Section I. Basic knowledge of coronary intervention
I. Definition of successful percutaneous coronary intervention (PCI)
Successful percutaneous coronary intervention (PCI) should include three aspects: (1) successful angiography: successful PCI results in significant lumen enlargement at the target site of the coronary artery, residual stenosis <50%, and TIMI grade 3 blood flow at the same time. With the widespread use of coronary stents and other technologies, a residual stenosis of <20% after the procedure is now considered the ideal standard for successful angiography. (2) Operation success: It means that the criteria for successful angiography have been met, while there are no major clinical complications during hospitalization (e.g., death, myocardial infarction, emergency coronary artery bypass grafting). Operation-related myocardial infarction is generally considered to be diagnosed by the presence of pathological Q waves and elevated cardiac enzymes (CK, CK-MB), but the significance of elevated cardiac enzymes without Q waves is controversial. The clinical significance of non-Q-wave myocardial infarction with a 3- to 5-fold increase in CK-MB levels above the upper limit of normal has been demonstrated. Significantly elevated CK-MB levels without Q-wave itself implies the presence of complications from PCI. (3) Clinical success: Near-term clinical success of PCI is defined as achieving anatomic and operative success in patients with remission of signs and/or symptoms of myocardial ischemia. Distant clinical success is defined as the persistence of these beneficial effects for more than 6 months. Restenosis is the main reason for near-term clinical success but not for distant clinical success.
II. Morphologic classification of coronary lesions
In 1988, the ACC/AHA classified coronary lesions into three types, A, B and C, based on the success rate and risk of PCI, which is a widely used clinical staging standard. Among them, type B lesions are divided into two subtypes, with only one lesion characteristic as type B1 lesion and type B2 lesion if there are two or more lesion characteristics.
The 1988 American College of Cardiology and American Heart Association (ACC/AHA) coronary lesion staging
Lesion characteristics Type A lesions Type B lesions Type C lesions
Lesion extent Limited, <10 mm Tubular, 10-20 mm Diffuse, >20 mm
Lesion morphology Concentric Eccentric —-
Easy to approach Easy Moderate curvature of proximal vessels Extreme curvature of proximal vessels
Is angular Not angular (<45.) Moderately angular (>45. but <90.) Severely angular (>90.)
Lesion appearance Smooth wall Irregular wall —-
Degree of calcification None or mild Moderately severe —-
Degree of occlusion Non-complete occlusion Complete occlusion <3 months Complete occlusion >3 months
Site of lesion Non-opening part Opening part —-
Branch involvement or not None Bifurcation lesions requiring guidewire protection Large branches that cannot be protected
Thrombosis None Yes —-
Venous bypass graft vessels – brittle degenerative lesions
Success rate >85% 60%-85% <60%
Risk Low Moderate High
In recent years, with the improvement of devices and the accumulation of operator experience, especially the widespread use of coronary stents, the success rate of PCI has significantly increased and complications have decreased, and the value of predicting the success rate and complications of PCI by the above classification has decreased. Currently, lesions are classified as low, intermediate, or high risk (see Table 2).
Classification of lesion risk
Low risk Medium risk High risk
Isolated short lesions (<10 mm) Tubular lesions (10-20 mm) Diffuse lesions (>20 mm)
Conforming lesions Eccentric lesions Neoplastic expansion
Non-angular lesions Moderate angulation (>45. but <90.) Severe angulation (>90.)
No proximal segment curvature Mild to moderate proximal segment curvature Severe proximal segment curvature
Smooth wall Non-smooth wall
Non-complete occlusion Complete occlusion <3 months Complete occlusion >3 months with bridging lateral branches
Non-opening lesion Opening lesion Left main stem lesion
No involvement of large branches Bifurcation lesions requiring guidewire protection Large branches that cannot be protected
Absence of thrombus Small amount of thrombus Large amount of thrombus or degenerative lesions of venous bridges
III. Thrombolysis in myocardial infarction test blood flow classification
TIMI grade, originally used as an imaging grade to evaluate coronary blood flow velocity after thrombolytic therapy for acute myocardial infarction, is now commonly used to evaluate blood flow status before and after coronary intervention.
TIMI grade 0: complete occlusion of the vessel, with no antegrade flow filling the distal vessels at the occlusion.
TIMI grade 1: Only a small amount of contrast passes through the occlusion site, causing the distal vessels to be faintly visualized, but the filling of the vascular bed is incomplete.
TIMI grade 2: partial reperfusion or complete filling of the distal coronary artery with contrast, but slower antegrade filling and emptying of contrast than in normal coronary arteries.
TIMI grade 3: complete reperfusion and rapid filling and emptying of the contrast medium in the coronary artery.
