Overview of left trunk lesions
The left main trunk is the main vessel at the beginning of the left coronary artery and originates from the left coronary sinus at the root of the ascending aorta, travels between the pulmonary artery and the left atrium, is partially covered by the left auricle, and branches out after a brief anterior migration to the left. 2/3 of patients have two branches of the left main trunk, the left anterior descending branch and the gyrus branch, and 1/3 of patients have three branches of the left main trunk, issuing the anterior descending branch, the gyrus branch and the middle artery.
The normal left main trunk opening diameter is 5-10 mm and the length is less than 4 cm. coronary angiography is affected by the projection position and angle, showing a mean left main trunk diameter of 3.5 mm in women and 4.5 mm in men and a mean length of 13.5 mm. a left main trunk diameter stenosis of ≥50% is diagnosed as a left main trunk lesion.
Evidence-based medical evidence for CABG versus PCI for UPLM stenotic lesions
Left main stem lesions cause severe myocardial ischemia and are therefore very critical and an important cause of sudden death. In the era of bare metal stents, left main lesions were a no-go area for interventional stenting. With the improvement of interventional level and the development of interventional devices, especially the first clinical autopsy control description of left main stem lesion by Herrick in 1912. With the widespread development of coronary angiography, it is not uncommon to find left main stem lesions, which account for about 4-6% of patients with coronary artery disease.
Due to its special anatomical and physiological characteristics, unprotected leftmain disease (UPLM) is associated with high risk of percutaneous coronary intervention (PCI) and unsatisfactory long-term outcome. Previous guidelines have always considered coronary artery bypass grafting (CABG) as the standard treatment for left main lesions, while percutaneous coronary intervention (PCI) is a class III indication, even though it is unclear whether PCI is clearly beneficial for patients with coronary artery disease who are not suitable for CABG, which is a class IIb indication.
With the development of interventional devices, the improvement of interventional techniques and the application of eluting stents, the massive application of imaging techniques such as intravascular ultrasound (IVUS); and the in-depth understanding and knowledge of interventionalists on the anatomical and physiological characteristics of the left main stem, the success rate and mid- and long-term clinical outcomes of UPLM interventions have greatly improved. A large body of new clinical evidence has rewritten the previous guideline recommendation of coronary artery bypass surgery as the treatment of choice, and a subgroup analysis of the left main stem in the SYNTAX study showed that the 1-year outcomes of interventions were similar to, or even better than, those of conventional surgical bypass.
In particular, for simple left main lesions, there was a trend toward lower cardiac event rates with interventional stenting compared with surgical bypass. Since the introduction of drug-eluting stents, several studies have evaluated the overall efficacy of both, and in some patients with unprotected left main lesions, outcomes have been largely comparable between drug stents and surgical bypass, with recently published results from the MAIN-COMPARE registry showing no significant difference in cumulative survival and event rates consistent with the endpoint, despite higher 3-year target lesion-free revascularization survival rates with surgical bypass .
Therefore, in patients with low- and intermediate-risk unprotected left main lesions, long-term survival is essentially comparable between pharmacologic stenting and surgical bypass, for which intervention is the ideal treatment option, whereas in high-risk left main patients, surgical bypass should be chosen as much as possible because of its higher long-term survival.
Recent both large randomized controlled studies, prospective registry studies and meta-analyses have consistently found that the incidence of safety endpoints such as death and recurrent myocardial infarction with PCI treatment in patients with UPLM in the DES era is comparable to bare metal stent (BMS) and CABG procedures, and the incidence of stroke is lower than that of CABG procedures, and only the rate of re-blooding reconstruction is higher than that of CABG procedures, but significantly lower than that of BMS The reconstruction rate was significantly lower than that of BMS.
However, with the advantages of minimally invasive and short hospital stay, PCI may become a safe and effective option for hemodynamic reconstruction in patients with UPLM, and in some special populations PCI may even become the preferred procedure. Therefore, the recent American College of Cardiology (ACC)/American Heart Association (AHA)/Society for Cardiovascular Angiography and Interventions (SCAI) guidelines and our PCI guidelines both list UPLM patients with left main anatomical features suitable for PCI as a class IIb indication.
