is the large amount of residual mural thrombus and the presence of severe endothelial injury.
Second, the use of principles
Currently, contrast catheters are mainly produced by Cordis, Cook and Terumo companies, with the Codis catheter having the hardest body and good torque and maneuverability: the Terumo catheter has the softest body and is easy to complete selective cannulation; the Cook catheter is between the two >. The Cook catheter is somewhere in between. The choice of the three is usually dependent on the experience and habits of the operator. Routine diagnostic angiography tends to use a 4F or 5F catheter with a 0.0335-inch guidewire. Off-catheter reductions are sufficient for multi-site treatment; the use of counter-anastomosis or spin-grinding techniques usually requires a 6F or larger catheter. The choice of catheter length depends on the access route and insertion site. The catheter must be of sufficient length to reach the target vessel and of appropriate length outside the body to facilitate manipulation of the catheter: however, excessive catheter length can sometimes prevent manipulation of the catheter. Peripheral vascular disease differs from coronary artery disease in that multiple sites of elective cannulation are involved, and preoperative access should be planned and catheters of appropriate length should be selected. Typically, the femoral route is used to cannulate the superior aortic arch with a contrast catheter length of between 90-120. For retrograde femoral route for renal artery cannulation and ipsilateral or contralateral iliofemoral artery cannulation, the catheter length ranges from 65-lOO cm. The cis-femoral route for ipsilateral infrapopliteal or even pedicled artery cannulation usually requires a catheter length of about lOO cm.
In general, the catheter should be matched to the diameter of the guidewire, and the catheter should be advanced along the guidewire while the guidewire is continuously pulled to ensure that the catheter does not continue to slide forward. Do not advance the catheter until the guidewire is straightened. When using a hydrophilic guidewire, the posterior end of the guidewire must be clamped to prevent the guidewire from sliding forward suddenly in the catheter. The catheter site should not be too far from the sheath in vitro, as this may cause the catheter and guidewire to bend.
When the catheter reaches the softer part of the guidewire, the catheter may retain its original shape, resulting in a significant reduction in advancement. At this point, the catheter should continue to be advanced so that the catheter always advances over the stiffer portion of the guidewire. If the catheter cannot be advanced along the stiffer portion of the guidewire, the arterial dilator should be advanced to continue to dilate the artery or replaced with a stiffer guidewire to provide additional support for the catheter. If the catheter becomes less propulsive after entering the vessel, consider replacing the guidewire with a stiffer one. If the catheter does not follow the guidewire into the lesion, it is possible that the disease itself is resistant, or that the stenotic lesion is so stenotic that the guidewire is blocking the remaining arterial access, or that the guidewire has entered the subintima.
IV. Precautions.
1. The catheter should be flushed with heparin saline outside the body before entering the body to evacuate any solids and blood clots including air bubbles in the bladder lumen of the tube.
2. The appropriate size, length and head shape should be carefully selected based on the contrast site and experience when using the catheter.
3. When the guidewire is successfully placed through the vascular puncture site, careful finger pressure should be applied to the puncture site for arterial haemostasis before placing dilators, sheaths or placing catheters to stop bleeding; correct compression can effectively reduce haematoma formation at the puncture site.
4. Use mosquito forceps to dilate the epidermis to the appropriate size to facilitate subsequent dilation. Tensioner and catheter entry.
5. The dilator or catheter should be pushed into the vessel along the stiffer part of the guidewire.
6. advance the catheter gradually under fluoroscopy, a few centimeters at a time.
7, advancing the catheter guidewire process should pay attention to experience the forward resistance and feel, avoid entering the subendothelial lamina channel;
8, the operation should be intermittently pulling the guidewire to prevent the guidewire and the catheter from advancing at the same time;
9.If the catheter needs to advance too far and is not easily put in place smoothly, it is usually due to the large friction force. In this case, it is necessary to place a long sheath, replace the hard guidewire or choose another arterial puncture site.
10.The catheter should be intermittently flushed with heparin saline during in vivo operation to prevent micro-thrombosis of the wall.
11. No substance (heparin saline and contrast medium) should be injected into the catheter until the outer end of the catheter has returned blood; under normal blood pressure, the catheter generally has returned blood unless the catheter tip is embedded and adhered to the vessel wall.
12. the catheter tip should be adjusted under constant fluoroscopy prior to high pressure injection of contrast medium to ensure that it is free of the vessel lumen; otherwise, entrapment or perforation may be induced
13. Before high pressure injection of contrast medium, the contrast medium should be pumped back until there is blood return in the injection syringe to avoid air bubbles entering the body at the interface between the syringe and the end of the catheter.
14.If the end of the catheter becomes knotted, use a stiffer guidewire to untie the knot through the catheter;
15, to determine the catheter is located in the vascular cavity in addition to the blood return judgment, but also in vitro rotation of the catheter fluoroscopic observation of the catheter tip in the lumen of the free mobility;.
16.When a small amount of contrast agent is injected, the contrast agent should be rapidly washed and diluted by the blood flow, rather than being retained in the vessel wall causing lamellar staining.
The catheter is located in the lumen of the free vessel ;
17.After removal of the guidewire, if the position of the catheter tip is uncertain under fluoroscopy, a small amount of contrast agent can be injected to help visualize the catheter;
18.When withdrawing the catheter or exchange operation, the guidewire should be fixed in the original position and the catheter should be withdrawn at the same time; intermittent fluoroscopy should be performed to check whether the guidewire is in the original position.