Complete and incomplete revascularization
The concept of complete revascularization is derived from early surgical experience that bypass grafting of all ≥2.0 mm vessels with >50% stenosis can reduce angina, improve mobility, and increase event-free survival for 5-7 years. In clinical practice, complete revascularization is not possible in many patients. Incomplete revascularization is usually considered to be the presence of >50% residual stenosis in coronary arteries above 1.5 mm. Incomplete revascularization is considered to be either: (1) the operator dilates only the offender lesion or offender vessel that is causing the patient’s symptoms and does not dilate other lesions or vessels; (2) the patient has one or several lesions that cannot be dilated at all, or the attempted dilatation fails. Incomplete revascularization is more common in patients with older age, poor left heart function, and other comorbidities than in those with complete revascularization.
Reconstruction can be divided into “anatomic” and “functional” revascularization. The same “functional” revascularization is achieved with PTCA and CABG, and the long-term prognosis is similar. In patients with poor left heart function, more emphasis is placed on complete anatomic revascularization, whereas in most patients with good left heart function, complete functional revascularization is preferred. In principle, complete revascularization should be done for all serious lesions that can be dilated, as long as it is safe to do so, by first dilating the offender lesion or offender vessel and then dilating the other lesions in order of importance. Sometimes staged treatment is possible and will improve the safety of the intervention. Relatively unimportant vascular lesions may be left untreated if the patient is at high risk for surgery or if there are lesions that cannot be dilated or are functionally unimportant. If the patient is a multi-branch lesion, the surgical risk is low and the cost of doing interventional treatment is high, bypass surgery should be chosen.
When performing incomplete revascularization, the offender lesion or offender vessel should first be determined, which can be helped by electrocardiography and the anatomical features of the lesion. Irregularity of the lesion suggests plaque rupture, and contrast filling defects at the lesion suggest the presence of thrombus, and these changes are common in unstable angina or recent myocardial infarction. For some patients the lesion is difficult to determine the offender lesion. Preoperative exercise testing or isotope myocardial imaging, intraoperative intravascular ultrasound and Doppler flowmetry, and the use of pressure guidewires are helpful in determining offender lesions. The decision to perform incomplete revascularization in patients with multiple lesions must be based on a combination of factors, such as the severity of angina pectoris, the presence of heart failure, the presence of combined diabetes mellitus, and economic conditions. If the patient has diabetes mellitus combined with three branches, especially if the lesion is diffuse, bypass surgery is the best option.
In addition, minimally invasive surgery combined with interventional treatment can be used to achieve complete hemodynamic reconstruction, which is suitable for limited lesions of the anterior descending branch combined with another vessel, that is, a small incision to build a bridge between the left internal mammary artery and the anterior descending branch, and interventional treatment for other vessels.
V. “Stent-like” results
This refers to a residual stenosis of less than 20% after balloon dilation alone, without intimal tears or entrapment, and with normal coronary blood flow. Coronary flow reserve (CFR) measured by coronary Doppler flow or coronary flow reserve fraction (FFR) measured by using pressure guidewire can help to determine the result. A normal CFR should be >2.5 and FFR should be >0.85-0.90. Some studies have shown that “stent-like” outcomes are achieved after balloon dilation and that patients have fewer adverse events, such as low restenosis rates and fewer re-interventions. In patients with conventional PTCA, just under 40% of patients achieve satisfactory results.
Section 2: Coronary stenting
Coronary stenting has developed rapidly since its clinical application, with increasing applications, and is now the mainstay of myocardial revascularization. In the cardiac catheterization laboratories of many hospitals, coronary stents are implanted in 80% of the cases of percutaneous coronary interventions. The reasons for this are: (1) the imaging of the angiogram after stent implantation is very good, with good results in the acute phase; (2) the safety of the intervention is significantly improved due to the ability of the stent to treat acute or near occlusions caused by balloon dilation; (3) the stent can reduce the restenosis rate and improve the long-term prognosis of the patient; (4) the implantation of the stent is easy to operate; (5) the application of the stent can reduce the operation time; (6) for complex lesions, balloon dilation results are often unsatisfactory and stent implantation can yield satisfactory results. These widespread applications are attributed to the refinement of stenting techniques, in-depth understanding of the damage to the vessel wall with stenting, and advances in adjuvant drug therapy.
