Left main intervention
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Left Main Intervention
The left main coronary artery provides blood flow to two of the main coronary arteries (the left anterior descending artery as well as the circumflex coronary artery), and approximately 5% of all patients undergoing coronary angiography have significant (> 50%) left main coronary artery (LMCA) stenosis. Assessment of the left main is associated with the greatest amount of inter and intraobserver variability in angiography. The left main is short, and is often diseased with asymmetric lesions making its assessment on angiography difficult. There may be diffuse disease which may cause an underestimation of the extent of involvement on angiography. While luminal encroachment is defined as a minimum lumen area less than 4 mm² in the epicardial arteries, a minimum lumen area less than 6 mm² in the left main is considered to be significant. A minimum lumen area less than 6 mm² in the left main corresponds with a fractional flow reserve less than 0.75. A minimum lumen area less than 6 mm² also corresponds to a minimum lumen area less than 4 mm² in either the LAD or the circumflex arteries. In interrogating ostial lesions, it is critical to disengage the guide so that the guide is not mistaken for the lumen of the artery.
The ACC/AHA recommends coronary artery bypass grafting (CABG) in patients with significant LMCA disease who have angina and ACS. However, not all patients are operative candidates. Left main (LM) PCI can safely and effectively treat patients in whom coronary artery bypass grafting (CABG) is suboptimal, or in patients who have had prior CABG with a ‘protected’ LMCA. Protected left main in patients with prior CABG is defined as having at least one patent graft to the left anterior descending or circumflex artery. The main goal is to provide a treatment option for patients who would otherwise be poor surgical candidates, who are declined by surgery, or who refuse CABG. It is essential to properly select patients based on their anatomy as to whether they are optimal candidates for drug-eluting stents (DES) vs bare metal stents (BMS) vs bifurcation stents.
Appropriate Candidate Selection
Candidates for LMCA PCI include:
- Poor operative candidates
- Low-risk patients who refuse CABG
- Patients with 'protected' left main disease (see above)
- Syntax score less than or equal to 22 is considered reasonable based on the Syntax trial (remains subject to debate)
High-risk features in patients with left main disease PCI include:
- Absence of internal mammary artery, radial artery, or saphenous vein grafts distally leading to an ‘unprotected’ left main.
- Concomitant right coronary artery (RCA) disease and/or lack of collaterals from RCA
- Left ventricular dysfunction
Technical Aspects of Performing PCI in the Left Main
Hemodynamic Monitoring and Support
Hemodynamic support is not mandatory, but it should be considered for high-risk patients who have refractory angina or are awaiting CABG with persistent angina on maximal medical therapy. Options include an intra-aortic balloon pump (IABP), Impella, and Tandom Heart. Also, pulmonary artery (PA) line monitoring may be helpful.
Pre-interventional Preparation: Clearly Define Relevant Anatomy
- Intravascular ultrasound (IVUS): The extent of the plaque, as well as any calcification, can be characterized by IVUS.
- Multiple angiographic views: A layout of the anatomy can help characterize any disease in the LMCA ostium, the distal/ bifurcation lesion, as well as the extent of the lesion.
- Guiding catheter selection: Larger guiding catheters (i.e.: 7 or 8 French) can be used in the event that distal bifurcation intervention becomes necessary, as they provide good support and do not occlude the ostium. If necessary, side hole guiding catheters can be utilized.
- A pre-PCI loading dose of non-enteric coated Aspirin is essential.
- A pre-PCI loading dose of 600 mg of Clopidogrel should be administered, then 150 mg PO qd should be administered for one week, and then 75 mg should be given daily for the rest of the patient's life. Prasugrel could alternatively be administered if the patient is under age 75, over 60 kg, has no history of stroke or TIA, and is at low risk of bleeding. Patients should be told not to discontinue their thienopyridine unless they have spoken with their cardiologist.
- GP IIb/IIIa inhibitors are typically used to prevent thrombotic closure.
Reduce Ischemic Time
Besides selecting and prepping the equipment in advance, other methods can be employed to reduce ischemic time:
- A rapid exchange system may be used
- The contrast in the deflator should be diluted with saline to allow for faster deflation.
- For conventional angioplasty balloon inflations, a perfusion balloon can be utilized in the left anterior descending artery (if this is the dominant territory).
Appropriate Stent Selection
Consider using a BMS if the left main diameter is 3.5 mm or greater, and consider using a DES if the left main diameter is small or if the lesion is long. If there is an ostial lesion, the operator should assure that the aorto-ostial region is covered by a stent.
There is increasing evidence for better PCI outcomes using DES instead of BMS because of lower angiographic rates of restenosis and significant reductions in major adverse events. There are unclear benefits of using one DES over another based on their design (open/closed cell, modular), strut thickness/radial strength, and type of drug/polymer.
Approach Dictated by Lesion Morphology
Distal bifurcation involvement has poorer results when treated with a two stent approach (i.e. kissing stents, culotte, T, etc). The approach is similar to other bifurcation therapies, but it has a higher risk with:
- Directional coronary atherectomy (DCA) alone
- DCA plus stenting of the principal vessel
- Stenting of the principal vessel (which is usually the LAD) and rescuing circumflex. Bifurcation stenting (Crush, Culotte, T) have been shown to be non-inferior to each other and yield reasonable angiographic and clinical outcomes.
Exercise Tolerance Test Screening
There is a consensus opinion that it is important to aggressively screen for restenosis. Left main restenosis may unfortunately present as sudden cardiac death rather than recurrent angina. It is therefore recommended that repeat angiography be performed 2-3 months following the procedure, even in the absence of symptoms. Some operators also recommend additional angiography at 6 months to identify late restenosis.
Use of and Indwelling EKG Electrode and Alarming Device
In countries where it is available, implantation of an ischemia monitoring device, such as the AngelMed Guardian device, may permit ongoing surveillance for early detection of ischemia in these high risk patients.
Risk Factor Modification
Dual Antiplatelet Therapy
2011 ACCF/AHA/SCAI Guidelines for Percutaneous Coronary Intervention (DO NOT EDIT)
Revascularization to Improve Survival in Left Main Coronary Artery Disease (DO NOT EDIT)
|"1. CABG to improve survival is recommended for patients with significant (≥50% diameter stenosis) left main coronary artery stenosis. (Level of Evidence: B)"|
|Class III (Harm)|
"1. PCI to improve survival should not be performed in stable patients with significant (greater than or equal to 50% diameter stenosis) unprotected left main CAD who have unfavorable anatomy for PCI and who are good candidates for CABG.  (Level of Evidence: B)"
"2. PCI to improve survival is reasonable in patients with UA/NSTEMI when an unprotected left main coronary artery is the culprit lesion and the patient is not a candidate for CABG.  (Level of Evidence: B)"
"3. PCI to improve survival is reasonable in patients with acute STEMI when an unprotected left main coronary artery is the culprit lesion, distal coronary flow is less than TIMI (Thrombolysis In Myocardial Infarction) grade 3, and PCI can be performed more rapidly and safely than CABG.  (Level of Evidence: C)"
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