In the bare metal stent era, according to a patient-level meta-analysis of 5-year follow-up results of four clinical trials of CABG versus bare metal stent (BMS) placement for multiple lesions in ARTS, ERACI-II, MASS-II, and SOS, mortality and composite safety endpoints (death, stroke, and myocardial infarction) were similar in BMS versus CABG comparisons, and patients with BMS had similar mortality and composite safety endpoints (death, stroke, and myocardial infarction) primarily due to revascularization. Increased revascularization leads to increased 5-year adverse cardiovascular and cerebrovascular events (MACCE) (Circulation 2008, 118: 1146-1154).
A recently published meta-analysis of 3773 UPLM stented lesions compared with CABG (JAm Coll Cardiol Intv. 2009, 2:739-747) included two randomized controlled studies, SYNTAX and LEMENS, and eight registry studies, including MAIN-COMPARE, with DES utilization rates ranging from 35 to The results showed no significant difference between stent placement and CABG compared to 3-year morbidity and mortality (OR1.11, 95CI 0.66-1.86);
The composite safety endpoint (death, myocardial infarction, stroke) was not significantly different (OR, 1.16,95CI 0.68 to 1.98), and only re-target revascularization (TVR) was significantly increased in the stenting group (OR 3.30,95CI 0.96 to 11.33).
However, the interpretation of the incidence of TVR needs to be noted that many patients after CABG do not undergo re-TVR, especially when the left internal mammary artery (LIMA) collateral vessels are patent, not because the patient cannot benefit from reoperation, but because the procedure is too risky or has a low probability of success; in fact, after several years of CABG both the own vessels and the saphenous vein collateral vessels can degenerate to complete occlusion or diffuse stenosis, making recurrent CABG or PCI difficult;
Statistically, 30 of saphenous vein bypass graft vessels (SVG) are stenosed or occluded 12 to 18 months after surgery, and 50 SVG are stenosed or occluded 5 years later. And the relatively elevated TVR again after PCI observed in clinical trials is at least partly due to the fact that post-PCI remains a good indication for further revascularization.
In the recently published SYNTAX study, a randomized controlled study of CABG versus PCI with the TAXUS stent was performed in 1800 patients with left main and 3-branch vascular lesions, 2/3 of whom had 3-branch lesions and 1/3 had left main lesions, and all-cause death at 1-year follow-up was not significantly different between the stent placement and CABG groups (4.3 vs. 3.5, p=0.37), and stroke was significantly higher in the CABG group than in the stent placement group (2.2 vs 0.6, p=0.003), and myocardial infarction was not significantly different between the stent placement and CABG groups (4.8 vs 3.2, p=0.11);
The composite safety endpoint (death, stroke, myocardial infarction) was not significantly different (7.6 vs 7.7, p=0.98), but the revascularization stenting group was significantly higher than the CABG group (13.7 vs 5.9, p=0.001), resulting in a significantly higher incidence of MACCE in the primary endpoint stenting group than in the CABG group (17.8 vs 12.1, p=0.002). The study did not meet the criteria for a non-inferiority comparison for the trial design. The study proposed a SYNTAX score based on coronary lesion complexity, with a score of ≤22 for mild lesion complexity, 23 to 32 for moderate complexity, and ≥33 for severe lesion complexity.
The analysis showed that in CABG patients SYNTAX score had no significant effect on 12-month MACCE, whereas in patients with stent placement, the incidence of MACCE was significantly higher in those with SYNTAX score ≥33 than in those with mild (≤22) and moderately (23-32) complex lesions. Subgroup analysis of left main stem lesions showed no significant difference in all-cause death between the stent placement and CABG groups (4.4 vs 4.2, p=0.88), stroke was significantly higher in the CABG group than in the stent placement group (2.7 vs 0.3, p=0.009), and myocardial infarction incidence was not significantly different between the two groups (4.3 vs 4.1, p=0.97);
However, revascularization was significantly higher in the stent placement group than in the CABG group (12.0 vs. 6.7, p=0.02). Analysis of 2-year randomized outcomes in the left main stem subgroup showed that MACCE and the composite endpoint of death, stroke, and myocardial infarction were not significantly different between the stent placement and CABG groups (22.9 vs 19.3,p=0.27, and 10.2 vs 11.8,p=0.48, respectively), and revascularization was significantly higher in the stent placement group than in the CABG group (17.3 vs 10.4, p=0.01).