I. Classification of stents
A variety of stents are currently available in clinical practice. There are many ways to classify stents. Due to the different designs of stents, they can be divided into mesh stents (wallstent), tubular stents, winding stents, and ring stents. According to the different materials of stent, it can be divided into 316L stainless steel stent, nickel stent, and tantalum stent. According to the different delivery methods, they are divided into balloon expandable stents and self-expandable stents. Different stents are designed according to special applications, such as stents suitable for bifurcation lesions and stents suitable for branches and stents with membranes for coronary artery aneurysms or perforations. It is now considered that the ideal stent should have the following characteristics: (1) flexible; (2) good tracer; (3) small head end (profile); (4) impervious to x-ray; (5) thrombosis resistant; (6) biocompatible; (7) reliable expansion performance; (8) good support; (9) good coverage; (10) small surface area; and (11) hydrodynamic compliance. Among the currently applied stents, no stent can fully satisfy all the above characteristics, and each stent has its own characteristics. Familiarity with the characteristics of various stents is the guarantee of successful interventional treatment.
II. Indications for stent implantation
(i) For acute or near occlusion in PTCA
Despite the significant improvement of devices, the introduction of new methods, and the increasing experience of operators, the incidence of acute occlusion in interventional therapy has not decreased. The incidence of acute occlusion ranges from 2 to 14%. Acute occlusion is defined as a TIMI grade 0 or I flow in the target vessel after PTCA. Definitions of near occlusion vary, and usually include one or more of the following: (1) residual stenosis3 ≥50%, (2) entrapment ≥15 mm, (3) extra-luminal contrast retention, and (4) ischemic changes in angina or ECG. The causes of acute occlusion are multifactorial, including arterial entrapment, elastic retraction, thrombosis, vasospasm, and intramural hemorrhage. acute occlusion in PTCA is in turn an important cause of acute myocardial infarction, emergency bypass surgery, and death. Stents are used to treat acute occlusions for the following reasons: (1) complete coverage of the endothelial tear sheet, (2) elimination of elastic retraction, and (3) assurance of vessel geometry. The application of stents for the treatment of acute or near occlusions has a high success rate, but intra-stent thrombosis and clinical complications are more frequent, and restenosis is likely to occur later. Emphasizing the timing of stent implantation for the treatment of acute occlusions, the risk of myocardial infarction is approximately three times higher once an acute occlusion has already occurred and then stent implantation compared to stent implantation for a near occlusion only. the OPUS study showed a significant increase in major adverse cardiac events and target lesion revascularization at 6 months in the latter compared to stent implantation after balloon dilation with problems. In cases of acute or near occlusion, stent implantation has a very important role. Tubular stents are preferred whenever possible. In those caused by severe entrapment, the stent should be long enough to cover the entrapment; the size of the stent should be appropriate; and aggressive antithrombotic therapy should be used. Platelet glycoprotein IIb/IIIa receptor antagonists can be selected if available.
(ii) Low restenosis rate in 33.0 mm coronary vascular lesions
Stent implantation prevents elastic retraction, which occurs after PTCA and can reduce the maximum obtained lumen diameter or cross-sectional area by 32 to 47%, whereas implantation of P-S stents (first-generation stents) only retracts 4 to 18%. In addition, stent implantation is beneficial for vessel wall remodeling.
Several studies have compared the effect of stenting with balloon dilation on restenosis and have demonstrated that stenting reduces restenosis. However, it should be emphasized that the inclusion and exclusion criteria of these studies should be noted, and both STRESS and BENESTENT studies selected limited (≤15 mm) large vessel lesions (≥3.0 mm), which significantly reduced restenosis rates, clinical events (death, myocardial infarction), and revascularization. These findings are not applicable to long lesions, multiple lesions, left main lesions and different types of stents, implantation of multiple stents, etc. It is also important to point out that even patients included in these studies should be treated with caution, as in the meta-analysis BENESTENT and STRESS I and II, there was no difference between stent implantation in vessels <2.6 mm and >3.4 mm compared with balloon dilation alone, both in terms of restenosis and the occurrence of clinical events. Therefore, not all patients benefit from stent implantation, and stent implantation should be selective.
(iii) Limited venous bridge vascular lesions
Recurrent chest pain is increasingly common in patients after bypass surgery. In the first year after bypass surgery, 15% to 20% of venous bridges are occluded, and patency decreases by 4% per year from 1 to 6 years after surgery, with approximately 50% of bridges occluded by 10 years. Because of the decreased patency of the venous bridge and the development of coronary atherosclerotic lesions, 10-15% of bypass patients require re-surgical bypass within 10 years of bypass surgery. The reoperation technique is more difficult, with a higher mortality rate (3% to 7%) as well as a higher incidence of perioperative myocardial infarction (3% to 12%). For these reasons, attempts have been made to treat these post-bypass patients with a percutaneous approach. PTCA has a high success rate (75% to 94%) and relatively low complications and operation-related mortality, although the outcome of balloon dilatation of the bridge vessel is difficult to predict.