Left main intervention


 * Associate Editors-In-Chief: Neil M. Gheewala, M.D.

Overview
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.

Diagnosis
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 is critical to disengage the guide so the guide is not mistaken for the lumen of the artery.

Treatment
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) percutaneous coronary intervention (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
CABG has generally been accepted as the standard of care for patients with LMCA disease. Left main intervention is considered a high risk subset of PCI, but it may be necessary for certain patients.

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

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
Characterizing the patient's anatomy may reduce complications and the duration of the intervention. This can be done through several different methods:
 * 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.

In addition to characterizing the patient's anatomy, it is essential to have all stents and balloons on the table, prepped, and ready to be deployed so that no time is wasted.

Antiplatelet Regimen

 * 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 unlesss 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 indeflator 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
Outcome differences have been observed according to the location of the LMCA stenosis. For instance, distal left main involvement (~75%) lesions have worse outcomes compared to more proximal lesions.

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.

Calcified lesions can be treated with rotational atherectomy or stenting.

Bulky plaque can be treated with directional atherectomy and stenting, or stenting alone.

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
Treating a patient with non-surgical methods include smoking cessation and cardiac risk factor modification.

Dual Antiplatelet Therapy
If a stent is placed, the patient should placed on prolonged dual antiplatelet therapy. Either clopidogrel or Prasugrel for the rest of the patient's life are suitable choices.