Left main intervention

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Cardiogenic Shock Left Main Coronary Artery Disease Refractory Ventricular Arrhythmia Severely Depressed Ventricular Function Sole Remaining Conduit Unprotected Left Main Patient Adjuncts for High Risk PCI
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [12]; Associate Editors-In-Chief: Neil M. Gheewala, M.D.

Left Main Intervention

Diagnosis

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.

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) 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

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

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 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

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.

Follow-Up Care

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.

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)

Class I

"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)"

Class IIa

"1. PCI to improve survival is reasonable as an alternative to CABG in selected stable patients with significant (greater than or equal to 50% diameter stenosis) unprotected left main CAD with: a. Anatomic conditions associated with a low risk of PCI procedural complications and a high likelihood of good long-term outcome (e.g., a low SYNTAX score [lower than or equal to 22], ostial or trunk left main CAD); and (Level of Evidence: B) b. Clinical characteristics that predict a significantly increased risk of adverse surgical outcomes (e.g., Society of Thoracic Surgeons–predicted risk of operative mortality 5%). (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)"

Class IIb

"1. PCI to improve survival may be reasonable as an alternative to CABG in selected stable patients with significant (greater than or equal to 50% diameter stenosis) unprotected left main CAD with: a. Anatomic conditions associated with a low to intermediate risk of PCI procedural complications and an intermediate to high likelihood of good long-term outcome (e.g., low-intermediate SYNTAX score of lower than 33, bifurcation left main CAD); and (Level of Evidence: B) b. Clinical characteristics that predict an increased risk of adverse surgical outcomes (e.g., moderate-severe chronic obstructive pulmonary disease, disability from previous stroke, or previous cardiac surgery; Society of Thoracic Surgeons– predicted risk of operative mortality greater than 2%). (Level of Evidence: B)"