By lesion complexity (SYNTAX score), MACCE was not significantly different between stent placement and CABG in the low score (0-22) group (15.5 vs 18.8, p=0.45) and moderate score (23-32) group (22.4 vs 22.4, p=0.91); however, stent placement was significantly higher in the high score (≥33) group than in the CABG ( 29.7 vs 17.8,p=0.02), and the morbidity and mortality rate was also significantly higher in the stenting group than in the CABG group (10.4 vs 4.1,p=0.04).
Although the results of the left main subgroup analysis can only suggest hypotheses, it is at least clear that the outcome of PCI for UPLM lesions is significantly correlated with lesion complexity, with stent placement achieving similar outcomes to CABG for those with mild and moderate complexity (SYNTAX score 32) for at least 2 years, but for those with severe complexity (SYNTAX score ≥33), CABG is significantly superior to stenting.
In addition to lesion complexity, previous studies have shown that age, left ventricular EF, and renal function are also important factors in determining the prognosis of patients with UPLM stenosis.
According to current evidence-based medicine, stenting can be used as an alternative treatment to CABG in only some patients; therefore, the indications must be strictly selected.
How to make clinical decisions for UPLM stenotic lesions
The essence of evidence-based medicine is to apply the evidence appropriately to the specific patient and to develop the most appropriate treatment strategy for the patient.
The choice of CABG or stenting for patients with UPLM stenosis should take into account the following factors.
Complexity of the lesion (level of SYNTAX score)
Stenting can be considered for low to moderate SYNTAX scores (<32), while CABG should be preferred for those with ≥33.
Whether complete revascularization can be achieved in UPLM stenotic lesions combined with multiple lesions
In patients with right dominant coronary artery, CABG should be selected if the completely occluded right coronary artery is functionally significant (non-infarct-related artery) and cannot be recanalized by PCI; stenting of UPLM stenotic lesions in left dominant coronary artery also requires great caution.
Severe calcification in left main stem lesions
CABG is most often considered in those with severe calcification.
Whether the patient has insulin-requiring diabetes mellitus with UPLM combined with a 3-branch lesion
If yes, CABG should be considered more often.
What is the patient’s left heart function?
Reduced left ventricular EF is a high risk factor for both CABG and PCI, but CABG should be considered first for reduced EF with multiple lesions, and preemptive intra-aortic balloon counterpulsation (IABP) for protection if stenting is considered.
Whether the patient can tolerate at least 1 year of dual antiplatelet therapy
Patients with bleeding tendency, peptic ulcer, history of gastrointestinal bleeding, or allergic to or intolerant of antiplatelet agents are contraindicated for stenting and CABG should be selected.
Whether the patient has co-morbidities that make CABG inappropriate
If the patient has co-morbidities that contraindicate surgery, such as chronic obstructive pulmonary disease (COPD), stenting is feasible for those with appropriate lesions.
Technical level of the surgeon
Several studies have shown that operator experience and skill level correlate with patient prognosis, and PCI for UPLM stenosis should be performed by experienced operators in centers with a high number of treated cases.
Respect patient wishes and choices where reasonable
Considerations for the choice of indication for CABG or stent placement
Isolated UPLM open-ended or corporal stenoses are indications for stent placement. The choice of stent placement for these lesions is justified by the simplicity of the stenting approach, the large vessel lumen, the low number of in-stent thrombotic complications, and the low number of distant restenoses.
Stenting can be considered for relatively simple UPLM bifurcation stenoses with low or moderate SYNTAX scores <32).
