Chronic occlusive lesions (CTO) are the last bastion of coronary interventions because of their low success rate and high complications.CTO lesions are different from non-CTO lesions in terms of device selection and manipulation.The wire technique of manipulation of CTO lesions is the key to the success of the procedure. This article briefly discusses the above techniques from clinical practice.
I. Definition and basic pathological features of chronic occlusive lesions
Chronic occlusive lesions are defined mainly by the length of time the lesion has been in place. When occlusive lesions first occur, they mainly refer to loose thrombus as the main component, when even softer wires are easy to pass.
When these thrombotic lesions gradually become fibrotic and become part of the atherosclerotic lesion, the occlusive lesion thrombus becomes hard, and pathologically such a lesion should be called a CTO lesion. However, due to the heterogeneity of atherosclerosis and the different processes of fibrosis, it is difficult to define it pathologically, so in order to unify its definition, academics infer the time of CTO formation by clinical manifestations, and define those with occlusive lesions formed for 6 months as CTO lesions (but some people also define lesions formed for 3 months as CTO). Different research literature has different definitions, which should be noted when reading the literature.
In the author’s opinion, a 3-month occlusive lesion seems inappropriate to be defined as a CTO lesion because most general wires are easily passed. It is worth noting that some CTO lesions are still easy to pass due to the time of thrombosis even though they are more than 6 months old. Therefore, it is not only time that determines the pathological characteristics of CTO, but for the sake of consistency in research and statistics, it can only be defined compulsorily in terms of time.
The pathological characteristics of CTO lesions are determined by the formation process of CTO lesions, the underlying lesions before formation and the biological behavior after formation. If the occlusion is preceded by a moderate stenotic lesion that suddenly ruptures to form an occlusive thrombus, this thrombus gradually becomes fibrotic and forms a homogeneous structure, but can form some microtubules due to auto-fibrinolysis; furthermore, if the occlusion is preceded by a severe irregular stenosis, it becomes a non-homogeneous structure after the occlusion occurs, and such a structural wire can easily enter the subendothelium (pseudolumen).
After occlusion formation, due to blood flow, a stiff fibrous cap is formed at its most proximal end, which is stiffer than the tissue inside the occluded end. Sometimes the cap is calcified and hard, and it is difficult to pierce the cap with the tapered tip of the wire. The formation of an occlusion here results in the formation of bridging collateral and collateral circulation from other sites to supply the distal vessels, but it is far from adequate to meet the needs of the myocardium. In-depth understanding of the basic features of CTO lesions is very important for proper selection and operation of the wire. Generally, with the morphology of the lesion, medical history and necessary examinations such as CTA, the structure and characteristics of the CTO lesion can be inferred and “imagined”.
Second, the significance of interventional treatment of CTO lesions
Interventional treatment of CTO lesions has many complications, a high failure rate, and is time-consuming and costly, how significant is it? Strictly speaking, all CTO lesions should be opened to restore the “original” coronary artery. However, objectively speaking, the value of opening some CTO lesions is limited, so it is important to weigh the pros and cons before interventional treatment of CTO lesions. PCI should be aggressively performed in the following cases.
1, symptom-related CTO lesions, such as patients who still have clear exertional angina associated with CTO lesions.
2, Non-occlusive vessels providing collateral to the CTO vessel and who have a potential occlusion of their own.
3. A large amount of surviving myocardium exists in the area innervated by the CTO lesion. In these cases, even if the intervention is difficult, every effort should be made to open it.
However, PCI may not be performed in the following cases.
1. CTO vessels without viable myocardium.
2. CTO lesions are located in slender branches or end vessels. When there are multiple vascular lesions, one of which is a CTO lesion, the success rate of PCI for CTO lesions should be weighed. In particular, when PCI of a CTO lesion fails and other vascular interventions are transferred, the risk of PCI of the CTO lesion in other vessels in the event of failure should be repeatedly evaluated. If the risk is high, bypass surgery should be recommended, or PCI should be attempted again. Of course, other factors such as advanced age, renal function status, and general fitness should be considered when performing CTOPCI.
In conclusion, the significance of opening a CTO lesion is as follows.
1, alleviate ischemic symptoms ;
2.Improve cardiac function;
3.Reducing future cardiac events;
4.Improve myocardial electrical activity;
5.Provide safe support for other vascular interventions. Although the OAT study questioned the interventional treatment of CTO lesions, the population of the OAT study is not representative of the real-world CTO lesion population, and there are many problems and deficiencies in the study, so its findings do not affect the current view of CTO lesions.
