I. Balloon angioplasty
(I) IndicationsThe ideal indication is limited, isolated short-segment stenosis in medium-sized or large vessels. This is followed by multiple, scattered short-segment stenoses and occlusions. Long-segment stenosis or occlusion, small-vessel disease, ulcerative stenosis, or stenotic or occlusive lesions with existing calcification are not suitable for PTA treatment.
(2) After angiography to determine the lesion location, extent and collateral blood supply, as well as hemodynamic changes such as blood pressure above and below the stenosis, the contrast catheter is switched to a balloon catheter. The balloon is placed in the stenosis, and the balloon is inflated with a pressure pump or hand-pushed diluted contrast medium. The inflated balloon acts on the stenotic vessel to dilate it. After the dilation is complete, the angiogram is repeated to see how well the vessel has dilated, and the difference in blood pressure above and below the original stenosis is measured again to determine the effectiveness of the dilation treatment. To minimize complications and prevent restenosis, antiplatelet aggregating drugs, such as aspirin, are applied from the day before the procedure. Intraoperative anticoagulation with heparin is necessary, and drugs such as aspirin and Pansentin are taken for 1 to 6 months after surgery.
(3) Mechanism of vasodilation The pressure of the inflated balloon caused a limited tearing of the intima and intima of the vessel wall in the stenotic area. Overstretching of the vessel wall, especially the mid-membrane, as well as rupture of atheromatous plaques, leads to hypotonia of the vessel wall and enlargement of the lumen diameter.
(iv) Efficacy The immediate and long-term efficacy of PTA is good. The success rate of PTA in the iliac and renal arteries is over 90%, and the five-year average vessel opening rate is over 70%. The success rate of PTA for single-branch lesions of coronary artery veins is above 90%. Among the factors affecting the efficacy, in addition to the site of the lesion, the nature of the lesion, the anatomical and pathological characteristics of the lesion, the patient's general condition, the equipment, and the experience of the operator are also important factors. For example, in renal artery stenosis, the best efficacy of fibromuscular dysplasia, dilatation success rate of 90% to 95%, clinical hypertension cure and improvement rate of 93%; followed by atherosclerosis; and multiple aortitis of the efficacy of poor.
The advantage of PTA over surgery is that it is less traumatic to the patient, has fewer complications, produces faster results, is easier to operate, reduces costs, and can be performed on an outpatient basis, and once restenosis occurs, PTA can be repeated.
(5) The problem of restenosis is that although PTA has good therapeutic effect, the incidence of restenosis after dilatation is high, and the average incidence is about 30%. Restenosis mostly occurs within a few months to 1 year after PTA. The main reason is the result of endothelial fibroblast proliferation at the site of balloon dilatation. The mechanism of dilatation suggests that plasty is a mechanical treatment that damages components of the vessel wall and inevitably induces a series of repair reactions after the procedure, which becomes the basis for the pathology of restenosis . The outcome of balloon dilatation is therefore twofold. The limited tearing of the intima and mesentery caused enlargement of the vessel lumen and restoration of perfusion; at the same time, the tearing of the intima and mesentery became the cause of fibrous tissue proliferation leading to restenosis.
In order to reduce restenosis, the following three measures can be taken: ①Improvement of equipment: a new type of balloon into a new material has been developed, which can reduce the damage to the blood vessel. ② drug therapy: reduce, prevent and treat vasospasm, platelet adhesion, thrombosis and endothelial fibroblast proliferation in the process of PTA and after PTA. Commonly used drugs are aspirin, heparin, nitrophenylpyridine (cardioplegia) nitroglycerin, and prostacyclin, thromboxane synthase inhibitors and so on that are being tried. ③ the application of new technologies: that is, the following several angioplasty.
(VI) Complications PTA has fewer complications, sometimes can occur perforation of local hematoma, arterial wall tear holes, distal end vascular plug and balloon rupture.
Two, laser angioplasty
Early 80's used to recanalize peripheral arteries, is now used in a large number of clinics, has achieved promising results, laser energy ablation of atherosclerotic plaques or thrombus to make the vascular recanalization of the mechanism, mainly lies in the thermal effect and chemical desorption effect.