Complex UPLM bifurcation stenosis combined with complex multibranch lesions with SYNTAX score ≥33 should be considered for CABG.
Those with UPLM stenosis combined with multiple lesions for which complete revascularization cannot be achieved in important vessels, such as chronic total occlusion (CTO) of a functionally important right coronary artery (right dominant non-infarct-related artery) that cannot be recanalized by PCI, should not undergo PCI for UPLM stenosis and should instead undergo CABG.
CABG should be preferred in cases of significantly reduced left ventricular EF combined with multiple lesions.
Basic principles to be followed when selecting indications
CABG should be selected if the patient is at high risk of CABG preferring stent placement therapy; if the lesion complexity is high, such as diffuse stenosis or severe calcification, and PCI is difficult to achieve the desired result or is not expected to tolerate long-term dual antiplatelet therapy.
Technical requirements for UPLM stenting
Stenting of UPLM stenotic lesions must achieve perfect results to ensure near- and long-term outcomes.
Open stenosis
The best position must be selected to adequately visualize the tangential position of the opening under fluoroscopy, generally with the best deflection angle in the posterior anterior (slightly left-anterior or right-anterior) head position.
Body stenosis
The stent should cover the opening, and if the body is short, the stent can be extended to the anterior descending branch (the diameter of the vessel in the anterior descending branch should be large enough)
Bifurcation stenosis
Single stent placement (Cross-over) technique should be used whenever possible
It is particularly suitable for small h-rotation branches with no significant stenosis in the gyral opening. If the h-rotation opening is involved after single stenting, temporary stenting can be inserted if necessary;
Double stenting technique
Double stenting is usually required when the left mainstem bypass lesion involves the anterior descending branch and the h-rotation branch opening, and when the h-rotation branch vessel is large and the h-rotation branch opening stenosis is severe and involves its proximal vessels. When the angle of h-rotation and anterior descending branch is ≥70°, the “T” stent technique can be used. The SYNTAX study showed that the T stent technique is superior to other techniques (reducing revascularization); when the angle is <70°, the Mini-Crush technique can be used.
When the anterior descending and gyral branch vessel diameters are approximate, the angle of clamping is small, and the diameter of the left main stem is also approximate, the “Culotte” (skirt pants) technique can be used. If the opening and the proximal end of the anterior descending branch and the gyrus branch are involved, and the diameter of the vessel is small but the diameter of the left main stem is large, the Kissing stenting technique can be used, but the Kissing stenting technique will cause a metal crest (carina) in the left main stem, and its safety and long-term efficacy are yet to be evaluated.
Regardless of the technique used, as long as a double stent is placed, postdilation with the kissing balloon technique is necessary to ensure both near- and long-term outcomes.
Stenting of UPLM stenosis combined with multiple vascular lesions can be staged if necessary. For example, if UPLM stenosis is combined with CTO of the right coronary artery, the CTO lesion can be recanalized first and then stenting of the UPLM stenosis can be performed a few days later to increase safety.
Application of intravascular ultrasound (IVUS)
IVUS has an important guiding value for stent placement in left main stem lesions. Some studies have shown that IVUS-guided left main stem stent placement can achieve better near- and long-term results. Prior to stent placement IVUS allows precise measurement of vessel diameter and can determine the nature of the lesion, degree of lesion stenosis, lesion length, severity of calcification, and bifurcation involvement, thus assisting in strategy development and selection of the most appropriate diameter and length of stent.
After stent implantation, IVUS can determine whether the stent is dilated and adherent to the wall, whether the lesion is adequately covered, and whether there is stent edge entrapment or tearing, so as to achieve a perfect stent placement result.
FFR measurement
FFR measurement can help in the selection of treatment decisions for marginal stenoses shown by imaging. For example, when a single stent is placed using the Cross-over technique, FFR measurement can help determine whether the h-rotation opening needs further treatment, and if the angiogram shows a stenosis in the h-rotation opening and the FFR measurement is >0.80, no intervention can be made.