III. Evaluation of CTO lesions
Proper evaluation of CTO lesions is essential to reduce complications and improve success rates. Again, they are all vascular occlusions, but their morphology, location, configuration, and nature are different. Therefore, each CTO lesion has its own characteristics. While bifurcation lesions are academically typed, CTO lesions do not yet have a specific typing, but are graded for difficulty. For example, Japanese scholars classify CTO lesions into four levels (see Table 1), while the European Heart Association only classifies them into simple CTO and complex CTO. this difficulty grading helps in the proper evaluation of CTO lesions. In addition, it is not only the lesion itself that affects the difficulty of CTO treatment, but other factors such as abnormal coronary opening, curved catheter path, and deformation of the ascending aorta also affect the success of intervention to some extent.
For a specific CTO lesion the following aspects should be taken into account.
1, occlusion time: the longer the occlusion time, the more difficult it is to open.
2, occlusion length: short occluded segments are easy to open. Long occluded segment, the wire travels difficult and takes more time to cross the lesion.
3, the proximal end with or without fiber cap and its morphology: for “rat tail lesion”, the wire is easy to find the puncture force point, while “flat head lesion”, the wire’s action point is difficult to control. In addition, when the fibrous cap is small or the recently formed CTO lesion has not yet formed a fibrous cap, the wire is easy to pass. On the contrary, when the fiber cap is thicker and stronger, the wire is difficult to pass.
4, the occlusion is issued with or without branches: when there are branches, the wire is easy to enter the branches, which affects the fixation of the force point of the tip of the wire.
5, the formation of bridging collateral vessels: bridging vessels accompany the formation of CTO, marking a longer period of CTO formation, while indicating the difficulty of PCI of CTO lesions. Wire manipulation is difficult when bridging vessels are present.
Coronary angiography is the most basic and commonly used method to evaluate CTO lesions. For CTO lesions it is important to project from different sites to clarify the site of the CTO lesion, the length of the occluded segment, the emanation site of the branch, and the morphology of other non-CTO lesions in the proximal segment. The contralateral angiogram should be kept long enough to clearly show the length of the occluded segment. Coronary CT can provide additional information about CTO lesions. CTA can clearly show the length of the occluded segment, as well as the nature of the lesion within the occluded segment and the presence or absence of microvessels.
In addition CT can show the presence or absence of calcification of the fibrous cap. Studies have demonstrated that when CTO shows a fibrous cap with significant calcification, the resistance increases significantly and the balloon has difficulty passing through the CTO lesion even if the wire passes through it. When inhomogeneous calcified lesions exist in the occluded segment, a winding guidewire should be selected and its tip is easy to make a very small bend. Otherwise, other types of wires can easily enter the intima.
When softer components or microtubules are present in the occluded segment, a tapered guidewire of the twisted type can be chosen first to pierce the fibrous cap before using a hydrophilic superslip wire to enter the occluded segment. Experienced interventionalists, when encountering difficult CTO lesions, do not treat them immediately but perform PCI after a comprehensive evaluation, which includes a preoperative CT examination. Of course, it is not necessary to perform CT examinations for all general CTO lesions.
IV. Preparation for PCI of CTO lesions
Because of the long time required for interventional treatment of CTO lesions and the different instruments required for the procedure, adequate preparation should be done before the procedure. First of all, the operator should maintain a good working condition and state of mind, without impatience or fear, and without the influence of other things, such as rushing to do the next thing. This is very important.
From the patient level the following aspects should be prepared.
1. The patient’s state can be kept flat for a long enough time. In patients with cardiac insufficiency, preoperative cardiac function should be improved sufficiently so that the patient can remain recumbent for more than 12 hours. Patients with recumbent angina should be controlled with medication as much as possible so that the patient is not prone to angina attacks for 3-5 hours.
2. Patients with renal insufficiency should be adequately hydrated before surgery and the use of contrast agent should be minimized intraoperatively. If a certain amount of contrast agent has been used intraoperatively, which may cause serious deterioration of renal function, and the CTO lesion has not yet been opened, this operation should be abandoned and another attempt should be made at a later date.
3. Preparation of instruments. Strongly supportive guiding catheters, different types of wires and balloons, other aspects of preparation, including intravascular ultrasound (IVUS, intra-aortic balloon counterpulsation (IABP), stents with membranes and spring-ring embolization kits, etc.