Laser source has gas, solid and liquid substances. Laser angioplasty with more neodymium yttrium aluminum garnet (Nd-YAG) laser and excimer (excimer) laser. Multiple quartz fibers are used for the delivery system. To minimize perforation of blood vessels, metal caps and sapphire caps are added to the quartz ends. The laser is emitted in either continuous or pulsed mode. Continuous emission can cause significant thermal damage to the tissue. Pulsed emission of energy, easy to ablate the lesion tissue, there is no obvious thermal damage. Therefore, pulsed waves are now mostly used. Laser wavelength can be used ultraviolet (200 ~ 400mm). Visible light (400 ~ 700mm) or infrared (700 ~ 1000nm).
Laser angioplasty may have the following advantages: ①Treatment of chronic occlusion of blood vessels, diffuse lesions, calcified lesions is superior to balloon angioplasty, and is effective in acute vascular closure that occurs after balloon angioplasty. ② Thermal effect of thermal polishing or sealing effect, followed by application after balloon dilatation, can make the luminal surface of the blood vessel caused by balloon dilatation from irregular to smooth, and sealing welding peeled off the intima, thus reducing platelet adhesion near and thrombus formation. (3) The photothermal effect can change the compliance of the vascular wall, reduce the reaction of the arterial wall to the vasoactive substances, reduce the elasticity of the vascular wall caused by balloon dilatation, and facilitate the lasting expansion of blood vessels. Therefore, laser angioplasty is now used in conjunction with balloon angioplasty, which is called laser-assisted balloon angioplasty.
Laser revascularization is still in the research and development stage, and there are many technical problems that need to be further solved.
Three, atheromatous plaque resection
Some scholars simply referred to as the rotary cut method, mainly for highly narrowed or completely occluded blood vessels, is also a mechanical treatment.
According to the function of the catheter used for this therapy, its treatment is divided into two kinds: ① percutaneous cutting, take out the atherosclerotic material, called atherectomy, that is, resection: ② percutaneous broken atherosclerotic plaques, so that the particles become particles, to be stored in the blood circulation, to be cleared naturally by the body, called atheroablation, that is, crushing surgery.
The catheter used for this treatment has a high-speed or low-speed rotation of the head end of the chipper or grinding ball, when the catheter head end placed in the vascular occlusion lesion, the manipulation of extracorporeal catheter tail drive device, chipper or grinding ball rotation, excision or grinding lesions, so that the blood vessels reopen. There are many catheters under development, and the ones currently used in the clinic are Kensey catheter, Simpson catheter, and trans luminal extraction catheter (TEC).
The rotational dissection method is beginning to be used for renal and coronary arteries in addition to peripheral vessels. The success rate of recanalization of peripheral vessels is above 95%. Because rotational dissection is still a mechanical treatment, the repair response to damage to the vessel wall can also cause restenosis. This therapy is also under development.
Four, vascular support device
Vascular support device is the use of special alloy, made of different structures of the cylinder, supported in the stenosis lesions, so as to maintain blood flow. Currently there are three kinds of support device: ① thermal memory alloy support device (thermalmemoryalloystent): made of nickel-titanium alloy wire, known as Nitinol. ② self-expandablestent support device (self-expandablestent); with stainless steel alloy wire braided into a cylindrical shape, into the blood vessels, due to the elasticity of the metal and support the lumen of the blood vessels. ③ balloon expandablestent (balloon-expandablestent): the support is cylindrical mesh shaped, first on top of the balloon, put into the blood vessel after inflating the balloon, so that the support is supported in the lumen of the blood vessel open.
After the proppant is placed in the vessel, the body can tolerate it without foreign body reaction. Due to the fibrinogen coverage of the endothelium, a new endothelium can be formed soon, which connects with the normal endothelium at the two ends of the proppant, thus guaranteeing the patency of the blood vessel.
Supporters are mainly used in conjunction with balloon angioplasty, laser angioplasty, and rotational dissection. After the latter techniques dilate or recanalize the diseased vessel. Placement of the brace improves vessel opening and reduces restenosis.
In addition, the use of ultrasound energy to eliminate atheromatous plaques, thrombi, etc. to recanalize blood vessels has also been tried in the clinic, which is called ultrasonicangioplasty (ultrasonicangioplasty,angiosonoplasty). Some new vascular imaging techniques, such as angioscopy, intravascular ultrasound, and MRA, have been important in the development of percutaneous angioplasty.